Question

Identify A and B in each of the following reaction sequence:
(a) \[ CH_3CH_2Cl \xrightarrow{NaCN} A \xrightarrow{H_2/Ni} B \]
(b) \[ C_6H_5NH_2 \xrightarrow{NaNO_2/HCl} A \xrightarrow{C_6H_5NH_2} B \]

Hint:

Nucleophilic substitution with cyanide forms nitriles, which can be reduced to amines. Diazonium salts are highly reactive intermediates that can be converted to phenols by hydrolysis.

Answer 1

(a) Reaction Sequence: 1. The reaction of \(CH_3CH_2Cl\) with \(NaCN\) results in the formation of ethyl cyanide (A) through nucleophilic substitution, where the chlorine is replaced by the cyanide ion. \[ A = CH_3CH_2CN \] 2. The hydrogenation of ethyl cyanide (\(CH_3CH_2CN\)) in the presence of \(H_2\) and a nickel catalyst leads to the reduction of the nitrile group to an amine, yielding ethylamine (B). \[ B = CH_3CH_2NH_2 \] (b) Reaction Sequence: 1. The reaction of aniline (\(C_6H_5NH_2\)) with sodium nitrite (\(NaNO_2\)) and hydrochloric acid (\(HCl\)) forms a diazonium salt, \(C_6H_5N_2^+Cl^-\) (A). 2. The treatment of \(C_6H_5N_2^+Cl^-\) with an acid (e.g., \(H^+\)) causes the diazonium ion to undergo hydrolysis, leading to the formation of phenol (B). \[ B = C_6H_5OH \]