Ammoxidation heteroaromatic compounds

Supported vanadium oxides represent one of the technologically most important class of solid catalysts. These catalysts are useful for partial oxidation of various hydrocarbons 0), ammoxidation of alkyl substituted N-heteroaromatic compounds (2) and most recently for NO reduction (3) For a catalyst to be a successful one in industry, it should exhibit high activity with maximum selectivity, thermal and mechanical stability and long life etc. For getting some of these functionalities, the active component has to be dispersed uniformly on a support material. 

Ammoxidation refers to the formation of nitriles by oxidation of hydrocarbons with oxygen in the presence of ammonia (Figure 1) [1]. Ammoxidation is best conducted with olefins, or with aromatic or heteroaromatic compounds, containing a readily abstractable H atom (allylic or benzylic intermediates are formed), although the ammoxidation of alkanes (e. g. propane to acrylonitrile [e. g. 2-4] or ethane to acetonitrile [e. g. 5]) is also possible. An exceptional example is the ammoxidation of methane to hydrogen cyanide by the Andrussov reaction [6]. 

Figure 1. Formation of nitriles by ammoxidation of alkanes, alkenes, methyl aromatic and heteroaromatic compounds.

Many heterogeneous catalytic systems have been developed and applied to ammoxidation reactions. Vanadium-containing oxides are preferred as supported, bulk, or multicomponent catalysts for the ammoxidation of aromatic or heteroaromatic compounds. Favored supports are titanium oxide (anatase) [18,19], zirconium oxide [20,21], tin oxide [22], or mixed supports such as titanium-tin oxide [23]. Catalytic systems used as bulk materials include vanadium-phosphorus oxides [24], crystalline vanadium phosphates [25], and vanadium oxide combined with antimony oxide [26] or molybdenum oxide [27]. Other important catalysts include multicomponent systems such as KNiCoFeBiPMoO c on silica... 

The ammoxidation of methyl aromatic and heteroaromatic compounds is a convenient route to many nitriles required for further synthesis of fine chemicals. For example, for the production of amines by hydrogenation or of carboxylic acids and amides by hydrolysis. 

Vanadium phosphorus oxides (VPO) are good catalysts for selective O- and N-insertion reactions of aliphatics and methylaromatics, in particular for the oxidation of -butane to maleic anhydride (MA) and for the ammoxidation of methylaromatics and heteroaromatics to the corresponding benzonitriles (47,48). VOHPO4 O.5H2O is a well-defined crystalline compound used as a precursor of... 

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