Question

Which of the following reactions is called ‘Bouveault-Blanc reduction’?
A) Reduction of acyl halide with ${{\text{H}}_{\text{2}}}{\text{/Pd}} - {\text{BaS}}{{\text{O}}_4}$
B) Reduction of ester with ${\text{Na/}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}$
C) Reduction of anhydride with ${\text{LiAl}}{{\text{H}}_{\text{4}}}$
D) Reduction of carbonyl compounds with ${\text{Na}} - {\text{Hg/HCl}}$

Answer 1

Hint: Bouveault-Blanc reduction involves use of alkali metals as reagent. Bouveault-Blanc reduction was used before the availability of lithium aluminium hydride as a reducing agent.

Complete step by step answer:
The Bouveault-Blanc reduction is used for the reduction of ester. The Bouveault-Blanc reduction is named after Louis Bouveault and Gustave Louis Blanc who first reported it.
In the Bouveault-Blanc reduction, esters are reduced to alcohols in presence of alkali metals like sodium and ethyl alcohol. The product of the reaction is a terminal alcohol of the ester.
The general representation of the Bouveault-Blanc reduction is as follows:
${\text{R}} - {\text{CO}} - {\text{OR'}}\xrightarrow[{{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}{\text{OH}}}]{{{\text{Na}}}}{\text{R}} - {\text{C}} - {\text{OH}} + {\text{R'}} - {\text{OH}}$
In the Bouveault-Blanc reduction, sodium metal $\left( {{\text{Na}}} \right)$ acts as a reducing agent and ethyl alcohol $\left( {{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}} \right)$ acts as a proton donor.
Thus, the reduction of ester with ${\text{Na/}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}$ is known as the ‘Bouveault-Blanc reduction’.

Thus, the correct option is (B) reduction of ester with ${\text{Na/}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}$.

Additional Information: Large amount of sodium metal is consumed in the Bouveault-Blanc reduction. Thus, excess of sodium is required. As sodium hydrolyses rapidly, anhydrous ethyl alcohol is used in the Bouveault-Blanc reduction because hydrolysis of sodium is an explosive reaction. The Bouveault-Blanc reduction requires vigorous reaction conditions and it has significant risk of fire.

Note: The Bouveault-Blanc reduction is used as a replacement for the lithium aluminium hydride in industrial reductions of esters. In the Bouveault-Blanc reduction, when the reaction proceeds if the proper source of proton is not provided then the dimerization of the intermediate occurs. A dimer will be produced instead of alcohol. Thus, a proper source of proton like ethyl alcohol must be provided.