Toluene heterogeneous oxidation

Washing for over 100 h in a solvent such as toluene before the reaction resulted in no significant loss of the catalytic activity, and recovery and reusability studies at high turnover number also indicated the catalyst stability. Same catalysts, H5[PV2Mo10O40] supported on fiber and fabric carbon materials, catalyzed 02-based oxidations of acetaldehyde and 1-propanethiols [113], This aerobic heterogeneous oxidation proceeded under mild reaction conditions. 

The object of the present study was the application of this approach to the preparation of heterogeneous oxidative catalysts using cobalt phtalocyanine as precursor of cobalt deposited on y-alumina and silica that are traditional supports for oxidative catalysts, and test of the catalysts in partial oxidation of n-butane and toluene. 

Among the methods effective to oxidize toluene, heterogeneous photocatalysis is one of the most attractive, due to the mild conditions under which this process is usually carried out. Photocatalysis has been largely used for the photo-oxidation of many organic molecules in the liquid-solid regime [1-5], but a few papers report photoreactions in the gas-solid regime [6-lOj. 

The low temperature limitation of homogeneous catalysis has been overcome with heterogeneous catalysts such as modified Ziegler-Natta (28) sohd-supported protonic acids (29,30) and metal oxides (31). Temperatures as high as 80°C in toluene can be employed to yield, for example, crystalline... 

Attenlion should be drawn to ihe use of tin oxide systems as heterogeneous catalysts. The oldest and mosi extensively patented systems are the mixed lin-vanadium oxide catalysis for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recenily mixed lin-aniimony oxides have been applied lo the selective oxidaiion and ammoxidaiion of propylene to acrolein, acrylic acid and acrylonilrile. 

A particularly interesting system for the epoxidation of propylene to propylene oxide, working under pseudo-heterogeneous conditions, was reported by Zuwei and coworkers [61]. The catalyst, which was based on the Venturello anion combined with long-chained alkylpyridinium cations, showed unique solubility properties. I11 the presence of hydrogen peroxide the catalyst was fully soluble in the solvent, a 4 3 mixture of toluene and tributyl phosphate, but when no more oxidant was left, the tungsten catalyst precipitated and could simply be removed from the... 

The IR study performed in static controlled atmospheres in the IR cell allowed us to identify a number of adsorbed intermediate and secondary products, together with the main reaction products in oxidation and ammoxidation of toluene and the three xylene isomers. Surface reactions schemes are proposed that account for most of the mechanistic features of the heterogeneously-catalyzed industrial reactions. Our data support the following conclusions ... 

HETEROGENEOUS) photocatalytic oxidation of toluene using pure and iron-doped TITANIA CATALYSTS... 

We study here the heterogeneous photocatalytic oxidation of neat toluene, using unloaded and iron-loaded Ti02 as photocatalysts. The influence on the... 

On the other hand, the heterogeneous photocatalytic oxidation of toluene, in aqueous suspensions of TiO, has been studied with some details, by Fujihira et al. (refs.4-5). These authors have reported that, in aqueous media, up to 2 h of UV-irradiation, benzaldehyde was one of the main products benzyl alcohol was de tected as traces and benzoic acid was not detected (refs.4-5). However, in our experimental conditions using neat-liquid toluene, not only benzaldehyde but both benzyl alcohol and benzoic acid were detected as main products. 

In summary, although the heterogeneous photocatalyt.ir oxidation of toluene has been previously investigated by several authors, our investigation, has attempted to further correlate experimental conditions ( such as structural as pects and concentration of photocatalysts, irradiation times, etc.) with chemi-... 

Table 2.1 Catalytic performances of homogeneous and heterogeneous V catalysts for asymmetric oxidative coupling of 2-naphthol. The Vdimer/2-naphthol ratio was 1 36 and 100 mg of supported catalysts were used in 5 ml of toluene.

Since these early studies, a variety of other heterogeneous catalyst, have been reported to promote the copolymerization of PO and C02, with the most active of these being air-stable zinc derivatives of dicarboxylic acid [10, 11]. These catalysts are readily synthesized by the reaction of zinc hydroxide or zinc oxide with dicarboxylic acids in toluene. Recently, the crystal structure of zinc glutarate has been determined from its powder pattern of polycrystalline material [12] or single crystals [13], and shown to be a layered structure of zinc ions with bridging dicar-boxylates between the layers (see Figure 8.1). 

Ruthenium-exchanged hydrotalcites were shown by Kaneda and coworkers [156], to be heterogeneous catalysts for the aerobic oxidation of reactive allylic and benzylic alcohols. Ruthenium could be introduced in the Brucite layer by ion exchange [156]. The activity of the ruthenium-hydrotalcite was significantly enhanced by the introduction of cobalt(II) in addition to ruthenium(III), in the Brucite layer [157 ]. For example, cinnamyl alcohol underwent complete conversion in 40 min in toluene at 60 °C, in the presence of Ru/Co-HT, compared with 31% conversion under the same conditions with Ru-HT. A secondary aliphatic... 

Other oxidative procedures have been described. The heterogeneous liquid-phase oxidation of toluene with manganese dioxide in 65% sulfuric acid is imponant in the production of benzaldehyde and salicylaldehyde. An example of its application in the laboratory is found in the preparation of 3,5-dimethylbenzaldehyde (48%) from mesitylene. In a comparison... 

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