Theory and Defination :
The Curtius rearrangement is an organic reaction used to convert an acyl azide to an isocyanate under thermal conditions. The mechanism consists of an alkyl shift of the R group from the carbonyl carbon to the closest nitrogen with the release of nitrogen gas. The release of gas drives the reaction forward and results in the formation of the isocyanate product which can potentially react further in the presence of nucleophiles in solution.
The Curtius rearrangement occurs with complete retention of configuration at the migrating carbon, and the migration from the carbon to the nitrogen atom is an irreversible intramolecular reaction in first order kinetics.
The Curtius rearrangement has been used for the preparation of non-commercially available isocyantes from a diverse assortment of carboxylic acids.
In addition, this rearrangement is good for the preparation of tetrazoles, cyanamides, oxazolidones, etc. It has also been found that benzenesulfonyl azide also undergoes a similar rearrangement and gives a sulfurylaniline intermediate.
General Reaction :
Mechanism :
1st step involves preparation of azides:
and finally it decomposed.
Reaction with water to the unstable carbamic acid derivative which will undergo spontaneous decarboxylation:
Isocyanates are also of high interest as monomers for polymerization work and in the derivatisation of biomacromolecules.
Examples and Application :
1) One-Pot Rearrangement of Carboxylic Acids to Carbamates
2) Mild and Efficient One-Pot Curtius Rearrangement
3) Radical Azidonation of Aldehydes
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