Benzyl alcohol radical

Benzyl Chloride. Benzyl chloride is manufactured by high temperature free-radical chlorination of toluene. The yield of benzyl chloride is maximized by use of excess toluene in the feed. More than half of the benzyl chloride produced is converted by butyl benzyl phthalate by reaction with monosodium butyl phthalate. The remainder is hydrolyzed to benzyl alcohol, which is converted to ahphatic esters for use in soaps, perfume, and davors. Benzyl salicylate is used as a sunscreen in lotions and creams. By-product benzal chloride can be converted to benzaldehyde, which is also produced directiy by oxidation of toluene and as a by-product during formation of benzoic acid. By-product ben zotrichl oride is not hydrolyzed to make benzoic acid but is allowed to react with benzoic acid to yield benzoyl chloride. 

Carbocations can also be generated during the electrolysis, and they give rise to alcohols and alkenes. The carbocations are presumably formed by an oxidation of the radical at the electrode before it reacts or diffuses into solution. For example, an investigation of the electrolysis of phenylacetic acid in methanol has led to the identification of benzyl methyl ether (30%), toluene (1%), benzaldehyde dimethylacetal (1%), methyl phenylacetate (6%), and benzyl alcohol (5%), in addition to the coupling product bibenzyl (26%). ... 

This is consistent with the observed products of oxidation, i.e. benzyl alcohol, benzaldehyde and benzoic acid and with the observed oxidation of cyclohexane. Radical-cations are, however, probably formed in oxidation of napthalene and anthracene. The increase of oxidation rate with acetonitrile concentration was intepreted in terms of a more reactive complex between Co(III) and CH3CN. The production of substituted benzophenones at high CH3CN concentration indicates the participation of a second route of oxidation. 

The main oxidation product from dibenzyl ether is benzaldehyde (up to 80% yield) with smaller amounts of benzyl alcohol and benzoic acid. The rates of oxidation are only slightly affected by major stereochemical changes, and it is considered that an outer-sphere oxidation of the ether is followed by radical breakdown, viz. 

Benzyl methyl ether produces methyl benzoate, benzaldehyde and benzoic acid but essentially no dibenzyl or benzyl alcohol. The initial radical is, therefore C6H5CHOCH3 and methyl benzoate is produced via the paths... 

When reactions with oxygen-containing acceptors were performed [3] in the 300-400°C region, the formation of adducts occurred with both Tetralin and mesitylene. This reaction was observed when benzyl radicals were generated from dibenzyl ether, dibenzyl sulfide, benzyl alcohol, and benzaldehyde. 

Organolithium reagent 35 was added to aldehyde 31 (Scheme 7.6) to obtain alcohol 36 as an inconsequential 1 1 mixture of diastereomers. The benzylic alcohol was removed using a Barton two-step radical deoxygenation protocol, followed by electrophilic aromatic bromination to provide the desired coupling partner 37. 

The hydroxyl group of alcohol weakens the a-C—H bond. Therefore, free radicals attack preferentially the a-C—H bonds of the secondary and primary alcohols. The values of bond dissociation energy (BDE) of C—H bonds in alcohols are presented in Table 7.1. The BDE values of C—H bonds of the parent hydrocarbons are also presented. It is seen from comparison that the hydroxyl group weakens BDE of the C—H bond by 23.4 kJ mol 1 for aliphatic alcohols and by 8.0 kJ mol 1 for allyl and benzyl alcohols. 

Polar solvents have no effect on the rate constant of the reaction R02 + RH [56], This means that the solvation energies of the peroxyl radical R02 and TS R02 HR are very close. A different situation was observed for the reaction of cumylperoxyl radical with benzyl alcohol (see Table 7.10). The rate constant of this reaction is twice in polar dimethylsulfoxide (s = 33.6) than that in cumene (a 2.25). It was observed that the very important property of the solvent is basicity (B), that is, affinity to proton. A linear correlation... 

Comparison of Solvent in Fluence on Rate Constants and Activation Energy of Cumylperoxyl Radical with Cumene and Benzyl Alcohol [56]... 

The method uses a simple electrode made of a thin film of sol-gel organosilica doped with nitroxyl radicals deposited on the surface of an indium tin oxide (ITO) electrode. Thus, whereas in water benzyl alcohol is rapidly oxidized to benzoic acid, the use of the hydrophobic sol-gel molecular electrode TEMPO DE affords benzaldehyde only (Figure 1.9), with an unprecedented purity, which is highly desirable for the fragrance and pharmaceutical industries where this aromatic aldehyde is employed in large amounts. 

Oxidation of benzyl alcohol catalysed by chloroperoxidase exhibits a very high prochiral selectivity involving only the cleavage of the pro-S C-H bond. The reaction mechanism involved the transfer of a hydrogen atom to the ferryl oxygen of the iron-oxo complex. An a-hydroxy-carbon radical and the iron-hydroxy complex P-Fe -OH form. They may lead to the hydrated benzaldehyde or stepwise with the formation of the intermediate a-hydroxy cation. 

Chemical/Physical. Products identified from the reaction of toluene with nitric oxide and OH radicals include benzaldehyde, benzyl alcohol, 3-nitrotoluene, p-methylbenzoquinone, and o, m, and p-cresol (Kenley et ah, 1978). Gaseous toluene reacted with nitrate radicals in purified air forming the following products benzaldehyde, benzyl alcohol, benzyl nitrate, and 2-, 3-, and 4-nitro-toluene (Chiodini et al., 1993). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of benzaldehyde, benzyl nitrate, 3-nitrotoluene, and o-, m-, and p-cresol (Finlayson-Pitts and Pitts, 1986 Atkinson, 1990). 

Photolytic. A n-hexane solution containing /n-xylene and spread as a thin film (4 mm) on cold water (10 °C) was irradiated by a mercury medium pressure lamp. In 3 h, 18.5% of the p-xylene photooxidized into p-methylbenzaldehyde, p-benzyl alcohol, p-benzoic acid, and p-methylacetophenone (Moza and Feicht, 1989). Glyoxal and methylglyoxal were produced from the photooxidation of p-xylene by OH radicals in air at 25 °C (Tuazon et al., 1986a). The rate constant for the reaction of p-xylene and OH radicals at room temperature was 1.22 x lO " cmVmolecule-sec (Hansen et al., 1975). A rate constant of 7.45 x 10 L/molecule-sec was reported for the reaction of p-xylene with OH radicals in the gas phase (Darnall et al, 1976). Similarly, a room temperature rate constant of 1.41 x 10 " cm /molecule-sec was reported for the vapor-phase reaction of p-xylene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 1.29 x lO " cmVmolecule-sec was reported for the same reaction (Ohta and Ohyama, 1985). 

Additional clues confirm the radical nature of the reaction of BTNO with RH substrates. A Hammett correlation, obtained on plotting log A h for reaction of BTNO with p-substimted benzyl alcohols, gave a p value of —0.55 vs. a+. This small value, which is reasonable for a radical reaction, compares well with the p values ranging from —0.54 to —0.70 and obtained vs. the same substrates with the aminoxyl radicals generated from X-aryl-substituted HPIs (Table 5). In all cases better Hammett correlations were obtained vs. the values. Hence, a uniform pattern of selectivity emerges among these electrophilic >N—O" species in H-abstraction reactions. 

Besides having smaller oxidation potential values than substituted benzyl alcohols (E° > 1.4 V/NHE), the DMAs have larger energy values (90-92 kcalmoD ) for the NC—H bond with respect to C—H bond energies around 75-85 kcalmoD of the benzyl alcohols (Scheme 12). Both factors disfavour the operation of the radical HAT route for PINO with the DMAs, and cause a mechanistic changeover to the ET route, as opposed to the reactions with the benzylic substrates listed in Table 4. 

---