Question

The amine which reacts with p-toluene sulfonyl chloride to give a clear solution which on acidification gives insoluble compounds:
A. $C_2{H}_{5}N{H}_2$
B. $(C_2{H}_5{)}_{2}NH$
C. $(C_2{H}_5{)}_{3}N$
D. $C{H}_{3}NH{C}_2{H}_5$

Answer 1

Hint: The reaction of an amine with p-toluenesulfonyl chloride (tosyl chloride) is a test for distinguishing primary secondary and tertiary amines. The sulfonamide formed as a result of the reaction is a stable solid which can be purified by crystallization.

Complete step by step answer: In this test, the amine is shaken with p-toluenesulfonyl chloride in the presence of excess aqueous KOH solution. If we talk about the option A, ethylamine which is a primary amine when reacted with p-toluene sulphonyl chloride i.e. tosyl chloride in the presence of excess potassium hydroxide solution it gives a clear solution which on acidification gives insoluble compound as:

In the case of option B i.e. $(C_2{H}_5{)}_{2}NH$, this is a secondary amine. When $(C_2{H}_5{)}_{2}NH$ reacts with p-toluene sulphonyl chloride i.e. tosyl chloride in the presence of excess potassium hydroxide solution it gives an insoluble compound that remains unaffected on the addition of acid. The chemical reaction is given as:

In case of option C i.e. $(C_2{H}_5{)}_{3}N$, this is a tertiary amine. Here there is no hydrogen atom to replace hence it does not react with p-toluene sulphonyl chloride and remains insoluble in an alkaline solution.
In the case of option D i.e. $C{H}_{3}NH{C}_2{H}_5$, again this is a secondary amine. On reaction with p-toluene sulphonyl chloride in the presence of excess KOH, it gives an insoluble product that remains unaffected after acidification. The chemical reaction is given as:

Hence the amine which reacts with p-toluenesulfonyl chloride to give a clear solution which on acidification gives insoluble product is ethylamine i.e. $C_2{H}_{5}N{H}_2$.
Hence the correct answer is option A.

Note: In the case of tertiary amine as we know that no chemical reaction take places with p-toluene sulphonyl chloride in an alkaline medium but in the case of acidic medium tertiary amine dissolve and give a clear solution as: