Question

The silver salt of fatty acid is treated with ${I_2}/CC{l_4}$ . If the ratio of silver salt & iodine is $1:1$ then alkyl iodide is formed, if the ratio is $2:1$ then ester is formed. Why?

Answer 1

Hunsdiecker reaction is the reaction in which the silver salt of carboxylic acid reacts with ${I_2}/CC{l_4}$ to form alkyl iodide. Simonini reaction is the reaction in which two moles of the silver salt of carboxylic acid react with ${I_2}/CC{l_4}$ to form an ester.

Complete answer:
Fatty acids are the long chain carboxylic compounds. When silver salt of fatty acid is treated with ${I_2}/CC{l_4}$ then the reaction proceeds in four steps as follows:
The first step is $RCOOAg + I - I \to RCOOI + AgI$
The second step is $RCOOI \to RCO{O^ \bullet } + {I^ \bullet }$
The third step is $RCO{O^ \bullet } \to {R^ \bullet } + C{O_2}$
The fourth step is $RCOOI + {R^ \bullet } \to RO{O^ \bullet } + R - I$
Where $R - I$ represents an alkyl halide
The above reaction is known as hunsdiecker reaction.
When two molecules of the silver salt of fatty acid are treated with ${I_2}/CC{l_4}$ , then that alkyl halide formed in the above reaction reacts with another molecule of the silver salt of carboxylic acid forms a chemical compound known as an ester. The chemical reaction proceeds as follows:
$2RCOOAg + I - I \to RCOOR + AgI$
The above reaction is known as simonini reaction.
Thus, when the ratio of silver salt & iodine is $1:1$ then alkyl iodide is formed, if the ratio is $2:1$ then ester is formed which was explained in the above reactions.

Note:
Though all the reagents used for the above two reactions were the same. The number of reagent molecules only results in the two different reactions namely hunsdiecker reaction and simonini reaction. These reactions take place via a radical mechanism.