Curtius Rearrangement: Mechanism & Applications | Chemca

Chemca.in

Home Organic Inorganic Take Quiz

Organic Chemistry

Curtius Rearrangement: Synthesis of Amines

By Chemca Editorial Team • Last Updated: January 2026 • 8 min read

The Curtius Rearrangement is the thermal decomposition of an Acyl Azide to an Isocyanate with the loss of nitrogen gas. The resulting isocyanate can be hydrolyzed to give a primary amine. This reaction is a popular method for preparing amines from carboxylic acids with the loss of one carbon atom.

1. General Reaction

The overall process typically converts an acid chloride to a primary amine via an acyl azide and isocyanate intermediate.

$$ R-COCl \xrightarrow{NaN_3} R-CO-N_3 \xrightarrow{\Delta, \ -N_2} \underbrace{R-N=C=O}_{\text{Isocyanate}} \xrightarrow{H_2O} R-NH_2 + CO_2 $$

Steps involved:

1. Formation of Acyl Azide ($RCON_3$).
2. Rearrangement to Isocyanate ($RNCO$).
3. Hydrolysis to Primary Amine ($RNH_2$).

2. Detailed Mechanism

The rearrangement step is concerted and stereospecific.

Step 1: Preparation of Acyl Azide

Acyl azides are prepared by reacting acid chlorides with Sodium Azide ($NaN_3$).

$$ R-COCl + NaN_3 \rightarrow R-CO-\ddot{N}-N^+ \equiv N + NaCl $$

Step 2: Thermal Decomposition (The Rearrangement)

Upon heating, the acyl azide loses Nitrogen gas ($N_2$). Simultaneously, the alkyl group ($R$) migrates from the carbonyl carbon to the nitrogen atom.

$$ R-C(=O)-\ddot{N}-N^+ \equiv N \xrightarrow{\Delta} [R-N=C=O] + N_2 \uparrow $$

Note: This step is concerted; no free nitrene intermediate is usually formed in non-photochemical conditions.

Step 3: Hydrolysis

The isocyanate reacts with water to form an unstable carbamic acid, which decarboxylates to give the amine.

$$ R-N=C=O + H_2O \rightarrow [R-NH-COOH] \xrightarrow{-CO_2} R-NH_2 $$

3. Stereochemistry

Retention of Configuration

The migration of the group $R$ is strictly intramolecular. If the migrating carbon is chiral, it migrates with complete Retention of Configuration.

4. Variations (Trapping the Isocyanate)

Since the isocyanate intermediate is stable enough to be isolated (in the absence of water), it can be reacted with nucleophiles other than water to yield different products.

Reaction with Alcohol ($R'OH$)

Forms Carbamates (Urethanes).

$$ R-N=C=O + R'OH \rightarrow R-NH-COOR' $$

Reaction with Amine ($R'NH_2$)

Forms Ureas.

$$ R-N=C=O + R'NH_2 \rightarrow R-NH-CO-NHR' $$

5. Comparison: Hofmann vs. Curtius vs. Schmidt

All three reactions involve the migration of an alkyl group to an electron-deficient nitrogen to form an Isocyanate.

Reaction	Starting Material	Intermediate
Hoffmann Bromamide	Amide ($RCONH_2$)	Nitrene / Isocyanate
Curtius	Acyl Azide ($RCON_3$)	Isocyanate
Schmidt	Carboxylic Acid + $HN_3$	Isocyanate

Curtius Rearrangement Quiz

Test your concepts on Isocyanate intermediates. 10 MCQs with explanations.

Chemca.in

© 2026 Chemca. All rights reserved. | Privacy Policy

Quiz Revision Notes Downloads Class Notes Video Lectures