Kinetics and spectral properties of electron and •OH adducts of dimethylpyridines: a pulse radiolysis study

Abstract

The reactions of eaq -, •OH, O•- and SO•- 4 with 2,4-, 2,6- and 3,5-dimethylpyridines have been investigated in aqueous solution by pulse radiolysis with optical detection. Both eaq - and •OH radicals have high reactivity toward these compounds with k = (4-8) × 109 dm3 mol-1 s-1. The rates of O•- and SO•4 - reactions ((1-3) × 109 dm3 mol-1 s-1) were lower compared to the rate observed with the •OH radical. The transient absorption spectra obtained in the reaction of eaq - with three isomers exhibited a weak broad band around 340-410 nm. The absorption maxima of the intermediates formed in the •OH and SO•4 - reactions were centred around 320-330 nm (e = 2450-3500 dm3 mol-1 cm-1) with an additional broad peak in the range 460-520 nm which are attributed to the corresponding •OH adducts. The spectra in the O•- reaction have absorption maxima between 300 and 320 nm and it reacts both by addition and H-abstraction from the CH3 group. A reaction mechanism consistent with the observed results is proposed.