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1、SynthesisandReactionsofAlkenes:CyclohexenefromCyclohexanolfromK.L.Williamson,MacroscaleandMicroscaleOrganicExperiments,2ndEd.1994,HoughtonMifflin,Bostond.p268;revised10/10/98,adaptedfromthemicroscalesynthesispostedby:http://courses.chem.psu.edu/chem35/HTML/Experi
2、ments/Exp72.pdfPrelabExercise:Prepareadetailedflowsheetforthepreparationofcyclohexene,indicatingateachstepwhichlayercontainsthedesiredproduct.IntroductionDehydrationofcyclohexanoltocyclohexenecanbeaccomplishedbypyrolysisofthecyclicsecondaryalcoholwithanacidcataly
3、statamoderatetemperatureorbydistillationoveraluminaorsilicagel.Theprocedureselectedforthisexperimentinvolvescatalysisbysulfuricacid.Whenamixtureofcyclohexanolandsulfuricacidisheatedinaflaskequippedwithafractionatingcolumn,theformationofwaterissoonevident.Onfurthe
4、rheating,thewaterandthecyclohexeneformeddistilltogetherbytheprincipleofsteamdistillation,andanyhigh-boilingcyclohexanolthatmayvolatilizeisreturnedtotheflask.However,afterdehydrationiscompleteandthebulkoftheproducthasdistilled,thecolumnremainssaturatedwithwater-cy
5、clohexenethatmerelyrefluxesanddoesnotdistill.Hence,forrecoveryofotherwiselostreactionproduct,a“chaser”solventisadded,anddistillationiscontinued.Asuitablechasersolventisthewater-immiscible,aromaticsolventtoluene,boilingpoint110°C;asitsteam-distills,itcarriesoverth
6、emorevolatilecyclohexene.Whenthetotalwater-insolublelayerisseparated,dried,andredistilledthroughthedriedcolumn,thechaseragaindrivesthecyclohexenefromthecolumn;thedifferenceinboilingpointsissuchthatasharpseparationispossible.Thecolumnholdup(retentionofdistillate)i
7、nthemetalsponge-packedcolumnissogreatthatifachasersolventisnotusedintheprocedure,theyieldwillbemuchlower.Themechanismofthisreactioninvolvesinitialrapidprotonationofthehydroxylgroupbythesulfuricacid.Thisisfollowedbylossofwatertogivetheunstablesecondarycarbocation,
8、whichquicklylosesaprotontowaterortheconjugateacidtogivethealkene.¥Procedure:PreparationofCyclohexene•Add1.5mLofwaterintoa25mLroundbottomedflask.Tothis,add2.0mL
