Electron spin resonance studies. Part XXI. Reactions of the phenyl and substituted phenyl radicals in aqueous solution
Evidence is reported that the one-electron reduction of arenediazonium ions either by titanium(III) ions in weakly basic conditions or by certain organic radicals in acidic conditions gives aryl radicals. The e.s.r. spectra of these radicals have not been observed, but the spectra of a large number of species derived from their reactions with other compounds have been measured. For example, the phenyl radical reacts with nitrite ion to give the nitrobenzene radical-anion, with nitric oxide to give diphenyl nitroxide, and with maleic acid or its anion, trimesic acid or its anion, acetylenedicarboxylate, or azodicarboxylate, by addition to an unsaturated bond. A brief survey has been made of the ability of various aryl radicals to abstract a halogen atom or a hydrogen atom from the corresponding bond to carbon. The reaction of aryl radicals with oxygen gives aromatic semiquinone radicals, evidently by a multistage process. In some cases information has been obtained about the relative ease of reaction of aryl radicals with the various species which are present, and in the light of these and other data possible reasons are discussed for the failure to detect aryl radicals directly under the conditions used.