Hofmann Reactions

Hofmann Reactions 

the name given to three reactions that were proposed by the German chemist A. W. Hofmann.

(1) The synthesis of primary amines by the action of bromine and an alkali on the amides of carboxylic acids. The amines formed contain one less carbon atom than the initial amide:

RCONH₂ + Br₂ + OH⁻ → RNH₂ + CO₂ + H₂O + Br⁻

As a result of this reaction, aliphatic, aliphatic-aromatic, aromatic, and heterocyclic amines can be obtained. The realization of this reaction in an alcohol medium leads to the formation of the urethanes (RNHOCOR).

(2) The synthesis of aliphatic amines by the action of alkylating reagents (such as alkyl halides and dialkyl sulfates) on ammonia. The result is the formation (in the form of salts) of a mixture of primary, secondary, and tertiary amines and the salt of a quaternary ammonium base. For example, if CH₃I is used, [CH₃NH₃]I, [(CH₃)₂NH₂]I, [(CH₃)₃NH]I, and [(CH₃)₄N]I are obtained, respectively.

(3) The thermal decomposition of hydroxides of quaternary ammonium bases with the formation of a tertiary amine and an olefin:

[RCH₂CH₂NR’R”R”’]OH⁻ → RCH=CH₂ + R’R”R”’N + H₂O

If the nitrogen atom in the quaternary base is bound to various substitutes, an olefin is formed that contains the smallest number of alkyl substitutes possible with a double bond (Hofmann rule).

The most important field of application of the Hofmann reactions is the study of the structure of alkaloids.

L. S. GERMAN