The effect of catalysts in homolytic arylation

Abstract

The effects of additives such as ferric benzoate and cupric benzoate on the thermal decomposition of benzoyl peroxide in benzene, fluorobenzene, chlorobenzene, bromobenzene, p-dichlorobenzene, 1,3,5-trichlorobenzene, methyl benzoate, benzophenone and benzonitrile have been investigated. In the reactions of benzene, chlorobenzene and bromobenzene, the effects of m-dinitrobenzene, nitrosobenzene, penta-fluoronitrosobenzene, o- and p-chloranil and cupric p-substituted (methyl-, chloro- and nitro-) benzoates were also examined. The additives catalysed the reactions so as to results in high yields of biaryl and benzoic acid to the exclusion of all other products and also exhibited different effects on the isomeric distribution of these substrates. Explanations have been suggested to account for these observations.

The effects of cupric benzoate and ferric benzoate on the competitive reactions of fluorobenzene, chlorobenzene, bromobenzene pdichlorobenzene, 1,3,5-trichlorobenzene, methyl benzoate, benzophenone and benzonitrile with benzene as a standard solvent have been studied. Relative rates and partial rate factors are significantly altered in the presence of these metal benzoates.

Competitive reactions of chlorobenzene and bromobenzene with p-dichlorobenzene as a standard solvent in the presence and absence of cupric- or ferric benzoate, also of chlorobenzene with 1,3,5-trichlorobenzene as a standard solvent in the presence and absence of ferric benzoate have been studied. The relative rates obtained from these reactions in the absence of additives converted into the relative rates with respect to benzene as a standard solvent disagreed with those determined directly from the competitive reactions between these substrates and benzene in the absence of additives. However good agreement is obtained in the presence of additives.

The assumption regarding the additivity of directing group on activation for phenylation reactions were tested in the presence and absence of additives, by comparing the relative rates obtained from the competitive reactions of p-dichlorobenzene and 1,3,5-trichlorobenzene with benzene as a standard solvent to those values calculated by substitution of measured partial rate factors for chlorobenzene in the presence and absence of additives. A good agreement is obtained with regard to the additivity of effects of the substitution in the presence of additives, although the agreement is much poorer for the uncatalysed reactions.