Question

Identify ‘A’, ‘B’ and ‘C’ in the following chain reaction and rewrite the chemical reactions: \[ CH_3CH_2OH \xrightarrow{\text{red P}, \, Br_2} A \xrightarrow{\text{KCN, alc.}} B \xrightarrow{\text{LiAlH}_4, \text{Ether}} C \]

Hint:

This reaction sequence involves nucleophilic substitution \( (S_N2) \) followed by reduction of nitriles to primary amines.

Answer 1

Conversion of Ethanol to Ethyl Bromide (A): Ethanol reacts with bromine in the presence of red phosphorus to form ethyl bromide. \[ CH_3CH_2OH + Br_2 \xrightarrow{\text{red P}} CH_3CH_2Br + HBr \] So, \( A = \) Ethyl Bromide \( (CH_3CH_2Br) \). 
Conversion of Ethyl Bromide to Propanenitrile (B): Ethyl bromide reacts with alcoholic potassium cyanide \( (KCN) \) to form propanenitrile. \[ CH_3CH_2Br + KCN \rightarrow CH_3CH_2CN + KBr \] So, \( B = \) Propanenitrile \( (CH_3CH_2CN) \). 
Conversion of Propanenitrile to Propylamine (C): Propanenitrile undergoes reduction with lithium aluminum hydride \( (LiAlH_4) \) in ether to form propylamine. \[ CH_3CH_2CN + 4[H] \xrightarrow{\text{LiAlH}_4, \text{Ether}} CH_3CH_2CH_2NH_2 \] So, \( C = \) Propylamine \( (CH_3CH_2CH_2NH_2) \).