Question

Give conversions: Benzaldehyde to alpha-Hydroxyphenylacetic acid

Answer 1

Hint: Draw the structure of benzaldehyde and $\alpha$-Hydroxyphenylacetic acid and observe the change in conversion of benzaldehyde to $\alpha-$Hydroxyphenylacetic acid. First, benzaldehyde undergoes nucleophilic addition reaction with \[{\text{NaCN}}\] in presence of \[{\text{HCl}}\] and give benzaldehyde cyanohydrins. Acid hydrolysis of cyanohydrins gives rise to alphaHydroxyphenylacetic acid.

Complete answer:
First, we will write the desired reaction.

From this reaction, we can say that there is one additional carbon atom of carboxylic acid in the product. So we have to use the reagent that will add one extra carbon atom. So benzaldehyde reacts with \[{\text{NaCN}}\] in presence of \[{\text{HCl}}\] that will increase the carbon atom. The intermediate benzaldehyde cyanohydrins on further reaction with water in presence of acid give rise to alpha-Hydroxyphenylacetic acid.

The detailed mechanism of the reaction is as follows:
Step 1: Nucleophilic addition of \[{\text{NaCN}}\] in presence of \[{\text{HCl}}\] gives Benzaldehyde cyanohydrin.

In this reaction, there is a nucleophilic attack of the cyanide group on the carbonyl carbon, which in presence of acid converts into benzaldehyde cyanohydrins.

Step 2: Acid hydrolysis of cyanohydrins gives rise to alpha-Hydroxyphenylacetic acid.

Acid hydrolysis converts the cyanide group of benzaldehyde cyanohydrins to the carboxylic acid group.

Note:
The common name of the alpha-Hydroxyphenylacetic acid is mandelic acid. The IUPAC name of alpha-Hydroxyphenylacetic acid is 2-hydroxy-2-phenyl acetic acid. It has medical applications and is used as an antibacterial agent. Due to the presence of carboxylic and hydroxyl groups, it is a slightly polar compound.