Res. Chem. lntermed. Vol. 21, No. 1, pp. 47-58 (1995) 9VSP 1995 KINETIC AND SPECTRAL PROPERTIES OF THE INTERMEDIATES FORMED IN THE PULSE RADIOLYSIS OF 2-MERCAPTOBENZIMIDAZOLE G.R. DEY, D.B. NAIK, K. KISHORE, AND P.N. MOORTHY Applied Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India Received 6 July 1994; accepted 18 August 1994 Abstract--The reactions of primary species of water radiolysis such as e-aq , H ~ and "OH, and some specific one electron reductants and oxidants with 2-mercaptobenzimidazole have been studied at various pHs. "OH radical reaction with MBZ at pH 7 gave a transient species having absorption maxima ()~m~x) a t 330 and 590 nrn. The transient species (pKa = 3.6) was found to be neutral at this pH and was a mild oxidant. The initial transient species formed by the reaction of MBZ with e~q at pH 7 and with H atom at pH 0 were found to react with the parent molecule to form another transient species which has an absorption spectrum similar to that obtained by "OH radical reaction with kma x at 590 rim. However the reaction is not quantitative. The kinetic, spectral, acid- base and redox properties of the transient species are reported. INTRODUCTION 2-Mercaptobenzimidazole (MBZ) is a well known corrosion inhibitor [1] and can be used in chemical decontaminant formulations for minimizing base metal corrosion of the structural materials. During decontamination of nuclear reactor systems, the inhibitor will be exposed to high radiation fields. Hence, there is interest in the study of the reactions of this compound with the radiolytic species produced in irradiated water. No work on the radiation chemistry of this compound has been reported so far. In photochemical studies, it has been shown [2] that C-centred radicals can abstract H-atom from MBZ to give benzimidazolyl radicals. We have studied the reactions of e-aq , H ~ ~ and some one electron reducing and oxidizing radicals such as (CH3)2C~ ~ and Br2", N3 ~ C12 ~ with MBZ at different pHs using the pulse radiolysis technique and determined the kinetic, spectral and acid-base properties of the intermediates formed in the above reactions. The detailed results are reported in this communication. EXPERIMENTAL 2-Mercaptobenzimidazole from Fluka was purified by repeated crystallization from hot water.