Curtius Rearrangement

Curtius Rearrangement Definition:

The Curtius rearrangement is a rearrangement of acyl azides to give isocyanates, expelling the nitrogen gas. The isocyanates can then be used in the other reactions to give products such as ureas and carbamates.

Curtius Rearrangement Explained:

The Curtius rearrangement is similar to the Hofmann rearrangement. But as the starting material, acid chloride is used instead of the amide. And the reaction takes place under neutral conditions instead of the basic conditions.

The mechanism of this reaction consists of an alkyl shift of the R group from the carbonyl carbon to the closest nitrogen with the release of nitrogen gas. Unlike Hofmann rearrangement, where isocyanate is intermediate which cannot be isolated, but here the isocyanate can be isolated and further reacted in the presence of nucleophiles.

The first step of the mechanism is the formation of acyl azides. When added azide (NaN3) to acid chloride, the