Question

Which of the below reaction Hunsdiecker favours?:
A. Carboxylation reaction
B. Decarboxylation reaction
C. Electrophilic substitution
D. None of these

Answer 1

Hint: Hunsdiecker reaction is an organic name reaction. It is also known by the name of Borodine Hunsdiecker reaction. It is used for the formation of alkyl halide.

Complete step by step answer: In this reaction silver salt of fatty acid reacts with halogen to give out organic halide as a product.
Hunsdiecker reaction is carried out as given below:
\[RCOOAg + B{r_2}\xrightarrow{{cc{l_4},\operatorname{Re} flux}}RBr + C{O_2} + AgBr\]
Mechanism of reaction:
The mechanism of reaction involves organic radical intermediate.
Step1: This step involves the formation of acyl hypohalite intermediate by the quick action of bromine with silver salt of fatty acid.
$RCOOAg\xrightarrow[{ - AgBr}]{{B{r_2}}}RCOOBr$
Step2: In this step, formation of a di-radical pair takes place.
\[RCOOBr\overset {} \leftrightarrows RO\dot O\dot Br\]
Step3: In this step, decarboxylation and formation of di-radical takes place. They combine to form organic halide.
\[RCO\dot O\dot Br\xrightarrow[{ - C{O_2}}]{}\dot R{\text{ }}\dot Br \to R - Br\]
Since there is removal of carbon dioxide as a side product, it is considered to be a decarboxylation reaction.
Hence the correct answer is option (B).

Additional Information:
 In this method the yield of alkyl halide follows the following order:
Primary >secondary >tertiary
Chloroalkanes are prepared by this method using $C{l_2}$ instead of $B{r_2}$ which gives poor yield. But in the case of ${I_2}$, silver salt gives esters instead of iodoalkanes and this reaction is known as Birnbaum-simonini reaction.
The reaction was first demonstrated by Alexander Borodine. Methyl Bromide was first reported to be formed from Silver Acetate

Note: Hunsdiecker reaction is also used for the formation of aryl halide from aryl salt of fatty acid. Fatty acids are long chain carboxylic acids. By refluxing we mean heating the liquid in a flask with condenser so that vapour is condensed back into the flask.