Question

The compound which on reacts with aqueous nitrous acid at low temperature produces an oily nitrosamine is:
A) Methyl amine
B) Ethyl amine
C) Diethylamine
D) Triethylamine

Answer 1

Hint: The compound which has a Secondary amine $( - NH - )$ group attached gives an oily nitrosamine when reacted with $HN{O_2}$ at low temperature. In all the aforesaid compounds identify the compound which have a secondary amide group.

Complete answer:
An amine group is the inorganic derivative of ammonia. Compounds with a nitrogen atom attached to a carbonyl group, thus having the structure $R - CO - NR'R''$ are called amides.
Nitrous acid $(HN{O_2})$ is a monobasic weak acid which when reacts forms nitrite salts used in making diazides from amines. Nitrous acid $(HN{O_2})$ reacts with aliphatic amines and helps us to distinguish between primary, secondary and tertiary amines. All amine groups have different types of reactions.
Primary amines when reacted with nitrous acid undergo diazotization reaction and nitrogen is liberated. whereas, Tertiary amines don't react with nitrous acid and form ammonium salt.
 Secondary amine on reaction with aqueous nitrous acid at low temperature produces an oily nitrosamine. The reaction takes place due to nitrosonium $(N{O^ + })$ an electrophilic species present in nitrous acid .
In this reaction nucleophilic attack of the amine on the nitrite deprotonating group by the surrounding solvent and double elimination of water takes place. The equilibrium of this reaction goes toward forward direction because nitrous acid, as a reagent is a weak acid. The reaction goes like:
${({C_2}{H_5})_2}NH + HN{O_2} \to {({C_2}{H_5})_2}N - N = O + {H_2}O$
Diethylamine, being a secondary group when reacted with nitrous acid at low temperature generates nitrosamine.

Therefore the correct option is option (C).

Note: The reaction in the amides takes place due to the tendency of the amine group to bind a proton due to the unshared pair of electrons present on the nitrogen. In the secondary amine reaction with nitrous acid no gas is produced. Yellow coloured oil formed is known as nitrosamine.