Question

Choose an appropriate set of reagents to carry out the synthetic step shown below.QUESTION 11 What is the role of PCl3 in the following reaction? It converts the carboxylic acid to an enolizable acid chloride. It acts as a base and deprotonates the a carbon. It converts the carboxylic acid to an acid bromide. It activates Br2 and forms a better nucleophile. It increases the rate of the reaction.

Answer 1

1)

in the given reaction

a ketone is reduced to alcohol

in general it can be done using NaBH4 or LiAlH4 in the presence of water

The H+ ion that attacks the 0xygen atom in the ketone is provided by H20 not by LiAlH4 or NaBH4

But

in the given reaction

A deuterium atom is attached to the Oxygen atom in the alcohol instead of H atom

so

a D+ should attack the OXygen atom in the ketone instead of H+ atom

so

it is provided by D30+ instead of H30+ and

in the presence of NaBH4 or LiAlH4

from the given options

the possible answer is

option D) 1. LiAlH4 2. D30+

2)

the reaction steps are given as

C6H5-Ch2- COOH + PCl3 ---> C6h5-Ch2-C0Cl

C6H5-CH2-C0Cl rearranges and forms enolate

C6H5-CH2-C0Cl = C6H5 - CH=C(Cl)OH

now this reacts with Br2

C6H5 - CH=C(Cl)OH + Br2 ---> C6H5 - CH(Br)-C0Cl + HBr

C6H5 - C(Br)-C0Cl + H20 ----> C6h5 - CH(Br) - COOH

so the correct answer for the role of PCl3 is

option A) It converts the carbolxylic acid to an enolizable acid chloride