Reaction of hydroxyl radical with p-hydroxymercuribenzoic acid

Radiolysis of a 0.1mmoll−1 aqueous solution of p-hydroxymercuribenzoic acid (p-HMBA) results in the formation of p-hydroxybenzoic acid (p-HBA) and 3,4-dihydroxybenzoic acid (3,4-DHBA). Spectrophotometric and liquid chromatographic analysis of irradiated nitrous oxide saturated solutions indicate a disappearance yield G(-HMBA) of 3.1×10−7molJ−1, a formation yield of 1.5×10−7molJ−1 for p-HBA and 0.44×10−7molJ−1 for 3,4-DHBA. Pulse radiolysis of N2O saturated solutions of p-HMBA at pH 9.2 provides a rate constant of (6.3±0.8)×109M−1s−1 for the formation of a hydroxycyclohexadienyl radical. Similar experiments provided rate constants at pH 7.0 and 12.0 of (6.6±1.0)×109 and (1.6±0.3)×109M−1s−1, respectively. The UV/Vis absorption spectrum of the hydroxycyclohexadienyl radical has a λmax=340nm with a molar absorption coefficient of 4.1×103lmol−1cm−1.