有机合成 第6章 氧化.ppt

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1、1Chapter6OxidationTheoppositeofreductionDehydrogenationSubstitutionofhydrogenbyafunctionalgroupOne-electronabstractionfromanucleophiliccentreAdditonofoxygen-containingreagentstomultiplebondsandheteroatoms23CatalyticdehydrogenationDehydrogenationbysuccessivehydrideandprotontransfersDeh

2、ydrogenationbysubstitution-eliminationandaddition-eliminationprocess4ThreegeneralcategoriesTransitionmetaloxidants(Cr,Mn,Ti,Hgetc.)Cr(VI)--->Cr(III)    Mn(+7)--->Mn(+2)i.e.2CrO3+3R2CHOH+6H+--->3R2C=O+2Cr+3+6H2O2MnO4-+5R2CHOH+6H+--->5R2C=O+2Mn+2+8H2ONote:ineachcase,acidisconsumedandH2

3、Oproduced.Oxygenators(O2,O3,RCO2OH)Others(DMSO,Pb(OAc)4,NCS,Al(O-iPr)3etc.)5Transitionmetaloxidants:Cr(Oxidationofalcohols)CrO3(Chromiumtrioxide)dissolvesinH2OChromateion(sodiumchromate)dimerizes:6Mechanismof2oAlcoholOxidationCr(+4)+Cr(+6)---->2Cr(+5)Cr(+5)+R2CHOH---->R2C=O+Cr(+3)+2H

4、+FirstformingachromateesterThenE2eliminationNote!7Jones’reagentAqueoussolutionofchrominium(VI)oxideandsulfuricacid.Alcoholscontainingdoubleortriplebondsmaybeselectiveoxidized.Usage:AddreagenttoicecoldsolutionofROHinacetone.Watchcolorchange:Orange-red---->green.Destroyexcessreagentwith

5、i-PrOH.(---->acetone)8Chrominium(VI)oxideinpyridine(CollinsreagentandSarettreagent)CrO3isaddedtopyridine,notreverse.UsedassolutioninCH2Cl2;MilderOxidant.Beusedforoxidationsofalcoholshavingacidsensitivegroup.GoodforPrimaryROH---->aldehydes.Alsogoodforallylicalcoholsandbenzylicalcohols

6、.910PCC(pyridiniumchlorochromate,CrO3ClH-pyridine)PDC(pyridiniumdichromate,[(C5H5NH+)2Cr2O72-])GoodforPrimaryROH---->aldehydes.Alsogoodforallylicalcoholsandbenzylicalcohols.11Transitionmetaloxidants:Cr(OxidationofC-HBonds)OccurswithCr(VI)undermoreforcingconditions12Etardreagent(chromy

7、lchloride,CrO2Cl2,inaninertsolvent(CCl4,CS2))Controlledbenzylicoxidationtoaldehyde.13Transitionmetaloxidants:ManganeseKMnO4-Potassiumpermanganate-lessselective-tendstowardover-oxidationMnO2-Manganesedioxide-moreselectiveReactivityofKMnO4:acidic>basic>neutralHeatingmakesstrongerreactiv

8、ityFr