Delépine Reaction

Theory and Defination :

The preparation of primary aliphatic amines by acidic hydrolysis of Quaternary amines formed from alkyl halides and urotropine (i.e., hexamethylene tetramine) is known as Delépine reaction. This reaction has an importance in the conversion of alkyl halides into primary amines.

General Reaction :

primary amines (4) is obtained by reaction of a benzyl or alkyl halides

(1) with hexa methylenetetramine

(2) followed by acid hydrolysis of the Quaternary ammonium salt

(3) with aldehyde (5) and ammonium chloride salt .Advantages of this reaction are selective access to the primary anime without side reactions from easily accessible reactants with short reaction times and relatively mild reaction conditions.

Mechanism :

An SN2 reaction leads to the hexa methylene tetramine salt. In chloroform, the starting materials are soluble whereas the products crystallize out. It is usually not possible to purify the salt:

Hexa methylenetetramine is formed in nearly quantitative yield from the condensation of ammonia and formaldehyde.

The compound is rather stable, although dihetero-substituted methylene groups are usually highly reactive. In neutral, aqueous solution, urotropine remains stable even at elevated temperatures. Urotropine decomposes in dilute aqueous acid, and the derived ammonium salts also decompose to form the amine hydrochloride and formaldehyde (and formaldehyde diethylacetal):

During acidic hydrolysis or ethanolysis, semiaminals are formed first; these further decompose to yield formaldehyde or the di-ethylacetal, ammonium salt and the amine hydrochloride: