Mention chemical tests to differentiate between the pairs of compounds given below.
(i) dimethylamine & Methylamine
(ii) Tertiary amines & Secondary
(iii) Aniline & Ethylamine
(iv) benzylamine & Aniline
(v) N – methylaniline & Aniline
Answers
(i) dimethylamine & Methylamine can be made notable by the carbylamine test.
Carbylamine test : foul – smelling isocyanides or carbylamines are formed when Aliphatic & aromatic primary amines are heated with chloroform & ethanol potassium hydroxide .
Methylamine ( being an aliphatic primary amine ) gives a positive carbylamine test, but dimethylamine does not.
(ii) Tertiary amines & Secondary can be made notable by allowing them to react with Hinsberg’s reagent ( benzene sulphonyl chloride, C6 H5 SO2 Cl
A product which is insoluble in an alkali is formed when Secondary amines react with Hinsberg’s reagent to form a product that is insoluble in an alkali. For example, N, N – diethyl amine reacts with Hinsberg’s reagent to form N, N – diethyl benzene sulphonamide , which is insoluble in an alkali. Tertiary amines, however, do not react with Hinsberg’s reagent.
(iii) azo – dye test can distinguish aniline & Ethylamine.
When aromatic amines are made to react with HNO 2 ( NaNO 2 + dil. HCl ) at 0 – 5 ° C, A dye is obtained which is followed by making it react with the alkaline solution of 2 – naphthol. The dye is observed to be in the following colours : yellow, red, or orange in color. A brisk effervescence is given out by Aliphatic amines due to the evolution of N2 gas under analogous conditions.
(iv) benzylamine & Aniline can be made notable by reacting them with nitrous acid, which is made ready in situ from a sodium nitrite & mineral acid. Unstable diazonium salt is formed when nitrous acid reacts with Benzylamine , which gives a by – product as alcohol along with the evolution of N2 gas
In another case, HNO 2 reacts with aniline at a very low temperature which in turn forms stable diazonium salt. Hence, evolution of nitrogen gas does not happen.
(v) N – methylaniline & Aniline can be made notable by using the Carbylamine test.
On heating Primary amines with ethanolic , chloroform & potassium hydroxide, a foul smelling isocyanides or carbylamines are formed. As, Aniline is a primary aromatic primary, it gives a positive carbylamines test. On the other h&, as,N – methyl aniline is a secondary amine it does not give a positive carbylamines test.
Answer:
Methylamine (being an aliphatic primary amine) gives a positive carbylamine test, but dimethylamine does not. Aniline and benzylamine can be distinguished by their reactions with the help of nitrous acid, which is prepared in situ from a mineral acid and sodium nitrite.