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

Abstract

The reactions of e^-_aq, ^•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 e^-_aq 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 e^-_aq 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 (ε= 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.