Photochemical generation of carbonate radicals and their reactivity with phenol

The reaction of carbonate radical with phenol in aqueous solution has been investigated in systems in which carbonate radicals were generated by UV irradiation of an aqueous solution of [Co(NH3)5CO3]+ (pH 8.0 phosphate buffer). Both steady state and time resolved photolysis experiments were performed. Upon continuous irradiation of complex phenol mixtures, phenol was converted into benzoquinone and dihydroxybenzenes. Benzoquinone was the major by-product in the early stages of the reaction. Laser flash excitation (266 and 355 nm) of the cobalt complex clearly showed the formation of the carbonate radical. When phenol was added to the solution of the complex, a second species was observed which was assigned to the phenoxyl radical. The second-order rate constant of reaction between phenol and carbonate radical was found to be equal to 1.6 × 107 M−1 s−1, in agreement with literature data of 2.2 × 107 M−1 s−1.