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

1. Determine compounds A and B in the provided reaction sequences:

(a) Reaction Sequence:
CH₃CH₂Cl + NaCN → A → H₂/Ni → B

Analysis:
The initial step involves the reaction of CH₃CH₂Cl (ethyl chloride) with NaCN via nucleophilic substitution, yielding a nitrile identified as compound A. The reaction is represented as:

CH₃CH₂Cl + NaCN → CH₃CH₂CN (ethyl cyanide, A)

Subsequently, the nitrile group in compound A undergoes hydrogenation with H₂ in the presence of a nickel catalyst, producing an amine, compound B. The transformation is as follows:

CH₃CH₂CN + H₂/Ni → CH₃CH₂NH₂ (ethylamine, B)

Identified Compounds:
A = CH₃CH₂CN (ethyl cyanide)
B = CH₃CH₂NH₂ (ethylamine)

(b) Reaction Sequence:
C₆H₅NH₂ + NaNO₂/HCl (0–5°C) → A → C₆H₅NH₂ + H⁺ → B

Analysis:
In the first stage, aniline (C₆H₅NH₂) reacts with sodium nitrite (NaNO₂) under acidic conditions (HCl) at a temperature range of 0–5°C, forming a diazonium salt, compound A. This reaction proceeds as:

C₆H₅NH₂ + NaNO₂/HCl → C₆H₅N₂⁺Cl⁻ (benzenediazonium chloride, A)

In the second stage, the diazonium salt (A) is reduced by the addition of a proton source (H⁺), regenerating aniline, which is designated as compound B. The reaction is depicted as:

C₆H₅N₂⁺Cl⁻ + H⁺ → C₆H₅NH₂ (aniline, B)

Identified Compounds:
A = C₆H₅N₂⁺Cl⁻ (benzenediazonium chloride)
B = C₆H₅NH₂ (aniline)