Selectivity toluene oxidation

The oxidation of toluene to benzaldehyde and benzoic add over V205/Ti02 assisted by microwaves was studied by Liu et al. [82]. The authors conduded that microwave energy can greatly improve the process of selective toluene oxidation. The highest yields of benzoic add were, however, only 38—41% and the highest selectivity was 51% at 80% conversion to benzoic add. 

Bulushev, D.A., Kiwi-Minsker, L., Zaikovski, V.I., Lapina, O.B., Ivanov, A.A., Reshetnikov, S.I., and Renken, A. Effect of potassium doping on the structural and catalytic properties of V/Ti-oxide in selective toluene oxidation, zlpp/. Catal. A Gen. 2000, 202, 243-250. 

The activity and selectivity of 19 oxides at 400—450°C were investigated by Germain and Laugier [133], The activities are compared with those for the oxidation of toluene in Fig. 8, and show a linear relationship for the major part of the oxides, the toluene oxidation being approximately twice as fast as the benzene oxidation. The only selective catalysts, i.e. those that produce substantial amounts of benzoquinone and maleic anhydride from benzene, and benzaldehyde and benzoic acid from toluene are the oxides of V, Mo and W. Remarkably, these oxides clearly deviate from the average correlation in Fig. 8 and show a much higher tol-uene/benzene activity ratio (about 10/1). The order of activity, maximum yield of maleic aldehyde and initial selectivity with respect to benzoquinone is the same for these oxides V > Mo > W. 

That mercury(ll) acetate allylic oxidatimi can be a usrful reaction in the case of complex and sensitive substrates is demonstrated by the oxidation of avomectin A2a (38). The reaction, carried out in anhydrous toluene at 100 C for 40 min, was mnaikably selective, allylic oxidation occurring exclusively at the 3,4-double bond with rearrangement to give (39) in up to 73% yield (equation 17). 

Table 13.4 Conversion and selectivity data for toluene oxidation using U-based mixed oxides at 500°C [51],...

In early attempts to oxidize hydrocarbons electrochemically, organic solvents and corrosion-resistant electrodes (PbO, C, Pt) were used to overcome low reactant solubility and anode dissolution at extreme potentials, -I-1.8 V and up to 4.5 V (326, 327). The primary anodic reaction was usually oxygen evolution or solvent decomposition. The electrode material, nonetheless, affected the product even at the small attainable yields. Thus, toluene oxidized to traces of aldehydes on PbO2 (333), while on Pt it yielded up to 19% benzaldehyde (326). The catalytic efifect of the anode, however, on rate and selectivity was not realized. 

Runs of toluene oxidation depicted in Table 3 also indicate improved activity of catalyst 1. Similar conversion of toluene on promoted and non-promoted catalysts 1 and 3 was reached at 400°C and 500°C accordingly. Selectivity to benzaldehyde was also higher on the promoted catalytic system however, the total performance of this catalyst was lower than results reported for the vanadia based catalysts [13]. 

In particular, the study was centered on the analysis of the behavior in toluene selective oxidation of a series of V-containing micro- and mesoporous materials [mesoporous (MCM-41), MFI (2SM-5) and P type]. The formation of phenol as a by-product has also been observed in some cases. This product does not form in toluene oxidation over vanadium oxide supported on AI2O3 or TiOa [2-6] and is an interesting first example of the possibility of direct synthesis of phenol from toluene using gaseous O2. A further objective of this work therefore was to identify the key aspects in this reaction as well as the possible reaction mechanism. 

Above a temperature of about 450°C the catalyst deactivates due to the formation of heavier products which remain on the zeolite, explaining the lowering of the selectivity above this temperature, but at lower temperatures benzaldehyde selectively transforms to benzoic acid. Phenol and benzene are the main by-products of benzaldehyde oxidation with selectivities up to about 10% each. The other by-products observed in toluene oxidation, including phenylbenzoate, were also detected in benzaldehyde oxidation. 

Isolated V oct. sites are probably responsible for the selective behavior in toluene oxidation to benzaldehyde as indicated by the characterization of Vx-HMS catalysts. It should be remarked that unsupported or supported vanadium oxides oxidize toluene to benzoic acid [12] or a mixture of benzaldehyde and benzoic acid [2], whereas all V-containing zeolites tested form only benzaldehyde. The nature of the zeolite influences the nature of isolated species, as well as the ratio between isolated to polynuclear vanadium species. 

The toluene oxidation reaction was used as a probe to study the catalytic properties of the Mo-Ce complex oxides. The as-prepared oxides were introduced into a U-type quartz fixed bed microreactor and their catalytic properties for selective oxidation of toluene to benzaldehyde were evaluated under the reaction conditions of O.lMPa, 400 C, air/toluene = 9 (vol/vol), F/W =1900 ml/h g cat. The reaction products were analyzed by an on-line gas chromatography. Under the above reaction conditions, the main products were CO, CO2, H2O and benzaldehyde. 

Silylation of 276 with TBSOTf furnishes the bis-TBS ether, which undergoes an osmium tetroxide hydroxylation to afford the syn,anti,syn,anti,syn- iQi o 278 in 73% yield and with high diastereoselectivity. Selective diol oxidative cleavage with periodic acid, PCC oxidation of the resulting epimeric lactols to the lactone, followed by deprotection with /7-toluene-... 

Additives of MP enhance the selectivity of oxidation of toluene to BH, catalyzed with Ni(II)(acac)2, to 27% at [MP] = 3.0 10 mol/1 (Fig. 2(a)) with the same extent of oxidation. Thereby on initial reaction steps the yield of BH significantly increases ( in 4 times). With concentration of [MP] increase, when [MP] > 10 mold, the character of dependence 5gjj from degree of conversion C is changed the value of is maximal on initial reaction steps =30-40% at 0.5% of conversion C, and selec-... 

In the first chapter of this book, the selective alkylarens oxidations with dioxygen in the presence of catalytical systems is studied. Kinetics and mechanism toluene and cumene oxidation by dioxygen with nickel (II) complexes are presented in the second chapter. 

The chlorobenzene processes for the production of phenol have lost then-importance since the 1970 s. Occasionally, the toluene oxidation process, also developed by Dow is still used. In the first stage of this process, toluene is oxidized to benzoic acid with air in the liquid phase at 150 to 170 °C and 5 to 10 bar, in the presence of cobalt salts, with 90% selectivity. By-products are methylbiphenyls, benzyl alcohol, benzaldehyde and esters. Following the purification of the crude product by distillation or crystallization, the benzoic acid is transformed into phenol in the presence of copper (II) salts with air and steam at 230 to 250 °C, and 2 to 10 bar, by way of the intermediate compounds copper benzoate, benzoyl-salicylic add and phenyl benzoate. The recovered crude phenol is refined by distillation. The molar yield of phenol is around 85 to 90%. 

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