At 95-115", paraformaldehyde and hydriodic acid completely C-methylate aromatics such as benzene and phenol. Pyrroles are C-methylated similarly, carbethoxy and acetyl groups being lost. In hydriodic acid at 1545", typical pyrroles retain these groups and all free positions are C-alkylated, methylated by paraformaldehyde, or otherwise alkylated by the appropriate carbonyl compound. The alkylation of a 2-free-by a 2-formylpyrrole led to a dipyrrylmethane. With pyrroles, hydriodic acid may be replaced by another strong acid and a reducing agent. This was necessary when a 0-free pyrrole gave the iodo-alkyl derivative rather than the expected product.

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A mechanistic scheme is suggested which rationalises the effect of added nitrobenzene on the nature of the products from the thermal decomposition of benzoyl peroxide in benzene. A small fraction of the nitro-compound is reduced to nitrosobenzene, which scavenges phenyl radicals to form diphenyl nitroxide. The nitroxide radicals efficiently oxidise phenylcyclohexadienyl radicals to biphenyl, and thus prevent side-reactions (e.9.. dimerisation), which would give high molecular weight products. The nitroxide is regenerated by oxidation of diphenylhydroxylamine by molecular benzoyl peroxide. Evidence in support of this scheme is evaluated, and several complicating features are discussed.

THE thermal decomposition of benzoyl peroxide in benzene1 generates benzoyloxy-, and thence phenyl, radicals. The latter react with the solvent to form phenylcyclohexadienyl radicals (I). The ensuing radical reactions lead to a complex mixture of products from which biphenyl and benzoic acid can be isolated, each in yields of up to ca. 0.5 mole/mole peroxide. Much of the remaining product is a mixture of involatile substances, arising initially from dimerisation reactions of the radical (I). Substantial modification of the product mixture is observed when the reaction proceeds in the presence of various additives. Thus small quantities of aromatic nitro-compounds result in yields of biphenyl and benzoic acid of as much as 0.9 mole/ mole peroxide, with correspondingly less involatile product.2 It has been suggested that the nitrocompounds accept a hydrogen atom from the radical (I), and transfer i t to a benzoyloxy-radical, or to a benzoyl peroxide molecule.8 Alternatively,

An improved procedure for the preparation of arylbenzenes from aroyl peroxides and benzene is described.K. S. Y . L.).