Question

The amine A when treated with nitrous acid gives yellow oily substances. The amine A is:
A. triethylamine
B. trimethylamine
C. aniline
D. methylphenylamine

Answer 1

Hint: In organic chemistry amines are those compounds and functional groups that contain a basic nitrogen atom with lone pair. These are derivatives of ammonia in which one or more hydrogen atoms of ammonia is replaced by any alkyl or aryl group.

Complete step by step solution:
Amines can also be known by the name alkylamines and arylamines as one or more hydrogen groups of ammonia is replaced with alkyl or aryl groups. Amines can be further classified according to the nature and number of substituents on nitrogen. Aliphatic amines contain only H and alkyl substituents while Aromatic amines have the nitrogen atom connected to an aromatic ring. These can also divided into three subcategories based on the number of carbon atoms adjacent to the nitrogen these categories are $1^{{}^{\circ }},2^{{}^{\circ }}$ and $3^{{}^{\circ }}$ in which $1^{{}^{\circ }}$ represents one hydrogen atom is replaced by a substituent, $2^{{}^{\circ }}$ shows 2 hydrogen atoms replaced by two substituents while $3^{{}^{\circ }}$ represents all the hydrogen atoms of ammonia is replaced by substituents.
The amine A when treated with nitrous acid gives yellow substance. The amine A should be methylphenylamine which is a secondary amine in which one hydrogen atom is replaced by methyl and another by phenyl ion and the reaction is given as follows which forms N-nitrosamine as a product.
$Ph-NH-C{H}_3+OH-N=O\to Ph-N(C{H}_3)-N=O+H_{2}O$

Hence, option D is the correct answer.

Note: Amines are very important in biology. Amino acids break to release amines and many neurotransmitters are amines including epinephrine, norepinephrine, dopamine, serotonin, and histamine which are used as drugs. Protonated amino groups are the most common positively charged moieties in proteins.