Benzaldehyde is treated with HCN, and the product is then heated with water and HCl. The final product is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 2-Hydroxy-2-phenylethanoic acid
Step 1 – Addition of HCN: the cyanide ion adds to the carbonyl carbon of benzaldehyde and gives a cyanohydrin, 2-hydroxy-2-phenylethanenitrile. This is only the intermediate.
\( \displaystyle \ce{C6H5CHO + HCN} \xrightarrow{\ce{OH^-}} \ce{C6H5CH(OH)CN} \)
Step 2 – Heating with water and HCl: the –CN group is hydrolysed through the amide to –COOH; the –OH group and the phenyl group stay on the same carbon.
\( \displaystyle \ce{C6H5CH(OH)CN + 2H2O + HCl} \xrightarrow{\Delta} \ce{C6H5CH(OH)COOH + NH4Cl} \)
Final product: \( \ce{C6H5CH(OH)COOH} \), 2-hydroxy-2-phenylethanoic acid (Option 1).
NCERT (2026-27 edition):
8.4 Chemical Reactions – “(a) Addition of hydrogen cyanide (HCN): Aldehydes and ketones react with hydrogen cyanide (HCN) to yield cyanohydrins. This reaction occurs very slowly with pure HCN. Therefore, it is catalysed by a base …”
8.7 Methods of Preparation of Carboxylic Acids – “3. From nitriles and amides
Nitriles are hydrolysed to amides and then to acids in the presence of H+ or OH− as catalyst.”