Alkylaromatic ammoxidation

In the presence of anunonium bromide cobalt (ref. 22) and manganese (ref. 23) have been shown to catalyze the ammoxidation of methylaromatics to the corresponding aromatic nitriles (Fig. 20). It is interesting to compare this homogeneous, liquid phase system with the more well-known vapour phase ammoxidation of alkylaromatics over oxidic catalysts (ref. 4). 

Typical performance is a selectivity higher than 90% at a conversion in the 50-90% range, mainly depending on the type of substrate. Substituted pyridines yield better selectivities at high conversion than the equivalent alkylaromatics. The nature and position of the substituents in substituted alkylaromatics also play an important role in determining selectivity and activity. The commercial application of this technology is mainly hindered by the relatively small plant necessary for these products as compared to full-scale processes. The further implementation of the process of alkylaromatic catalytic ammoxidation would thus require the development of multi-purpose small-size continuous plants using small fluidized bed-reactors (to better control temperature and allow easier substitution of the catalyst). 

The ammoxidation of methylaromatic compounds has been shown to be a convenient route to produce many nitriles required for further syntheses of side-chain functionalized products. This method is versatile and can be carried out very easily because of the stability, and undamaged desorption, of the nitriles formed under severe gas-phase conditions. A series of interesting new patents on catalysts for the ammoxidation of alkylaromatics have been issued, indicating that there is still commercial interest in this reaction [117]. 

The ammoxidation of (substituted) alkylaromatics, with or without heteroatoms, is also a well established reaction of interest for the production of fine and specialty chemicals. Although commercial, the number of processes is still limited. However, there is a growing interest in new market areas such as China, and new processes may be expected in the near future. 

Centi G (1996) Nature of active layer in vanadium oxide supported on titanium oxide and control of its reactivity in the selective oxidation and ammoxidation of alkylaromatics. Appl Catal A 147 (2) 267-298... 

Centi, G. (1996). Nature of Active Layer in Vanadium Oxide Supported on Titanium Oxide and Control of its Reactivity in the Selective Oxidation and Ammoxidation of Alkylaromatics, Appl. Catal. A Gen., 147, pp. 267-298. 

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