Amines by Reduction

Abstract

Abstract Amines are derivatives of ammonia in which one or more of the hydrogens is replaced with an alkyl, aryl, cycloalkyl or heterocyclic group. When more than one hydrogen has been replaced, the substituents can either be the same or different. Amines are classified as primary, secondary, or tertiary depending on the number of hydrogens which have been replaced. Many different types of nitrogen‐containing compounds can be reduced to amines. In practice, however, nitriles or nitro compounds are usually used because they are the most easily obtained starting materials. There are several commercial processes for reducing nitro or nitrile groups to amines. Most large volume aromatic and aliphatic amines are made by continuous high‐pressure catalytic hydrogenation. Nitro compounds can also be reduced in good yields with iron and hydrochloric acid in the Bèchamp process. Aromatic amines are usually made by hydrogenating the corresponding nitro compound, whereas the aliphatic amines generally start with the corresponding nitrile. In the Bèchamp process, nitro compounds are reduced to amines in the presence of iron and an acid. This is the oldest commercial process for preparing amines, and is still used in the dyestuff industry. The method of reducing aromatic nitro compounds with divalent sulfur is known as Zinin reduction. This reaction is carried out in a basic media using sulfides, polysulfides, or hydrosulfides as the reducing agent. Amines, nitro compounds, nitriles, and the various solvents and reagents used in the preparation of amines by reduction vary widely in the hazards they may pose. Some of these materials are acutely toxic by ingestion, inhalation, or absorption through the skin. Others are skin irritants or sensitizers. Still others, by chronic exposure, may cause damage to organs such as the liver or may be carcinogenic. No general rules can govern their safe use in all cases. Regulations governing the safe handling and shipping of amines are given in U.S. Department of Transportation publications. Specific information on safe handling and hazards can be found in the Material Safety Data Sheet for a given material.