有机化学英文chapter10课件

OrganicChemistryWilliamH.BrownChristopherS.FooteBrentL.IversonAlcohols

andThiolsChapter10Structure-AlcoholsThefunctionalgroupofanalcoholisan-OHgroupbondedtoansp3hybridizedcarbonbondanglesaboutthehydroxyloxygenatomareapproximately109.5°Oxygenissp3hybridizedtwosp3hybridorbitalsformsigmabondstocarbonandhydrogentheremainingtwosp3hybridorbitalseachcontainanunsharedpairofelectronsNomenclature-AlcoholsExamplesNomenclatureofAlcoholsCompoundscontainingmorethanoneOHgrouparenameddiols,triols,etc.CH3CHCH2HOOHCH2CH2OHOHCH2CHCH2HOHOOH1,2-Ethanediol(Ethyleneglycol)1,2-Propanediol(Propyleneglycol)1,2,3-Propanetriol(Glycerol,Glycerine)NomenclatureofAlcoholsUnsaturatedalcoholsshowthedoublebondbychangingtheinfixfrom-an-to-en-showthetheOHgroupbythesuffix-olnumberthechaintogiveOHthelowernumberPhysicalPropertiesHydrogenbonding:

whenthepositiveendofonedipoleisanHbondedtoF,O,orN(atomsofhighelectronegativity)andtheotherendisF,O,orNthestrengthofhydrogenbondinginwaterisapproximately21kJ(5kcal)/molhydrogenbondsareconsiderablyweakerthancovalentbondsnonetheless,theycanhaveasignificanteffectonphysicalpropertiesHydrogenBondingPhysicalPropertiesEthanolanddimethyletherareconstitutionalisomers.Theirboilingpointsaredramaticallydifferentethanolformsintermolecularhydrogenbondswhichincreaseattractiveforcesbetweenitsmoleculesresultinginahigherboilingpointthereisnocomparableattractiveforcebetweenmoleculesofdimethyletherbp-24°CEthanolbp78°CDimethyletherCH3CH2OHCH3OCH3PhysicalPropertiesAcidityofAlcoholsIndiluteaqueoussolution,alcoholsareweaklyacidicAcidityofAlcoholsReactionwithMetalsAlcoholsreactwithLi,Na,K,andotheractivemetalstoliberatehydrogengasandformmetalalkoxidesAlcoholsarealsoconvertedtometalalkoxidesbyreactionwithbasesstrongerthanthealkoxideiononesuchbaseissodiumhydrideReactionwithHX3°alcoholsreactveryrapidlywithHCl,HBr,andHIlow-molecular-weight1°and2°alcoholsareunreactiveundertheseconditions1°and2°alcoholsrequireconcentratedHBrandHItoformalkylbromidesandiodidesReactionwithHXwithHBrandHI,2°alcoholsgenerallygivesomerearrangedproduct1°alcoholswithextensive-branchinggivelargeamountsofrearrangedproductReactionwithHX-SN1Step1:protontransfertotheOHgroupgivesanoxoniumionStep2:lossofH2OgivesacarbocationintermediateReactionwithHX-SN1Step3:reactionofthecarbocationintermediate(anelectrophile)withhalideion(anucleophile)givestheproductReactionwithHX-SN21°alcoholsreactwithHXbyanSN2mechanismStep1:rapidandreversibleprotontransferStep2:displacementofHOHbyhalideion

Step1:protontransfergivesanoxoniumionStep2:concertedeliminationofHOHandmigrationofamethylgroupgivesa3°carbocationReactionwithHXReactionwithHXStep3:reactionofthecarbocationintermediate(anelectrophile)withhalideion(anucleophile)givestheproductReactionwithSOCl2Thionylchlorideisthemostwidelyusedreagentfortheconversionof1°and2°alcoholstoalkylchloridesabase,mostcommonlypyridineortriethylamine,isaddedtocatalyzethereactionandtoneutralizetheHClReactionwithSOCl2ReactionofanalcoholwithSOCl2inthepresenceofa3°amineisstereoselectiveitoccurswithinversionofconfigurationReactionwithSOCl2Step1:formationofanalkylchlorosulfiteStep2:nucleophilicdisplacementofthisleavinggroupbychlorideiongivesthechloroalkaneAlkylSulfonatesSulfonylchloridesarederivedfromsulfonicacidssulfonicacids,likesulfuricacid,arestrongacidsAsulfonylchlorideAsulfonateanion(averyweakbaseandstableanion;averygoodleavinggroupAsulfonicacid(averystrongacid)R-S-OHR-S-O-R-S-ClOOOOOOAlkylSulfonatesAcommonlyusedsulfonylchlorideisp-toluenesulfonylchloride(Ts-Cl)AlkylSulfonatesAnothercommonlyusedsulfonylchlorideismethanesulfonylchloride(Ms-Cl)AlkylSulfonatesSulfonateanionsareveryweakbases(theconjugatebaseofastrongacid)andareverygoodleavinggroupsforSN2reactionsConversionofanalcoholtoasulfonateesterconvertsHOH,averypoorleavinggroup,intoasulfonicester,averygoodleavinggroupAlkylSulfonatesThistwo-stepprocedureconverts(S)-2-octanolto(R)-2-octylacetateStep1:formationofap-toluenesulfonate(Ts)esterStep2:nucleophilicdisplacementoftosylateDehydrationofROHAnalcoholcanbeconvertedtoanalkenebyacid-catalyzeddehydration(atypeof-elimination)1°alcoholsmustbeheatedathightemperatureinthepresenceofanacidcatalyst,suchasH2SO4orH3PO42°alcoholsundergodehydrationatsomewhatlowertemperatures3°alcoholsoftenrequiretemperaturesatorslightlyaboveroomtemperatureDehydrationofROH180°CCH3CH2OHH2SO4CH2=CH2

+

H2O140°CCyclohexanolCyclohexeneOH+

H2OH2SO4CH3COHCH3CH3H2SO4CH3C=CH2CH3+H2O50°C2-Methyl-2-propanol(tert-Butylalcohol)2-Methylpropene(Isobutylene)DehydrationofROHwhereisomericalkenesarepossible,thealkenehavingthegreaternumberofsubstituentsonthedoublebond(themorestablealkene)usuallypredominates(Zaitsevrule)DehydrationofROHDehydrationof1°and2°alcoholsisoftenaccompaniedbyrearrangementacid-catalyzeddehydrationof1-butanolgivesamixtureofthreealkenesOHH2SO4140-170°C+3,3-Dimethyl-2-butanol2,3-Dimethyl-2-butene(80%)2,3-Dimethyl-1-butene(20%)DehydrationofROHBasedonevidenceofeaseofdehydration(3°>2°>1°)prevalenceofrearrangementsChemistsproposeathree-stepmechanismforthedehydrationof2°and3°alcoholsbecausethismechanisminvolvesformationofacarbocationintermediateintherate-determiningstep,itisclassifiedasE1DehydrationofROHStep1:protontransfertothe-OHgroupgivesanoxoniumionStep2:lossofH2OgivesacarbocationintermediateDehydrationofROHStep3:protontransferfromacarbonadjacenttothepositivelychargedcarbontowater;thesigmaelectronsoftheC-Hbondbecomethepielectronsofthecarbon-carbondoublebondDehydrationofROH1°alcoholswithlittle-branchinggiveterminalalkenesandrearrangedalkenesStep1:protontransfertoOHgivesanoxoniumionStep2:lossofHfromthe-carbonandH2Ofromthe-carbongivestheterminalalkeneDehydrationofROHStep3:shiftofahydrideionfrom-carbonandlossofH2Ofromthe-carbongivesacarbocationStep4:protontransfertosolventgivesthealkeneDehydrationofROHDehydrationwithrearrangementoccursbyacarbocationrearrangementDehydrationofROHAcid-catalyzedalcoholdehydrationandalkenehydrationarecompetingprocessesPrincipleofmicroscopicreversibility:

thesequenceoftransitionstatesandreactiveintermediatesinthemechanismofareversiblereactionmustbethesame,butinreverseorder,forthereversereactionasfortheforwardreactionPinacolRearrangementTheproductsofacid-catalyzeddehydrationofaglycolaredifferentfromthoseofalcoholsPinacolRearrangementStep1:protontransfertoOHgivesanoxoniumionStep2:lossofwatergivesacarbocationintermediatePinacolRearrangementStep3:a1,2-shiftofmethylgivesamorestablecarbocationStep4:protontransfertosolventcompletesthereactionOxidation:1°ROHOxidationofaprimaryalcoholgivesanaldehydeoracarboxylicacid,dependingontheexperimentalconditionstoanaldehydeisatwo-electronoxidationtoacarboxylicacidisafour-electronoxidationOxidationofROHAcommonoxidizingagentforthispurposeischromicacid,preparedbydissolvingchromium(VI)oxideorpotassiumdichromateinaqueoussulfuricacidPotassiumdichromateChromicacidK2Cr2O7H2SO4H2Cr2O7H2O2H2CrO4+ChromicacidChromium(VI)oxideCrO3H2OH2CrO4H2SO4Oxidation:1°ROHOxidationof1-octanolgivesoctanoicacidthealdehydeintermediateisnotisolatedOxidation:2°ROH2°alcoholsareoxidizedtoketonesbychromicacidChromicAcidOxidationofROHStep1:formationofachromateesterStep2:reactionofthechromateesterwithabase,hereshownasH2OChromicAcidOxidationofRCHOchromicacidoxidizesa1°alcoholfirsttoanaldehydeandthentoacarboxylicacidinthesecondstep,itisnotthealdehydepersethatisoxidizedbutratherthealdehydehydrateOxidation:1°ROHtoRCHOPyridiniumchlorochromate(PCC):

aformofCr(VI)preparedbydissolvingCrO3inaqueousHClandaddingpyridinetoprecipitatePCCasasolidPCCisselectivefortheoxidationof1°alcoholstoaldehydes;itdoesnotoxidizealdehydesfurthertocarboxylicacidsOxidation:1°ROHPCCoxidizesa1°alcoholtoanaldehydePCCalsooxidizesa2°alcoholtoaketoneOxidationofAlcoholsbyNAD+biologicalsystemsdonotusechromicacidortheoxidesofothertransitionmetalstooxidize1°alcoholstoaldehydesor2°alcoholstoketoneswhattheyuseinsteadisaNAD+theAdpartofNAD+iscomposedofaunitofthesugarD-ribose(Chapter25)andoneofadenosinediphosphate(ADP,Chapter28)OxidationofAlcoholsbyNAD+whenNAD+functionsasanoxidizingagent,itisreducedtoNADHintheprocess,NAD+gainsoneHandtwoelectrons;NAD+isatwo-electronoxidizingagentOxidationofAlcoholsbyNAD+NAD+istheoxidizinginawidevarietyofenzyme-catalyzedreactions,twoofwhichareOxidationofAlcoholsbyNAD+mechanismofNAD+oxidationofanalcoholhydrideiontransfertoNAD+isstereoselective;someenzymescatalyzedeliveryofhydrideiontothetopfaceofthepyridinering,otherstothebottomfaceOxidationofGlycolsGlycolsarecleavedbyoxidationwithperiodicacid,HIO4OxidationofGlycolsThemechanismofperiodicacidoxidationofaglycolisdividedintotwostepsStep1:formationofacyclicperiodateStep2:redistributionofelectronswithinthefive-memberedringOxidationofGlycolsthismechanismisconsistentwiththefactthatHIO4oxidationsarerestrictedtoglycolsthatcanformafive-memberedcyclicperiodateglycolsthatcannotformacyclicperiodatearenotoxidizedbyHIO4Thiols:StructureThefunctionalgroupofathiolisanSH(sulfhydryl)groupbondedtoansp3hybridizedcarbonThebondangleaboutsulfurinmethanethiolis100.3°,whichindicatesthatthereisconsiderablymorepcharactertothebondingorbitalsofdivalentsulfurthanthereistooxygenNomenclatureIUPACnames:theparentisthelongestchainthatcontainsthe-SHgroupchangethesuffix-eto-thiolwhen-SHisasubstituent,itisnamedasasulfanylgroupCommonnames:namethealkylgrou