Side-reactions, Choice of Catalyst, and Reaction Conditions

3 Side-reactions, Choice of Catalyst, and Reaction Conditions 

All metal hydrogenation catalysts including supported Pt metals, Cu, Co, Ni, Fe, and Cu-Cr203 are suitable for amination of alcohols [2,11]. There is a wide range of commercially available metal amination catalysts and development of a special multicomponent catalyst might be necessary for demanding reactions only [9]. The choice of a particular catalyst is determined mainly by its selectivity pattern 

A further role of hydrogen in the reaction mixture is to prevent catalyst deactivation by formation of surface nitride, carbide, or unsaturated oligomeric deposit 

The metal catalysts are oxidized during storage in air and have to be reduced (activated) with hydrogen before use. Activation of carbon-supported Pt metals occurs smoothly at ambient temperature but reduction of Cu, Ni, Co, or Fe oxides requires at least 150-200 °C. Major roles of the support (usually AI2O3, SiO, or carbon) and additives are to stabilize the high surface area of the metal and possibly contribute to acid or base-catalyzed reactions. The amount of catalyst in a batch reactor is usually between 5 and 30 % (jntm), relative to the alcohol. 

Both batch reactors (autoclaves) and continuous fixed-bed reactors are suitable for alcohol amination. High pressure in the range 50-150 bar is necessary only for reactions with ammonia. The usual temperature is ca 200 °C, but achieving good selectivity for unsaturated amines, nitriles, or heteroaromatic compounds requires 300-400 °C. Solvents other than ammonia are rarely applied. 

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