造纸专业英语4.ppt

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1、RecationofcarbohydrateswithbleachingagentsandalkaliAlthoughthechemistryofpulpbleachingmainlyinvolvesthereactionsofligninwithbleachingchemicals,carbohydratesneverthelessundergoconcurrenttransformationsduringbleachingthatoftenhaveanimportantbearingonthestrengthpropertiesandyieldoftheresultingpulp.Thei

2、mpactofthesereactionsbecomesincreasinglymoresignificantasthelignincontentofthepulpdecreases.concurrent同时发生的，并存的；nevertheless还是,然而bearing关系,影响;方面;意义RecationofcarbohydrateswithbleachingagentsandalkaliThereactivesitesforattackbyelectrophilicbleachingspeciesoncarbohydratesareacetal(glycosidic)linkages,r

3、educingend-groupsandenonestructuresformedinitiallybyattackofanelectrophilicbleachingspecies.Thereactionsofcarbohydrateswithbleachingchemicalsmaybeconvenientlyclassifiedaccordingtowhethertheyoccuratacetalsitesorelsewhere.acetal缩醛glycosidic[生化]糖苷的enone烯酮Recationofcarbohydrateswithbleachingagentsandalk

4、ali1.reactionsatacetalsitesInafreeradicalchainprocess,thechlorineradicalabstractsahydrogenatomfromtheC-1atomoftheglycosideforminganorganicradicalwhichthenreactswithelementalchlorinetoregeneratechlorineradicalsandformachlorinatedanhydroglucoseunit.Inanensuinghydrolysisstep,theacetallinkageisdirectlyc

5、leavedandanaldonicacidendgroupisultimatelyformed.chlorinatevt.使氯化,用氯消毒anhydroglucose【化】葡糖酐aldonicacid醛酮酸aldonicacidChemicalstructureofgluconicacid,thealdonicacidderivedfromglucose.UronicacidRecationofcarbohydrateswithbleachingagentsandalkaliIntheozonationofcarbohydratemodelcompoundsandcellulose,thed

6、ominantreactionsintheinitialphaseareionicandinvolveadirectattackontheacetallinkage.TheC-Hbondisattackedbyozoneandahydrotrioxideisformedbya1,3-dipolaradditionmechanism.Thehydrotrioxideundergoesfragmentationtothelactonewithreleaseofoxygenwhichmaybeinthesingletform.ozonation臭氧化，臭氧处理lactone内酯singlet【物】单

7、线;独态triplet三线态Recationofcarbohydrateswithbleachingagentsandalkali2.Reactionatnon-acetalsitesOxidationofhydroxylgroupsTheoxidationofasecondaryalcoholgroupisinitiatedbyabstractionofahydrogenatomfromahyd