Question

Write short notes on the following:
(i) Carbylamine reaction
(ii) Hofmann's bromamide reaction
(iii) Schmidt reaction

Hint:

- Carbylamine test $\Rightarrow$ identification of primary amines by foul-smelling isocyanides.
- Hofmann's bromamide $\Rightarrow$ converts amides to amines with one C less (useful in organic synthesis).
- Schmidt reaction $\Rightarrow$ converts carboxylic acids to amines, also reducing chain length by one C.

Answer 1

(i) Carbylamine Reaction:
- This is a test for primary amines (both aliphatic and aromatic).
- When a primary amine is heated with chloroform and alcoholic KOH, it gives an isocyanide (carbylamine) with a very offensive odour.
\[ RNH_2 + CHCl_3 + 3KOH \;\longrightarrow\; R{-}NC + 3KCl + 3H_2O \] - Secondary and tertiary amines do not respond to this test.
(ii) Hofmann's Bromamide Reaction:
- This reaction converts amides into amines with one carbon atom less than the parent amide.
- The reaction involves treatment of amide with bromine and alkali (KOH/NaOH).
\[ RCONH_2 + Br_2 + 4NaOH \;\longrightarrow\; RNH_2 + Na_2CO_3 + 2NaBr + 2H_2O \] - This is a useful method for descending homologation of amides to amines.
(iii) Schmidt Reaction:
- This reaction involves treatment of carboxylic acids with hydrazoic acid (HN$_3$) in the presence of concentrated H$_2$SO$_4$ to form amines.
\[ RCOOH + HN_3 \;\xrightarrow[\;]{conc.\ H_2SO_4}\; RNH_2 + CO_2 \] - It is used for the conversion of acids into amines (with loss of one carbon atom).