Question

How many of the following rearrangement forms isocyanate
1.Curtius rearrangement
2.Lossen rearrangement
3.Schmidt rearrangement
4.Hofmann bromamide degradation reaction

• A. 4
• B. 4.0
• C. 4.00

Answer 1

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

In all the given rearrangement, the intermediate formed is isocyanate.

Curtius rearrangement:
$RCOCl\underset{\Delta }{\overset{Na{N}_3}{\to }}RN{H}_2+NaCl+C{O}_2+N_2$

Lossen rearrangement:
$RCONHOOC{R}^{\prime }\stackrel{{}^{-}OH}{\to }RN{H}_2+C{O}_2+R^{\prime }-CO{O}^{-}$

Schmidt rearrangement:
$RCOOH+N_{3}H\stackrel{H_{2}S{O}_4}{\to }R-N{H}_2+C{O}_2+N_2$

Hoffmann Bromamide degradation:
$RCON{H}_2\stackrel{B{r}_2+4NaOH}{\to }RN{H}_2+N{a}_{2}C{O}_3+2NaBr+2H_{2}O$

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

Hence, (1), (2), (3) and (4) are correct