Question

Mixture of $1^0,2^0$ and $3^0$ amines can be separated by :

• A. Hinsberg's method
• B. Hofmann's isocyanide test
• C. Fractional distillation
• D. $NaN{O}_2/HCl$

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A Hinsberg's method
B Hofmann's isocyanide test
C $NaN{O}_2/HCl$
D Fractional distillation

All the given methods can be used for the separation of amines.

(A) Hinsberg reaction is a chemical test for the detection of amines. A primary amine will form a soluble sulfonamide salt which precipitates after addition of diluted hydrochloric acid. A secondary amine in the same reaction will directly form an insoluble sulfonamide. A tertiary amine will not react with the sulfonamide but is insoluble. After adding dilute acid this insoluble amine is converted to a soluble ammonium salt.

(B) In Hofmann's isocyanide test the mixture of three amines is treated with diethyl oxalate. The primary amine forms a solid oxamide, a secondary amine gives a liquid oxamic ester while tertiary amine does not react.

(C) In fractional distillation primary amine is recovered when solid oxamide is heated with caustic potash solution and collected as distillate on distilling the reaction mixture. The liquid is subjected to fractional distillation when tertiary amine distils over. The remaining liquid is distilled with KOH to recover secondary amine.

(D) Nitrosation of Amines can also be used for separation as primary amine with $NaN{O}_2+HCl$ forms $R{N}_2$, secondary amine forms $R_2{N}_{2}O$ and tertiary amine forms $R_{3}NO$ which decomposes into $N{R}_3$.