Toluene from heterogeneous oxidation

The synthesis of optically active cyclohex-2-enone oxide (55) from cyclohex-2-enone has been reported. The epoxidizing medium contained a chiral catalyst (quininium benzyl chloride) with Bu OOH and a small amount of solid NaOH in toluene. This heterogeneous mixture avoided the use of the strongly alkaline aqueous phase which may have been responsible for the failure of earlier attempts at direct, chiral synthesis of (55). Chemical yields of 60% were obtained, with an e.e. of 20 3%. 

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... 

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). 

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... 

An oxidizing reagent based on potassium ferrate(Vl) has been described [78], This potassium ferrate, when used in conjunction with an appropriate heterogeneous catalyst such as KIO montmorillonite clay, is a strong oxidant which produces cycloalkanols and cycloaUcanones from cycloalkanes, and benzyl alcohol and benzaldehyde from toluene. 

The copolymers resulting from the anodic copolymerization of (DMA)3(SBF) P-RuCO and (DMA)2(SBF)2PRuCO with SBF, copoly(DMA)3(SBF)PRuCO and copoly(DMA)2(SBF)2PRuCO, lead to cyclopropane yields almost identical to those obtained with their respective monomers (Table 5, entries 5-16). The enantioselectivity nevertheless decreases from the homogeneous phase to heterogeneous phase. The best result in term of enantioselectivity, ee 53 % for the tram isomer, is obtained in toluene with copoly(DMA)3(SBF)PRuCO at low temperature (-40 C) (Table 5, entry 7). It is difficult to provide a precise answer to the enantiomeric excess decrease from monomer to polymer. This effect may be related to a restricted access to the active site of the polymetalloporphyrins. The presence of high oxidation states mthenium species (Ru or Ru for instance) in the polymer (due to incomplete reduction after anodic polymerization) may also decrease the enantioselectivity. 

We believe that initiator-derived phenyl radicals abstract benzylic hydrogen from toluene to produce benzyl radicals. The high yields of the imine suggest that benzyl radicals are efficiently trapped and oxidized by the imido complexes presumably via the intermediacy of M(V) amido complexes. Apparently the amide ligand of this intermediate is further oxidized to the Schiff base, again consistent with the proposed chemistry on the heterogeneous catalyst surface [15]. 

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