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20.18
PreparationofNitriles
nucleophilicsubstitutionbycyanideon
alkylhalides(Sections8.1and8.13)cyanohydrinformation(Section17.7)dehydrationofamidesPreparationofNitrilesNitrilesarepreparedby:
Example(95%)CH3(CH2)8CH2ClKCNethanol-
waterCH3(CH2)8CH2CNSN2
Example(75%)KCNH+CH3CH2CCH2CH3OCH3CH2CCH2CH3OHCN
usesthereagentP4O10(oftenwrittenasP2O5)PreparationofNitrilesBydehydrationofamides(CH3)2CHCNH2OP4O10200°C(CH3)2CHCN(69-86%)
20.19
HydrolysisofNitriles
HydrolysisofNitrilesHydrolysisofnitrilesresemblesthehydrolysis
ofamides.Thereactionisirreversible.
Ammoniaisproducedandisprotonatedto
ammoniumioninacidsolution.+NH4+RCOHORCN+2H2OH++
HydrolysisofNitrilesInbasicsolutionthecarboxylicacidproductisdeprotonatedtogiveacarboxylateion.+–RCOOHO+–NH3RCN+H2O
Example:AcidHydrolysis(92-95%)OH2OH2SO4
heatCH2CNNO2CH2COHNO2
Example:BasicHydrolysis(80%)CH3(CH2)9COHOCH3(CH2)9CN1.KOH,H2O,heat2.H+
Hydrolysisofnitrilesproceedsviathe
correspondingamide. Wealreadyknowthemechanismofamide
hydrolysis. Therefore,allweneedtodoistoseehow
amidesareformedfromnitrilesunderthe
conditionsofhydrolysis.MechanismofHydrolysisofNitrilesRCNH2ORCNH2OH2ORCOHO
Themechanismofamideformationisanalogous
tothatofconversionofalkynestoketones. Itbeginswiththeadditionofwateracrossthe
carbon-nitrogentriplebond. Theproductofthisadditionisthenitrogen
analogofanenol.Itistransformedtoanamide
underthereactionconditions.MechanismofHydrolysisofNitrilesRCNH2ORCNH2ORCNHOH
Step1O?
?H?
???–RCN?
?
Step1O?
?H?
???–RCN?
?RCON?
??
??
?–?
?H
Step2RCON?
??
??
?–?
?HO?
???HH
Step2RCON?
??
??
?–?
?HO?
???HH?
?–O?
???HRCON?
??
?HH??
Step3?
?–O?
???HRCON?
??
?HH??
Step3?
?–O?
???HRCON?
??
?HH????–??RCON?
??
?H?
?O?
?HH
Step4??–??RCON?
??
?HO?
?HH??
NStep4??–??RCON?
??
?HO?
?HH????RCO?
??
?HH–O?
?H???
?
20.20
AdditionofGrignardReagents
toNitriles
Grignardreagents
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