Free radical reactions of polyhalogenoaromatic compounds

Abstract

Pentachlorophenyl radicals, previously unreported in the literature, have been obtained by a variety of routes analogous to those used for the generation of pentafluorophenyl radicals. These include the decomposition of pentachloroaniline by amyl nitrite, the oxidation of pentachlorophenylhydrazine, the photolysis of pentachloroiodobenzene and the thermal decomposition of pentachlorophenylazotriphenylmethane. 2,3,4,5,6-Pentachlorobiphenyl is obtained when the radicals are generated in benzene. Mixtures of isomers of the respective biaryls are obtained from reactions in chlorobenzene and in toluene.

The formation of penta- and hexa-chlorobenzene in reactions with pentachloroaniline and amyl nitrite are investigated and discussed.

The reaction with benzene of 2,4- and 2,6-dichloro- and 2,4,6-trichlorophenyl radicals, generated from the corresponding amines with amyl nitrite were studied. Evidence has been found which suggests that crowding of the radical site may be a possible explanation for the relatively low yields of binuclear products formed in the reactions of the pentachlorophenyl radical.

The thermal decomposition of benzoyl peroxide in chloropentafluorobenzene and in 1,3,5-trichlorotrifluorobenzene, and the effect on it of catalytic amounts of trichloroacetic acid, have been investigated. The overall yield of biaryl material is increased by the addition of the acid, but there is no change in the isomer distribution.

A study was also made of the thermal decomposition of benzoyl peroxide in mixed solvents. The solvent pairs studied were hexafluorobenzene/chloropentafluorobenzene and hexafluorobenzene/1,3,5-trichlorotrifluorobenzene. Partial rate factors and relative rates were evaluated and are discussed.