Question

Addition of hydrogen cyanide to aldehydes and ketones occurs in presence of a base. The role of base is to
(i) catalyse the reaction
(ii) generate $C{N}^{-}$ion
(iii) slow down the reaction
(iv) to stabilize the cyanohydrins

• A. (i) and (iii)
• B. (i) and (ii)
• C. (i) and (iv)
• D. (ii) and (iv)

Answer 1

Answer: (B)

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 and the generated cyanide ion $\left(C{N}^{-}\right)$being a stronger nucleophile readily adds to carbonyl compounds to yield corresponding cyanohydrins.