What is the Difference Between Hofmann and Curtius Rearrangement?

The Hofmann and Curtius rearrangements are different types of chemical reactions that have applications in organic chemistry. Here are the key differences between the two:

1. Starting materials: The Hofmann rearrangement starts with a primary amide and converts it into an amine using a halogen (such as Br2 or Cl2), a base (like OH-), and water. On the other hand, the Curtius rearrangement starts with an acid chloride and converts it into an isocyanate using sodium azide (NaN3) and water.
2. Migration: In the Hofmann rearrangement, an alkyl group migrates during the reaction, while in the Curtius rearrangement, an acyl group migrates.
3. Intermediate steps: In the Hofmann rearrangement, there is a key rearrangement step where heating results in the breakage of a C-C bond, formation of a C-N bond, and breakage of an N-Br bond. In the Curtius rearrangement, heating the acyl azide results in rearrangement, with nitrogen gas (N2) as the leaving group.
4. Final products: The Hofmann rearrangement produces an amine as the final product, while the Curtius rearrangement generates an isocyanate.

Both rearrangement reactions involve the migration of a group, but the migration occurs at different positions and results in different final products.

Comparative Table: Hofmann vs Curtius Rearrangement

The Hofmann and Curtius rearrangements are both organic chemical reactions that involve the migration of a functional group, but they differ in the starting materials and the products formed. Here is a comparison table outlining the differences between the two reactions:

Both reactions involve a key rearrangement step where a carbon atom migrates to displace a leaving group. In the Hofmann rearrangement, a primary amide is converted into a secondary or tertiary amine, while in the Curtius rearrangement, an acyl azide is converted into an isocyanate.