Benzyl partial oxidation

The degradation of acenaphthene is initiated by benzylic monooxygenation, and the pathway was determined using [l- C]acenaphthene by the isolation of intermediate metabolites (Selifonov et al. 1998). Importantly, the method proved applicable even when only limited biotransformation of the substrates had taken place by partial oxidation. 

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... 

The partial oxidation of alcohols, to afford carbonyl or carboxylic compounds, is another synthetic route of high industrial interest For this, scC02 was investigated as a reaction medium for the aerobic oxidation of aliphatic, unsaturated, aromatic and benzylic acids with different catalytic systems, mainly based on the use of noble metals, both in batch [58-64] and in continuous fixed-bed reactors [65-70]. In this context, very promising results have been obtained when studying the catalytic activity of supported palladium and gold nanoparticles in the oxidation of benzyl alcohol to benzaldehyde these allowed conversions and selectivities in excess of 90% to be achieved [71-73]. 

Tsuruya and co-workers (83,84) recently reported that addition of alkaline earth metals (e.g., Ca, Sr, and Ba) to an Ag/SiOi catalyst by a coimpregnation method enhanced the catalytic activity of the partial oxidation of benzyl alcohols into benzaldehydes, with production of only small amounts of byproducts (carbon dioxide, toluene, and benzene). The formation of carbonaceous material was thought to be inhibited by the alkaline earth metals, which also helps to disperse the metallic silver and facilitate oxygen adsorption. This effect causes the formation of an oxygenated silver surface that is generally believed to be responsible for the partial oxidation of benzyl alcohol. 

Kinetic investigations of dibenzyl ether oxidation shows that like benzyl alcohol oxidation, there are the same two areas of process parameters with different reaction kinetics area A with "low" acidity ([HC104]=5.0-5.8 M) and high oxygen partial pressure (( 0.5-1.0)x lO Pa), and area B with "high" acidities [HC104]= 5.8-6 6 M) and low oxygen pressures ((0.05-0.5)x 10 Pa). The main kinetic features of oxidation, that is rate dependence on concentrations and temperatures, both for dibenzyl ether and benzaldehyde are one and the same. The mechanism of dibenzyl ether oxidation appears as follows ... 

Partial oxidation of benzyl alcohol has been studied in detail. Benzyl alcohol undergoes dehydration to dibenzyl ether and water, disproportionation to benzaldehyde and toluene over alumina and other acid catalysts [2] whereas it undergoes dehydrogenation on metal oxides to yield benzaldehyde and toluene as major products and benzylbenzoate, benzene and methanol in small amounts depending upon the reaction conditions [10]. The various products formed as a result of catalytic decomposition may be represented as... 

Figure 4 Effect of partial pressure of oxygen on conversion and selectivity in benzyl alcohol oxidation on, BaPbOj, o BaPbo.6Bio.4O3, A BaBi03. Reaction temperature 623K, W/F 5 g.h/mole...

The addition of an oxidizing reagent makes reactions catalytic with respect to palladium(II). Palladium compounds catalyze many other reactions invol-ving C-H bond activation. For example, benzaldehyde and benzoic acid can be produced by partial oxidation of toluene applying the fuel cell reaction in the gas phase using palladium black as the anode. The authors proposed a n-aliyl-benzyl-Pd"" complex as the reactive intermediate [16]. 

The safe industrial oxidation of furanics using the Co/Mn/Br catalyst system needs a similar heat removal system as FDCA, like TA, is a very insoluble diacid, preventingthe use of jacketed cooling. In contrast to para-xylene, HMF, MMF, and AcMF are already partially oxidized on the benzylic positions, and consequently less heat is formed in their oxidation to FDCA, and reactor temperature may be... 

Kinetic resolution of some secondary allylic and benzylic alcohols has been shown to occur efficiently in the presence of the chiral ligand (—)-sparteine. For example, partial oxidation of the racemic alcohol 43 with a palladium(II) catalyst under an atmosphere of oxygen in the presence of (—)-sparteine occurs to give a mixture of the ketone 44 and recovered alcohol (5)-43 (6.39). Selective oxidation of the (i )-alcohol occurs with the chiral catalyst system. 

Initially, the as-synthesized catalyst was characterized by EXAFS and XANES (region a), and then the reaction mixture comprising benzyl alcohol/cyclohexane (solvent) saturated with 02/mixture was introduced to the catalyst at 50 °C (region b). Palladium was found to be in a partially oxidized state and there was no catalytic activity for this material under this condition as evidenced from the IR spectrum of the effluent from the reactor. Then, the catalyst material was exposed to H2-saturated cyclohexane to reduce the palladium to metallic state (region C). After about 30 min of the exposure, aU the palladium atoms are found to be in the metallic state. This has been confirmed by both XANES and EXAFS data, as shown in Figure 12.10. Analysis of the EXAFS data showed evidence for the formation of palladium hydride. This leads to a more elongated EXAFS function and to a shift... 

Figure 22.1. Toluene conversion and selectivity to partial oxidation products. Reaction conditions 160°C, 0.1 MPap02, 20 ml toluene, 0.8 g of catalyst (1 wt% AuPd/C prepared by sol-immobilisation with 1 1.85 Au/Pd ratio), toluene/metal molar ratio of 3,250 and reaction time 110 h. Key o conversion, selectivity to benzyl alcohol, selectivity to benzaldehyde, selectivity to benzoic acid, selectivity to benzyl benzoate.

PEG 600 has been used in the phase transfer catalysis of the partial oxidation of benzyl alcohol to benzaldehyde ]164]. This reaction was conducted in ethyl-acetate for 30 min at room temperature. 

Toke, L., and Szabo, G. T., Polyethylene glycol derivatives as complexing agents and phase transfer catalysts, Acta Chem. Acad. Sci. Hung., 93, 421, 1977. Balasubramanian, D., Sukamar, P, and Chandoni, B., Synthesis of benzaldehyde by partial oxidation of benzyl alcohol. Tetrahedron Lett., 1979, 3543. 

Oxidation at Benzylic Position. Nitric acid oxidizes many aromatic alkyl substituents to the carboxylic acid group. Thus toluene is oxidized to benzoic acid in 85-90% yield. Oxidation of ethylbenzene with 15% nitric acid also gives benzoic acid in 80% yield. The reaction is general and has also been applied to the oxidation of pyridine derivatives. When 4-methylpyridine is treated with 10% nitric acid in phosphoric acid at elevated temperature and pressure, 4-pyridinecarboxylic acid is obtained in 93% yield. The reaction of p-isopropyltoluene can be controlled to give the partially oxidized product, p-methylbenzoic acid, in 56-59% yield. Additional examples of selective benzylic oxidations are shown in eqs 13 and... 

Spasiano D, Marotta R, Di Somma I, Andreozzi R, Caprio V. Fe(III)-photocatalytic partial oxidation of benzyl alcohol to benzaldehyde under UV-solar simulated radiation. Photochem Photobiol Sd. 2013 12 1991-2000. 

In general, the ammoxidation reaction of methyl aromatics and/or hetero aro-maties runs via redox mechanism as proposed by Mars and van Krevelen [12]. Most of the catalysts used so far eontain transition metal oxides with easily ehanging valence states (e.g., V, Mo, etc.). Essential steps of the reaction mechanism are (i) chemisorption of the methyl aromatic or hetero aromatic reactant on the catalyst surface followed by H-abstraetion (i.e., C-H bond disassociation) to form a benzylic intermediate, (ii) insertion of nitrogen into a surface bonded partially oxidized intermediate and (iii) desorption of the formed nitrile and iv) reoxidation of the catalyst by gas-phase oxygen. Literature survey [114, 115] revealed that the H-abstraction oeeurs via C-H bond dissociation in three different possible ways, such as (i) heterolytic with the abstraction of hydrogen atom in an anionic form followed by carbocation. 

---