The heterogeneous catalytic hydrogenation of nitriles is an important industrial process for the production of diverse amines. The reaction scheme based on the von Braun and Greenfield proposals has been widely accepted for many years and it remains the most frequently cited reaction sequence for the formation of secondary and tertiary amines via the hydrogenation of nitriles. Over the past decade, there has been a stream of published papers that, using modern scientific techniques, have intensively investigated the detailed mechanism underlying the surface reactions of heterogeneously catalyzed nitrile hydrogenation and the surface intermediates. On the one hand, the results of these studies bring some light to this issue; on the other hand, entirely new, unanswered questions arise from new knowledge. The studies suggest that the mechanism of nitrile hydrogenation on solid catalysts is much more complicated than expected based on the reaction formalism of von Braun and Greenfield. Unfortunately, there are as yet no physicochemical studies available that could confirm in a straightforward manner the intimate details of the reaction mechanism of surface reactions. In this review, the various speculative mechanisms proposed for heterogeneous nitrile hydrogenation are discussed. It seems very likely from current knowledge that aminocarbene complexes and aldimines, coordinated to a metal via the -system of a C=N double bond and/or via the nitrogen lone pair, will prevail among the surface intermediates suggested for nitrile hydrogenation on palladium or platinum, whereas hydrogenation on a cobalt or nickel surface will likely be associated with the formation of nitrene intermediates. This duality provides a satisfactory explanation for the selectivity differences between metal catalysts in nitrile hydrogenation to primary amines.

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Two highly sulfonated micro/mesoporous polymers, P(1,3‐DEB)‐SO3H and P(1,4‐DEB)‐SO3H, with permanent porosity, the specific surface area about 550 m2 ⋅ g−1 and the content of SO3H groups of 2.7 mmol ⋅ g−1 were prepared as new acid Porous Polymer Catalysts, PPCs. The PPCs were achieved by easy sulfonation of parent hyper‐cross‐linked micro/mesoporous polyacetylene‐type networks resulting from a chain‐growth homopolymerization of 1,3‐ and 1,4‐diethynylbenzenes. New PPCs are reported as highly active and reusable heterogeneous catalysts of esterification of fatty acids with methanol and ethanol, Prins cyclization of aldehydes with isoprenol and intramolecular Prins cyclization of citronellal to isopulegol. The catalytic activity of the micro/mesoporous PPCs (TON values up to 522 mol ⋅ mol−1) was higher than that of commercial polymer‐based heterogeneous catalyst Amberlyst 15 possessing gel texture without permanent pores and that of p‐toluenesulfonic acid applied as a homogeneous catalyst.

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Technological aspects of the reductive amination of benzaldehyde with ammonia in the absence of solvents are discussed. The reaction kinetics in a slurry reactor was experimentally studied in order to maximize the yield of benzylamine. Effects of reaction conditions and type of solid catalyst on the content of undesirable by‐products were investigated. In particular, benzyl alcohol and trimers of benzylimine, namely, hydrobenzamide and 2,4,5‐triphenyl‐4,5‐dihydro‐1H‐imidazole, were found as significant by‐products. The formation of poorly soluble high‐boiling trimers of benzylimine was minimized by semi‐batch arrangement of the process with continuous addition of benzaldehyde into the load of benzylamine, ammonia, and Raney‐Ni catalyst. Some important features of benzaldehyde amination, which make it less advantageous for benzylamine production compared to the benzonitrile hydrogenation, are described.