One electron reduction and oxidation of 2-, 3- and 4-chlorobenzonitrile in aqueous solution: A pulse radiolysis study

Solvated electrons (e(aq)(-)) react with very high rates (k > 10(10) dm(3) mol(-1) s(-1)) with 2-, 3- and 4-monochlorbenzonitriles (2-, 3- and 4-C1BN) to yield the corresponding radical anions. The anions decay in neutral solution under dechlorination by a first-order reaction, where the k(1)-values of 2- and 4-C1BN species are about three orders of magnitude higher than that of 3-C1BN.

At low pHs, the 3-CIBN.- transient protonates k = 2.6 x 10(10) dm(3) mol(-1) s(-1) and the resulting species disappears by a second-order process (2k = 2 x 10(9) dm(3) mol(-1) s(-1)). The spectrum of the protonated 3-C1BN(.-) transient strongly differs from that of the H-adduct. Hence, the protonation of the radical anions seems to occur at the cyano group.

The H-atoms form the respective adducts with rates from 2.2 to 3.4 x 10(9) dm(3) mol(-1) s(-1), which disappear by a second-order process with rate constants of 3.6-6.1 x 10(8) dm(3) mol(-1) s(-1). The OH-attack leads to the formation of the corresponding adducts (k = 1.3-1.5 x 10(9) dm(3) mol(-1) s(-1)) which decay by a second-order reaction (2k = 6.1-7.4 x 10(8) dm(3) mol(-1) s(-1)).

The absorption spectra observed by the attack of e(aq)(-) H- and OH-radicals are presented. Some probable reaction steps are also given. (C) 2000 Elsevier Science Ltd. All rights reserved.