Which of the following rearrangement(s) forms isocyanate?

Curtius rearrangement

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Lossen rearrangement

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Schmidt rearrangement

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Hofmann bromamide degradation reaction

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Solution

The correct option is D Hofmann bromamide degradation reaction
In all the given rearrangement, the intermediate formed is isocyanate.

Curtius rearrangement:
$R C O C l N a N_{3} - -- \to Δ R N H_{2} + N a C l + C O_{2} + N_{2}$

Lossen rearrangement:
$R C O N H O O C R^{'}^{-} O H - -- \to R N H_{2} + C O_{2} + R^{'} - C O O^{-}$

Schmidt rearrangement:
$R C O O H + N_{3} H H_{2} S O_{4} - --- \to R - N H_{2} + C O_{2} + N_{2}$

Hoffmann Bromamide degradation:
$R C O N H_{2} B r_{2} + 4 N a O H - ------- \to R N H_{2} + N a_{2} C O_{3} + 2 N a B r + 2 H_{2} O$

In all these reaction, isocyanate formed is hydrolysed to amine.

Hence, (a), (b), (c) and (d) are correct.

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