Ammoxidation aromatic compounds

Selective and Nonselective Pathways in Oxidation and Ammoxidation of Methyl-Aromatic Compounds over Vanadia—Titania... 

Attention should be drawn It) the use of tin o.xide systems as heterogeneous catalysts. The oldest and most extensively patented systems are the mixed tin-vanadium oxide catalysts for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recently mixed tin-antimony oxides have been applied to the selective oxidation and ammoxidation of propylene to acrolein, acrylic acid and acrylonitrile. 

In 1922 Wohl [13] published his observation that the oxidation of naphthalene in the presence of ammonia over vanadia gives phthalimide but this result went unnoticed both by the scientific community and by industry. Andrussov [6] found, in 1935, a route to produce hydrogen cyanide effectively by conversion of methane in the presence of air and ammonia over platinum catalysts at ca 1273 K. Thus, the first steps towards the development of ammoxidation had been taken. The conversion of aliphatic olefins was first claimed by Cosby in the late forties [e. g. 14] and the conversion of toluene to benzonitrile was first performed by Cosby and Erchak in 1950 [15]. The term ammoxidation was introduced by Hadley in 1961 [16]. Since the fifties the fundamentals of the reaction and the reaction technique, for different aromatic compounds, have been reviewed [e.g. 9,16,17]. 

The selectivity of a partial-oxidation catalyst can change with slight variations in its composition but is also dependent on the substrate and the reaction conditions. The design of catalysts optimized for a specific reaction should be based on a detailed knowledge and understanding of the reaction mechanism. The state of the art of catalyst development, mechanistic features, kinetics, and reaction technology in the ammoxidation of methyl aromatic compounds was summarized in 1992 by Rizayev et al. [38]. 

A redox mechanism (Mars-van Krevelen) is generally accepted for the ammoxidation reaction of methyl aromatic compounds, thus most catalysts applied contain transition metal oxides (e. g. vanadium, molybdenum) readily enabling changes in valence states. 

In addition to toluene higher condensed methyl aromatic compounds and biphenyl derivatives, e. g. 1-methylnaphthaIene (on Cu-Na-mordenite [36]) or p-methylbiphenyl (to / -cyanobiphenyl and terephthalodinitrile [60]) can also be ammoxidized. The ammoxidation route can also be used to insert nitrogen into very highly condensed products, e. g. lignins [61,62], or active carbon [63]. 

AMMOXIDATION OF HETERO AROMATIC COMPOUNDS TO THE CORRESPONDING NITRILES... 

Besides the use of vanadium-based catalysts, a wide variety of other catalyst compositions were reported. A recent review focussed on FeSbO based catalysts promoted by appropriate additives as suitable for the ammoxidation of alkyl-substituted aromatics and hetero aromatic compounds. A unique preparation method of a fluid-bed catalyst is presented using nitric acid oxidation of antimony trioxide catalyzed with iron ions. The catalysts thus prepared have superior catalytic and physical properties. [78]. In addition, some unique compositions were reported by different research groups. For instance, new ammoxidation catalysts based on rhenium carbonyl cluster complexes containing antimony and bismuth ligands were reported by Adam et al. [79]. Single-site multifunctional catalysts based on [Cu RUj C ] nanocluster anchored to inner walls of mesoporous silica were also used in the ammoxidation of 3P [80]. 

Pi coline Acetonitrile Acrylonitrile Ammoxidation Hetero-aromatic compounds Nicotinonitrile Pyrazinamide... 

The selectivity of the ammoxidation of molecules like toluene and xylene is much higher than that of the oxidation of these compounds to aldehydes. The selectivity difference is more pronounced here than in case of propene. The initial selectivities of the propene oxidation and ammoxidation are practically the same, and the selectivity difference is mainly due to the high stability of acrylonitrile compared with acrolein. For aromatic (amm)oxidation, however, the initial selectivities also differ. Apparently, ammonia interacts with the catalyst in such a way that the activity for oxidation of the aromatic nucleus is reduced. 

The literature on ammoxidation is very wide. The majority of papers and patents published in this field deal with propene and propane ammoxidation to acrylonitrile, of isobutane and isobutene ammoxidation to methacrylonitrile and methyl-aromatics and methylpyridines (picoUne) ammoxidation to the corresponding cyano-containing compounds, as discussed in the previous sections. A small amount of literature deals with the ammoxidation of the following molecules ... 

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. 

Zheng Q, Huang C, Xie G, Xu C, Chen Y (1999) A direct synthesis of aromatic nitriles from methylaromatic compounds by ammoxidation on DC-108 catalyst. Synth Commun 29 (13) 2349-2353... 

---