Dolbier HW Solutions 468

Dolbier HW Solutions 468 - 562 CARBOXYLIC ACID DERIVATIVES:...

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Unformatted text preview: 562 CARBOXYLIC ACID DERIVATIVES: NUCLEOPHILIC ACYL SUBSTITUTION ( j) A Hofmann rearrangement of benzamide affords aniline. O Br2 CNH2 Benzamide [prepared as in part (d )] HO NH2 H2 O Bromine Aniline O 20.30 O The problem specifies that CH3CH2COCH2CH3 is to be prepared from 18O-labeled ethyl alcohol (O 18 O) . O O CH3CH2CCl CH3CH2O OH Propanoyl chloride CH3CH2COCH2CH3 O Ethyl alcohol Ethyl propanoate Thus, we need to prepare 18O-labeled ethyl alcohol from the other designated starting materials, acetaldehyde and 18O-enriched water. First, replace the oxygen of acetaldehyde with 18O by the hydration–dehydration equilibrium in the presence of 18O-enriched water. O O OH CH3CH H2O Acetaldehyde 18O-enriched CH3CH H2O 18O-enriched Water CH3CH OH Hydrate of acetaldehyde water acetaldehyde Once 18O-enriched acetaldehyde has been obtained, it can be reduced to 18O-enriched ethanol. O CH3CH 20.31 (a) NaBH4, CH3OH or 1. LiAlH4 2. H2O CH3CH2OH The rate-determining step in basic ester hydrolysis is nucleophilic addition of hydroxide ion to the carbonyl group. The intermediate formed in this step is negatively charged. O O CH3COCH2CH3 HO CH3COCH2CH3 OH Ethyl acetate Hydroxide ion Rate-determining intermediate The electron-withdrawing effect of a CF3 group stabilizes the intermediate formed in the ratedetermining step of ethyl trifluoroacetate saponification. O O CF3COCH2CH3 HO CF3COCH2CH3 OH Ethyl trifluoroacetate Hydroxide ion Rate-determining intermediate Because the intermediate is more stable, it is formed faster than the one from ethyl acetate. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website ...
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This note was uploaded on 09/30/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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