Silver salt of fatty acid treated with #I_2#/#C Cl_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?
These are the Hunsdiecker and the Simonini reactions, respectively.
The decarboxylation of the silver salt of a carboxylic acid with one molar equivalent of bromine or iodine to form an alkyl halide is called the Hunsdiecker reaction.
The mechanism of the Hunsdiecker reaction probably involves a radical chain reaction.
Step 1. Formation of the acyl hypoiodite
Step 2. Initiation
The acyl hypoiodite undergoes homolytic cleavage.
Step 3. Propagation
The acyl radical undergoes decarboxylation to form an alkyl radical.
Step 4. Propagation
The alkyl radical reacts with the acyl hypoiodite.
The reaction of the silver salt of a carboxylic acid with two molar equivalents of iodine to form an ester is called the Simonini reaction.
In the mechanism, the alkyl halide that is formed in a Hunsdiecker type reaction probably undergoes an ionic substitution with the excess silver salt.