Kinetic and spectroscopic properties of intermediates formed by the reaction of same oxidizing and reducing radicals with 2-mercaptothiazoline (2-MT) in aqueous solutions

Resonance-stabilized 2-MT. radicals, generated pulse radiolytically in neutral aqueous solutions from 2-MT by the reaction with OH., Br-., and Br-2(.-) radicals have a broad absorption band between 300-550 nm. The rate constants for the reactions of OH., Tl2+, Cl-2(.-), Br-. and Br-2(.-) with 2-MT have been determined at pH 2.2 and 6 and are close to the diffusion controlled values. At pH 6 the OH. radicals react only to an extent of similar to 45% with 2-MT. The 2-MT. radicals are able to oxidize phenothiazine [PH] drugs [E-1 congruent to 0.8 V] and ABTS with k congruent to 2-5 x 10(9) dm(3) mol(-1) s(-1). The semi-reduced species have been formed by the reaction of e(aq)(-) with 2-MT with a k congruent to 5.7 x 10(9) dm(3)mol(-1)s(-1) at pH 7. They show lambda(max) ranging from 300-325 nm depending on the solution pH. The radical pK(a) has been measured, pK(a)=6. The semi-reduced form of 2-MT efficiently reduced MV2+ to MV.+. Our results indicate that if 2-MT is to be used as a corrosion inhibitor it will be more conducive to use it under reducing conditions than under oxidizing conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.