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. Ethyl chloride (\(CH_3CH_2Cl\)) reacts with sodium cyanide (\(NaCN\)) via nucleophilic substitution, replacing chlorine with a cyanide group to form ethyl cyanide (A). \[ A = CH_3CH_2CN \] 2. Hydrogenation of ethyl cyanide (\(CH_3CH_2CN\)) using \(H_2\) and a nickel catalyst reduces the nitrile functional group to an amine, producing ethylamine (B). \[ B = CH_3CH_2NH_2 \] (b) Reaction Sequence: 1. Aniline (\(C_6H_5NH_2\)) reacts with sodium nitrite (\(NaNO_2\)) and hydrochloric acid (\(HCl\)) to generate a diazonium salt, \(C_6H_5N_2^+Cl^-\) (A). 2. The diazonium ion in \(C_6H_5N_2^+Cl^-\) undergoes hydrolysis upon treatment with acid (\(H^+\)), yielding phenol (B). \[ B = C_6H_5OH \]