Amines by Reduction

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 that 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.

Efficient Ruthenium-Catalyzed N-Methylation of Amines Using Methanol

“…The direct N-methylation of amines is one of the most important transformations in the synthesis of fine chemicals and pharmaceuticals as well as natural products . The conventional N-methylation methods using reactive and toxic methyl halides as methylating agents have serious selectivity issues, forming overalkylated products that not only reduce the overall yield of the desired product but also render the separation of the products tedious. In addition to the use of excess base, the generation of toxic halogenated byproducts makes the downstream processing challenging and expensive.…”

Reduction of the Nitro Group to Amine by Hydroiodic Acid to Synthesize o-Aminophenol Derivatives as Putative Degradative Markers of Neuromelanin

“…In the literature, several methods for the reduction of nitro groups to amines have been reported. Aromatic amines are known to be produced by catalytic hydrogenation under continuous high pressure [24,25,26,27]. Nitro compounds can also be reduced to amines in good yields with iron and hydrochloric acid in the Béchamp reaction [25], which is the oldest commercial process for preparing amines, and is still used in the dyestuff industry.…”

Liquid-phase permethylation of diethylenetriamine using methanol over robust composite copper catalysts

“…The direct N -methylation of amines is a central chemical transformation for the synthesis of fine chemicals, pharmaceuticals and natural products. 1 Traditional N -methylation methods driven by direct nucleophilic substitution using methyl halides, dimethyl sulfate and diazomethane often suffer from low green footprint due to poor selectivity, use hazardous reactants and generation of salt waste. 2 N -Methylarylamines can also be prepared by Buchwald–Hartwig C–N coupling of methylamines with aryl halides in excess of base using palladium or nickel catalysts, 3 copper powder under air (Ullmann type), 4 or homogeneous copper in the presence of base (Buchwald–Taillefer).…”