Curtius rearrangement

What is Curtius rearrangement?

The Curtius rearrangement is a chemical reaction that allows for the synthesis of compounds containing an isocyanate group. This reaction is named after the German chemist Adolph von Curtius, who first described it in 1886..

Curtius rearrangement - Curtius reaction - Curtius degradation
Curtius rearrangement

The Curtius rearrangement involves the rearrangement of a compound called an “acyl azide” to a compound containing an isocyanate group. The reaction is typically carried out in the presence of a base, such as sodium hydroxide, and a solvent, such as ethanol..

One of the advantages of the Curtius rearrangement is its high yield and efficiency. It is a relatively simple reaction that can be carried out under mild conditions and does not require the use of expensive or specialized reagents..

The Curtius rearrangement has a wide range of applications in the synthesis of pharmaceuticals, agrochemicals, and other chemicals. It has also been used in the synthesis of natural products, such as alkaloids and terpenoids..

Summary

The Curtius rearrangement is a valuable tool for the synthesis of compounds containing an isocyanate group and has played an important role in the development of a number of important chemical compounds..

Example

The following is an example of a Curtius rearrangement:

Reactants:

Acetyl isocyanate
Trifluoroacetic anhydride

Experimental procedure:

In a round-bottomed flask, combine the acetyl isocyanate and trifluoroacetic anhydride.
Heat the mixture to 120°C for 2 hours.
Allow the mixture to cool to room temperature.

Product: Isocyanate-acid anhydride (a compound containing both an isocyanate and an anhydride group)

Mechanism of reaction

The mechanism of the Curtius rearrangement involves several steps. Here is a step-by-step description of the mechanism:

  • The isocyanate reactant is treated with an acid anhydride, such as trifluoroacetic anhydride.
  • The acid anhydride acts as a protonating agent, donating a proton to the isocyanate group and forming a protonated isocyanate.
  • The protonated isocyanate undergoes a rearrangement, with the nitrogen atom shifting its position and forming a double bond with the carbon atom. This results in the loss of nitrogen gas and the formation of an isocyanate-acid anhydride compound.
  • The isocyanate-acid anhydride compound can then be isolated and purified through standard chemical techniques.

References

Curtius, T. (1894), 20. Hydrazide und Azide organischer Säuren I. Abhandlung. [20. hydrazides and azides of organic acids I. Treatise.] J. Prakt. Chem., 50: 275-294. https://doi.org/10.1002/prac.18940500125

Shares