Hydrogenation of nitro compounds

Reduction of Nitro Compounds. The mechanism for catalytic hydrogenation of nitro compounds has been the subject of many iavestigations and there is much evidence that this reaction proceeds through several iatermediate species. The most widely accepted mechanism for the hydrogenation of nitro compounds was proposed by Haber ia 1898 (2) (see Fig. 1). 

Fig. 1. Mechanism for the hydrogenation of nitro compounds. FunctionaHties are labeled.

Hydrogenation Catalysts. The key to catalytic hydrogenation is the catalyst, which promotes a reaction which otherwise would occur too slowly to be useful. Catalysts for the hydrogenation of nitro compounds and nitriles are generally based on one or more of the group VIII metals. The metals most commonly used are cobalt, nickel, palladium, platinum, rhodium, and mthenium, but others, including copper (16), iron (17), and tellurium... 

Hatziantoniou, V., Andersson, B., and Schbon, N.-H., Mass transfer and selectivity in liquid phase hydrogenation of nitro compounds in a monolithic catalyst reactor with segmented gas-liquid flow. Ind. Eng. Chem. Process Des. Dev. 25, 964-970 (1986). 

Aqueous Two-Phase Hydrogenations of Nitro-Compounds, Imines, Nitriles,... 

Amination. A continuous process in which aliphatic and aromatic amines are produced by (1) high pressure, catalytic hydrogenation of nitro compounds (-NO2 or nitriles (-CN)) and (2) action of ammonia on a chloro- or hydroxy-compound. 

CoH(CN)5] catalyses the hydrogenation of nitro compounds either to amines (aliphatic substrates) or to products of reductive dimerization, i.e. to azo and hydrazo derivatives. Ketoximes and oximes of 2-oxo-adds are hydrogenated to amines. This latter reaction gives a possibihty to directly produce a-amino-acids in the reductive amination of 2-oxo-acids in aqueous ammonia at a temperature of40-50 °C and 70 bar H2 (Scheme 3.1). Yields are usually high (approximately 90%) [18]. 

Chemoselective Hydrogenation of Nitro Compounds to the Corresponding Amines on... 

Some examples of bubble fixed-bed reactors application are the hydrogenation of nitro compounds, animation of alcohols, and ethylnylation of formaldehyde to butynediol (Ramachandran and Chaudhari, 1984). 

The C=N bonds of imines, oximes and hydrazones can be hydrogenated to form the corresponding amines even under ambient conditions on Pt, Pd, Rh and Raney Ni catalysts in acidic, neutral or basic media (equation 42). The imines, furthermore, are intermediates in the hydrogenation of nitro compounds, nitriles and oximes, and likewise play a key role as intermediates in the reductive amination of carbonyl compounds. 

The addition of other metals to promote skeletal catalysts has been the subject of a number of investigations including the use of V, Cr, Mn, and Cd for hydrogenation of nitro compounds [23], Cd in the hydrogenation of unsaturated esters to unsaturated alcohols [24], and Ni and Zn for the dehydrogenation of cyclo-hcxanol to cyclohexanone. The use of Cr as a promoter is particularly attractive as copper chromite catalysts arc used in a wide range of industrial applications. Lainc and co-workers [25] have made a detailed study of the structure of chromium promoted skeletal copper catalysts. 

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