Benzyl liquid-phase oxidation

Purification. Small amounts of reaction by-products are produced during the liquid-phase oxidation of toluene. These by-products include acetic and formic acids, benzene, benzaldehyde, benzyl alcohol, aliphatic benzyl esters such as benzyl formate and benzyl acetate, biphenyl, 2-, 3-, and 4-methylbiphenyls, and phthalic acid. Of these only benzaldehyde and benzene [71 -43-2] are currendy separated commercially. 

Such regioselectivities are unique and suggest that redox pillared clays may have broad scope and utility as selective, heterogeneous catalysts for liquid phase oxidations. Indeed, V-PILC also catalyzes the oxidation of benzyl alcohol (to a mixture of benzoic acid and benzylbenzoate) whilst a-methyl benzylalcohol is left completely untouched.71 Similarly, p-substituted benzyl alcohols are oxidized whilst o-substituted benzyl alcohols are inert.71... 

Harada et al. [42] prepared nanosized palladium particles supported on activated carbons using a simple liquid-phase reduction of aqueous Pd complexes with KBH4. They found that the addition of appropriate amounts of NaOH into aqueous solutions of Na2PdCLt, followed by reduction with KBH4, produced highly dispersed Pd particles (less of 5 nm in diameter), irrespective of the carbon support used. The prepared catalysts were used efficiently in the liquid-phase oxidation of benzyl alcohol to benzaldehyde and in the liquid-phase hydrogenation of cinnamaldehyde to obtain the saturated aldehyde. 

One example (36) describes Co-TUD-1 for liquid-phase oxidation of cyclohexane. Another example (37) describes the synthesis, characterization, and catalytic performance of Fe-TUD-1 for Friedel-Crafts benzylation of benzene. Other reactions were described ... 

Similar synergic Au-Pd interactions were reported for bimetallic Au-Pd catalysts supported on polyaniline (PANI) [79] for benzyl alcohol oxidation. Here, the colloidal preparative route provided a narrow particle size distribution ( 3nm) with a Pd-rich shell encapsulating an Au-rich core. In this instance, the optimal composition was Au Pd =1 9. Benzyl alcohol oxidation has likewise been studied over an Au-Pd/Ti02 catalyst in which the deposition-precipitation method was used to improve the particle size distribution and activity versus wet impregnation [80]. In contrast, liquid-phase oxidation of cinnamyl, benzylic, octenol, and octenal... 

Premalatha, K., Raghavan, P.S., and Viswanathan, B. (2012) Liquid phase oxidation of benzyl alcohol with molecular oxygen catalyzed by metal chromites. Appl Catal A Gen.,... 

Ferri, D., Mondelli, C., Krumeich, F., et al. (2006). Discrimination of Active Palladium Sites in Catalytic Liquid-Phase Oxidation of Benzyl Alcohol,/ Phys. Chem. B, 110, pp. 22982-22876. 

Dimitratos, N., Lopez-Sanchez, J., Morgan, D., et al (2007). Solvent Free Liquid Phase Oxidation of Benzyl Alcohol Using Au Supported Catalysts Prepared Using a Sol Immobilization Technique, Catal Today, 122, pp. 317-324. 

N. Dimitratos, J. A. Lopez-Sanchez, D. Morgan, A. Carley, L. Prati and G. J. Hutchings, Solvent free liquid phase oxidation of benzyl alcohol using Au supported catalysts prepared using a sol immobilization technique, Catal Today, 2007, 122, 317-324. 

SankarM, NowickaE, TiruvalamR, etal. Controlhng the duality ofthe mechanism in liquid-phase oxidation of benzyl alcohol catalysed by supported Au—Pd nanoparticles. Chem Eur J. 2011 17 6524-6532. 

Patel A, Singh S. Undecatungstophosphate anchored to MCM-41 an ecofnendly and efficient bifunctional solid catalyst for non-solvent liquid-phase oxidation as well as esterification of benzyl alcohol. Mkroporous Mesoporous Mater. 2014 195 240-249. 

In earlier work, Bhaumik and Kumar (1995) have reported that the use of two liquid phases in the oxidation of hydrophobic organic substances with aqueous H2O2 using titanium silicate as the catalyst not only enhances the rate of oxidation but also improves selectivity for species like toluene, anisole, and benzyl alcohol. For a single liquid phase acetonitrile was u.sed a solvent. The solid-liquid system gives high ortho selectivity. Thus, in the case of anisole the ratios of o to p for. solid-liquid and solid-liquid-liquid system were 2.22 1 and 0.35 1, respectively. 

In SL-PC, a catalyst is supported on a solid matrix in the form of the film of a nonvolatile liquid phase adsorbed on the solid. The catalytic film can be, for example, a molten salt or a molten oxide (e.g., Deacon s catalyst (CUCI2/KCI) used to oxidize HCl with oxygen for the chlorination of ethylene in the synthesis of vinyl chloride. Figure 6.1 V2O5 for the oxidation of sulphurous to sulphuric anhydride). Alternately, it can be a liquid phase (e.g., ethylene glycol, PPh3, butyl benzyl phthalate, etc.) that contains a soluble catalytic species such as a metal complex. 

Toluene is, in low conversion, oxidized, with air, in the liquid phase to benzyl hydroperoxide, which yields mainly benzyl alcohol and some benzaldehyde upon hydrolysis, for example, in the presence of a cobalt salt. Benzyl alcohol thus obtained requires a more thorough purification for use in perfumes and flavors. 

The rearrangement of light and deuterium-labelled cis- and trans-2-methyl-3-phenyloxiranes (1, 2 and 1, 2 ) was studied on ZnO, Al-O-j and WO, and in the presence of BF,. Both in the gas phase (473-673 K) and in the liquid phase (298-413 K), l-phenyl-2-propanone (3) and 2-phenylpropanal (4) were formed with high selectivities (0-90% and 11-80%, respectively). Ring-opening was found to occur by selective fission of the benzyl C-0 bond. Mechanistic studies revealed the formation of an open carbenium ion or a double-bonded surface intermediate. The acidic (electrophilic) and basic characters of the oxides determine the product distributions by affecting the relative importance of the competing mechanisms. 

Na5PV2Moio04o supported on active carbon is active for oxidative dehydrogenation of benzylic alcohols and amines without overoxidation of benzalde-hyde and benzylamine in the liquid phase (357). The suppression of the overoxidation may be due to the lower oxidizing ability of Na5PV2Moio04o relative to its acid form. 

Chemical kinetics deductions are, in some circumstances, possible from a reaction system using a dispersed solid. If the solid is entirely insoluble, for example a supported catalyst, true surface kinetics can be obtained provided (i) it can be shown that the chemical reaction on the surface is much slower than the associated mass transfer, and (ii) the surface area of the solid can be obtained. These conditions applied in the case of the oxidation of an aqueous solution of hydrazine using a dispersion of insoluble barium chromate [16]. Another case is where it can be shown that an increase in the amount of the solid component does not increase the reaction rate. In this case, exemplified by the formation of benzyl acetate from benzyl bromide and solid sodium acetate in toluene solvent, it is likely that the reaction occurs in the solution phase and that the reaction is proceeding at the saturation concentration of the solid reactant in the liquid phase [17]. 

Benzylic oxidation of aromatic side-chains is also a well established technology in the bulk chemicals arena, e. g. toluene to benzoic acid and p-xylene to ter-ephthalic acid [1,2]. These processes involve homogeneous catalysis by, e. g., cobalt compounds, however, and also fall outside the scope of this book. Ammoxi-dation of methyl-substituted aromatic and heteroaromatic compounds is performed over heterogeneous catalysts in the gas phase but this reaction is treated elsewhere (Section 9.5). Transition metal-substituted molecular sieves have been widely studied as heterogeneous catalysts for oxidation of aromatic side-chains in the liquid phase, but there are serious doubts about their heterogeneity [5,6]. Here again, a cursory examination of the literature reveals that supported palladium seems to be the only heterogeneous catalyst with synthetic utility [4]. 

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