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

摘要

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) * 10~9 dm~3 mol~(-1) s~(-1). The rates of O~(·-) and SO_4~(·-) reactions (1-3) * 10~9 dm~3 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 dm~3 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 CH_3 group. A reaction mechanism consistent with the observed results is proposed.