The oxidation of simple, monohydric phenols at a lead dioxide anode in aqueous sulphuric acid has been studied.The effects of current density, electrolysis time, pH, concentration of phenol, and method of anode preparation on conversion and product distribution have been investigated, and optimal conditions for anodic hydroxylation of simple phenols have been deduced. In all cases studied the hydroxy-group entered the 4-position : thus 4-substituted phenols gave 4-substituted 4-hydroxycyclohexa-2.5-dienones, and phenols without substituents at C-4 gave p-benzoquinones. The former reaction provides a simple and efficient synthesis of these cyclohexa-2.5dienone derivatives. A mechanism involving hydrolysis of an anodically generated phenoxonium ion is suggested. Evidence is presented which indicates that the phenoxonium ion is formed by ' chemical ' oxidation with anodically generated lead dioxide. The lead dioxide anode is superior to carbon, nickel, and platinum anodes for hydroxylation.

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2.6-Di-t-butyl-4-alkylphenols undergo anodic hydroxylation giving high yields of the corresponding 4-hydroxycyclohexa-2.5-dienones providing that the medium is buffered to avoid acid-catalysed dealkylation and quinone formation. The use of nucleophiles other than water affords a general synthesis of 4-substituted cyclohexa-2.5-dienones. 3 F. J. Vermillion, jun., and I. A. Pearl, J . Electrochem. SOC., 1964, 111, 1392.

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The anodic oxidation in methanol of a series of alkylanisoles and hydroquinone ethers, and of p-xylene has been studied. It was established that the initial step in the product formation always involves direct anodic oxidation of the aromatic compound to the corresponding cation radical. If the electrolysis is conducted under conditions where formation of methoxyl radicals also takes place (platinum anode, supporting electrolyte NaOMe) nuclear methoxylation dominates. Substitution in the nucleus of the aromatic compound presumably occurs either by nucleophilic attack of a methoxide ion on the anodically generated cation radical or by a coupling reaction between the latter and an anodically generated methoxyl radical. If the electrolysis is conducted under conditions where formation of methoxyl radicals does not take place (carbon or platinum anode with supporting electrolyte LiBF4) side-chain oxidation of p-alkylanisoles and p-xylene, with the formation of benzyl ethers, benzaldehyde dimethyl acetals, or ortho-esters of benzoic acids becomes important. This side-chain oxidation occurs via nucleophilic attack of methanol on a benzyl cation formed by deprotonation-anodic oxidation of the initially formed cation radical. Phenol ether cation radicals without p-alkyl substituents under these conditions either dimerise or undergo nuclear methoxylation via nucleophilic attack of methanol on the cation radical.For a review of previous work see N. I,. \Yeinberg, ' 'I'ecliniques of Electro-organic Synthesis,' P a r t I , 1' . 2 3 7 ; vol. \ r .of ' Technique5 of Organic Chemistry,' ed. :I. \Vt.issbc.rger,