Physical thermal index of the drying material.
\\n\\n
Dr. Pletser’s experience includes 30 years of working with the European Space Agency as a Senior Physicist/Engineer and coordinating their parabolic flight campaigns, and he is the Guinness World Record holder for the most number of aircraft flown (12) in parabolas, personally logging more than 7,300 parabolas.
\\n\\nSeeing the 5,000th book published makes us at the same time proud, happy, humble, and grateful. This is a great opportunity to stop and celebrate what we have done so far, but is also an opportunity to engage even more, grow, and succeed. It wouldn't be possible to get here without the synergy of team members’ hard work and authors and editors who devote time and their expertise into Open Access book publishing with us.
\\n\\nOver these years, we have gone from pioneering the scientific Open Access book publishing field to being the world’s largest Open Access book publisher. Nonetheless, our vision has remained the same: to meet the challenges of making relevant knowledge available to the worldwide community under the Open Access model.
\\n\\nWe are excited about the present, and we look forward to sharing many more successes in the future.
\\n\\nThank you all for being part of the journey. 5,000 times thank you!
\\n\\nNow with 5,000 titles available Open Access, which one will you read next?
\\n\\nRead, share and download for free: https://www.intechopen.com/books
\\n\\n\\n\\n
\\n"}]',published:!0,mainMedia:null},components:[{type:"htmlEditorComponent",content:'
Preparation of Space Experiments edited by international leading expert Dr. Vladimir Pletser, Director of Space Training Operations at Blue Abyss is the 5,000th Open Access book published by IntechOpen and our milestone publication!
\n\n"This book presents some of the current trends in space microgravity research. The eleven chapters introduce various facets of space research in physical sciences, human physiology and technology developed using the microgravity environment not only to improve our fundamental understanding in these domains but also to adapt this new knowledge for application on earth." says the editor. Listen what else Dr. Pletser has to say...
\n\n\n\nDr. Pletser’s experience includes 30 years of working with the European Space Agency as a Senior Physicist/Engineer and coordinating their parabolic flight campaigns, and he is the Guinness World Record holder for the most number of aircraft flown (12) in parabolas, personally logging more than 7,300 parabolas.
\n\nSeeing the 5,000th book published makes us at the same time proud, happy, humble, and grateful. This is a great opportunity to stop and celebrate what we have done so far, but is also an opportunity to engage even more, grow, and succeed. It wouldn't be possible to get here without the synergy of team members’ hard work and authors and editors who devote time and their expertise into Open Access book publishing with us.
\n\nOver these years, we have gone from pioneering the scientific Open Access book publishing field to being the world’s largest Open Access book publisher. Nonetheless, our vision has remained the same: to meet the challenges of making relevant knowledge available to the worldwide community under the Open Access model.
\n\nWe are excited about the present, and we look forward to sharing many more successes in the future.
\n\nThank you all for being part of the journey. 5,000 times thank you!
\n\nNow with 5,000 titles available Open Access, which one will you read next?
\n\nRead, share and download for free: https://www.intechopen.com/books
\n\n\n\n
\n'}],latestNews:[{slug:"stanford-university-identifies-top-2-scientists-over-1-000-are-intechopen-authors-and-editors-20210122",title:"Stanford University Identifies Top 2% Scientists, Over 1,000 are IntechOpen Authors and Editors"},{slug:"intechopen-authors-included-in-the-highly-cited-researchers-list-for-2020-20210121",title:"IntechOpen Authors Included in the Highly Cited Researchers List for 2020"},{slug:"intechopen-maintains-position-as-the-world-s-largest-oa-book-publisher-20201218",title:"IntechOpen Maintains Position as the World’s Largest OA Book Publisher"},{slug:"all-intechopen-books-available-on-perlego-20201215",title:"All IntechOpen Books Available on Perlego"},{slug:"oiv-awards-recognizes-intechopen-s-editors-20201127",title:"OIV Awards Recognizes IntechOpen's Editors"},{slug:"intechopen-joins-crossref-s-initiative-for-open-abstracts-i4oa-to-boost-the-discovery-of-research-20201005",title:"IntechOpen joins Crossref's Initiative for Open Abstracts (I4OA) to Boost the Discovery of Research"},{slug:"intechopen-hits-milestone-5-000-open-access-books-published-20200908",title:"IntechOpen hits milestone: 5,000 Open Access books published!"},{slug:"intechopen-books-hosted-on-the-mathworks-book-program-20200819",title:"IntechOpen Books Hosted on the MathWorks Book Program"}]},book:{item:{type:"book",id:"7360",leadTitle:null,fullTitle:"Fillers - Synthesis, Characterization and Industrial Application",title:"Fillers",subtitle:"Synthesis, Characterization and Industrial Application",reviewType:"peer-reviewed",abstract:"Fillers - Synthesis, Characterization and Industrial Application comprises a set of chapters that brings an interdisciplinary perspective to accomplish a more detailed understanding of filler materials for the synthesis and characterization of different industrial applications. This book embraces all the chapters that are concerned with the effect of incorporating different fillers or particulates in fabricated composites. Significant research efforts all around the world are continuing to explore the properties of composite materials. Researchers are collectively focusing their efforts on the use of particulate fillers in composites for miscellaneous applications. This book delivers a comprehensive study associated with the sections of material science, polymer technology, anisotropic elasticity phenomena, fracture mechanics, applied mechanics, material synthesis, mechanical and thermo-mechanical characteristics, tribological behavior, etc.",isbn:"978-1-78985-792-4",printIsbn:"978-1-78985-791-7",pdfIsbn:"978-1-83962-102-4",doi:"10.5772/intechopen.75241",price:100,priceEur:109,priceUsd:129,slug:"fillers-synthesis-characterization-and-industrial-application",numberOfPages:96,isOpenForSubmission:!1,isInWos:1,hash:"4cb5f0dcdfc23d6ec4c1d5f72f726ab4",bookSignature:"Amar Patnaik",publishedDate:"April 3rd 2019",coverURL:"https://cdn.intechopen.com/books/images_new/7360.jpg",numberOfDownloads:2480,numberOfWosCitations:2,numberOfCrossrefCitations:2,numberOfDimensionsCitations:6,hasAltmetrics:0,numberOfTotalCitations:10,isAvailableForWebshopOrdering:!0,dateEndFirstStepPublish:"June 28th 2018",dateEndSecondStepPublish:"July 19th 2018",dateEndThirdStepPublish:"September 17th 2018",dateEndFourthStepPublish:"December 6th 2018",dateEndFifthStepPublish:"February 4th 2019",currentStepOfPublishingProcess:5,indexedIn:"1,2,3,4,5,6,7",editedByType:"Edited by",kuFlag:!1,editors:[{id:"43660",title:"Associate Prof.",name:"Amar",middleName:null,surname:"Patnaik",slug:"amar-patnaik",fullName:"Amar Patnaik",profilePictureURL:"https://mts.intechopen.com/storage/users/43660/images/system/43660.jpeg",biography:"Dr. Amar Patnaik is currently working as an associate professor in the Department of Mechanical Engineering, Malaviya National Institute of Technology, Jaipur, India. His area of specialization is composite materials and alloys. He has more than fourteen years of teaching experience and has taught a broad spectrum of courses related to mechanical engineering. Dr. Patnaik has guided twenty-one Ph.D. students successfully and several MTech students as well. He has published more than 250 research papers in international journals (SCI), written thirteen chapters in different books, and filed seven patents. Dr. Patnaik has delivered more than thirty invited guest lectures in different institutions and organizations. He is a lifetime member of the Tribology Society of India, Electron Microscope Society of India, and International Society for Technology in Education.",institutionString:"Malaviya National Institute of Technology Jaipur",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"1",totalChapterViews:"0",totalEditedBooks:"2",institution:{name:"Malaviya National Institute of Technology Jaipur",institutionURL:null,country:{name:"India"}}}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,coeditorOne:null,coeditorTwo:null,coeditorThree:null,coeditorFour:null,coeditorFive:null,topics:[{id:"14",title:"Materials Science",slug:"materials-science"}],chapters:[{id:"64862",title:"The Effects of Novel Additives Used in PVA/Starch Biohybrid Films",doi:"10.5772/intechopen.81727",slug:"the-effects-of-novel-additives-used-in-pva-starch-biohybrid-films",totalDownloads:976,totalCrossrefCites:0,totalDimensionsCites:3,signatures:"Eyyup Karaogul, Ertugrul Altuntas, Tufan Salan and Mehmet Hakki Alma",downloadPdfUrl:"/chapter/pdf-download/64862",previewPdfUrl:"/chapter/pdf-preview/64862",authors:[{id:"223720",title:"MSc.",name:"Tufan",surname:"Salan",slug:"tufan-salan",fullName:"Tufan Salan"},{id:"252376",title:"Dr.",name:"Ertugrul",surname:"Altuntas",slug:"ertugrul-altuntas",fullName:"Ertugrul Altuntas"},{id:"275214",title:"Dr.",name:"Eyyup",surname:"Karaogul",slug:"eyyup-karaogul",fullName:"Eyyup Karaogul"},{id:"275289",title:"Prof.",name:"M. Hakki",surname:"Alma",slug:"m.-hakki-alma",fullName:"M. Hakki Alma"}],corrections:null},{id:"65603",title:"Determining the Filler Activity in the Sintering of Pitch Composites",doi:"10.5772/intechopen.82012",slug:"determining-the-filler-activity-in-the-sintering-of-pitch-composites",totalDownloads:366,totalCrossrefCites:0,totalDimensionsCites:0,signatures:"Vladimir Shmalko, Valeriia Karchakova, Oleh Zelenskyi and Fedir Cheshko",downloadPdfUrl:"/chapter/pdf-download/65603",previewPdfUrl:"/chapter/pdf-preview/65603",authors:[{id:"249063",title:"Ph.D.",name:"Vladimir",surname:"Shmalko",slug:"vladimir-shmalko",fullName:"Vladimir Shmalko"}],corrections:null},{id:"65018",title:"Dynamic Mechanical Behaviour of Coir and Coconut Husk Particulate Reinforced Polymer Composites: The Effect of Exposure to Acidic Environment",doi:"10.5772/intechopen.82889",slug:"dynamic-mechanical-behaviour-of-coir-and-coconut-husk-particulate-reinforced-polymer-composites-the-",totalDownloads:356,totalCrossrefCites:1,totalDimensionsCites:1,signatures:"David O. Obada, Laminu S. Kuburi, David Dodoo-Arhin, Yongdan Hou,\nMuyideen B. Balogun and Mahmud Muhammad",downloadPdfUrl:"/chapter/pdf-download/65018",previewPdfUrl:"/chapter/pdf-preview/65018",authors:[{id:"207044",title:"Dr.",name:"David",surname:"Obada",slug:"david-obada",fullName:"David Obada"},{id:"278195",title:"Dr.",name:"David",surname:"Dodoo-Arhin",slug:"david-dodoo-arhin",fullName:"David Dodoo-Arhin"},{id:"278196",title:"Dr.",name:"Yongdan",surname:"Hou",slug:"yongdan-hou",fullName:"Yongdan Hou"},{id:"278197",title:"Mr.",name:"Muyideen",surname:"Balogun",slug:"muyideen-balogun",fullName:"Muyideen Balogun"},{id:"278198",title:"Mr.",name:"Mahmud",surname:"Muhammad",slug:"mahmud-muhammad",fullName:"Mahmud Muhammad"}],corrections:null},{id:"64639",title:"Active Solders and Active Soldering",doi:"10.5772/intechopen.82382",slug:"active-solders-and-active-soldering",totalDownloads:439,totalCrossrefCites:1,totalDimensionsCites:2,signatures:"Shih-Ying Chang, Yan-Hua Huang and Lung-Chuan Tsao",downloadPdfUrl:"/chapter/pdf-download/64639",previewPdfUrl:"/chapter/pdf-preview/64639",authors:[{id:"94540",title:"Dr.",name:"Lung-Chuan",surname:"Tsao",slug:"lung-chuan-tsao",fullName:"Lung-Chuan Tsao"},{id:"152504",title:"Prof.",name:"Shih-Ying",surname:"Chang",slug:"shih-ying-chang",fullName:"Shih-Ying Chang"},{id:"280517",title:"BSc.",name:"Yan-Hua",surname:"Huang",slug:"yan-hua-huang",fullName:"Yan-Hua Huang"}],corrections:null},{id:"64255",title:"Carbothermal Synthesis of Spherical AlN Fillers",doi:"10.5772/intechopen.81708",slug:"carbothermal-synthesis-of-spherical-aln-fillers",totalDownloads:343,totalCrossrefCites:0,totalDimensionsCites:0,signatures:"Qi Wang, Kexin Chen and Wenbin Cao",downloadPdfUrl:"/chapter/pdf-download/64255",previewPdfUrl:"/chapter/pdf-preview/64255",authors:[{id:"48383",title:"Prof.",name:"Wenbin",surname:"Cao",slug:"wenbin-cao",fullName:"Wenbin Cao"},{id:"270605",title:"Associate Prof.",name:"Qi",surname:"Wang",slug:"qi-wang",fullName:"Qi Wang"},{id:"273510",title:"Prof.",name:"Kenxin",surname:"Chen",slug:"kenxin-chen",fullName:"Kenxin Chen"}],corrections:null}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"}},relatedBooks:[{type:"book",id:"9865",title:"Tribology in Materials and Manufacturing",subtitle:"Wear, Friction and Lubrication",isOpenForSubmission:!1,hash:"45fdde7e24f08a4734017cfa4948ba94",slug:"tribology-in-materials-and-manufacturing-wear-friction-and-lubrication",bookSignature:"Amar Patnaik, Tej Singh and Vikas Kukshal",coverURL:"https://cdn.intechopen.com/books/images_new/9865.jpg",editedByType:"Edited by",editors:[{id:"43660",title:"Associate Prof.",name:"Amar",surname:"Patnaik",slug:"amar-patnaik",fullName:"Amar Patnaik"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"6188",title:"Solidification",subtitle:null,isOpenForSubmission:!1,hash:"0405c42586170a1def7a4b011c5f2b60",slug:"solidification",bookSignature:"Alicia Esther Ares",coverURL:"https://cdn.intechopen.com/books/images_new/6188.jpg",editedByType:"Edited by",editors:[{id:"91095",title:"Dr.",name:"Alicia Esther",surname:"Ares",slug:"alicia-esther-ares",fullName:"Alicia Esther Ares"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"6802",title:"Graphene Oxide",subtitle:"Applications and Opportunities",isOpenForSubmission:!1,hash:"075b313e11be74c55a1f66be5dd56b40",slug:"graphene-oxide-applications-and-opportunities",bookSignature:"Ganesh Kamble",coverURL:"https://cdn.intechopen.com/books/images_new/6802.jpg",editedByType:"Edited by",editors:[{id:"236420",title:"Dr.",name:"Ganesh Shamrao",surname:"Kamble",slug:"ganesh-shamrao-kamble",fullName:"Ganesh Shamrao Kamble"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"6517",title:"Emerging Solar Energy Materials",subtitle:null,isOpenForSubmission:!1,hash:"186936bb201bb186fb04b095aa39d9b8",slug:"emerging-solar-energy-materials",bookSignature:"Sadia Ameen, M. Shaheer Akhtar and Hyung-Shik Shin",coverURL:"https://cdn.intechopen.com/books/images_new/6517.jpg",editedByType:"Edited by",editors:[{id:"52613",title:"Dr.",name:"Sadia",surname:"Ameen",slug:"sadia-ameen",fullName:"Sadia Ameen"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"6320",title:"Advances in Glass Science and Technology",subtitle:null,isOpenForSubmission:!1,hash:"6d0a32a0cf9806bccd04101a8b6e1b95",slug:"advances-in-glass-science-and-technology",bookSignature:"Vincenzo M. Sglavo",coverURL:"https://cdn.intechopen.com/books/images_new/6320.jpg",editedByType:"Edited by",editors:[{id:"17426",title:"Prof.",name:"Vincenzo Maria",surname:"Sglavo",slug:"vincenzo-maria-sglavo",fullName:"Vincenzo Maria Sglavo"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"10049",title:"Advanced Functional Materials",subtitle:null,isOpenForSubmission:!1,hash:"58745a56d54c143e4de8433f3d6eb62e",slug:"advanced-functional-materials",bookSignature:"Nevin Tasaltin, Paul Sunday Nnamchi and Safaa Saud",coverURL:"https://cdn.intechopen.com/books/images_new/10049.jpg",editedByType:"Edited by",editors:[{id:"94825",title:"Associate Prof.",name:"Nevin",surname:"Tasaltin",slug:"nevin-tasaltin",fullName:"Nevin Tasaltin"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"7666",title:"Synthesis Methods and Crystallization",subtitle:null,isOpenForSubmission:!1,hash:"cd26687924373b72a27a0f69e7849486",slug:"synthesis-methods-and-crystallization",bookSignature:"Riadh Marzouki",coverURL:"https://cdn.intechopen.com/books/images_new/7666.jpg",editedByType:"Edited by",editors:[{id:"300527",title:"Dr.",name:"Riadh",surname:"Marzouki",slug:"riadh-marzouki",fullName:"Riadh Marzouki"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"8812",title:"Contemporary Topics about Phosphorus in Biology and Materials",subtitle:null,isOpenForSubmission:!1,hash:"86c427901f631db034a54b22dd765d6a",slug:"contemporary-topics-about-phosphorus-in-biology-and-materials",bookSignature:"David G. Churchill, Maja Dutour Sikirić, Božana Čolović and Helga Füredi Milhofer",coverURL:"https://cdn.intechopen.com/books/images_new/8812.jpg",editedByType:"Edited by",editors:[{id:"219335",title:"Dr.",name:"David",surname:"Churchill",slug:"david-churchill",fullName:"David Churchill"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"7960",title:"Assorted Dimensional Reconfigurable Materials",subtitle:null,isOpenForSubmission:!1,hash:"bc49969c3a4e2fc8f65d4722cc4d95a5",slug:"assorted-dimensional-reconfigurable-materials",bookSignature:"Rajendra Sukhjadeorao Dongre and Dilip Rankrishna Peshwe",coverURL:"https://cdn.intechopen.com/books/images_new/7960.jpg",editedByType:"Edited by",editors:[{id:"188286",title:"Associate Prof.",name:"Rajendra",surname:"Dongre",slug:"rajendra-dongre",fullName:"Rajendra Dongre"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"7676",title:"Zeolites",subtitle:"New Challenges",isOpenForSubmission:!1,hash:"4dc664fa55f94b38c13af542041fc3cc",slug:"zeolites-new-challenges",bookSignature:"Karmen Margeta and Anamarija Farkaš",coverURL:"https://cdn.intechopen.com/books/images_new/7676.jpg",editedByType:"Edited by",editors:[{id:"216140",title:"Dr.",name:"Karmen",surname:"Margeta",slug:"karmen-margeta",fullName:"Karmen Margeta"}],equalEditorOne:null,equalEditorTwo:null,equalEditorThree:null,productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}}],ofsBooks:[]},correction:{item:{id:"68579",slug:"corrigendum-to-industrial-heat-exchanger-operation-and-maintenance-to-minimize-fouling-and-corrosion",title:"Corrigendum to: Industrial Heat Exchanger: Operation and Maintenance to Minimize Fouling and Corrosion",doi:null,correctionPDFUrl:"https://cdn.intechopen.com/pdfs/68579.pdf",downloadPdfUrl:"/chapter/pdf-download/68579",previewPdfUrl:"/chapter/pdf-preview/68579",totalDownloads:null,totalCrossrefCites:null,bibtexUrl:"/chapter/bibtex/68579",risUrl:"/chapter/ris/68579",chapter:{id:"52929",slug:"industrial-heat-exchanger-operation-and-maintenance-to-minimize-fouling-and-corrosion",signatures:"Teng Kah Hou, Salim Newaz Kazi, Abu Bakar Mahat, Chew Bee Teng,\nAhmed Al-Shamma’a and Andy Shaw",dateSubmitted:"March 23rd 2016",dateReviewed:"October 10th 2016",datePrePublished:null,datePublished:"April 26th 2017",book:{id:"6080",title:"Heat Exchangers",subtitle:"Advanced Features and Applications",fullTitle:"Heat Exchangers - Advanced Features and Applications",slug:"heat-exchangers-advanced-features-and-applications",publishedDate:"April 26th 2017",bookSignature:"S M Sohel Murshed and Manuel Matos Lopes",coverURL:"https://cdn.intechopen.com/books/images_new/6080.jpg",licenceType:"CC BY 3.0",editedByType:"Edited by",editors:[{id:"24904",title:"Prof.",name:"S. M. Sohel",middleName:null,surname:"Murshed",slug:"s.-m.-sohel-murshed",fullName:"S. M. Sohel Murshed"}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"}},authors:[{id:"93483",title:"Dr.",name:"Salim Newaz",middleName:null,surname:"Kazi",fullName:"Salim Newaz Kazi",slug:"salim-newaz-kazi",email:"salimnewaz@um.edu.my",position:null,institution:{name:"University of Malaya",institutionURL:null,country:{name:"Malaysia"}}},{id:"187135",title:"Ph.D.",name:"Kah Hou",middleName:null,surname:"Teng",fullName:"Kah Hou Teng",slug:"kah-hou-teng",email:"alex_teng1989@hotmail.com",position:null,institution:{name:"Liverpool John Moores University",institutionURL:null,country:{name:"United Kingdom"}}},{id:"194347",title:"Prof.",name:"Abu Bakar",middleName:null,surname:"Mahat",fullName:"Abu Bakar Mahat",slug:"abu-bakar-mahat",email:"ir_abakar@um.edu.my",position:null,institution:null},{id:"194348",title:"Dr.",name:"Bee Teng",middleName:null,surname:"Chew",fullName:"Bee Teng Chew",slug:"bee-teng-chew",email:"chewbeeteng@um.edu.my",position:null,institution:null},{id:"194349",title:"Prof.",name:"Ahmed",middleName:null,surname:"Al-Shamma'A",fullName:"Ahmed Al-Shamma'A",slug:"ahmed-al-shamma'a",email:"A.Al-Shamma'a@ljmu.ac.uk",position:null,institution:null},{id:"194350",title:"Prof.",name:"Andy",middleName:null,surname:"Shaw",fullName:"Andy Shaw",slug:"andy-shaw",email:"A.Shaw@ljmu.ac.uk",position:null,institution:null}]}},chapter:{id:"52929",slug:"industrial-heat-exchanger-operation-and-maintenance-to-minimize-fouling-and-corrosion",signatures:"Teng Kah Hou, Salim Newaz Kazi, Abu Bakar Mahat, Chew Bee Teng,\nAhmed Al-Shamma’a and Andy Shaw",dateSubmitted:"March 23rd 2016",dateReviewed:"October 10th 2016",datePrePublished:null,datePublished:"April 26th 2017",book:{id:"6080",title:"Heat Exchangers",subtitle:"Advanced Features and Applications",fullTitle:"Heat Exchangers - Advanced Features and Applications",slug:"heat-exchangers-advanced-features-and-applications",publishedDate:"April 26th 2017",bookSignature:"S M Sohel Murshed and Manuel Matos Lopes",coverURL:"https://cdn.intechopen.com/books/images_new/6080.jpg",licenceType:"CC BY 3.0",editedByType:"Edited by",editors:[{id:"24904",title:"Prof.",name:"S. M. Sohel",middleName:null,surname:"Murshed",slug:"s.-m.-sohel-murshed",fullName:"S. M. Sohel Murshed"}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"}},authors:[{id:"93483",title:"Dr.",name:"Salim Newaz",middleName:null,surname:"Kazi",fullName:"Salim Newaz Kazi",slug:"salim-newaz-kazi",email:"salimnewaz@um.edu.my",position:null,institution:{name:"University of Malaya",institutionURL:null,country:{name:"Malaysia"}}},{id:"187135",title:"Ph.D.",name:"Kah Hou",middleName:null,surname:"Teng",fullName:"Kah Hou Teng",slug:"kah-hou-teng",email:"alex_teng1989@hotmail.com",position:null,institution:{name:"Liverpool John Moores University",institutionURL:null,country:{name:"United Kingdom"}}},{id:"194347",title:"Prof.",name:"Abu Bakar",middleName:null,surname:"Mahat",fullName:"Abu Bakar Mahat",slug:"abu-bakar-mahat",email:"ir_abakar@um.edu.my",position:null,institution:null},{id:"194348",title:"Dr.",name:"Bee Teng",middleName:null,surname:"Chew",fullName:"Bee Teng Chew",slug:"bee-teng-chew",email:"chewbeeteng@um.edu.my",position:null,institution:null},{id:"194349",title:"Prof.",name:"Ahmed",middleName:null,surname:"Al-Shamma'A",fullName:"Ahmed Al-Shamma'A",slug:"ahmed-al-shamma'a",email:"A.Al-Shamma'a@ljmu.ac.uk",position:null,institution:null},{id:"194350",title:"Prof.",name:"Andy",middleName:null,surname:"Shaw",fullName:"Andy Shaw",slug:"andy-shaw",email:"A.Shaw@ljmu.ac.uk",position:null,institution:null}]},book:{id:"6080",title:"Heat Exchangers",subtitle:"Advanced Features and Applications",fullTitle:"Heat Exchangers - Advanced Features and Applications",slug:"heat-exchangers-advanced-features-and-applications",publishedDate:"April 26th 2017",bookSignature:"S M Sohel Murshed and Manuel Matos Lopes",coverURL:"https://cdn.intechopen.com/books/images_new/6080.jpg",licenceType:"CC BY 3.0",editedByType:"Edited by",editors:[{id:"24904",title:"Prof.",name:"S. M. Sohel",middleName:null,surname:"Murshed",slug:"s.-m.-sohel-murshed",fullName:"S. M. Sohel Murshed"}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"}}},ofsBook:{item:{type:"book",id:"7301",leadTitle:null,title:"Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques and Environmental Issues",subtitle:null,reviewType:"peer-reviewed",abstract:"Geochemistry has become an essential subject to understand our origins and face the challenges that humanity will meet in the near future. This book presents several studies that have geochemistry as their central theme, from the description of different geological formations, through its use for the characterization of contaminated sites and their possible impact on ecosystems and human health, as well as the importance of geochemical techniques as a complement to other current scientific disciplines. Through the different chapters, the reader will be able to approach the world of geochemistry in several of its subfields (e.g. environmental, isotope, or biogeochemistry) and learn through practical cases.",isbn:"978-1-78985-915-7",printIsbn:"978-1-78985-884-6",pdfIsbn:"978-1-78985-916-4",doi:"10.5772/intechopen.74885",price:119,priceEur:129,priceUsd:155,slug:"applied-geochemistry-with-case-studies-on-geological-formations-exploration-techniques-and-environmental-issues",numberOfPages:140,isOpenForSubmission:!1,hash:"ef869f841dcf3a00819a693b21784892",bookSignature:"Luis Felipe Mazadiego, Eduardo De Miguel Garcia, Fernando Barrio-Parra and Miguel Izquierdo-Díaz",publishedDate:"February 5th 2020",coverURL:"https://cdn.intechopen.com/books/images_new/7301.jpg",keywords:null,numberOfDownloads:2975,numberOfWosCitations:4,numberOfCrossrefCitations:10,numberOfDimensionsCitations:10,numberOfTotalCitations:24,isAvailableForWebshopOrdering:!0,dateEndFirstStepPublish:"July 4th 2018",dateEndSecondStepPublish:"October 11th 2018",dateEndThirdStepPublish:"December 10th 2018",dateEndFourthStepPublish:"February 28th 2019",dateEndFifthStepPublish:"April 29th 2019",remainingDaysToSecondStep:"2 years",secondStepPassed:!0,currentStepOfPublishingProcess:5,editedByType:"Edited by",kuFlag:!1,biosketch:null,coeditorOneBiosketch:null,coeditorTwoBiosketch:null,coeditorThreeBiosketch:null,coeditorFourBiosketch:null,coeditorFiveBiosketch:null,editors:[{id:"169369",title:"Dr.",name:"Felipe Luis",middleName:null,surname:"Mazadiego",slug:"felipe-luis-mazadiego",fullName:"Felipe Luis Mazadiego",profilePictureURL:"https://mts.intechopen.com/storage/users/169369/images/system/169369.png",biography:"Luis F. Mazadiego is a mining engineer, doctor, and professor at the Universidad Politécnica de Madrid (UPM). He teaches in several master’s degree subjects (Mining Engineering, Energy Engineering, Research, Modeling and Risk Analysis in the Environment, Oil and Gas Engineering, Teacher Training) and is oriented, in many cases, to the planning and management of projects. For his research on the applications of surface geochemistry, he obtained the Extraordinary Doctorate Award and the Juan Artieda Award. He is an elected member of INHIGEO, a scientific association dependent on UNESCO. He has participated in research projects on environment, mining heritage, shale gas, and natural radioactivity and published more than 100 scientific articles and congress communications.",institutionString:"Universidad Politécnica de Madrid",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"1",totalChapterViews:"0",totalEditedBooks:"1",institution:{name:"Technical University of Madrid",institutionURL:null,country:{name:"Spain"}}}],coeditorOne:{id:"265733",title:"Dr.",name:"Eduardo",middleName:null,surname:"De Miguel Garcia",slug:"eduardo-de-miguel-garcia",fullName:"Eduardo De Miguel Garcia",profilePictureURL:"https://mts.intechopen.com/storage/users/265733/images/system/265733.jpeg",biography:null,institutionString:"Universidad Politécnica de Madrid",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"0",totalChapterViews:"0",totalEditedBooks:"0",institution:null},coeditorTwo:{id:"265744",title:"Dr.",name:"Fernando",middleName:null,surname:"Barrio-Parra",slug:"fernando-barrio-parra",fullName:"Fernando Barrio-Parra",profilePictureURL:"https://mts.intechopen.com/storage/users/265744/images/system/265744.jpeg",biography:"Fernando Barrio-Parra is an Assistant Professor at the School of Mining Engineering of the Polytechnic University of Madrid. He has a bachelor’s degree in Environmental Sciences, a Master Research, Modelling and Environmental Risk Analysis and a PhD in Natural Resources Conservation. His research is related to the modelling of environmental processes, covering human-environment interaction, littoral geodynamics, geochemical / soil / groundwater pollution processes and prospecting, including human health and environmental risk assessment. His teaching is related to chemistry, geochemistry and environmental risk assessment.",institutionString:"Universidad Politécnica de Madrid",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"0",totalChapterViews:"0",totalEditedBooks:"0",institution:null},coeditorThree:{id:"265751",title:"Dr.",name:"Miguel",middleName:null,surname:"Izquierdo-Diaz",slug:"miguel-izquierdo-diaz",fullName:"Miguel Izquierdo-Diaz",profilePictureURL:"https://mts.intechopen.com/storage/users/265751/images/system/265751.jpeg",biography:"Miguel Izquierdo Díaz is a Teaching Assistant at the School of Mining Engineering of the Polytechnic University of Madrid. He has a BSc in Environmental Sciences and a MSc in Research, Modelling and Environmental Risk Analysis. He is a member of the research group of Prospecting and Environment and of the International Medical Geology Association. His research is focused on environmental pollution biomonitoring and remediation, environmental and human health risk assessment, urban geochemistry, and sustainable agriculture.",institutionString:"Universidad Politécnica de Madrid",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"0",totalChapterViews:"0",totalEditedBooks:"0",institution:null},coeditorFour:null,coeditorFive:null,topics:[{id:"671",title:"Geochemistry",slug:"geochemistry"}],chapters:[{id:"65507",title:"Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield: Emphasis on the Eastern Desert of Egypt",slug:"geochemistry-and-tectonic-setting-of-neoproterozoic-rocks-from-the-arabian-nubian-shield-emphasis-on",totalDownloads:774,totalCrossrefCites:2,authors:[{id:"267666",title:"Dr.",name:"Gaafar",surname:"El Bahariya",slug:"gaafar-el-bahariya",fullName:"Gaafar El Bahariya"}]},{id:"66393",title:"Tsunami Elemental Signatures in the Samoan Islands: A Case Study",slug:"tsunami-elemental-signatures-in-the-samoan-islands-a-case-study",totalDownloads:404,totalCrossrefCites:2,authors:[{id:"280166",title:"Dr.",name:"Shaun",surname:"Williams",slug:"shaun-williams",fullName:"Shaun Williams"}]},{id:"68012",title:"Soil Carbon Biogeochemistry in Arid and Semiarid Forests",slug:"soil-carbon-biogeochemistry-in-arid-and-semiarid-forests",totalDownloads:332,totalCrossrefCites:1,authors:[{id:"280742",title:"Prof.",name:"Wei-Yu",surname:"Shi",slug:"wei-yu-shi",fullName:"Wei-Yu Shi"}]},{id:"65876",title:"The Geochemical Data Imaging and Application in Geoscience: Taking the Northern Daxinganling Metallogenic Belt as an Example",slug:"the-geochemical-data-imaging-and-application-in-geoscience-taking-the-northern-daxinganling-metallog",totalDownloads:464,totalCrossrefCites:0,authors:[{id:"277411",title:"Prof.",name:"Jiang",surname:"Chen",slug:"jiang-chen",fullName:"Jiang Chen"}]},{id:"67287",title:"Geochemical Methods to Assess Agriculture Sustainability",slug:"geochemical-methods-to-assess-agriculture-sustainability",totalDownloads:245,totalCrossrefCites:0,authors:[{id:"278252",title:"Prof.",name:"Trolard",surname:"Fabienne",slug:"trolard-fabienne",fullName:"Trolard Fabienne"},{id:"290280",title:"Dr.",name:"David",surname:"Kaniewski",slug:"david-kaniewski",fullName:"David Kaniewski"},{id:"290281",title:"Dr.",name:"Guilhem",surname:"Bourrié",slug:"guilhem-bourrie",fullName:"Guilhem Bourrié"}]},{id:"65979",title:"Geoenvironmental Characterization of Sulfide Mine Tailings",slug:"geoenvironmental-characterization-of-sulfide-mine-tailings",totalDownloads:528,totalCrossrefCites:4,authors:[{id:"279624",title:"Associate Prof.",name:"Tomás",surname:"Martín-Crespo",slug:"tomas-martin-crespo",fullName:"Tomás Martín-Crespo"},{id:"280234",title:"Dr.",name:"David",surname:"Gómez-Ortiz",slug:"david-gomez-ortiz",fullName:"David Gómez-Ortiz"},{id:"280235",title:"Dr.",name:"Silvia",surname:"Martín-Velázquez",slug:"silvia-martin-velazquez",fullName:"Silvia Martín-Velázquez"}]},{id:"69958",title:"Implications of Sediment Geochemistry and Diet Habits in Fish Metal Levels and Human Health Risk",slug:"implications-of-sediment-geochemistry-and-diet-habits-in-fish-metal-levels-and-human-health-risk",totalDownloads:228,totalCrossrefCites:1,authors:[{id:"268271",title:"Prof.",name:"Wanilson",surname:"Luiz-Silva",slug:"wanilson-luiz-silva",fullName:"Wanilson Luiz-Silva"},{id:"280311",title:"Dr.",name:"Alice",surname:"Bosco-Santos",slug:"alice-bosco-santos",fullName:"Alice Bosco-Santos"}]}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"},personalPublishingAssistant:{id:"247041",firstName:"Dolores",lastName:"Kuzelj",middleName:null,title:"Ms.",imageUrl:"https://mts.intechopen.com/storage/users/247041/images/7108_n.jpg",email:"dolores@intechopen.com",biography:"As an Author Service Manager my responsibilities include monitoring and facilitating all publishing activities for authors and editors. From chapter submission and review, to approval and revision, copyediting and design, until final publication, I work closely with authors and editors to ensure a simple and easy publishing process. I maintain constant and effective communication with authors, editors and reviewers, which allows for a level of personal support that enables contributors to fully commit and concentrate on the chapters they are writing, editing, or reviewing. I assist authors in the preparation of their full chapter submissions and track important deadlines and ensure they are met. I help to coordinate internal processes such as linguistic review, and monitor the technical aspects of the process. As an ASM I am also involved in the acquisition of editors. Whether that be identifying an exceptional author and proposing an editorship collaboration, or contacting researchers who would like the opportunity to work with IntechOpen, I establish and help manage author and editor acquisition and contact."}},relatedBooks:[{type:"book",id:"1420",title:"Geochemistry",subtitle:"Earth's System Processes",isOpenForSubmission:!1,hash:"241a9c3bf3c9264f35b6c989ca996d9a",slug:"geochemistry-earth-s-system-processes",bookSignature:"Dionisios Panagiotaras",coverURL:"https://cdn.intechopen.com/books/images_new/1420.jpg",editedByType:"Edited by",editors:[{id:"139895",title:"Dr.",name:"Dionisios",surname:"Panagiotaras",slug:"dionisios-panagiotaras",fullName:"Dionisios Panagiotaras"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"1591",title:"Infrared Spectroscopy",subtitle:"Materials Science, Engineering and Technology",isOpenForSubmission:!1,hash:"99b4b7b71a8caeb693ed762b40b017f4",slug:"infrared-spectroscopy-materials-science-engineering-and-technology",bookSignature:"Theophile Theophanides",coverURL:"https://cdn.intechopen.com/books/images_new/1591.jpg",editedByType:"Edited by",editors:[{id:"37194",title:"Dr.",name:"Theophanides",surname:"Theophile",slug:"theophanides-theophile",fullName:"Theophanides Theophile"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"3092",title:"Anopheles mosquitoes",subtitle:"New insights into malaria vectors",isOpenForSubmission:!1,hash:"c9e622485316d5e296288bf24d2b0d64",slug:"anopheles-mosquitoes-new-insights-into-malaria-vectors",bookSignature:"Sylvie Manguin",coverURL:"https://cdn.intechopen.com/books/images_new/3092.jpg",editedByType:"Edited by",editors:[{id:"50017",title:"Prof.",name:"Sylvie",surname:"Manguin",slug:"sylvie-manguin",fullName:"Sylvie Manguin"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"3161",title:"Frontiers in Guided Wave Optics and Optoelectronics",subtitle:null,isOpenForSubmission:!1,hash:"deb44e9c99f82bbce1083abea743146c",slug:"frontiers-in-guided-wave-optics-and-optoelectronics",bookSignature:"Bishnu Pal",coverURL:"https://cdn.intechopen.com/books/images_new/3161.jpg",editedByType:"Edited by",editors:[{id:"4782",title:"Prof.",name:"Bishnu",surname:"Pal",slug:"bishnu-pal",fullName:"Bishnu Pal"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"72",title:"Ionic Liquids",subtitle:"Theory, Properties, New Approaches",isOpenForSubmission:!1,hash:"d94ffa3cfa10505e3b1d676d46fcd3f5",slug:"ionic-liquids-theory-properties-new-approaches",bookSignature:"Alexander Kokorin",coverURL:"https://cdn.intechopen.com/books/images_new/72.jpg",editedByType:"Edited by",editors:[{id:"19816",title:"Prof.",name:"Alexander",surname:"Kokorin",slug:"alexander-kokorin",fullName:"Alexander Kokorin"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"1373",title:"Ionic Liquids",subtitle:"Applications and Perspectives",isOpenForSubmission:!1,hash:"5e9ae5ae9167cde4b344e499a792c41c",slug:"ionic-liquids-applications-and-perspectives",bookSignature:"Alexander Kokorin",coverURL:"https://cdn.intechopen.com/books/images_new/1373.jpg",editedByType:"Edited by",editors:[{id:"19816",title:"Prof.",name:"Alexander",surname:"Kokorin",slug:"alexander-kokorin",fullName:"Alexander Kokorin"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"57",title:"Physics and Applications of Graphene",subtitle:"Experiments",isOpenForSubmission:!1,hash:"0e6622a71cf4f02f45bfdd5691e1189a",slug:"physics-and-applications-of-graphene-experiments",bookSignature:"Sergey Mikhailov",coverURL:"https://cdn.intechopen.com/books/images_new/57.jpg",editedByType:"Edited by",editors:[{id:"16042",title:"Dr.",name:"Sergey",surname:"Mikhailov",slug:"sergey-mikhailov",fullName:"Sergey Mikhailov"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"371",title:"Abiotic Stress in Plants",subtitle:"Mechanisms and Adaptations",isOpenForSubmission:!1,hash:"588466f487e307619849d72389178a74",slug:"abiotic-stress-in-plants-mechanisms-and-adaptations",bookSignature:"Arun Shanker and B. Venkateswarlu",coverURL:"https://cdn.intechopen.com/books/images_new/371.jpg",editedByType:"Edited by",editors:[{id:"58592",title:"Dr.",name:"Arun",surname:"Shanker",slug:"arun-shanker",fullName:"Arun Shanker"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"878",title:"Phytochemicals",subtitle:"A Global Perspective of Their Role in Nutrition and Health",isOpenForSubmission:!1,hash:"ec77671f63975ef2d16192897deb6835",slug:"phytochemicals-a-global-perspective-of-their-role-in-nutrition-and-health",bookSignature:"Venketeshwer Rao",coverURL:"https://cdn.intechopen.com/books/images_new/878.jpg",editedByType:"Edited by",editors:[{id:"82663",title:"Dr.",name:"Venketeshwer",surname:"Rao",slug:"venketeshwer-rao",fullName:"Venketeshwer Rao"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"4816",title:"Face Recognition",subtitle:null,isOpenForSubmission:!1,hash:"146063b5359146b7718ea86bad47c8eb",slug:"face_recognition",bookSignature:"Kresimir Delac and Mislav Grgic",coverURL:"https://cdn.intechopen.com/books/images_new/4816.jpg",editedByType:"Edited by",editors:[{id:"528",title:"Dr.",name:"Kresimir",surname:"Delac",slug:"kresimir-delac",fullName:"Kresimir Delac"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}}]},chapter:{item:{type:"chapter",id:"69778",title:"Study on Designing and Manufacturing a Radio-Frequency Generator Used in Drying Technology and Efficiency of a Radio Frequency-Assisted Heat Pump Dryer in Drying of Ganoderma lucidum",doi:"10.5772/intechopen.88825",slug:"study-on-designing-and-manufacturing-a-radio-frequency-generator-used-in-drying-technology-and-effic",body:'
Drying is a common and effective preservation technique that reduces moisture content of material to lower levels required. Therefore, drying can minimize the spoilage of various microbes in material and the physical, chemical, and biochemical changes within the drying products thereby increasing overall shelf life by considerable periods of time. However, the drying process will affect the quality of the product such as nutritional standards, sensory standards, and physical and chemical standards. Therefore, the drying method and drying parameters should be considered to find a suitable drying method with optimum drying condition to retain a high quality of drying products, especially in food technology, agricultural products, and medicinal products.
Ganoderma lucidum is a medicinal product that contains various bioactive ingredients. Polysaccharide is a main bioactive ingredient in Ganoderma lucidum which has been found to be medically active in several therapeutic effects such as antitumor, anti-inflammatory, antiviral, anticancer, and anti-HIV [1]. However, polysaccharide and other bioactive ingredients in Ganoderma lucidum are heat sensitive and the high drying temperature tends to cause higher loss of active ingredients in dehydrated Ganoderma lucidum. Therefore, in drying Ganoderma lucidum, drying method as well as drying parameters should be considered carefully.
RF technology has shown some unique advantages in drying technology. RF heating is a volumetric heating method, which provides fast and deeper heat generation within material that increases heating rate and shortens drying time significantly. RF heating mechanism is described in Figure 1. In which, the RF generator creates an alternating electric field between two electrodes. The material is placed between the electrodes. The wet molecules within material continuously reorient themselves to face opposite poles of the alternating electric field. The friction resulting from the rotational movement of the molecules and the space-charge displacement causes the material to rapidly heat throughout its mass.
RF heating mechanism.
There were numerous studies of RF drying technology in which RF is combined with other drying methods as convection drying using hot air and freeze-drying for drying food and agricultural products [2, 3, 4, 5, 6, 7, 8, 9]. The results show that heat generation within the whole volume of drying material that supports the heat transfer and moisture diffusion process to take place faster shortens the drying time and the temperature, and moisture distribution within material becomes more uniform. The drying products still retain their characteristic color and taste.
In heat pump drying with circulating drying air, drying air after being blown through the heat pump has the specific temperature, velocity, and humidity. Drying air will be blown into the drying chamber, and the drying process is performed here. In heat pump drying, the drying air temperature is at low level. So, the drying products can retain a high content of bioactive ingredients and their characteristic color and taste.
The drying technology using RF and heat pump drying has been found to be suitable for drying medicinal products. The objectives of this study are (1) to design and manufacture a RF generator applied in drying technology for drying Ganoderma lucidum, in which RF-assisted heat pump drying method is applied, and (2) to investigate the effects of the input drying parameters as drying air temperature, drying air velocity and RF power on the drying rate, and the quality of Ganoderma lucidum in RF-assisted heat pump drying process.
A RF generator applied in drying technology is designed and manufactured in order to achieve a required maximum RF power of 3 kW and frequency of 27 MHz.
Ganoderma lucidum used for the experiments is red Ganoderma lucidum (Ganoderma boninense). After being harvested, Ganoderma lucidum has a moisture content of 3 (d.b) (i.e., 75% (w.b)), diameter of 12 cm, thickness of 1.5 cm, and glossy red brown color. Ganoderma lucidum samples are cleaned with dry tissues. The initial moisture content of the material is determined by a moisture analyzer (see Table 1).
No | Symbol | Value |
---|---|---|
1 | Gb | 20 kg/batch |
2 | 20 kg | |
3 | ωi | 75% (w.b) |
4 | ωf | 13% (w.b) |
5 | Cp | 3.613 kJ/(kg °C) |
6 | r | 3150 kJ/kg |
7 | ti | 30°C |
8 | tf | 45°C |
Physical thermal index of the drying material.
The required RF power is calculated based on physical and thermal properties of Ganoderma lucidum and theory of designing and calculating drying system.
The circuit diagram and the components of the RF generator are designed and manufactured based on theory of RF heating mechanism, heat exchanger, and oscillator circuit of RF generator.
The components of RF generator are manufactured in a single unit as designed and installed to complete a RF operator. Some standard components are selected and purchased in the market.
The parameters can be measured by specialized measuring instruments directly such as temperature, velocity of drying air, voltage, and electric current. The other parameters are determined by the exchange formulas.
Experiments for investigation of the effects of the input drying parameters on drying rate in the RF-assisted heat pump drying of Ganoderma lucidum are conducted at the drying air temperature of 40, 45, and 50°C; drying air velocity of 1.2, 1.6, and 2.0 m/s; and RF power of 0.65, 1.3, and 1.95 kW.
The Ganoderma lucidum weight measurements are taken regularly after intervals of 20 minutes by an electronic scale digital balance (see Table 1). Each experiment is conducted until the drying material achieves the moisture content of 0.15 (d.b) (i.e., 13% (w.b)) and completed in triplicates.
The color of the drying products is measured by a colorimeter (see Table 1). The colorimeter displays three reflected light intensities corresponding to the lab color values. The total change in color of the drying Ganoderma lucidum sample with reference to the original sample is calculated as
The parameters in Eq. (1) are described in detail in part of 3.4.2 c. (3.4.2 c. Color of drying material).
Polysaccharide content of Ganoderma lucidum is determined by high-performance liquid chromatography (HPLC) method.
Statistical parameters such as mean and standard deviation are used to solve the experiment data. Examining the differences of the statistical data is conducted by means of least significant difference (LSD).
The heat required for drying process was calculated based on the theory of calculating and designing drying system [10].
Physical and thermal property index of the drying material (Ganoderma lucidum) is given in Table 2.
No | Name | Description |
---|---|---|
1 | Colorimeter | Type: Minolta CR-200 |
2 | Frequency measurement instrument | Type: Acoustimeter CAT #A139 Max frequency: 70 ± 0.01 MHz |
3 | High-voltage voltmeter | Type: Voltmeter-MDP-50 K Voltage range resolution: 0.5–10 kVAC ±5% |
4 | Amperemeter | Type: Amperemeter-C.A401 Ampere range resolution: 0.1–10 A ± 1% |
5 | Thermal sensor | Type: AYN-MF59-104F-3950FB-1000 Measurement ranges: −60–300°C ± 0.05°C |
6 | Moisture analyzer | Type: DBS 60–3 model Maximum capacity: 60 g ± 0.01% Temperature range: 50–200°C Temperature increments: 1°C Repeatability (sd) with 2 g sample: 0.15% Moisture value predicted: 0–100% |
7 | Electronic scale digital balance | Type: DS-2002-N Max weighing capacity of 2000 ± 0.001 grams |
Parameter index of the measurements.
The heat required for heating the material in drying process is the heat of heating the drying material until the material achieves the required temperature. The required temperature of 45°C is chosen for calculation:
The predictive time period required for Ganoderma lucidum to get the temperature of 45°C is 35 minutes. The heat required is calculated as
In the drying process, an amount of heat must be supplied to vaporize the water within drying material at specific drying temperature in order that the material achieves the required final moisture. The heat required depends on the mass of vaporized water in the material and latent heat of drying material.
The mass of vaporized water in the material (kg) is
So,
The initial moisture content of Ganoderma lucidum is 75%. The predictive time period required for Ganoderma lucidum to get the final moisture content of 13% is 7 hours. The heat required is calculated as
In the drying process, the drying material is placed on a drying tray which is normally a plastic mesh grid. So, there must be an amount of heat loss for heating the drying tray until the drying tray gets the drying air temperature:
in which mtray is the mass of the tray, mtray = 1 kg, and CP_plastic is the specific heat capacity of plastic, CP_plastic = 1.67 kJ/(kg °C).
The predictive time period required for the drying tray to get the temperature of 45°C is 45 minutes. The heat loss is calculated as
In the drying process, the drying air flows inside a pipe system, and the outside wall of the pipe is in contact with environment. So, the heat loss through pipes should be considered, and it depends on the pipe material, size, length of the pipe, and drying temperature. The pipe is normally made of PVC plastic.
The length of pipe from the pump to the drying chamber is 1.5 m, so the surface area of the pipe is
So, the heat loss through pipes is calculated as
in which
The drying process is performed in a drying chamber that is also heated up to the drying temperature. So, the heat loss for heating the drying chamber should be considered, and it depends on the material and mass of the chamber and drying temperature. In drying process of food and agricultural products, the drying chamber is normally made of a galvanized steel for food hygiene:
The predictive time period required for the drying chamber to get the temperature of 45°C is 25 minutes. The heat loss is calculated as
in which mch (30 kg),
The inside wall of drying chamber is in contact with drying air, and the outside wall is in contact with the environment. This causes the heat loss through the drying chamber wall in the drying process, and it depends on the material and area of the drying chamber. The area of the drying chamber (F) includes the area of the drying chamber wall (Fw) and two tops (Ft).
The area of the drying chamber wall is
After expanding the top of the drying chamber on computer by AutoCAD software, the surrounding area of a top is
So, the area of the drying chamber is
The heat loss is calculated as
in which k is thermal conductivity of galvanized steel and k is 2.06 W/(m.oC). lch, wch, and hch are the length, the width, and the height of the drying chamber.
The radiation heat loss is calculated as
in which ε is the radiation ratio of galvanized steel, ε = 0.85, and C0 is the radiation ratio of absolute black object,
Thus, the total heat required for drying process is
In current study, the RF operator will be designed, manufactured, and applied in RF-assisted heat pump drying. So, in the drying process, RF heating has the main function of heating the material, vaporizing water within the material, and heating the drying tray. The other heat losses are supplied by heat pump. Thus, the heat required for RF generator is.
Therefore, the RF power of RF generator is chosen P = 3 kW.
The circuit diagram of RF generator was designed based on the theory of RF heating mechanism, heat exchanger, and oscillator circuit of RF generator [11]. The circuit diagram of RF generator is described in Figure 2.
The circuit diagram of RF generator.
The power supply unit consists of a transformer, a wire supply voltage transformer, and a rectifier.
The transformer has the function of changing three-phase voltage 380 VAC into 6.5 kVAC. This high voltage is converted into DC voltage of 6.5 kVDC by the rectifier and supplied to the oscillation circuit. Besides, the wire supply voltage transformer will change the voltage from 380 VAC to 12.6 VAC to supply the triode tube filament.
The oscillation circuit consists of a high-frequency triode tube and LC oscillation circuits. A high voltage of 6.5 kVDC is applied to the anode of the triode tube after passing through an induction circuit including L1, L2, and C1 that acts as a filter circuit to remove the alternating current components of the supply power.
A high voltage of 12.6 VAC is applied to the filament and grid pin of the triode tube. A 12.6 VAC power is applied to the grid pin of the triode tube through an induction circuit that consists of L5, L6, and C4. The induction circuit controls the voltage of the grid pin to generate the output frequency at 27 MHz.
The RF emitting circuit is a circuit consisting of L3 and C3 in parallel. The RF high-frequency energy at the output of the high-frequency triode tube passes through the RF emitting circuit, and it is supplied to the electrode plates of the drying applicator.
The drying applicator is composed of two parallel electrode plates which are called RF electrodes. The drying material is placed between the electrodes during drying process. The material is heated based on dielectric heating principle.
The high-frequency triode tube is selected in the market according to the required RF power, and it has the specific specifications as follows:
Type: Toshiba 7T69RB.
Voltage applied to filament: 12.6 VAC.
Frequency: 27 MHz.
Voltage applied to anode: 6.5 kVDC.
Output power (maximum): 5 kW.
The output power of 5 kW will be converted to RF electrode plates in drying applicator at 60% efficiency (Figure 3).
High-frequency triode tube.
The transformers and the rectifier were manufactured at the workshop with the engineering specifications required. The transformer and rectifier are shown in Figures 4 and 5.
Transformer.
Rectifier.
The oscillation circuit consists of numbers of capacitors and the inductor coils. The function of the oscillation circuit is amplifying the power and required generating frequency. The capacitors and the inductor coils are the industrial components that can work at the high voltage and high frequency (Figure 6).
Inductor coil and capacitor.
The oscillation circuit consists of two induction circuits:
The L1, L2, and C1 induction circuit works as a filter circuit to remove the alternating current components.
The L4, L5, and C4 induction circuit regulates the voltage at the grid pin of the high-frequency triode tube to generate the output RF.
These capacitors and the inductor coils are selected and manufactured according to the standard in Strayfield’s handbook for manufacturing RF generator [11], in which the capacitors C1 and C4 are selected in the market, while the inductors L1, L2, L4, and L5 are manufactured at the workshop. Their values are as follows:
The structure of RF emitting circuit is composed of L3 and C3 in parallel that forms an induction circuit. The RF emitting circuit has the function of generating operating frequency of 27 MHz that is the technical requirements. L3 and C3 are manufactured in the workshop according to the technical requirements with the specifications below.
The structure of the capacitor C3 consists of two parallel electrode plates. The capacitance value of capacitor C3 depends on the area of the parallel electrode plates and distance between them.
The electrode plates have an area of
The capacitance value of capacitor C3 is calculated as
in which
The function of the L3 and C3 induction circuit is generating operating frequency of 27 MHz. So, the inductance value of L3 is calculated with the parameter f = 27 MHz as follows:
The inductor L3 is manufactured in workshop with its specific specification as follows:
Inductance value:
Material: a copper wire.
Diameter of wire: 2.5 mm.
Diameter of wire coil: 40 mm.
The drying applicator consists of two electrode plates which are called RF electrodes. The RF electrodes are fabricated at the workshop. The material used for fabrication of RF electrodes must be a good electric conductive material, and aluminum is chosen. The electrodes have a rectangular surface and dimension of 1200 mm × 1100 mm. They are fixed in drying chamber and connect to the RF emitting circuit through thin copper connectors. The distance between two electrodes is fixed by Teflon plastic bars. The RF electrodes are shown in Figure 7.
Electrode plates.
The RF-assisted heat pump dryer used in drying experiment is shown in Figures 8 and 9. In the drying process, the drying air is circulated over the evaporator of heat pump. The evaporator cools the drying air further down below the condensation temperature. Below this temperature, the drying air will be dehumidified. Then, the drying air is heated to the desired temperature inside the condenser and blown inside the drying chamber for drying process. In the drying chamber, the drying air will combine with the RF generated by the RF generator to conduct drying process of Ganoderma lucidum.
RF-assisted heat pump dryer model. (1) compressor, (2) sub-condenser, (3) valve, (4) condenser, (5) evaporator, (6) heat pump controller, (7) air fan, (8) drying tray, (9) drying chamber, (10) RF electrodes, (11) RF operating controller, (12) operating current intensity controller, (13) unit of supplying the operating voltage.
RF-assisted heat pump dryer.
In drying experiment, the mass of Ganoderma lucidum selected is 4 kg. Thus, the RF power is adjusted to achieve the value of 0.65, 1.3, and 1.95 kW.
The RF generator is operated with the maximum RF power of 3 kW to inspect the operating parameters. The operating frequency of RF generator (f) is measured by a frequency measurement instrument, the operating voltage (U) is measured by a high-voltage voltmeter, and the operating current (I) is measured by an amperemeter. The temperature of the material in drying process is measured by a thermal sensor that is connected to a computer through an integrated circuit. The temperature is recorded each 2 minutes.
The measurement of the operating parameters of RF operator has got the results as follows:
f = 27 MHz, U = 6.5 kV, I = 0.46 A. So, the power P = U.I = 2.99 kW.
The material is heated and achieves the required temperature of 45°C in 28 minutes.
The results show that the operation parameters achieve the designing requirement.
The engineering parameters of measurement instruments are described in the Table 1.
The drying curves of RF-assisted heat pump drying process at the drying air temperature of 45°C, drying air velocity of 1.2 m/s, and RF power of 0.65, 1.3, and 1.95 kW is presented graphically in Figure 10.
Drying curves of RF-assisted heat pump drying process at different RF powers.
As shown in Figure 10, increasing RF power has a significant effect on moisture ratio; the moisture ratio is higher at higher RF power. At RF power of 1.95 kW, the drying time reduces by 9, 17, and 33% in comparison with RF power of 1.3, 0.65, and 0 kW (heat pump drying). It can be explained by RF heating mechanism, in which, increasing the RF power will increase energy absorption inside Ganoderma lucidum, which makes water dipole molecules and free ions in Ganoderma lucidum fluctuate faster. Thus, heat generation within Ganoderma lucidum becomes faster, and the moisture diffusion within Ganoderma lucidum occurs faster [12, 13].
The polysaccharide content of Ganoderma lucidum after drying is given in Table 3.
No | Input drying parameter | Polysaccharide content (mg/g) | ||
---|---|---|---|---|
ta (°C) | va (m/s) | PRF (kW) | ||
1 | 45 | 1.2 | 0 | 7.82 |
2 | 45 | 1.2 | 0.65 | 9.18 |
3 | 45 | 1.2 | 1.3 | 9.31 |
4 | 45 | 1.2 | 1.95 | 9.47 |
Polysaccharide content of Ganoderma lucidum after drying.
The data in Table 3 shows that RF power has a significant effect on polysaccharide content of Ganoderma lucidum after drying. The polysaccharide content of Ganoderma lucidum after RF-assisted heat pump drying is considerably higher than heat pump drying. Increase in RF power retains the higher content of polysaccharide in Ganoderma lucidum. Generally, the reason for the degradation of polysaccharide content during drying of Ganoderma lucidum is due to hydrolysis, in which the polysaccharide is hydrolyzed as water is bound to the molecule [14]. RF-assisted heat pump drying process with RF heating mechanism shortens the heat treatment time, and an increase in RF power makes the linkage between water dipole molecules to be broken more easily. That can reduce the hydrolysis degree of polysaccharides.
Evaluation of the color change of Ganoderma lucidum before and after drying is conducted with X-Rite colorimeter following CIELAB scale. Fresh Ganoderma lucidum has the CIELAB original color value as L0, a0, and b0. Ganoderma lucidum after drying has the CIELAB color value as L*, a*, and b*. The color change index of Ganoderma lucidum corresponding to input drying parameters is shown in Table 4, in which the International Commission on Illumination (CIE) parameters as L, a, and b are measured with a colorimeter (see Table 1). The corresponding L value is lightness of color from 0 (black) to 100 (white); a value is degree of redness (0 to 60) or greenness (0 to −60); and b value is yellowness (0 to 60) or blueness (0 to −60). The total change in color (
Color index | ||||||||
---|---|---|---|---|---|---|---|---|
Type of sample | CIELAB color value | Color change index | ||||||
L0 | a0 | b0 | ||||||
Fresh samples | 47.12 | 4.11 | 18.85 | |||||
L* | a* | b* | ΔL | Δa | Δb | ΔE* | ||
Heat pump drying (PRF = 0 kW) | 36.5a | 6.94a | 12.52a | 10.62 | 2.83 | 6.33 | 12.68a | |
RF-assisted heat pump drying (PRF = 0.65 kW) | 38.71b | 5.75b | 13.76b | 8.41 | 1.64 | 5.09 | 9.97b | |
RF-assisted heat pump drying (PRF = 1.3 kW) | 39.02c | 5.42c | 14.1c | 8.1 | 1.31 | 4.75 | 9.48c | |
RF-assisted heat pump drying (PRF = 1.95 kW) | 39.35d | 5.12d | 14.46d | 7.77 | 1.01 | 4.39 | 8.98d |
The CIELAB color values of Ganoderma lucidum.
Mean values in the same column with different letter symbols. Significant difference at significance level of 0.05.
The data in Table 4 shows that the color change index as ΔL, Δa, and Δb corresponding to RF-assisted heat pump drying is considerably smaller than heat pump drying and increase in RF power decreases the color change index values. Thus, the Ganoderma lucidum samples have retained the color better at higher RF power and at RF power of 1.95 kW, and the color of Ganoderma lucidum samples is nearly similar to the original brown red of fresh material samples.
The drying curves of RF-assisted heat pump drying process at the drying air temperature of 40, 45, and 50°C, drying air velocity of 1.2 m/s, and RF power of 1.3 kW is presented graphically in Figure 11.
Drying curves of RF-assisted heat pump drying process at different drying air temperatures.
As shown in Figure 11, increasing drying air temperature has a significant effect on moisture ratio; the moisture ratio is higher at higher drying air temperature. At drying air temperature of 50°C, the drying time reduces by 10% and 21% in comparison with drying air temperature of 40 and 45°C. It can be explained by the fact that the increase in drying air temperature will increase the amount of heat absorbed by material. Thus, the heating rate increases, and the moisture diffusion within Ganoderma lucidum occurs faster.
The drying curves of RF-assisted heat pump drying process at the drying air temperature of 45°C; drying air velocity of 1.2, 1.6, and 2 m/s; and RF power of 1.3 kW is presented graphically in Figure 12.
Drying curves of RF-assisted heat pump drying process at different drying air velocities.
As shown in Figure 12, increasing drying air velocity makes drying time become longer. This is explained by the fact that the increase in drying air velocity will increase the drying airflow in contact with the drying material surfaces. The temperature of drying material is maintained at a higher level than drying air temperature during drying process by RF heating mechanism. So, when drying air comes into contact with drying material surfaces, the temperature of material surfaces will decrease that causes the average temperature of material to decrease and drying time to become longer. However, drying air velocity does not significantly affect the drying rate. The drying time corresponding to three drying air velocity values differs only about 10–15 minutes, and the drying curves shown in Figure 12 are almost identical. The experimental results are in agreement with the previous studies of agricultural product drying [15, 16, 17, 18].
Based on the calculation and design results, the RF generator has been successfully manufactured and applied in drying technology. The RF generator worked efficiently and achieved the required RF power of 3 kW and frequency of 27 MHz as designed. The drying experiment results showed that in RF-assisted heat pump drying, increase in RF power and drying air temperature increases the drying rate considerably. Meanwhile, drying air velocity does not significantly affect the drying rate. Besides, when RF power increases, the Ganoderma lucidum samples retain the higher content of polysaccharide and the original color better after drying.
AC | alternating current |
C | capacitor |
Cp | specific heat of drying material, J/(kg °C) |
d.b | dry basic (kg H2O/kg dry solid) |
DC | direct current |
f | frequency, MHz |
Gb | drying capacity, kg/batch |
h | the height, m |
HP | heat pump |
HPLC | high-performance liquid chromatography |
I | ampere, A |
l | the length, m |
L | inductor coil |
LSD | least significant difference |
mLC | mass of Ganoderma lucidum, kg |
M | moisture of drying material, d.b |
PRF | RF power, kW |
Q | the heat, kW |
r | latent heat of vaporization of moisture in material, J/kg |
RF | radio frequency |
t | temperature of drying material, °C |
T | absolute temperature of drying material, °K |
U | voltage, kV |
w | the width, m |
w.b | wet basic (kg H2O/kg wet solid) |
Greek symbols | |
λ | thermal conductivity, W/m °C |
ω | moisture of drying material, w.b |
ε | radiation ratio of galvanized steel |
τ | the time, s |
Subscripts | |
i | initial |
f | final |
W | water |
ch | chamber |
In the first half of the 20th century, considerable effort was devoted to the oxidation of the heteroaromatic thiophene (1) with the understanding that the oxidation of thiophene to thiophene S,S-dioxide (2) (Figure 1) would be accompanied by the loss of aromaticity [1, 2]. The non-substituted thiophene S,S-dioxide (1) is not very stable in the pure state [3], but undergoes a slow dimerization with concurrent extrusion of SO2 from the primary cycloadduct (4) [4], leading to 5 (Scheme 1). Only much later were the properties and reactivity of pure, isolated non-substituted thiophene S,S-dioxide (2) described [5].
\nStructure of thiophene (1) and oxygenated thiophenes 2 and 3.
Dimerisation of unsubstituted thiophene S,S-dioxide (2).
Much of the early work on the oxidation of thiophenes to thiophene S,S-dioxides involved hydrogen peroxide (H2O2) as oxidant, later meta-chloroperoxybenzoic acid (m-CPBA). That thiophene S-oxide was an intermediate in such oxidation reactions [6, 7, 8] was evident from the isolation of so-called sesquioxides as dimerization products of thiophene S-oxides [9, 10, 11, 12]. Here, the thiophene S-oxide acted as diene with either another molecule of thiophene S-oxide or thiophene S,S-dioxide acting as ene [9, 10, 11, 12] to give cycloadducts 6–8 (Figure 2). Thiophene S-monoxide (3) as an intermediate in the oxidation process of thiophene (1) to thiophene S,S-dioxide (2) could not be isolated under the conditions.
\nSesquioxides obtained by dimerization of elusive thiophene S-oxide and by cycloaddition of thiophene S-oxide to thiophene S,S-dioxide.
Nevertheless, the idea that a thiophene S-oxide intermediate could be reacted with an alkene of choice led Torssell [13] oxidize methylated thiophenes with m-CPBA in the presence of quinones such as p-benzoquinone (12). This gave cycloadducts 13 and 14 (Scheme 2) [13]. Further groups [11, 12, 14, 15, 16, 17, 18, 19] used this strategy to react thiophene S-oxides such as 11, prepared in-situ with alkenes and alkynes in [4 + 2]-cycloadditions (Schemes 3 and 4). In the reaction with alkenes, 7-thiabicyclo[2.2.1]heptene S-oxides such as 13 were obtained, while the reaction of thiophene S-oxides with alkynes led to cyclohexadienes and/or to aromatic products, where the initially formed, instable 7-thiabicyclo[2.2.1]hepta-2,5-diene S-oxide system 21 extrudes its SO bridge spontaneously (Scheme 4). A number of synthetic routes to multifunctionalized cyclophanes 32 [17], aryl amino acids 25 [16] and to crown ethers 29 [15] (Scheme 5) have used the cycloaddition of thiophene S-oxides 19, created in-situ, as a key step. The formation of the 7-thiabicyclo[2.2.1]heptene S-oxides (such as 13, 18) proceeds with stereocontrol. The cycloadditions yield predominantly endo-cycloadducts, with the oxygen of the sulfoxy bridge directed towards the incoming dienophile, exhibiting the syn-π-facial stereoselective nature of the reaction (see below for further discussion of the stereochemistry of the cycloadducts). Thiophene S,S-dioxides 2 possess an electron-withdrawing sulfone group, which leads both to a polarization and to a reduction of the electron density in the diene [20]. This results in a decrease of the energy of the HOMO as compared to identically substituted cyclopentadienes [20]. Thiophene S,S-dioxides 2 are sterically more exacting than C5 non-substituted cyclopentadienes, with the lone electron pairs on the sulfone oxygens leading to adverse non-bonding interactions with potentially in-coming dienophiles of high π-electron density. Thus, thiophene S,S-dioxides 2 often require higher temperatures [21, 22] in cycloaddition reactions than identically substituted cyclopentadienes. Recent frontier molecular orbital calculations at the HF/6-311++G(d,p)//M06-2X/6-31+G(d) level theory have shown that both HOMO (by 0.5 eV) and LUMO (by 0.4 eV) in thiophene S-oxide (3) are slightly higher in energy than in thiophene S,S-dioxide (2) [23].
\nThiophene S-oxide (11), created in situ, reacts in Diels-Alder type fashion with p-benzoquinone (12).
Cycloaddition of thiophene S-oxides, prepared in situ, with alkenes.
Cycloaddition of thiophene S-oxides (19), prepared in situ, with alkynes.
Cycloaddition of thiophene S-oxides prepared in situ—applications in the synthesis of functionalized aminocarboxylic acids 25, crown ethers 29 and cyclophanes 32.
Oxidation of the thienyl-unit in 33 leads to an intramolecular cycloaddition, where indanones 34 are obtained (Scheme 6) [24].
\nIntramolecular cycloaddition of in situ prepared thiophene S-oxide 34.
Yields of cycloadducts have been found to be much higher, when oxidative cycloaddition reactions of thiophenes are carried out with meta-chloroperoxybenzoic acid (m-CPBA) or with H2O2 at lower temperatures such as at −20°C in the presence of a Lewis acid catalyst such as BF3·Et2O [11, 12, 25, 26] (Scheme 7) or of trifluoroacetic acid (CF3CO2H) [27]. Electron-poor dienophiles such as tetracyanoethylene, acetylene dicarboxylates, quinones, maleimides and maleic anhydride and mono-activated enes such as cyclopentenone and acrolein were used in these reactions.
\nOxidative cycloaddition of thiophene 36 to naphthoquinone (37) in the presence of BF3.Et2O.
Under the conditions m-CPBA/BF3·Et2O, the cycloadditive transformation of thiophene S-oxides, prepared in situ, was used in the synthesis of new cyclophanes such as 39 (Scheme 8) [25]. A series of 2,3-bis(hydroxyphenyl) substituted 7-thiabicyclo[2.2.1]hept-2-ene S-oxides as potential estrogen receptor ligands were prepared by oxidative cycloaddition of 3,4-bis(hydroxyphenyl)thiophenes in the presence of BF3·Et2O [28]. Also the key step in Yu et al.’s [27] synthesis of steroidal saponins 44, closely related to the E-ring areno containing natural products aethiosides A–C, is a BF3·Et2O catalyzed oxidative cycloaddition of the thieno-containing steroidal saponin 42 (Scheme 9) [26]. Furthermore, Zeng and Eguchi [29] were able to functionalize C60 (46) by cycloaddition with in-situ produced 2,5-dimethylthiophene S-oxide (45) [29, 30] (Scheme 10). Nevertheless, sterically hindered thiophenes are more difficult to be subjected to the oxidative cycloaddition reactions (Figure 3).
\nPreparation of multifunctionalized cyclophane 41 by oxidative cycloaddition of thiophenophane 39 in the presence of BF3.Et2O.
Preparation of aethiosides A–C (44a–c) by oxidative cycloaddition of thienosteroidal sapogenin 42.
Cycloaddition of 2,5-dimethylthiophene S-oxide (45), prepared in situ, to C60 (46).
Orthothiophenophanes 48 and 49 do not allow for enough reaction volume and do not undergo oxidative cycloadditions with either alkynes or alkenes under the conditions (m-CPBA, BF3.Et2O, CH2Cl2) [31].
Thiophene S-oxides could be isolated in pure form as side-products in a number of oxidative cycloaddition reactions using alkylated thiophenes as substrates run with m-CPBA in the presence of BF3·Et2O [11, 12]. Nevertheless, the first ascertained thiophene S-oxide (51) isolated in pure form came from the oxidation of the sterically exacting 2,5-bis-tert-butylthiophene (50) in absence of a Lewis acid or an added protic acid. 2,5-Bis-tert-butylthiophene S-oxide (51) could be isolated in 5% yield [32] (Scheme 11).
\nIsolation of 2,5-bis-tert-butylthiophene S-oxide 51 by simple thiophene oxidation with meta-chloroperoxybenzoic acid (m-CPBA) [32].
Previous to the isolation of thiophene S-oxides in pure form, based on UV-spectroscopic measurements, Procházka [33] had claimed that the parent thiophene S-oxide (3) could be prepared by double elimination from 3,4-dimesyloxy-2,3,4,5-tetrahydrothiophene S-oxide (53) and studied in solution. While subsequently the latter part of the assertion was thrown into doubt, the isolation of sesquioxides 7/8 from the reaction indicated at least the presence of thiophene S-oxide under these conditions [33] (Scheme 12).
\nIn situ preparation of parent thiophene S-oxide (3) by an elimination reaction [33].
Interestingly, a toluene solution of η5-ethyltetramethylcyclopentadienyl-η4-tetramethylthienyl rhodium complex [Cp*Rh(η4-TMT)] (54) can be oxidized with dry oxygen to [Cp*Rh(TMTO)] (56), which features a η4-coordinated thiophene S-oxide ligand. Complex 56 was isolated and an X-ray crystal structure was carried out. Alternatively, [Cp*Rh(η4-TMT)] (54) can be oxidized electrochemically to [Cp*Rh(η4-TMT)]2+ (55), which can also be obtained by protonation of [Cp*Rh(TMTO)] (56). Reaction of [Cp*Rh(η4-TMT)]2+ (55) with potassium methylsilanolate (KOSiMe3) leads back to [Cp*Rh(TMTO)] (56) [34] (Scheme 13).
\nOxidation of [Cp*Rh(η4-TMT)] (54) to [Cp*Rh(TMTO)] (56) [34].
The reaction of the cationic transitory ruthenium complex [Ru(C6R6)(C4R4S)]+ (57) with hydroxyl anion (OH−) gives Ru(C6H6)(C4R4SO) (58) [35] (Scheme 14). Here, in contrast to the complex [Cp*Rh(TMTO)] (56), the thiophene S-oxide ligand in Ru(C6H6)(C4R4SO) (58) is not stable, but opens to an acetylpropenethiolate. Stable osmium thiophene S-oxide complexes of type (cymene)Os(C4Me4S=O) have also been prepared [36]. In neither of the cases, was it tried to decomplex the thiophene S-oxide ligand.
\nBase hydrolysis of [Ru(C6R6)(C4R4S)]+ (57) [34].
In the 1990s, two main synthetic methodologies were developed to prepare thiophene S-oxides 63. The first involves the reaction of substituted zirconacyclopentadienes 62 with thionyl chloride (SOCl2), developed by Fagan et al. [37, 38] and by Meier-Brocks and Weiss [39]. Typically, tetraarylzirconacyclopentadienes 62a can be synthesized easily by reacting CpZrCl2 (59), n-BuLi and diarylethyne (61a) in one step (Scheme 15). This strategy was followed by Tilley et al. [40, 41] in their synthesis of substituted thiophene S-oxides. Miller et al. published results for a synthesis of 2,5-diarylthiophene S-oxides (63b) along the same lines, using ethynylarene (61b) [42].
\nSynthesis of tetraarylthiophene S-oxides 63a/b by reaction of tetraarylzirconacyclopentadienes 62a/b with SOCl2.
The other methodology involves an oxidation of a thiophene with either a peracid in the presence of a Lewis acid such as titanium tetrachloride (TiCl4) [43] or boron trifluoride etherate (BF3·Et2O) [44, 45] or with hydrogen peroxide in the presence of a protonic acid such as trifluoroacetic acid [46, 47] (Scheme 16). Also, the use of the reaction system H2O2 in presence of NaFe(III) ethylenediaminetetraacetate/Al2O3 has been reported [48, 49] (Scheme 16) as has been the use of the reaction system [(C18H37)2(CH3)2N]3[SiO4H(WO5)3] [50]. The thiophene S-oxides 65, suitably substituted, can be isolated by column chromatography and can be held in substance for a number of weeks without appreciable degradation, when in crystallized form and when kept in the dark. It is supposed that the Lewis acid not only activates the peracid, but also coordinates to the oxygen in the formed thiophene S-oxide, thus reducing the electron-density on the sulfur of the thiophene S-oxide, making it less prone to undergo a second oxidation to the thiophene S,S-dioxide.
\nPreparation of thiophene S-oxides 65 by oxidation of thiophenes 64 in the presence of a Lewis acid or a protonic acid.
It has been shown that in a molecule, such as 66 or 67, with two thienyl cores, both can be oxidized to thienyl-S-oxides with m-CPBA, BF3·Et2O CH2Cl2, −20°C) [11, 17] . Under these conditions, the second thiophene unit can compete successfully with a thiophene S-oxide for the oxidant (Figure 4).
\nKnown bisthienyl-S-oxides 66 and 67.
Even before thiophene S-oxides could be isolated in pure form, it was evident that thiophene S-oxides are good dienes in cycloaddition reactions, as “trapping” by cycloaddition reaction was one of the standard techniques to gauge the presence of thiophene S-oxide intermediates and provided a versatile preparative entry to 7-thiabi-cyclo[2.2.1]heptene S-oxides 68. These in turn could be converted to substituted arenes 71 by either pyrolysis [15], photolysis [51], or PTC-catalyzed oxidative treatment with KMnO4 [15] or electrochemical oxidation [18] or 7-thiabicyclo-[2.2.1]heptenes (70) by reaction of 68 with PBr3 [52]. Reaction of 68 with tributyltin hydride gives cyclic dienes such as 72 [▬X▬X▬ = ▬(CO)N▬Ph(CO)▬]. Base catalyzed cleavage of the sulfoxy bridge of 1,4-dihalo-7-thiabicyclo[2.2.1]heptane S-oxides 68 (R1 = Cl or Br) leads to the generation of diaryl disulfides such as 69 (Scheme 17).
\n7-Thiabicyclo[2.2.1]heptene S-oxides 68 as versatile precursors to arenes.
With the possibility of isolating the thiophene S-oxides, it became possible to carry out cycloaddition reactions with alkenes that themselves react with m-CPBA. Thiophene S-oxides such as 73 have been found to react equally well with electron-rich alkenes such as enol ethers (74) [53], with electron neutral alkenes such as with cyclopentene (76) [53, 54] and with electron-poor alkenes such as with cyclopentenone or with maleic anhydride [11, 54] (Scheme 18). Also, thiophene S-oxides react with bicyclopropylidene (82) [55] under high pressure (10 kBar, Scheme 19), with allenes [56] (such as 79, Scheme 19), with cyclopropylideneketone [55] (Scheme 20) and with benzyne (90) [56], both formed in-situ (Scheme 21). The reaction of tetrachlorocyclopropene (93) with 3,4-bis-tert-butylthiophene S-oxide (73) led to 6,7-bis-tert-butyl-2,3,4,4-tetrachloro-8-thiabicyclo[3.2.1]octa-2,6-diene 8-oxide (95), resulting from a ring opening of the primary cycloadduct 94 with a concomitant migration of a chloro atom [57] (Scheme 22). The ability of the thiophene S-oxides to undergo cycloadditions with alkenes, regardless of the electron demand of the reaction, has made Houk et al. say that thiophene 1-oxide cycloadditions warrant their classification as click reactions [23].
\n3,4-Bis-tert-butylthiophene S-oxide (73) cycloadding to electron-rich and electron-neutral alkenes.
Thiophene S-oxides cycloadd to allenes and to bicyclopropylidene (82) under high pressure.
One pot Wittig reaction—Diels Alder reaction with thiophene S-oxide 87 as diene.
Cycloaddition of thiophene S-oxide 91 with benzyne (90), prepared in situ.
Cycloaddition of thiophene S-oxide (73) with tetrachlorocyclopropene (93).
Thiophene S-oxides are good precursors for the preparation of heavily substituted arenes such as 100 [58] (Scheme 23). Often, tetraarylcyclopentadienones 97 are used to synthesize oligoaryl benzenes by cycloaddition reaction. However, tetraphenylthiophene S-oxide (96) is the more reactive diene when compared to tetraphenylcyclopentadienone (97) as can be seen in the competitive cycloaddition of 96 and 97 with N-phenylmaleimide (98), where at room temperature only tetraphenylthiophene S-oxide undergoes cycloaddition to give 99 (Scheme 23) [58]. 99 can be converted to the heavily substituted phthalimide 100 [58], either by extruding the SO group thermally in diphenyl ether (Scheme 23) or by reaction with KMnO4/PTC.
\nThiophene S-oxide 96 competes efficiently with tetracyclone 97 for N-phenylmaleimide (98).
Sometimes, tetraphenylthiophene S-oxide (96) and tetraphenylcyclopentadienone (97) give different products in cycloaddition reactions. A typical example is their cycloaddition to benzo[b]thiophene S,S-dioxide (101), where the reaction with 96 leads to the formation of dibenzothiophene S,S-dioxide 102, but with 97 gives dibenzothiophene 104 [59] (Scheme 24). The reason for this difference lies in the tendency of tetracyclines such as 94 to be oxidized to pyrones 102 at higher reaction temperatures, with the S,S-dioxides playing the oxidizing agent [59] (Scheme 24).
\nComparison of the cycloaddition of tetraphenylthiophene S-oxide 96 and tetracyclone 97 with benzo[b]thiophene S,S-dioxide (101). Tetracyclone 97 gives pyrone 105 as side product [59, 60].
Again, cycloaddition reactions of purified thiophene S-oxides can be used to prepare multifunctionalized arenes such as cyclophanes (Scheme 25) [25]. Nakayama et al. [61] have used thiophene S-oxides to prepare sterically over freighted anthraquinones. Thiemann et al. [62] used halogenated thiophene S-oxides, albeit prepared in-situ to synthesize halogenated anthraquinones, which can easily be transformed further to arylated anthraquinones [63, 64]. The cycloaddition reactions of purified thiophene S-oxides can be combined with other transformations in one pot, such as with Wittig olefination reactions (Scheme 20) [55].
\nMultifunctionalized cyclophanes 108 by cycloaddition of thiophenophane S-oxides 106.
Not all thiophene S-oxides undergo cycloaddition reactions with alkynes or alkenes. In general, appreciable reaction volume is needed to allow for the forming sulfoxy-bridge in the primary cycloadducts and, in some cases, of the subsequent extrusion of SO. Also, when considerable strain is associated with the thiophene S-oxides and/or the cycloadducts, reactions other than cycloadditions can occur. Thus, strained thiophenophane S-oxide 110 does not undergo a cycloaddition with 98, but undergoes a rearrangement leading to oxygen insertion into the ring with concomitant extrusion of sulfur, leading to furanophane 111 (Scheme 26) [25]. Fujihara et al. were able to prepare the thiacalixarene S-oxide 112; again, the thiacalixarene S-oxide did not undergo a cycloaddition reaction with alkyne 113, but rather formed the thiophene-S,C-sulfonium ylide 114 (Scheme 27) [65].
\n[2.2]Metathiophenophane S-oxide 109 does not undergo cycloaddition but rearranges to [2.2]furanophane 111.
Thiacalixarene S-oxide 112 reacts with dimethyl acetylenedicarboxylate (113) to the thiacalixarene S,C-ylide 114.
Thiophene S-oxides as cyclic dienes undergo hetero-Diels-Alder reactions, also (Scheme 28). Thus, Nakayama et al. could establish that 3,4-bis-tert-butylthiophene S-oxide 73 reacts with thioaldehydes 115/117 and thioketones 115, generated in-situ to give 2,7-dithiabicyclo[2.2.1]hept-5-ene 7-oxides 116 and 118 [66] (Scheme 28). The cycloadducts are endo-products as ascertained by X-ray crystallography and 1H NMR spectroscopy. Thiobenzophenone could be reacted with good yield; however, here two isomeric products are produced, the major product originating from the syn-π-face while the lesser product from the anti-π-face cycloaddition.
\nHetero-Diels-Alder reactions of 3,4-bis-tert-butylthiophene S-oxide (73).
Finally, 73 reacts with carbonyl cyanide [121, CO(CN)2], created in-situ by oxidation of tetracyanoethylene oxide (119, TCNO) with thiophene S-oxide 73, in hetero-Diels-Alder fashion to give 122 [67] (Scheme 29).
\nReaction of 3,4-tert-butylthiophene S-oxide (73) with tetracyanoethylene oxide (119, TCNO) and hetero-Diels Alder reaction to carbonyl cyanide (121).
Nakayama et al. have calculated that the cycloadditions of the thiophene S-oxides are inverse electron demand reactions [53]. All of the above cycloaddition reactions are highly stereoselective, regardless whether the thiophene S-oxide is prepared and used in-situ or an isolated thiophene S-oxide is used. It is known that the thiophene S-oxides invert at the sulfur and inversion barriers have been calculated and measured experimentally for a number of these compounds [32, 68, 69]. Nevertheless, the sulfoxy group in the 7-thiabicyclo[2.2.1]heptene S-oxide systems is configurational stable. All the cycloadducts are endo-products. In the cases where Lewis acids are used at low temperatures, this in itself is not surprising as it is known that low temperatures kinetically controlled cycloadducts are favored. Moreover, it has been stated that Lewis acid catalysis increases the extent of endo-addition in Diels-Alder reactions [70, 71]. The cycloadditions are seen to have syn-π-facial in that the dienophile adds syn to the oxygen. This means that the lone pair of the sulfur is directed towards the side of the newly formed double bond of the cycloadduct. A number of explanations have been given for the π-facial selectivity. Thus, Nakayama et al. rationalized that in the transition state less geometric change of the SO function would be required to reach the syn- rather than the anti-transition state geometry [53]. Also, a destabilizing interaction between the HOMO of the dienophile and the sulfur lone pair was noted in the anti-transition state [72]. The π-facial selectivity has also been explained by the Cieplak effect [73, 74, 75]. This effect was first proposed to account for the directing effect of remote substituents in addition reactions to substituted cyclohexanones. A large number of experimental observations in Diels-Alder reactions of dienophiles with 5-substituted cyclopentadienes have shown that the dienophiles will approach anti to the antiperiplanar σ-bond that is the better donor at the 5-position of the cyclopentadiene [76]. This σ-bond will best stabilize the σ-bonds formed in the transition state. Cycloadditions to thiophene S-monoxides have been predicted to occur anti to the lone electron-pair on sulfur, which is the better hyper-conjugative donor when compared to the oxygen of the sulfoxy-moiety. The lone pair electron orbital at the sulfur will stabilize the vacant σ*-orbitals of the developing incipient σ-bonds better than any orbital associated with the oxygen of the sulfoxy moiety [77] (Figure 5). This would be even more so, when the oxygen of the sulfoxy-unit is complexed by BF3·Et2O.
\nTransition state 123 preferred over transition state 124.
Based on DFT computational studies, Houk et al. [23] showed that the ground state geometry of a thiophene S-oxide already resembles the molecule in its syn transition state. This distortion from planarity of the molecule minimizes its potential antiaromaticity which would result from a hyperconjugative effect by an overlap of σ*S〓O with the π-system (see also above/below) [23] (Figure 6).
\nStructural feature of thiophene S-oxide 160.
When heated with 2-methylene-1,3-dimethylimidazoline (125), 3,4-bis(tert-butyl)thiophene S-oxide 73 undergoes a [4π + 4π]-cycloaddition to the head-to-head dimer 126 (Scheme 30) [78]. Oxidation of the two sulfoxy bridges to sulfone 127 with dimethyldioxirane as oxidant is followed by thermally driven extrusions of the SO2 bridges in 127 and gives 1,2,5,6-tetra(tert-butyl)octatetraene 128 [79] (Scheme 30).
\n[4π + 4π]-cycloaddition of thiophene S-oxide (73) to dimer 126.
Thiophene S-oxides react as enes in 1,3-dipolar cycloaddition reactions. Thus, 3,4-bis-tert-butylthiophene S-oxide (73) reacts with pyrroline N-oxide (129) to give cycloadduct 130 (Scheme 31) [80]. Nakayama et al. could show that 73 reacts with nitrile oxides, diazomethane, nitrile imides, nitrones, and azomethine ylides in syn-π-facial fashion [80].
\n[3 + 2]-cycloaddition of thiophene S-oxide (73) with pyrroline N-oxide (129) as 1,3-dipole.
1,4-Additions are known for both 3,4-disubstituted and 2,5-disubstituted thiophene S-oxides [81, 82, 83]. Thus, bromine adds cis to both 3,4-bis-tert-butylthiophene S-oxide (73) [81] and 2,5-bis-trimethylsilylthiophene S-oxide (134) [82] to give the 2,5-dibromo-2,5-dihydrothiophene S-oxide derivatives 131 and 135 (Scheme 32). 3,4-Bis-tert-butylthiophene S,S-dioxide (132) undergoes cis-1,4-bromination, too [81] (Scheme 32). Also, alcohols and mercaptans have been submitted successfully to 1,4-additions with 3,4-bis-tert-butyl thiophene S-oxide (73) (Scheme 33) [83]. Interestingly, disulfur dichloride (S2Cl2) could be added to thiophene S-oxide 73, leading to the rapid formation of adduct 137 (Scheme 34) [84]. 137, however, is not stable and transforms into 138. 138 can be obtained with a 98% yield, when 137 is treated with aq. NaHCO3 (Scheme 34) [84].
\nBromination of thiophene S-oxides 73 and 134 and thiophene S,S-dioxide 132.
Addition of methylthiolate to thiophene S-oxide (73).
Addition of disulfur dichloride (S2Cl2) to thiophene S-oxide 73.
The sulfoxy group in thiophene S-oxide can be transformed into a sulfilimine or a sulfoximine moiety [85, 86, 87]. When thiophene S-oxide 73 is reacted with trifluoroacetic acid anhydride or triflic anhydride at −78°C, a mixture of sulfonium salt 139 and sulfurane 140 forms, which can be reacted with p-toluenesulfonamide (141) to provide, as the reaction mixture warms to room temperature, sulfilimine 142 (Scheme 35) [85, 86]. Sulfoximine 145 could be prepared by action of N-[(p-tolylsulfonyl)imino]phenyliodinane (TsN〓IPh, 144) on 2,4-bis-tert-butylthiophene S-oxide (143) in the presence of Cu(CH3CN)4PF6 as catalyst. Further reaction of 145 with H2SO4 leads to N-unsubstituted sulfoximine 146 (Scheme 36) [86].
\nPreparation of thiophene S-imide 142 from thiophene S-oxide 73.
Thiophene sulfoximines 145 and 146 from thiophene S-oxide 143.
The photochemical deoxygenation of dibenzothiophene S-oxides has been studied for quite some time [88, 89, 90, 91] and has been found to proceed via the release of ground state atomic oxygen [O(3P)] upon photoirradiation (Scheme 37). Thiophene S-oxides deoxygenate photochemically as well. Nevertheless, the photochemistry of thiophene S-oxides is intrinsically more complex than that of dibenzothiophene S-oxides, often providing a mixture of products, depending on the substitution pattern of the photoirradiated thiophene S-oxide. The photolysis of 2,5-bis(trimethylsilyl)thiophene S-oxide (134) leads exclusively to deoxygenation to produce 2,5-trimethylsilylthiophene (149) (Scheme 38). Otherwise, in those cases, where the thiophene S-oxide does not exhibit a CH3 substituent on the ring system, furans are often the main products along with (deoxygenated) thiophenes (Scheme 39). This has been noted with phenyl-substituted (96, 160) and tert-butyl substituted thiophene S-oxides (73, 143, 153) as well as with 3,4-dibenzylthiophene S-oxide (158) (Scheme 40) [92, 93, 94, 95]. Different mechanisms have been forwarded for this photochemical formation of furans. A viable mechanism involves a cyclic oxathiin, where the first step within the photochemical reaction is initiated by the homolytic ring cleavage α to the sulfoxy group [92, 93, 94]. A rearrangement of thiophene S-oxides to produce furans can also proceed thermally as found by Thiemann et al. [18] in the transformation of thiophenophane S-oxide 110 to furanophane 111 (Scheme 26) and by Mansuy, Dansette et al. in their oxidation of 2,5-diphenylthiophene (162) with H2O2/CF3CO2H to 2,5-diphenylthiophene S-oxide (163), where an appreciable amount of furan 164 was formed as side-product [46] (Scheme 41). In the case of methyl substituted thiophene S-oxides, hydroxyl-alkylthiophenes such as 166 and follow-up products such as ether 167 have been isolated as photoproducts [96] (Scheme 42).
\nPhotodeoxygenation of dibenzothiophene S-oxide (147).
Photolysis of 2,5-bis(trimethylsilyl)thiophene S-oxide (134).
Photolysis of tetraphenylthiophene S-oxide (96).
Photolysis of 2,4-bis(tert-butyl)-, 2,5-bis(tert-butyl), 3,4-bis(tert-butyl), 3,4-dibenzyl-, and 2,5-diphenylthiophene S-oxide (143, 153, 73, 158, and 160).
Formation of furan 163 in the oxidation of 2,5-diphenylthiophene (162).
Photolysis of 3,4-dibenzyl-2,5-dimethylthiophene S-oxide (165).
Thiophene S-oxides such as 164 and 167 show well-defined, chemically irreversible CV reduction waves, where two reduction processes seem to compete. In the presence of a proton donor, the reduction waves experience a significant shift to more positive potentials, although the reduction potential is still dependent on the substitution pattern of the thiophene S-oxides [96]. In the presence of a proton donor such as benzoic acid at higher concentrations, the reduction of a thiophene S-oxide such as of 167 becomes a straightforward two proton—two electron reduction process to the corresponding thiophene [96]. Bulk electrolysis of thiophene S-oxides in presence of 10-fold excess of benzoic acid has been carried out and have led to the corresponding thiophenes in up to 90% isolated yield (Scheme 43) [96]. Also, thiophene S-oxides show oxidative electrochemistry at platinum in MeCN/Bu4NPF6 [97]. The electrochemical oxidation of tetraphenylthiophene S-oxide under the above conditions leads mainly to the formation of diphenylacylstilbene [98]. Here, more effort needs to be invested to identify the electro-oxidative transformations of other thiophene S-oxides.
\nElectrochemical reduction of 3,4-dibromo-2,5-dimethylthiophene S-oxide (167) in the presence of 10 eq. benzoic acid.
In 1990, Rauchfuss et al. published an X-ray crystal structure of the tetramethylthiophene S-oxide rhodium complex 56 [34]. The first X-ray single crystal structure determination of a non-liganded thiophene S-oxide was carried out by Meier-Brocks and Weiss on tetraphenylthiophene S-oxide. The crystal, however, showed some disorder, and only limited information could be gleaned from it [39]. In 1995, Mansuy et al. carried out an X-ray crystal structural analysis of 2,5-diphenylthiophene S-oxide (160) [46, 47], where the structure of 160 was compared to 2,5-diphenylthiophene (162) and 2,5-diphenylthiophene S,S-dioxide (169). The S▬O bond in the thiophene S-oxide was found with 1.484(3) Å to be appreciably longer than those of the thiophene S,S-dioxide with 1.418(5) Å and 1.427(5) Å, respectively [47]. The ring system of the thiophene S,S-dioxide 169 was found to be absolutely planar, while thiophene S-oxide 160 was found to be puckered, with the sulfur lying outside the plane constructed by the four ring carbons by 0.278 Å, and the sulfoxy oxygen lying outside of the plane on the side opposite to sulfur, located by 0.746 Å away from the plane. Previously, this non-planarity of thiophene S-oxides had been predicted by MNDO [99] and ab-initio calculations [100] of the parent thiophene S-oxide itself and dibenzothiophene S-oxide. A more pronounced alteration between double and single C▬C bond was found in thiophene S-oxide 160 in comparison to diphenylthiophene [47]. In probing the aromaticity of thiophene S-oxide 160, it can be seen that apart from its non-planarity, it exhibits relatively large bond order alternations [C(2)▬C(3) 2.11; C(3)▬C(4) 1.23, C(2)/C(5)▬S 1.11; for comparison, the bond orders in 162: C(2)▬C(3) 1.94; C(3)▬C(4) 1.46; C(2)/C(5) 1.53]. The corresponding 2,5-diphenylthiophene S,S-dioxide, though features even larger bond alternations than 160 [47]. An approach for an assessment of aromaticity is the A index as defined by Julg and François [101], which evaluates aromaticity in respect to bond alternation and bond delocalization in ring systems. Here, benzene as the aromatic system par excellence, has an A index of 1, the thiophene system in 2,5-diphenylthiophene has an A index of 0.99, the 5-membered ring system in 2,5-diphenylthiophene S-oxide’s A index is calculated at 0.79, and the parent thiophene S-oxide A index lies at 0.69 ([47], see also [102]).
\nSubsequently, further X-ray crystal structure analyses were carried out on thiophene S-oxide, such as on 2,5-bis(diphenylmethylsilyl)thiophene S-oxide [45], 3,4-bis-tert-butylthiophene S-oxide (73) [43], (1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl)thiophene S-oxide [68], 1,3-bis(thien-2yl)-4,5,6,7-tetrahydrobenzo[c]thiophene S-oxide [40], and the sexithiophene (170) (Figure 7), where two of the thienyl units were oxidized to sulfoxides [103]. As the thiophene S-oxides are not planar, they invert at the sulfur with different substituents at the C2/C5 positions leading to different barriers of inversion, which have in part been determined experimentally [32, 68, 69]. Structural features of thiophene S-oxides and thiophene S,S-dioxides have been reviewed before [104].
\nOligothiophene S-oxide 170.
Oligothiophenes and polythiophenes are being studied as advanced materials with interesting electronic and nonlinear optical properties [105] with applications in photovoltaic cells [106] and field effect transistors (FETs) [107], among others. It has been noted that oxidation of thienyl-units in oligothiophenes and polythiophenes leads to a lowering of energy gaps, to greater electron affinities, and to greater ionization energies [103, 108, 109]. The introduction of thienyl-S,S-dioxides into oligothiophenes often leads to solubility problems of the materials and often leads to a noticeable increase of oxidation potentials. Therefore, there has been a recent interest in incorporating thienyl S-oxide units in oligo- and polythiophenes with the aim of greater solubility and smaller oxidation potentials and narrower energy gaps with electron-affinities similar to thienyl S,S-dioxides [103].
\nA number of synthetic approaches exist towards the preparation of oligothiophenes with thienyl S-oxide units. Oxidation of a pre-prepared oligo- or polythiophene is more difficult to achieve and leads to modest yield [110]. However, two strategies can be seen as promising. One is the transformation of polyarylene-alkynes 171 via oligozirconacyclopentadienes 172 to polythiophene S-oxides 173, where the zirconacyclopentadienes are reacted with SO2 [41] (Scheme 44). The other takes advantage of the fact that certain thiophene S-oxides such as 2-bromo-3,4-diphenyl-thiophene S-oxide (175) are stable enough to be subjected to C▬C cross-coupling reactions and subsequent halogenation reactions with N-bromosuccinimide (NBS), leading to sequences as shown in Scheme 45 [103]. Already, an FET has been synthesized with a thienyl-thienyl S-oxide polymer [103]. Also, larger π-conjugated ring systems with a thienyl S-oxide unit such as 179 have attracted some attention because of their electronic and optical properties (Figure 8) [111]. As a drawback, it may be noted that thienyl S-oxides in oligomers and polymers would not be stable towards UV radiation as opposed to thienyl S,S-dioxides [112, 113].
\nPreparation with oligomer 173 via zirconacyclopentadiene 172.
Preparation of thienyl S-oxide containing oligomers 170 and 178 by Pd(0) Suzuki and Stille cross-coupling reactions.
Tetrakis(pentafluorophenyl)tetrathiaisophlorin dioxide (179).
Thiophenes have been known to have toxic effects [114, 115]. The understanding of the mechanism leading to the toxicity of thiophenes is of importance, as a number of drugs such as tienilic acid (180), ticlopidine (182), methapyrilene (183), thenalidine (184), tenoxicam (185), cephaloridine (186), suprofen (187), and clopidogrel (188) carry thienyl units, where some of the drugs have been taken off the market (Figure 9). Already in 1990, it was shown that hepatic cytochrome P450 mediated oxidation of the thienyl-containing tienilic acid (180) led to electrophilic metabolites that bind to hepatic proteins [116, 117]. Oxidative metabolism of thiophenes in rats involves thiophene S-oxides [118, 119, 120]. It has been found [119, 121] that rats administered with thiophene (1) in corn oil showed dihydrothiophene S-oxide 191 in their urine as a major metabolite [119] (Scheme 46). This metabolite was assumed to stem from the addition of glutathione (189) to a reactive intermediate thiophene S-oxide 3 (Scheme 46). Previously, it had been shown that rat liver microsomal cytochrome P450 oxidizes 3-aroylthiophene 181, a regioisomer of tienilic acid (180), to aroylthiophene S-oxide 192, which in the presence of mercaptoethanol (193) transformed into dihydrothiophene S-oxide 194 [121] (Scheme 47). Also, 181 was oxidized by clofibrate induced rat liver microsomes to S-oxide 191, which was then trapped as a Diels Alder product with maleimides, for example as 195 [120] (Scheme 48).
\nThiophene-containing pharmaceuticals.
Cytochrome P450 mediated transformation of thiophene 1 to adduct 191.
Transformation of tienilic acid regioisomer 181 to thiophene S-oxide and its addition of mercaptoethanol (193).
Cycloaddition of the thiophene S-oxide derivative of 181 to maleimide.
The oxidation of 2-(4-chlorobenzoyl)thiophene (196), a molecule in structure close to tienilic acid, by H2O2 in the presence of trifluoroacetic acid (TFA) and by m-CPBA, BF3·Et2O, both in CH2Cl2, gives sesquioxides 198–200 that clearly indicate that a thiophene S-oxide structure 197 is formed as an intermediate [122] (Scheme 49). Nevertheless, the oxidation of thiophene (1) itself with H2O2 in the presence of TFA produces apart from sesquioxides 6–8 thiophen-2-one (thiolactone 202). Thiophen-2-one (202) most likely is produced through thiophene-epoxide (201) [23] (Scheme 50). Thiophen-2-one (202) is in equilibrium with 2-hydroxythiophene (202). There is one report of a Pummerer-like rearrangement reaction that leads from the purified and isolated thiophene S-oxide 134 to thiophen-2-one (thiolactone 202) [123] (Scheme 51). Still, the current understanding is that the thiophene S-oxide intermediates formed in vivo do not lead to a 2-hydroxythiophene (203) [124] (Scheme 52), so that two separate mechanisms may exist for the cytochrome P450 2C9 (CYP2C9) mediated oxidation of thiophenes. In this regard, Dansette et al. [119] showed that CYP450s may catalyze both the reaction of thiophenes to thiophene S-oxide and to thiophene epoxides [125].
\nFormation of sequioxides 198–200 by dimerization of thiophene S-oxide 197.
Reaction of thiophene (1) leads via thiophene S-oxide (3) to sesquioxides 7–9 and in a separate pathway via thiophene epoxide 201 to thiolactone 202 and thus to 2-hydroxythiophene (203).
Pummerer reaction of thiophene S-oxide 134 to thiolactone 202.
Cytochrome P450 mediated oxidation of thiophene may lead to two pathways, one through thiophene S-oxide 3, the other through thiophene epoxide 201.
Also, the investigation of the metabolism of other thienyl-containing pharmaceuticals show that potentially both mechanisms, epoxidation of the thiophene-unit and oxidation of the thiophene-unit to thiophene S-oxide, operate concurrently. As to the thiophene S-oxide pathway, Shimizu et al. in their investigation of metabolites ticlopidine (182) in rats found both the glutathione conjugate of ticlopidine S-oxide 205 and the dimeric ticlopidine S-oxide cycloadduct 206 (Figure 10) [126, 127]. The structures could be identified by mass spectrometry, and 1H and 13C NMR spectrometry. Medower et al. have noted that cytochrome P450 mediated oxidation of cancer drug OSI-930 (207) leads to GSH conjugate 209, derived from OSI-930 S-oxide (208), as recognized by mass spectrometry (Scheme 53) [128].
\nMetabolites of ticlopidine that derive from a ticlopidine S-oxide intermediate.
In vivo oxidation of anticancer drug OSI-930 (207) to OSI-930 sulfoxide (208) and addition of glutathione (GSH) to provide identified metabolite 209.
Lastly, both possible metabolic pathways of thiophenes, via thiophene S-oxides and via thiophene epoxides, have been examined as to their energy profiles using density functional theory [129]. It was found that the formation of the thiophene epoxide (−23.24 kcal/mol) is more exothermic than the formation of the thiophene S-oxide (−8.08 kcal/mol) [129]. Also, the formation of thiophene epoxide seems kinetically favored [129]. Both possible metabolites, thiophene S-oxide and thiophene epoxide, are highly electrophilic, leading to bond formation with nucleophiles such as with amino acids, leading to a mechanism-based inactivation (MBI) of cytochrome P450.
\nSince the first unverified isolation of a thiophene S-oxide a little more than 50 years ago, research on thiophene S-oxides has reached a milestone. Due to mainly two synthetic routes, the controlled oxidation of thiophenes in presence of a Lewis- or proton acid and the reaction of zirconacyclopentadienes with thionyl chloride, a number of thiophene S-oxides have now become readily accessible. Thiophene S-oxides are noted to be reactive dienes in Diels-Alder type cycloadditions, where they react equally well with electron-poor and electron-rich dienophiles. Thiophene S-oxides can be stabilized by sterically exacting substituents. Then, they exhibit sufficient stability to be submitted to Pd(0)-catalyzed cross-coupling reactions without deoxygenation.
\nThis leads to the possibility of preparing aryl-oligomers with thiophene-S-oxide subunits. By comparing oligothiophenes and oligomers with thiophene S,S-dioxide subunits, oligomers with thiophene S-oxide subunits exhibit smaller oxidation potentials and narrower energy gaps with electron-affinities greater than oligothiophenes and similar to thiophene S,S-dioxides. Nevertheless, thiophene S-oxides are not stable photochemically, but deoxygenate to the corresponding thiophenes or transform to furans by photochemical rearrangement.
\nThiophene S-oxides have been found to act as intermediates in the cytochrome P540 mediated, oxidative metabolism of thiophene-containing compounds, including a number of important thiophene containing pharmaceuticals. Addition of nucleophiles in vivo leads to mechanism based inhibition (MBI) and to toxic side effects of the thiophenes, including nephrotoxicity.
\nOpen Access publishing helps remove barriers and allows everyone to access valuable information, but article and book processing charges also exclude talented authors and editors who can’t afford to pay. The goal of our Women in Science program is to charge zero APCs, so none of our authors or editors have to pay for publication.
",metaTitle:"What Does It Cost?",metaDescription:"Open Access publishing helps remove barriers and allows everyone to access valuable information, but article and book processing charges also exclude talented authors and editors who can’t afford to pay. The goal of our Women in Science program is to charge zero APCs, so none of our authors or editors have to pay for publication.",metaKeywords:null,canonicalURL:null,contentRaw:'[{"type":"htmlEditorComponent","content":"We are currently in the process of collecting sponsorship. If you have any ideas or would like to help sponsor this ambitious program, we’d love to hear from you. Contact us at info@intechopen.com.
\\n\\nAll of our IntechOpen sponsors are in good company! The research in past IntechOpen books and chapters have been funded by:
\\n\\nWe are currently in the process of collecting sponsorship. If you have any ideas or would like to help sponsor this ambitious program, we’d love to hear from you. Contact us at info@intechopen.com.
\n\nAll of our IntechOpen sponsors are in good company! The research in past IntechOpen books and chapters have been funded by:
\n\n