Oxidation of Methyl-Substituted Aromatics

Oxidation of Methyl-Substituted Aromatics. Autoxidation of alkyl-substituted 

The ready formation of benzylic hydroperoxides is used in industrial oxidations, as in the synthesis of propylene oxide and phenol (see Sections 9.5.2 and 9.5.4, respectively). In contrast with autoxidation of alkenes, where various secondary processes may follow, autoxidation of arenes is less complicated. Chain termination of 99 may lead to an alcohol and aldehyde [Eq. (9.151)], and the rapid autoxidation of the latter may produce the corresponding carboxylic acid [Eq. (9.152)]  

In the noncatalyzed autoxidation the further oxidation of the aldehyde is much faster than the hydrogen abstraction to form the benzylic radical. As a result, carboxylic acids become the main product. 

Metal ions [Co(III), Mn(m), Cu(II)] have a pronounced effect on the rate and product distribution of autoxidation. In the presence of metal ions, secondary transformations become dominant and selectivity in the formation of benzylic hydroperoxide 100 decreases. 

Most studies of the metal-catalyzed oxidation of methyl-substituted arenes 

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According to this hypothesis, the results are modified from what would be expected from classical radical reactions. The interest in this hypothesis is that, with the sole exception of saturated hydrocarbons, it could apply to all the compounds that can be coordinated at the Tiiv center, such as alkenes, aromatics, alcohols, and sulfides. According to this hypothesis, the weak Lewis acidity of Tilv would help to bring the reactant into its coordination sphere. The initial coordination of the reactant would explain the oxidation of methyl-substituted aromatics in the aromatic ring and not in the side chain, even with a radical-type mechanism. 

Similarly, cobaltic and argentic ion have been generated by anodic oxidation of cobaltous and argentous ion, respectively, and used for the oxidation of methyl-substituted aromatic hydrocarbons to aldehydes 18a Electrogenerated mercuric ion can be used for the conversion of propene to acrolein 18al ... 

Hydroxylation of monophenols to predominantely />-diphenols or oxidation of methyl-substituted aromatics by persulfates ... 

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