Milestones in Microwave Chemistry PDF
Preview Milestones in Microwave Chemistry
SPRINGER BRIEFS IN MOLECULAR SCIENCE GREEN CHEMISTRY FOR SUSTAINABILITY György Keglevich Editor Milestones in Microwave Chemistry 123 SpringerBriefs in Molecular Science Green Chemistry for Sustainability Series editor Sanjay K. Sharma, Jaipur, India More information about this series at http://www.springer.com/series/10045 ö Gy rgy Keglevich Editor Milestones in Microwave Chemistry 123 Editor György Keglevich BudapestUniversity of Technologyand Economics Budapest Hungary ISSN 2191-5407 ISSN 2191-5415 (electronic) SpringerBriefs inMolecular Science ISSN 2212-9898 SpringerBriefs inGreen Chemistry for Sustainability ISBN978-3-319-30630-8 ISBN978-3-319-30632-2 (eBook) DOI 10.1007/978-3-319-30632-2 LibraryofCongressControlNumber:2016933216 ©SpringerInternationalPublishingSwitzerland2016 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor foranyerrorsoromissionsthatmayhavebeenmade. Printedonacid-freepaper ThisSpringerimprintispublishedbySpringerNature TheregisteredcompanyisSpringerInternationalPublishingAGSwitzerland Contents 1 The Spread of the Application of the Microwave Technique in Organic Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Erika Bálint and György Keglevich 2 Microwave-Assisted Syntheses in Organic Chemistry. . . . . . . . . . . . 11 Nóra Zs. Kiss, Erika Bálint and György Keglevich 3 The Use of MW in Organophosphorus Chemistry. . . . . . . . . . . . . . 47 György Keglevich, Erika Bálint and Nóra Zs. Kiss 4 Interpretation of the Effects of Microwaves. . . . . . . . . . . . . . . . . . . 77 Péter Bana and István Greiner v Contributors Péter Bana Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Budapest, Hungary Erika Bálint MTA-BME Research Group for Organic Chemical Technology, Budapest University of Technology and Economics, Budapest, Hungary István Greiner Gedeon Richter Plc, Budapest, Hungary György Keglevich Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Budapest, Hungary Nóra Zs. Kiss Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Budapest, Hungary vii Introduction These days microwave (MW)-assisted chemistry has become an integrant part of environmentally-friendly (“green”) chemistry. In a part of the cases, the MW accomplishment offers special advantages compared to the thermal variation. Besidesthegeneralbenefitsofshorterreactiontimes,higheryields,andselectivity, certainreactionstakeplaceonlyunderMWconditions.Anadditionaladvantageis thatanumberofMW-assistedorganicchemicaltransformationsmaybeperformed under solvent-free conditions. In this publication, we tried to provide information that represents hot, but less reviewedtopics.Aftertheoverviewofthedevelopmentsofthethreedecadesofthe MW discipline, fashionable reactions, such as multicomponent reactions, conden- sations, coupling reactions, and cycloadditions are surveyed. This chapter is fol- lowed by a summary of the results attained in the field of organophosphorus chemistry. Theoretical calculations allowed the interpretation of the results and considerations on the scope and limitations of the possible use of the MW tech- nique. Possible simplification of catalysts or catalytic systems under MW condi- tions are also discussed. The last part is on the interpretation of advantageous reaction outcomes encounteredinMW-assistedorganicchemistryonthebasisofassumednonthermal and thermal effects. The different explanations for the rate enhancing effects are discussedcritically viawell-selected examples. Thecurrentlyacceptedtheoriesare presented in a way to elucidate the adequate phenomena, and the most common misconceptions. Modern experimental techniques in MW chemistry reveal the fundamentalroleoftemperatureininterpretingtheMWeffects.Thermaleffectscan be differentiated between macroscopic and microscopic effects, both of which are discussed in detail with illustrative examples. The concept of nonthermal MW effects is critically reviewed. ix Chapter 1 The Spread of the Application of the Microwave Technique in Organic Synthesis Erika Bálint and György Keglevich Abstract The first chapter summarizes the birth and spread of the application of the microwave (MW) technique in organic syntheses placing the stress on the developmentoftheMWequipment.Thesedaysprofessionalbatchandcontinuous flow reactorsareavailable,andtheapplicationisknockingatthedoor ofindustry. (cid:1) (cid:1) Keywords Microwave Batch reactors Continuous reactors These days, the protection of our environment and our health is becoming increasingly importantduetotheworldwide spread ofgreen chemistry.According to the 12 principles of green chemistry [1], preparation and development of environmentally-friendly and harmless products and technologies are the main tasks.Inthiscontext,theapplicationofthemicrowave(MW)techniqueinorganic, inorganic, medicinal, analytical and polymer chemistry has spread fast [2–8]. Thefirstdomesticmicrowaveovenwasintroducedbyattheendof1955,butthe widespreaduseoftheseovensinhouseholdsoccurredduringthe1970sand1980s. From the middle of 1970s, engineers and researchers started to apply the MW technique in food processing, in the drying industry, in waste remediation and in analytical chemistry. In the latter case, this technique has been used for sample preparation(e.g.digestion,extraction,dissolution,etc.)[9–12].Thefirstapplication ofmicrowaveirradiationinchemicalsynthesiswaspublishedin1986bythegroups ofGedyeandGiguere[13,14].Sincethen,thenumberofpublicationsinthisfield has sharply increased (Fig. 1.1). Most of these publications describe important acceleration of a wide range of organic chemical reactions, excellent repro- E.Bálint(&) MTA-BMEResearchGroupforOrganicChemicalTechnology, 1521Budapest,Hungary e-mail:[email protected] G.Keglevich DepartmentofOrganicChemistryandTechnology,BudapestUniversity ofTechnologyandEconomics,1521Budapest,Hungary ©SpringerInternationalPublishingSwitzerland2016 1 G.Keglevich(ed.),MilestonesinMicrowaveChemistry, SpringerBriefsinGreenChemistryforSustainability, DOI10.1007/978-3-319-30632-2_1 2 E.BálintandG.Keglevich Fig. 1.1 The number of publication on MW-assisted synthesis (1986–2015). Web of Science keywordsearchon“microwavesynthesis” ducibility, improved yields and less side reactions compared to conventional heating. EarlypioneeringexperimentswereperformedindomesticMWovens,wherethe irradiationpowerwascontrolledgenerallybyon-offcyclesofthemagnetron,andit was not possible to monitor the inner temperature in a reliable way, thus the reactions were not reproducible. The other problems were on the safety issues of suchexperiments[15–17].Fromtheearly2000s,dedicatedMWinstrumentsstarted appearing in market, which are indeed suitable for performing chemical reactions under controlled conditions [2, 3, 18]. All commercially available dedicated MW reactors consist of a MW cavity, magnetic stirrer, sensor probe (IR sensor or fiber optic probe), and software that enables on-line temperature/pressure control by regulating the MW power output. The MW instruments are classified in two types, monomode (single mode) and multimodeMWreactors.Themaindifferencebetweenthetwosystemsisthatwhile in monomode reactors only one reaction vessel can be irradiated, multimode reactors may accommodate several vessels simultaneously. A monomode instrument has a small compact cavity, where the microwave energy is generated by a single magnetron, and directed through a rectangular waveguidetothereactionmixture,whichispositionedatamaximizedenergypoint (Fig. 1.2). A highly homogenous energy field of high power intensity is provided, resulting in exceedingly fast heating rates. In addition, monomode instruments with a self-tuning circular waveguide are also available (Fig. 1.3). This cavity features multiple entry points for introducing the microwave energy into the vessel. Multimode reactors have larger cavities, in which the microwaves are reflected from the cavity walls, and distributed in a rather chaotic manner (Fig. 1.4). The reaction vessels are continuously rotated within the cavity, to provide a steady
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