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SYNTHESISOFDIMETHYLCARBONATEFROMMETHYLCARBAMATEANDMETHANOLWITHZINCCOMPOUNDSASCATALYSTSWENBOZHAO,FENGWANG,WEICAIPENG,NINGZHAO,JUNPINGLI,FUKUIXIAO,WEIWEI,ANDYUHANSUN,STATEKEYLABORATORYOFCOALCONVERSION,INSTITUTEOFCOALCHEMISTRY,CHINESEACADEMYOFSCIENCES,TAIYUAN030001,PEOPLESREPUBLICOFCHINA,ANDGRADUATEUNIVERSITYOFCHINESEACADEMYOFSCIENCES,BEIJING100039,PEOPLESREPUBLICOFCHINAVARIOUSZINCCOMPOUNDSWEREUSEDASTHECATALYSTSFORTHESYNTHESISOFDIMETHYLCARBONATEDMCFROMMETHYLCARBAMATEMCANDMETHANOLINABATCHREACTORAMONGTHEM,ZNCL2SHOWEDTHEHIGHESTCATALYTICACTIVITYANDLEDTOTHEDMCYIELDOF336UNDERTHEOPTIMALCONDITIONSINADDITION,APOSSIBLEREACTIONMECHANISMWASPROPOSEDBASEDONFOURIERTRANSFORMINFRAREDFTIRANDXRAYDIFFRACTIONXRDCHARACTERIZATIONRESULTS1INTRODUCTIONDIMETHYLCARBONATEDMCASANENVIRONMENTALLYBENIGNBUILDINGBLOCKHASATTRACTEDMUCHATTENTIONINRECENTYEARS15ITCANREPLACEPHOSGENE,DIMETHYLSULFATE,CHLOROMETHANE,ANDMETHYLCHLOROFORMATEASCARBONYLATION,METHYLATION,ESTERIFICATIONOR,ESTERINTERCHANGEREAGENT,ANDITCANALSOBEUSEDASADDITIVEFORGASOLINE,FLAVORINGAGENTOFFOODSTUFF,ELECTRONICCHEMICAL,ETCTHUS,THEEFFECTIVESYNTHESISOFDMCBECOMESMOREANDMOREIMPORTANTTHECURRENTPROCESSESREPORTEDMAINLYINCLUDEPHOSGENATIONOFMETHANOL,OXIDATIVECARBONYLATIONOFMETHANOL,ESTEREXCHANGE,ANDESTERIFICATIONOFCARBONDIOXIDEWITHMETHANOL,WHICHALLSUFFERFROMTHECORRESPONDINGSHORTCOMINGSSUCHASBEINGPOISONOUS,BEINGEASILYEXPLOSIVE,HAVINGACOMPLEXREACTIONCOURSE,ANDHAVINGEXTREMELYLOWCONVERSIONRECENTLY,ANEWROUTEOFTHEDMCSYNTHESISFROMUREAANDMETHANOLHASBEENDEVELOPEDFORLOWCOSTANDFACILESEPARATIONOFPRODUCTION6INTHISSYNTHESISAPPROACH,THEINTERMEDIATEMETHYLCARBAMATEMCISPRODUCEDFIRSTANDFURTHERCONVERTEDTODMCBYREACTIONWITHMETHANOLTHEFIRSTSTEPOFTHEREACTIONISFASTANDHIGHLYSELECTIVEEVENWITHOUTCATALYSTS,BECAUSEUREACANDECOMPOSEEASILYTOAMMONIAANDISOCYANICACIDTHELATTER,ASANACTIVEINTERMEDIATE,CANFURTHERREACTWITHSOLVENTMETHANOLTOPRODUCEMCHOWEVER,THESECONDSTEPOFTHEREACTION,MCTODMC,ISMOREDIFFICULTTHANTHEFIRSTSTEP79THEAMMONIAACCUMULATEDINTHEFIRSTSTEPWILLRESTRICTTHESHIFTOFTHEREACTIONEQUILIBRIUMTODMC,SINCEITISALSOTHEBYPRODUCTOFTHESECONDSTEPCONSEQUENTLY,DIVIDINGTHISREACTIONINTOTWOISOLATEDSTEPSWILLBEAMOREPROMISINGAPPROACHTOWARDTHESYNTHESISOFDMCTHEKEYTOTHETWOSTEPTECHNICSISTOEFFECTIVELYPROMOTETHESECONDREACTION,WHICHISTHERATECONTROLSTEPFORTHEREACTIONOFUREAMETHANOLYSIS,WITHPROPERCATALYSTALOTOFCATALYSTSSUCHASBASES,ORGANICTIN,METALOXIDE,ANDZINCCOMPOUNDSHAVEBEENTESTEDINABATCHREACTORTOWARDTHEDIRECTREACTIONOFUREAANDMETHANOLORITSANALOGUES1018HOWEVER,ASTOTHEISOLATEDSECONDREACTION,ONLYAFEWSTUDIESHAVEBEENREPORTEDABOUTTHEEXPLOITATIONOFCATALYSTUPTONOWINTHISREGARD,ORGANICTINCOMPOUNDWASCONSIDEREDASAFAVORABLECATALYSTFORTHISREACTIONINPREVIOUSLITERATURE,BUTITWASNOTPROMISINGFROMTHEVIEWPOINTOFTHEENVIRONMENTBECAUSEOFITSSTRONGTOXICITY19OURGROUPFOUNDTHATCAOWASTHEBESTONEAMONGSOLIDBASECATALYSTSTESTEDSINCEITACTIVATEDMETHANOLEFFECTIVELYWITHITSSTRONGESTBASICITY,BUTTHEDMCYIELDONITWASSTILLFARFROMSATISFACTORY7INTHISWORK,THESYNTHESISOFDMCFROMMCANDMETHANOLWASINVESTIGATEDOVERMANYZINCCOMPOUNDCATALYSTSINABATCHREACTORFURTHERMORE,THEREACTIONCONDITIONSWEREEXPLOREDINDETAILWITHZNCL2ASTHEMODELCATALYSTFORITSEXCELLENTCATALYTICPERFORMANCE2EXPERIMENTALSECTION21PREPARATIONOFCATALYSTZNCH3COO2ANDZNNO32WEREOBTAINEDBYEVACUATINGZNCH3COO22H2OAT110CFOR20HANDZNNO326H2OAT115CFOR24H,RESPECTIVELYOTHERCHEMICALSANDCATALYSTSWERECOMMERCIALANALYTICREAGENTSWITHOUTFURTHERPURIFICATION22CATALYTICREACTIONTHEREACTIONWASCONDUCTEDINA350MLSTAINLESSSTEELAUTOCLAVEREACTOREQUIPPEDWITHELECTRICHEATING,AREFLUXCOLUMN,ANDAMAGNETICSTIRRERUNDERTHEASSIGNEDCONDITIONSINATYPICALPROCESS,01MOLOFMC,20MOLOFMETHANOL,AND74MMOLOFCATALYSTWEREPUTINTOAUTOCLAVEFIRSTANDTHENWERERAPIDLYHEATEDTOTHEDESIREDTEMPERATUREANDKEPTFORACERTAINTIMEWITHMAGNETICSTIRRINGTHESTIRRINGSPEEDWAS60050RPM,ANDTHETEMPERATUREERRORWAS100GTHEEFFECTOFREACTIONTEMPERATUREISILLUSTRATEDBYFIGURE4THECONVERSIONOFMCWASCONSISTENTLYENHANCEDWITHTHEINCREASEOFTEMPERATURE,BUTTHEDMCYIELDREACHEDITSPEAKAT190CANDTHENDECREASEDINTHEORY,THEHIGHTEMPERATUREWASAPPROPRIATEFORSYNTHESISOFDMC,SINCETHISREACTIONWASANENDOTHERMICREACTION20HOWEVER,HIGHERTEMPERATUREALSOSHORTENEDTHETIMENEEDEDTOREACHTHEMAXIMUMDMCCONCENTRATIONANDACCELERATEDTHERATEOFFURTHERREACTIONACCORDINGLY,ALTHOUGHBYPRODUCTNMMCCOULDNOTBEDETECTEDAT170C,ASTHETEMPERATUREINCREASED,ITSYIELDINCREASEDSIGNIFICANTLYATTHECOSTOFDMCCONSUMPTIONSIMULTANEOUSLY,THETHERMALDECOMPOSITIONOFDMCMAYAGGRAVATEGRADUALLYTHEREFORE,THESUITABLEREACTIONTEMPERATURESHOULDBECONTROLLEDBELOW190CFIGURE5DEMONSTRATESTHEEFFECTOFREACTIONTIMETHEDMCYIELDINCREASEDATTHEFIRST10HANDREACHEDITSMAXIMUMOF336,ANDTHENTHECONSUMPTIONOFDMCINTHEFURTHERREACTIONSURPASSEDGRADUALLYTHEFORMATIONOFDMCFROMMCTHUS,10HWASTHEOPTIMALREACTIONTIMEFORTHEREACTIONOFMCWITHMETHANOLTHEDETAILEDREACTIONKINETICSFORTHESETHREEEXPERIMENTALFACTORSSTILLAWAITSFURTHEREXPLORATION34POSSIBLEMECHANISMASATRANSITIONMETALELEMENT,DIVALENTZN2IONWITHD10ELECTRONSCOULDCOORDINATEWITHNITROGEN,OXYGEN,ANDSULFURORPHOSPHORUSATOMTOREACHTHESTABLECONSTRUCTIONOF18ELECTRONS2830THUS,THENITROGENATOMOFAMINOANDTHETWOOXYGENATOMSOFCARBONYLANDMETHOXYINTHEMCMOLECULEALLHADACHANCETOCOORDINATEWITHZN2IONTHEIRELECTRONDENSITIESCOMPUTEDBYHYPERCHEM75BASEDONAM1SEMIEMPIRICALMETHODWERE0416,0404,AND0286OFNEGATIVECHARGE,RESPECTIVELYTHISMEANTTHATTHENITROGENATOMWASMOREPOSSIBLETHANTHEOXYGENATOMTOCOORDINATEWITHZN2IONFURTHERMORE,THEHYBRIDIZEDORBITALOFNITROGENATOMWOULDCHANGEFROMSP2TOSP3ONCEITCOORDINATEDWITHZN2ION,ANDCORRESPONDINGLY,THEDELOFIGURE2FTIRSPECTRAOFMETHANOLINTERACTEDWITHZNCL21,METHANOL2,80C3,130C4,170CFIGURE3EFFECTOFCATALYSTAMOUNTONDMCANDNMMCYIELDANDMCCONVERSIONREACTIONTEMPERATURE,190CREACTIONTIME,10HMC,75GMETHANOL,64GFIGURE4EFFECTOFREACTIONTEMPERATUREONDMCANDNMMCYIELDANDMCCONVERSIONREACTIONTIME,10HAMOUNTOFCATALYST,100GMC,75GMETHANOL,64GFIGURE5EFFECTOFREACTIONTIMEONDMCANDNMMCYIELDANDMCCONVERSIONREACTIONTEMPERATURE,190CAMOUNTOFCATALYST,100GMC,75GMETHANOL,64GINDENGCHEMRES,VOL47,NO16,20085915CALIZEDBONDOFAMIDEDISAPPEAREDCONSIDERINGTHEFTIRSPECTRARESULTS,APOSSIBLEMECHANISMFORCATALYSTZNCL2WASPROPOSEDASSHOWNINSCHEME1ATFIRST,BYTHECOORDINATIONOF2EQUIVOFMCTHROUGHTHENITROGENATOMOFAMIDE,1EQUIVOFZN2IONREACHEDTHESTABLECONSTRUCTIONOF18ELECTRONSTHETWOCHLORIDEATOMSWOULDPROVIDEONEPAIROFELECTRONSEACHINTHEZNNH2COOCH32CL2COMPLEX,THEAMINOBONDOFLIGANDMCWASWEAKENED,WHICHFACILITATEDTHENUCLEOPHILICATTACKOFMETHANOLTHEN,ALONEPAIROFELECTRONSOFOXYGENINMETHANOLCOULDFORMABONDTOTHEELECTROPHILICCARBONYLCARBON,ANDATTHESAMETIME,THERELATIVELYWEAKBONDOFTHECARBONYLGROUPBROKECONSEQUENTLY,BOTHELECTRONSMOVEDTOTHEOXYGENANDPROVIDEDTHETHIRDLONEPAIROFELECTRONSANDANEGATIVECHARGEITWASNOTEWORTHYTHATTHEOXYGENINMETHANOLGAINEDAPOSITIVECHARGE,SINCEITHADEFFECTIVELYLOSTANELECTRONBYSHARINGITSLONEPAIRWITHCARBONINTHENEWBONDSUCHAZWITTERIONINTERMEDIATEMIGHTBESTABILIZEDBYANOTHERZN2IONTHEN,THEPROTONOFOHMOVEDTONITROGEN,ANDTHELONEPAIROFELECTRONSONOXYGENRETURNEDTOREFORMTHECARBONYLBONDASARESULT,THECNBONDBROKEWITHBOTHELECTRONSMOVINGONTOTHENITROGENTOPRODUCETHECORRESPONDINGCOMPLEXZNNH32CL2ANDDMCBECAUSEOFTHESTRONGNUCLEOPHILICABILITYOFMCANDTHELIBERATIONOFNH3,THENH3INTHECOMPLEXWASSUBSTITUTEDBYMCTOFINISHTHECATALYTICCIRCLENOTABLY,AWHITECRYSTAL,WHICHWASPROVEDTOBEZNNH32CL2BYXRDSEEFIGURE6,WASPRECIPITATEDAFTERTHEREACTIONSOLUTIONWASCOOLEDTO0CINOUREXPERIMENTITSHOWEDTHESAMECATALYTICACTIVITYASZNCL2ENTRY11,WHICHPOWERFULLYSUPPORTEDTHEABOVEREACTIONMECHANISMINADDITION,ITWASOBVIOUSTHATTHEHIGHERZNCL2AMOUNT,THEHIGHERREACTIONTEMPERATUREANDTHELONGERREACTIONTIME,WOULDGIVERISETOTHEHIGHERYIELDOFCOMPLEXZNNH2COOCH32CL2THUS,THEMCCONVERSIONWASOBSERVEDTOINCREASEMONOTONICALLYALONGWITHTHOSEVARIABLESHOWEVER,THEYIELDOFDMCDIDNOTALWAYSINCREASEASDESCRIBEDINTHEREACTIONMECHANISMBECAUSEOFTHESIDEREACTIONSOFDMC4CONCLUSIONSAMONGTHEZINCCOMPOUNDCATALYSTSFORTHESYNTHESISOFDMCFROMMCANDMETHANOL,ZNCL2ANDZNBR2SHOWEDTHEHIGHESTACTIVITY,PROBABLYDUETOTHEIRFAVORABLESOLUBILITYINMETHANOLTHEIRHIGHCATALYTICPERFORMANCEONLYORIGINATEDFROMZN2IONFTIRSPECTRAANDXRDCHARACTERIZATIONINDICATEDTHATMCWASACTIVATEDBYZN2THROUGHTHECOORDINATIONOFTHENITROGENATOMINADDITION,THEREACTIONTIME,REACTIONTEMPERATURE,ANDCATALYSTAMOUNTHADASTRONGEFFECTONTHEPERFORMANCEOFMODELCATALYSTZNCL2THEMCCONVERSIONANDDMCYIELDUNDERTHEOPTIMALCONDITIONSREACHED509AND336,RESPECTIVELYACKNOWLEDGMENTTHEAUTHORSACKNOWLEDGETHEFINANCIALSUPPORTFROMSTATEKEYPROGRAMFORDEVELOPMENTANDRESEARCHOFCHINANO2006BAC02A08LITERATURECITED1SHAIKH,AASIVARAM,SORGANICCARBONATESCHEMREV1996,963,9512TUNDO,PNEWDEVELOPMENTSINDIMETHYLCARBONATECHEMISTRYPUREAPPLCHEM2001,737,11173ONO,YCATALYSISINTHEPRODUCTIONANDREACTIONSOFDIMETHYLCARBONATE,ANENVIRONMENTALLYBENIGNBUILDINGBLOCKAPPLCATAL,A1997,1552,1334DELLEDONNE,DRIVETTI,FROMANO,UDEVELOPMENTSINTHEPRODUCTIONANDAPPLICATIONOFDIMETHYLCARBONATEAPPLCATAL,A2001,22112,2415PACHECO,MAMARSHALL,CLREVIEWOFDIMETHYLCARBONATEDMCMANUFACTUREANDITSCHARACTERISTICSASAFUELADDITIVEENERGYFUELS1997,111,26BALL,PFUELLMANN,HHEITZ,WCARBONATESANDPOLYCARBONATESFROMUREAANDALCOHOLANGEWCHEM,INTEDENGL1980,199,7187WANG,MWANG,HZHAO,NWEI,WSUN,YSYNTHESISOFDIMETHYLCARBONATEFROMUREAANDMETHANOLOVERSOLIDBASECATALYSTSCATALCOMMUN2006,71,68SUN,JJYANG,BLLIN,HYASEMICONTINUOUSPROCESSFORTHESYNTHESISOFMETHYLCARBAMATEFROMUREAANDMETHANOLCHEMENGTECHNOL2004,274,4359KAMINSKAIA,NVKOSTIC,NMALCOHOLYSISOFUREACATALYZEDBYPALLADIUMIICOMPLEXESINORGCHEM1998,3717,430210CHO,TTAMURA,TCHO,TSUZUKI,KPROCESSFORPREPARINGDIALKYLCARBONATESUSPATENT5,534,649,199611LIN,HYANG,BSUN,JWANG,XWANG,DKINETICSSTUDIESFORTHESYNTHESISOFDIMETHYLCARBONATEFROMUREAANDMETHANOLCHEMENGJ2004,10313,2112SALEH,RYMICHAELSON,RCSUCIU,ENKUHLMANN,BPROCESSFORMANUFACTURINGDIALKYLCARBONATEFROMUREAANDALCOHOLUSPATENT5,565,603,199613RYU,JYGELBEIN,APPROCESSANDCATALYSTFORMAKINGDIALKYLCARBONATESUSPATENT6,392,078,2002SCHEME1REACTIONMECHANISMFIGURE6XRDPATTERNOFTHEWHITECRYSTAL5916INDENGCHEMRES,VOL47,NO16,200814WU,CZHAO,XWANG,YEFFECTOFREDUCTIONTREATMENTONCATALYTICPERFORMANCEOFZNBASEDCATALYSTFORTHEALCOHOLYSISOFUREATODIMETHYLCARBONATECATALCOMMUN2005,610,69415WANG,MZHAO,NWEI,WSUN,YSYNTHESISOFDIMETHYLCARBONATEFROMUREAANDMETHANOLOVERZNOINDENGCHEMRES2005,4419,759616BHANAGE,BMFUJITA,SIKUSHIMA,YARAI,MTRANSESTERIFICATIONOFUREAANDETHYLENEGLYCOL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