Aromatic ammoxidation

Since these results are far less well known than those reported for C3 and alkyl-aromatic ammoxidation, they are discussed in a more detail below. 

An alternative process scheme for alkyl aromatic ammoxidation has been described by the Lummus Co. It uses the approach originally developed for the... 

The catalyst chemistry of alkyl aromatic ammoxidation has been extended to other alkyl substrates in addition to toluene and lenes. The effectiveness of vanadium oxide-based catalysts to selectively catalyze the conversion of methyl groups attached to aromatic rings is wide-ranging. An example is the ammoxidation of alkyl naphthalenes, notably the ammoxidation of 2,6-dimethylnaphthalene to the corresponding dicyanonaphthalene. 

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). 

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

Vanadia-titania ( 5 and other supported vanadia catalysts (9) can also be applied for the production of aromatic nitriles by ammoxidation of toluene and of the three xylene isomers allumina-supported V-Sb-based oxides seem to be the best catalysts (10). Detailed kinetic studies of toluene ammoxidation have been reported recently using different vanadia-titania catalysts ( 77,72). Ammonia inhibits toluene conversion, while benzonitrile yields (up to 80 % near 610 K) are mainly limited by... 

The purpose of the present paper is to offer a contribute to the understanding of the mechanisms of these reactions by using an IR spectroscopic method and well-characterized "monolayer" type vanadia-titania (anatase) as the catalyst. We will focus our paper in particular on the following subjects i) the nature of the activation step of the methyl-aromatic hydrocarbon ii) the mechanism of formation of maleic anhydride as a by-product of o-xylene synthesis iii) the main routes of formation of carbon oxides upon methyl-aromatic oxidation and ammoxidation iv) the nature of the first N-containing intermediates in the ammoxidation routes. 

V-containing silicalite, for example, has been shown to have different catalytic properties than vanadium supported on silica in the conversion of methanol to hydrocarbons, NOx reduction with ammonia and ammoxidation of substituted aromatics, butadiene oxidation to furan and propane ammoxidation to acrylonitrile (7 and references therein). However, limited information is available about the characteristics of vanadium species in V-containing silicalite samples and especially regarding correlations with the catalytic behavior (7- 6). 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

Many substances can be partially oxidized by oxygen if selective catalysts are used. In such a way, oxygen can be introduced in hydrocarbons such as olefins and aromatics to synthesize aldehydes (e.g. acrolein and benzaldehyde) and acids (e.g. acrylic acid, phthalic acid anhydride). A selective oxidation can also result in a dehydrogenation (butene - butadiene) or a dealkylation (toluene -> benzene). Other molecules can also be selectively attacked by oxygen. Methanol is oxidized to formaldehyde and ammonia to nitrogen oxides. Olefins and aromatics can be oxidized with oxygen together with ammonia to nitriles (ammoxidation). 

Ammoxidation can be successfully applied to methyl aromatics (e.g. toluene and xylene) as it can to propene. However, the subject has not received much attention in the literature, mainly due to the fact that there are no important applications for aromatic nitriles at present. 

Methyl side chains of aromatic hydrocarbons can be selectively ammox-idized to nitrile groups. The process is very similar to the ammoxidation of propene and the same catalysts are found to be effective. Identical mechanisms have been proposed, and will not be discussed here. 

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. 

A few contributions with respect to the ammoxidation of aromatic hydrocarbons that have appeared in the literature concern toluene and xylene. 

IsophLhalonitrile (1,3-dicyanoben/ene, 1PN), is a white solid which mells at 161°C and sublimes at 265°C. It is slightly soluble in water but readily dissolves in diinethylfonnamide, jV-inethylpyiToliclinoiie and hot aromatic solvents. IPN undergoes the reactions expected of an aromatic nitrile. It is prepared by vapor-phase ammoxidation of metci- ylcnc. Its principal use is as an intermediate to amines, As a reagent, TPN can be used to convert aromatic acids to nitriles in near quantitative yields. 

The synthesis of intermediates and monomers from alkanes by means of oxidative processes, in part replacing alkenes and aromatics as the traditional building blocks for the chemical industry [2]. Besides the well-known oxidation of n-butane to maleic anhydride, examples of processes implemented at the industrial level are (i) the direct oxidation of ethane to acetic acid, developed by Sabic (ii) the ammoxidation of propane to acrylonitrile, developed by INEOS (former BP) and by Mitsubishi, and recently announced by Asahi to soon become commercial (iii) the partial oxidation of methane to syngas (a demonstration unit is being built by ENI). Many other reactions are currently being investigated, for example, (i) the... 

Ammoxidation of Aromatic Hydrocarbons. - The ammoxidation of toluene with V2O5, both pure and supported on A1203, was studied by Murakami et 0/.27,46,97,98 They conclude that the catalyst is bifunctional toluene is adsorbed oxidatively on V2O5, the oxidized product is stabilized as a benzoate ion on the alumina carrier and subsequently reacts with ammonia giving benzonitrile. It was observed that the oxidation state of the vanadium oxide was close to V204 and that benzaldehyde is probably the product formed in the initial step. 

Lanthanides in oxy-anion systems In aluminosilicates In molybdates In phosphates In other systems For cracking reactions For ammoxidation reactions For hydrolysis of chlorinated aromatics... 

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