Oxidation toluene product distribution

When the same [NiI (NHC)2] complexes are employed as alkene dimerisation catalysts in ionic liquid (IL) solvent [l-butyl-3-methylimidazolium chloride, AICI3, A-methylpyrrole (0.45 0.55 0.1)] rather than toluene, the catalysts were found to be highly active, with no evidence of decomposition. Furthermore, product distributions for each of the catalyst systems studied was surprisingly similar, indicating a common active species may have been formed in each case. It was proposed that reductive elimination of the NHC-Ni did indeed occur, as outlined in Scheme 13.8, however, the IL solvent oxidatively adds to the Ni(0) thus formed to yield a new Ni-NHC complex, 15, stabilised by the IL solvent, and able to effectively catalyse the dimerisation process (Scheme 13.9) [25-27],... 

The same commercial Bi—Mo—P—O catalyst was used in a study by Van der Wiele [347], which included the oxidation of the xylenes at 400— 500° C. In contrast to the oxidation of toluene, dealkylation cannot be neglected. Table 33 presents an example of the product distribution at a 71—74% conversion level for both the xylenes and toluene. Remarkably, substantial amounts of the dialdehyde are only formed from p-xylene, while an enhanced benzene production is found in the case of o-xylene. The reaction schemes shown on p. 208 are proposed the combustion reactions, applicable to each component in the scheme are left out for simplicity. 

Kinetic and mechanistic investigations on the o-xylene oxidation over V205—Ti02 catalysts were carried out by Vanhove and Blanchard [335, 336] using a flow reactor at 450°C. Possible intermediates like o-methyl-benzyl alcohol, o-xylene-a,a -diol, toluic acid and phthalaldehyde were studied by comparing their oxidation product distribution with that of toluene. Moreover, a competitive oxidation of o-methylbenzyl alcohol and l4C-labelled o-xylene was carried out. The compounds investigated are all very rapidly oxidized, compared with o-xylene, and essentially yield the same products. It is concluded, therefore, that these compounds, or their adsorbed forms may very well be intermediates in the oxidation of o-xylene to phthalic anhydride. The ratio in which the partial oxidation products are formed appears to depend on the nature of the oxidized compounds, i.e. o-methylbenzyl alcohol yields relatively more phthalide, whereas o-xylene-diol produces detectable amounts of phthalan. This... 

Product distributions. The reaction was conducted at 550°C by changing the contact time, while fixing the other conditions as presented under Experimental. The main products were benzaldehyde and carbon oxides. The formation of benzoic acid, acetic acid, and maleic anhydride was also detected, but their amounts were much smaller. The yields of each product are shown as a function of the toluene conversion in Fig. 1. The selectivities are given by the slopes from the origin (dashed lines). The selectivity to benzaldehyde decreases with an increase in conversion, while that to carbon oxides increases, indicating that the benzaldehyde formed initially is oxidized gradually to carbon oxides. 

The ease of oxidation in the presence of the CAB system with hydrogen peroxide is generally benzyl alcohols > aldehydes > toluenes. This series accounts for the reactivity and subsequent product distributions when 1,4-dimethybenzene is oxidized with the CAB system. Here, 4-methylbenzoic acid forms preferentially to attack at the second methyl group. Similarly, oxidation of 1,3,5-trimethylbenzene yields 3,5-dimethylbenzoic acid. This is complementary to the reactivity observed with the HBr/hydrogen peroxide/hv method (see... 

Table 3 compares our results on the oxidation of toluene over the Sn-silicalite samples. The Sn-samples are active in this reaction (39.4, 36.4 and 34.2 mol % H2O2 efficiency in 24 h for samples with Si/Sn ratios of 70). Both the hydroxylation of the aromatic nucleus to give cresols and the oxidation of the methyl substitutent to give benzyl alcohol and benzaldehyde take place simultaneously on the Sn-silicalites. Based on the product distribution, it can be seen that the rate of the oxidation of the methyl substituent is about 6 times faster than the rate of aromatic hydroxylation on all the samples. After 24 h, the concentration of benzaldehyde is the highest in the product. In this respect, the Sn-silicalite molecular sieves are more similar to the V-silicalites, VS-2 than the Ti-silicalites, TS-1 or TS-2 [16]. 

Fig. 6 Oxidation of toluene over V-MFI samples influence of duration of run on conversion and product distribution. A, V-MFI(A) B, V-MFI(B) ( ), side chain oxidation products and (A), cresols.

The two principal oxidation pathways for toluene are shown in Fig. 6-11. The relative significance of OH addition to the benzene ring and H-atom abstraction from the methyl group has been determined by Perry et al. (1977a) from a study of the temperature dependence of the reaction rate coefficient, and by Kenley et al. (1978) from a detailed analysis of the product distribution. Both groups of authors conclude that at ambient temperatures the probability for H-atom abstraction is about 15% of that for the overall reaction. Figure 6-11 shows that the subsequent reactions lead to the formation of benzaldehyde unless the toluenylperoxy radical enters into a termination reaction with H02 radicals. In that case toluenyl-hydroperoxide would be formed. 

The selectivities of CO2 in COjc were not dependent on either the specific input energy or the type of VOCs, and showed constant values. This observation indicates that the channel to produce CO2 was determined by the decomposition pathway (i.e. the type of intermediates). Again, once CO is formed, further oxidation of CO to CQz in the PDC reactor is negligible under the tested SIE range. Since the decomposition of HCOOH preferably produced CO in the PDC reactor, HCOOH is believed to be an important precursor for CO2 formation. Except for HCOOH which shows 100% CO selectivity, 6 aromatic compounds showed almost the same CO2 selectivity at about 71-77%. These similar by-product distributions and selectivities indicate that the decomposition mechanism of aromatic compounds in the PDC reactor is quite similar. From a long-term test over 150 hours, the PDC system showed a stable performance without any catalyst deterioration for the decomposition of benzene and toluene [170]. 

Product distributions resulting from the OH radical induced oxidation of the following hydrocarbons have been determined 2-methyl-propane, 2,3-dimethyl-butane, 2-methyl-butane, n-pentane, cyclohexane, methySubstituted 1-butenes, isoprene, toluene. Whenever possible, branching ratios for the self-reactions of alkylperoxy radicals and decomposition rate coefficients for alkoxyl radicals were derived. 

Further oxidation of these products can result in the consumption of many equivalents of oxidant for each molecule of DBP. This is the chemistry by which antioxidants protect many commercial products from spoilage or material damage by oxidation (20). Antioxidants such as DBP, and the more familiar BHT (butylated hydroxy toluene or 2,6-di-(t-butyl)-4-methyl phenol), are used very widely, so these compounds and their oxidation products are widely distributed in the environment (21). 

The liquid-phase oxidation of toluene with molecular oxygen is another example of a well established process (Table 4, entry 40). A cobalt catalyst is used in the process and the reaction proceeds via a free-radical chain mechanism. Heat of reaction is removed by external circulation of the reactor content and both bubble columns or stirred tanks are employed. It is important to note that air distribution is critical to prevent the danger of a runaway. Another example of direct oxidation is the commercial production of nitrobenzoic acid by oxidation of 4-nitrotoluene with oxygen (Table 4, entry 41). 

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