Study of kinetics and absorption spectra of OH adducts of hydroxy derivatives of benzaldehyde and acetophenone

Abstract

Radiation chemical reactions of √ OH, O √ ¯, N₃ √ and SO₄ √ ¯ with hydroxy derivatives of benzaldehyde and acetophenone were studied. The second-order rate constants for the reaction of √OH with o-, m- and p-hydroxybenzaldehydes are in the range (5.2-12) × 10⁹ dm³ mol^-1 s^-1, the order being para>meta>ortho. In O √ ¯ reaction, a reverse trend (k_para<k_meta) with much lower rates was noticed. The transient absorption spectra measured in the √ OH reaction with o- and m-hydroxybenzaldehydes exhibited absorption maxima at 370 and 400 nm, respectively, whereas two peaks centred around 325 and 410 nm were seen in the case of para isomer. The absorption at 370 and 325 nm rapidly decayed in ortho and para isomers, with k=5.5 × 10⁵ s^-1 in the latter. The spectra measured in the √ OH reaction at 10 µs after the pulse are attributed to the phenoxyl radical formed by dehydration reaction, the rates being dependent on the position of the substituent. The major pathways in the O √ ¯ reaction are electron transfer in the case of the meta isomer and addition reaction with the para isomer.