How does a Curtius rearrangement differ from a Hofmann rearrangement?

A Curtius rearrangement involves the migration of an acyl group, while a Hofmann rearrangement involves the migration of an alkyl group.

The Curtius rearrangement, named after its discoverer Theodor Curtius, is a process in organic chemistry where an acyl azide is heated to give an isocyanate. This reaction involves the migration of an acyl group (R-CO-) from nitrogen to oxygen. The isocyanate product can then react with a variety of nucleophiles to give amines, ureas, or carbamates. This reaction is particularly useful in the synthesis of amines and other nitrogen-containing compounds.

On the other hand, the Hofmann rearrangement, named after August Wilhelm von Hofmann, is an organic reaction where an amide is converted to an amine with one fewer carbon atom. This reaction involves the migration of an alkyl group (R-) from carbon to nitrogen. The process begins with the oxidation of the nitrogen in the amide to give a nitrene intermediate, which then rearranges to give an isocyanate. The isocyanate can then be hydrolysed to give an amine.

In summary, while both the Curtius and Hofmann rearrangements involve the migration of a group from one atom to another, the key difference lies in the type of group that migrates. In a Curtius rearrangement, it's an acyl group, while in a Hofmann rearrangement, it's an alkyl group. Furthermore, the Curtius rearrangement is typically used to synthesise amines and other nitrogen-containing compounds, while the Hofmann rearrangement is used to convert amides to amines with one fewer carbon atom.