Question

The reagent that gives an acid chloride on treatment with carboxylic acid is?
A.$PC{l_5}$
B.$PC{l_3}$
C.$SOC{l_2}$
D.${(COCl)_2}$

Answer 1

In organic chemistry acid chloride are the compounds with functional group $- COCl$ and overall these organic compounds are represented by $RCOCl$ where $R$ is side chain. These are also known as acyl chloride and these are the reactive derivatives of carboxylic acid.

Complete step by step answer:
We will check whether these reagents produce acid chloride or not by reacting with carboxylic acid by their reactions. The reactions are as follows:
Reaction of carboxylic acid with $PC{l_5}$:
$RCOOH + PC{l_5} \to RCOCl + POC{l_3} + HCl$
We can see that in this reaction $RCOCl$ is produced as a product which is acid chloride.
Reaction of carboxylic acid with $PC{l_3}$:
$RCOOH + PC{l_3} \to RCOCl + {H_3}P{O_3}$
In this reaction $RCOCl$ (acid chloride) is produced.
Reaction of carboxylic acid with $SOC{l_2}$:
$RCOOH + SOC{l_2} \to RCOCl + S{O_2} + HCl$
$RCOCl$ is produced in this reaction as a product.
Reaction of carboxylic acid with ${(COCl)_2}$:
$\;RCOOH + {(COCl)_2} \to RCOCl + C{O_2} + CO$
$RCOCl$ (acid chloride) is produced in this reaction as a product.
Hence we can see that all the given reagents give acid chloride on treatment with carboxylic acid.
So all options are correct (A), (B), (C) and (D).
Note:
During the reaction of carboxylic and sulphonyl chloride the hydroxyl group of the carboxylic acid is converted to a chlorosulfite intermediate making it a better leaving group.