Preparation of secondary amines by reductive amination with metallic magnesium

Abstract

A novel and efficient method for the preparation of secondary amines by reductive amination of carbonyl compounds with primary amines has been developed. The reduction, effected with metallic magnesium in methanol, utilizing triethylamine–acetic acid as a buffer, gave pure secondary amines, mostly in good yields (65–80%). No formation of tertiary amines or alcohols was observed. Use of ammonium acetate as an amino component gave primary amines in modest yields (ca. 50%), together with variable amounts of secondary amines. Enamines failed to undergo reduction. The method is inexpensive, relatively rapid, operationally simple and suitable for large-scale preparations. In addition, a simple method for separation of primary amines from secondary ones has been developed.