Using the pulse radiolysis technique, studies on reactions of 3,4,5-trihydroxybenzoic acid [gallic acid (GA)] with radical species generated in water are reported. At pH 6.8 and 9.7, OH radicals react with GA to give an adduct initially with rate constants of the order of 1 ] 1010 dm3 mol~1 s~1. This adduct then reacts with parent GA molecules with rate constants of the order 5 ] 108 dm3 mol~1 s~1 to give phenoxyl type radical species having absorption maxima in the 350 nm region. At pH 12 and 13.6, OH/O~radicals directly bring about oxidation of GA. SpeciÐc oxidants like azidyl radical bring about one electron oxidation at neutral and alkaline pHs with almost di †usion controlled rate constants. Rate constants for the reaction of radicals Br 2 ãre found to be lower than those for OH radicals by an order of magnitude. At pH 0, both OH and Cl 2 radicals react with GA to give phenoxyl type radicals. The phenoxyl radicals formed are quite stable at higher pHs, which make GA a good antioxidant. Rate constants for the reactions of with di †erent protolytic e aq forms of GA are determined.

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Pulse radiolysis technique was used to study the reactions of e aq -, H atoms, and other reducing radicals such as COO -/COOH, (CH 3 ) 2 COH, CH 3 CHOH, and CH 2 OH radicals with 8-hydroxyquinoline (8HQ) at various pH's. e aqreacts with 8HQ with high rate constants (k 2 ) 3 × 10 10 at pH 7 and 2.6 × 10 10 at pH 12). Absorption spectra of the transient species were recorded in the wavelength region 300-800 nm. Semireduced species formed by the reaction of e aqwith 8HQ as well as that formed by H atom reaction were found to be strong reductants and were found to transfer an electron to methylviologen. COO -/COOH and alcohol radicals were found to react with 8HQ by addition reactions. The rate constants for the reactions were much higher at acidic pH's (≈10 9 dm 3 mol -1 s -1 ), where 8HQ is in the protonated form, as compared to those at neutral pH (≈10 8 dm 3 mol -1 s -1 ), where it is present in the neutral form. These adduct radicals were also found to be reducing in nature. The rate constant for OH radical reaction with 8HQ was estimated to be 7.6 × 10 9 dm 3 mol -1 s -1 at pH 7 and 1.3 × 10 10 dm 3 mol -1 s -1 at pH 0; a cyclohexadienyl type of radical is formed in both the cases. These adducts react with oxygen (k ) 3.2 × 10 9 dm 3 mol -1 s -1 at pH 7) to give peroxyl radicals. Br 2and N 3 radicals react with 8HQ by electron transfer at pH 13 giving a phenoxyl-type radical. At pH 7, N 3 and SO 4radicals react with 8HQ by electron transfer whereas the reaction of the Br 2radical is quite slow. Only SO 4is able to oxidize 8HQ in its protonated form existing at acidic pH.

Rate constants of OH radical reaction with some amino polycarboxylic acids (APCAs) such as EDTA, DTPA, HEDTA, NTA, and HIDA have been determined at different pHs using pulse radiolysis competition kinetics method with thiocyanate as the reference solute. The rate constants varied with pH (possibly due to their various pKs) and the plots of rate constants vs. pH are given. Rate constants for OH radical reaction with the various acid-base forms of these amino polycarboxylic acids are estimated from the plateau values in the plots.

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