Imine ammoxidation

Ammonia also reacts with the acrolein intermediate, via the formation of an imine or possibly oxime intermediate which transforms faster to the acrylonitrile than to the acrylamide intermediate. This pathway of reaction occurs at lower temperatures in comparison to that involving an acrylate intermediate, but its relative importance depends on the competitive reaction of the acrolein intermediate with the ammonia species and with catalyst lattice oxygens. NH3 coordinated on Lewis sites also inhibits the activation of propane differently from that absorbed on Brsurface reaction network in propane ammoxidation. 

The ammoxidation reaction mechanism for xylenes is similar to that for toluene. The xylene substrate is activated by hydrogen abstraction from the methyl groups with subsequent reaction with activated ammonia converting the methyl group to an amine, then to an imine, and finally to a nitrile. In the case of xylene ammoxidation, the ammoxidation of the methyl groups to cyano functionalities occurs sequentially rather than concurrently (73,76). 

Mmakami et al. [120] and Niwa et al. [121] investigated the reaction mechanism of ammoxidation by FTIR spectroscopy using V Oj/Al Oj catalysts. They claim that the reaction proceeds via interaction of ammonium ions with surface benzoate ions. Cavalli et al. [5, 122] and Busca et al. [123] proposed benzyl amine and benzaldehyde species as reaction intermediates in the ammoxidation of toluene over V Oj/TiO catalysts. Otamiri and Andersson [124] proposed vanadium imido species (V=NH) and vanadium hydroxylami-no species (V-NH-OH) as nitrogen insertion sites in V Oj catalysts. These species in turn react with adsorbed toluene to form an amine (R-CH -NH ) and/or imine (R-CH=NH) surface intermediate, which subsequently transform into nitrile as a final product. A mechanism proposed by Sanati and Andersson [125] includes (CgHj)CH(NH2)0- and (CgHj)CH(NH2)(0-)2 species as reaction intermediates. Ramis et al. [126] reported the formation of amido... 

Another facet of surface organometallic chemistry involves modelling of the mechanisms of surface reactions on the basis of the reactivity of molecular models. For example, the reactivity of metal-imine complexes of molybdenum is considered by CHAN, who proposes elementary steps constituting the catalytic cycle of the surface-catalyzed alkene ammoxidation reaction, which is of great industrial importance. HERRMANN provides some very fine examples of molecular models of the rhenium oxide catalysts used commercially in the alkene metathesis reaction. 

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