Advances in Green Chemistry: Chemical Syntheses Using Microwave Irradiation (AZREFI Special Publications)

553 Pages·2002·15.345 MB·English

by  Rajender Varma

Cravotto,Carnaroglio(Eds.)
MicrowaveChemistry
DeGruyterGraduate
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Microwave
Chemistry
|
Edited by
Giancarlo Cravotto, Diego Carnaroglio
Editors
ProfessorGiancarloCravotto
UniversityofTurin
Dip.diScienzaeTecnologia
delFarmaco
ViaPetroGiuria9
10125Turin
Italy
Dr.DiegoCarnaroglio
MilstoneSrl
ViaFatebenefratelli1/5
24010Sorisole(BG)
Italy
ISBN978-3-11-047992-8
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Thisbookisdedicatedtomyentireresearchgroup,afantasticteamofresearchers,
post-docs,andPhDstudentsfromdifferentcountrieswhosharethesamepassionand
enthusiasm.
GiancarloCravotto
TomyparentsGiovannaandLudovico,
towhomIamgratefulforteachingmeaneffectiveworkingmodelthatcombinespro-
fessionalismandcompetenceininnovationandglobalbusiness.
AndtoGiancarloforhishigh-qualityadvice,support,direction,andpastoralrespon-
sibilityduringmyPhDperiodandbeyond.
DiegoCarnaroglio
Preface
The 1940s brought with them the discovery of the heating effects of microwaves
which,tento 15yearslater, becameaninnovationthatwasprideofplaceinmany
Americankitchens.Atthesametime,microwave(MW) pioneerscarriedoutchemi-
calexperiments on polymers and glasses, and generated little more thancuriosity.
Inthemid-1980s,however,theMWheatingtechniquewasusedwidelyinchemical
experimentationasanewenergysourceanditssalientadvantagesoverconventional
heating were well documented. In the initial absence of dedicated MW ovens dur-
ing the 1990s, kitchen MW ovens were frequently used by chemists to provide the
activationenergy; inthiswayProf. Rajender Varmaexplored a widevariety ofoxi-
dation,reduction,cleavage,condensation,multicomponentreactions,combinatorial
chemistryandsynthesisofheterocyclesinlessthanthreeminutesundersolvent-free
conditions¹ .Despite the inadequatemeasurementof temperaturesinsidethe reac-
tion vessels during irradiation,often erroneously described as a ‘magic effect’, the
gradualdiffusionofprofessionalmono-andmultimodereactorsfinallyshedlighton
the spectacular reaction rate enhancements that the technique can generate. MW-
assisted organic synthesis conducted in dedicated MW equipment has now grown
intoamaturefieldthathasbeenwidelyadaptedindrugdiscovery,particularlydueto
therapidsynthesisofalargenumberof‘lead’compounds,highyields,improvedpu-
rityand,frequently,greenerreactionconditions².Althoughreadersaremostfamiliar
withthegreatpotentialofdielectricheating,theadvantagesanddisadvantagesofa
particular deviceor the conditions needed for maximizingefficiency and function-
alitymayperhapsbelessclear.SincethepublicationofVanNoorden’s2008report
entitledMicrowavingmyths³,inwhichseveralexpertsdescribedthecurrentstatusof
MW-assistedchemistry,newtechnologicaladvanceshavebeenmadethathavebroad-
enedboththechemicalapplicationsandscientificinterest;J.Moseley(AstraZeneca)
quipped“virtuallyallnewcompoundsnowhavetheirfirstsynthesisinamicrowave”
andthisfacthasacquiredevenmorerelevanceyearslater.Thelatestgenerationof
lab-scale reactors⁴ are extremely versatile and can accommodate a wide range of
reactionconditions.Rapidtechnologicaladvanceshaveenabled faster heatingand
cooling,accurateparametermeasurementandcontrol,andawiderrangeofopera-
tivepressuresandtemperatures,andthesecoupledwiththeavailabilityofgasinlets
and pressurization mean that the technique can now be used in a much broader
1 VarmaRS.Greenchemistry,1999,1(1),43–55.
2 VarmaRS.Advancesingreenchemistry:chemicalsynthesisusingmicrowaveirradiation(2002),
AstraZenecaResearchFoundation,Bangalore,India,ISBN:81-901238-5-8.
3 VanNoordenR.Microwavingmyths,Chem.World,2008,5,40.
4 RinaldiL,CarnaroglioD,RotoloL,CravottoG.JAMicrowave-BasedChemicalFactoryintheLab:
FromMilligramtoMultigramPreparationsofChemistry2015,ID879531,8pp.
https://doi.org/10.1515/9783110479935-201
Preface | VII
array of fields: organic and inorganic (nanomaterial) synthesis, plant extraction,
biomassdepolymerisationandpollutantdegradationaresomeofthebeneficiaries.⁵
Therapidcoolingoffoncompletionofreactionscanminimizedegradationandside
reactions.Furthermore,recentadvanceshavebeenachievedonthe‘kilolab’scaleus-
ingacontinuousflowMWsystem,asdescribedbyMorschhauseretal.⁶thatinvolves
atransmissionlineshort-circuitedwaveguidereactor,whichcombinesthebenefitsof
theexistingmono-andmultimodetechnologies.
Anumberofresearchfieldshavetakenadvantageofthefast,molecularlyselec-
tiveandvolumetricheatingthatiscreatedbythedirectcouplingofMWenergyand
thebulkmixture;aconditionthatoftencannotbereproducedbyclassicalconductive
heating.SeveralarticlespublishedintheJournalofChemicalEducation⁷convinceda
numberofinstitutionstousethisheatingtooltoreducethetimeofexperimentsinun-
dergraduateorganicchemistrylaboratories.Theinitialreportsofexplosionscaused
byscientificallymisplaceduseofpressurisedcontainersandTeflon®bombswithsol-
vents indomesticMWovensevoked generalconcernover studentsafety,whichre-
flectedadverselyonthetechnologyitself.TheuseofdomesticMWovensinchemical
laboratoriesisnownotadvisable.
Amongotherbenefits,theefficientheattransferandshorterreactiontimesofMW
technologyrendersitavaluableassettogreenchemistryconcepts.MWtechnologyal-
lowsthereactionstobeperformedonsmallscales:inmilligramsratherthangrams
tobeusedinteachinglaboratories,thusreducingthecostofreagentsandchemicals
andtheassociatedwastedisposal,whilealsomultiplyingthecreativityofmoreeffi-
cientstudents.AlthoughMWtechnologiesarenowusedineveryfacetofchemistry,
fromthedissolutionofsamplesforlaboratoryanalysistolarge-scalepreparationsof
high-valuefinechemicalsandevenlarger-scaleprocessingofceramicproducts,itis
quitedifficulttofinddedicatedundergraduatecoursesonthesubject,withsomerelief
duringadvancedPhDresearchactivities.
DespitethepublicationofanumberofexcellentbooksonMWchemistryandpro-
cessing,thereisalackofsuitabletextbooksthataddresstheneedsofMSandPhDstu-
dents,whoneedreadyaccesstotherelevantknowledgetohelpthemappropriately
designandcarryoutnewexperimentsunderdielectricheating.Althoughnumerous
otheractivationmethodsandtechnologiesareaccessibleforconductingachemical
5 TagliapietraS,CravottoG,CalcioGaudinoE,VisentinS,MussiV,Functionalizationofsingle-walled
CarbonNanotubesviathe1,3-CycloadditionofCarbonylylidesunderMicrowaveIrradiation,Synlett,
2012,1459–1462.
6 MorschhauserR,KrullM,KayserC,BoberskiC,BierbaumR,PuschnerPA,GlasnovTN,KappeCO.
Microwave-assistedcontinuousflowsynthesisonindustrialscale,GreenProcessSynth.1,2012,281–
290.
7 ParquetE,LinQ,MicrowaveAssistedWolff-Kischner-ReductionReaction,J.Chem.Educ.,1997,74
(10),1225;CresswellSL,HaswellSJ,Microwaveovens–outofthekitchen,J.Chem.Educ.,2001,78
(7),900;ColemanWF,Microwave-assistedheterocyclicchemistry,J.Chem.Educ.,2006,83(4),621.
VIII | Preface
reaction,itishardtoimagineachemicalresearchlaboratorywithoutaMWreactor
likeatypicalhouseholdkitchen.
Wesincerelyhopethatthistextbookwillcontributetoencouraginganewgener-
ationofchemiststoexploittheMWheatingtechniqueasacommontoolintheirre-
searchendeavours.Alltheeminentauthorsofthechaptersinthistextbookarestead-
fastMWusersthatdeservemyheartfeltthanksforbeingwillingtotakethetimeand
energytocontributetheirwealthofknowledgeinwritingtheirchapters.
AfterseveralyearsoffascinatinginvestigationsintotheuseofMW-assistedchem-
ical processes and beyond, I would like to highlight my own personal pleasure in
coeditingthisbookwithanexpertthatwasonceoneofmymostsuccessfuleverPhD
students.Wewouldalsoliketoacknowledgethreeentrepreneursthathavemadea
remarkablecontributiontothesuccessofMWchemistrybygarneringexcellentrepu-
tationsworldwidefortheirrespectivecompanies;Ihadthehonourofpersonallymeet-
ingWernerLautenschläger,FrancoVisinoniandMikeCollins.
Prof.GiancarloCravotto
DirectoroftheDepartmentof
DrugScienceandTechnology
(UniversityofTurin–Italy)
Contents
Preface|VI
GiancarloCravottoandPedroCintas
1 Microwavechemistry:history,developmentandlegacy|1
1.1 Introduction|1
1.2 Howitallbegan|1
1.3 Fromcookingtochemistry|3
1.4 Thethermalconundrum|5
1.4.1 Thesearchforspecificeffects:alongjourney|6
1.5 Efficientandfine-tunedheating:theroleofoutliers|11
1.5.1 ConveyingMWenergy:susceptors|11
1.5.2 Apeculiardevice:coolingwhileheating|12
1.6 Efficientbydesign:tailor-madereactors|13
1.7 Conclusions|14
PaoloVeronesi
2 AnIntroductiontodielectricheating|18
2.1 Theelectromagneticspectrumandtheindustrial,scientific,andmedical
frequencies|18
2.2 Basisofdielectricheating|19
2.2.1 Selectivity|24
2.2.2 Self-regulatingreactions|26
2.2.3 Volumetricheating|26
2.2.4 Inversionoftemperatureprofile|27
2.2.5 Rapidheating|28
2.2.6 Thermalrunaway|28
CristinaLeonelli
3 Microwavegenerators,transmission,andinteractionwithdifferent
materials|31
3.1 Introduction|31
3.2 Microwavegenerators|33
3.2.1 Magnetron|33
3.2.2 Solid-stategenerators|34
3.2.3 Othermicrowavesources|35
3.3 WavePropagation|36
3.3.1 Waveguidemodes|36
3.4 Antennas|38