Question

Answer the following questions: Why is L-B acid catalysis required to convert a carboxylic acid and an alcohol to an ester? Why is acyl bromide less reactive than acyl chloride? What reagent will you use to convert benzoic acid to benzoyl chloride: SOCl_2; PCl_3; or PCl_5 or any one of them? Why is Fischer Esterification reaction is not universal (i.e. not applicable to many acids and or alcohols)? Please draw the FIRST mechanistic step in ALL L-B acid catalyzed acyl transfer reactions. Use any acids you like.

Answer 1

1) the Bronsted Lowry acid provides protons which are needed to start the reaction

The addition of acid (proton) catalyze the reaction.

the first step in the esterification is protonation of carooxylic acid, which generates positive charge on carbonyl carbon and make it more facile to be attacked by the weak nucleophile , alcohol.

2) In the acyl substitution reaction the acyl halides undergo formation of transition state.

The transition state has a negative oxygen which will be more stabilized by more electronegative element (chlorine than bromine) so due to stabilization of transition state by chlorine acyl chloride is more reactive than acyl bromide

3) The best reagent is SOCl2. It is highly reactive and esily transfer chloride ion

4) The esterification will not be possible if the acid and alcohol have a lower boiling point than either the ester or water. The extraction become difficult.

5) The acyl transfer is

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