Some reactions of pentafluorophenyl radicals

Abstract

The decomposition of pentafluorobenzoyl peroxide in carbon tetrachloride and also in hexafluorobenzene, either alone or in the presence of nitrogen dioxide (15--230 fold molar excess), has been studied. In all reactions, except that in the absence of nitrogen dioxide, high yields of fluoride ion and pentafluorobenzoic acid were formed. Evidence was obtained to suggest the presence of pentafluorobenzoic anhydride as an important reaction product, although this evidence was lacking in the case of the reaction in hexafluorobenzene. In reactions carried out in the presence of nitrogen dioxide, the formation of pentafluorobenzoyl nitrate is considered to be an important step in the route to pentafluorobenzoic acid. Pentafluorobenzoyl nitrate may also lead indirectly to the production of fluoride ion through the intermediacy of nitryl fluoride, the formation of which may depend on an intramolecular rearrangement of the nitrate. Other reaction products were nitropentafluorobenzene, pentafluorophenyl pentafluorobenzoate and decafluoro-biphenyl, all detected in low yields in reactions carried out in the presence of nitrogen dioxide; whereas, in carbon tetrachloride in the absence of nitrogen dioxide, the predominant reaction was abstraction of chlorine from the solvent with formation of chloropentafluorobenzene.

The kinetics of the decomposition of pentafluoro-phenylazotriphenylmethane in aromatic solvents have been studied. The synthesis of this new azo-compound is described. The rate of the decomposition reaction has been measured by collecting the volume of nitrogen evolved with time atconstant pressure, and also by observing the change in optical density at 23,800 cm-1. The first method suffered from physical sources of error and led to anomalies in the results, while the second indicated that the reaction was a simple first order decomposition into pentafluorophenyl and triphenylmethyl radicals and nitrogen. Activation parameters have been calculated and these suggest for pentafluorophenyl-azotriphenylmethane a higher stability and a greater degree of solvation than for phenylazotriphenylmethane. Triphenylmethane and pentafluorobiphenyl have been isolated as two reaction products of the decomposition of pentafluoro-phenylazotriphenylmethane in benzene.