The generation of hydroxyl ( • OH) radicals produced by irradiation of aqueous TiO 2 suspensions was investigated by electron paramagnetic resonance (EPR) and product analysis employing a stable free nitroxide radical (3-carboxyproxyl) as a spin trap of • OH. Product analysis demonstrated that the attack of • OH on 3-carboxyproxyl produces a diamagnetic product (proxyl-NH) with a trapping efficiency of ca. 80%. It could also be shown that a small amount of the nitroxides is reduced by conducting band electrons. The rate of formation of • OH could be determined by monitoring the time dependence of the decrease in the concentration of 3-carboxyproxyl monitored by EPR spectroscopy or the time dependence of the increase in the concentration of proxyl-NH monitored by gas chromatography analysis. The rate of formation of • OH serves as a mechanistic parameter to investigate the mechanism of formation of this reactive species by the photoexcitation of TiO 2 . The dependence of the rate of formation of • OH was shown to be a linear function of light intensity at low intensities. It was observed that molecular oxygen, a good scavenger of conduction band electrons, only slightly influences the rate of formation of • OH and supports the production of • OH from photogenerated holes. Addition of selected anions to the photolysis mixtures results in a diminished rate of disappearance of the spin trap as the result of a competition between the spin trap and the anion for • OH. From a SternVolmer analysis of the data, the rate constant for the reaction of hydroxyl radicals with the anions was determined.

The effect of benzenethiol and its methyl, amino, and carboxylic ring substituted derivatives, benzylthiol and thioglycollic acid on the electrochemical and corrosion behavior of zinc in CH3000H, H2SO4, and HCI solutions was studied using the galvanostatic technique. In CH3000H, compounds which function by an adsorption mechanism were found to have inhibitive effects on the corrosion of zinc, while those functioning by surface chelation were ineffective. In H 2SO4 and HCI, with the exception of o-methylbenzenethiol (H 2SO4 and HCI) and benzylthiol (H2SO4 ), all investigated compounds were found to accelerate zinc dissolution. Adsorption of the inhibitors followed the Langmuir isotherm, and the mechanism of both the hydrogen evolution reaction and zinc dissolution were found to be the same in the uninhibited and inhibited states. Experimental Corrosion InhibitorsReagent grade (Fluka AG, Buchs SG Switzerland) benzenethiol ortho, meta, and para methylbenzenethiols, ortho and para aminobenzenethiols, thiosalicylic acid and its methyl ester, benzylthiol and thioglycollic acid were used without further purification. The inhibitor solution was prepared by dissolving the appropriate amount in 10 ml of redistilled methanol. The desired volume was added to the electrolyte (200 ml).Electrolytes 0.5N CH3000H (pH 3.0), 0.5N H 2SO4 (pH 0.8), and 0.1N HCI (pH 1.1) were prepared from the Analar reagent and bidistilled water and were deaerated by 02 free nitrogen for at least 6 hours. The pH of these solutions was adjusted by adding NaOH to the desired value. Zinc SpecimensSpecimens were cut from extra pure zinc rods 0.5 cm in diameter. These were cast from extra pure granular zinc (Merck) by vacuum melting) and were inserted into Teflon mounts so that the flat surface was in contact with solution.

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and Hg(I1) ions. I t i s concluded t h a t t h e ligands a r e bonded t o t h e metal ion through t h e a-nitrogen atom of t h e a r y l azo group and N-3 of t h e imidazole ring. The apparent formation cons t a n t s of t h e complexes i n solution have been determined.