Reaction rate constants for the reactions of 3-pyridinol with oxidizing radicals viz. OH, N3, Br
and O– have been determined in aqueous solutions at different, pH's. Absorption spectra of the product transient species have been recorded in the 320–600 nm region. In the alkaline region (pH 13) the N3 reaction product decays in two steps and O– does not bring about one-electron oxidation. Similarly, at neutral pH, SO
does not cause selective one-electron oxidation of 3-pyridinol.
On pulse radiolysis of N2O saturated aqueous solutions of atropine, an optical absorption band (
max at 320 nm,e=2.81·103 dm3·mol–1·cm–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·108 dm3·mol–1·s–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·109 dm3·mol–1·s–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e
was found to react with atropine forming a transient band with
max at 310 nm (=3.55·103 dm3·mol–1). Its decay was also second order with a rate constant of 1.64·109 dm3·mol–1·s–1. The bimolecular rate constant for the reaction of e
with atropine as estimated from the decay of e
absorption at 720 nm is 3.9·109 dm3·mol–1·s–1. Specific one-electron oxidizing and reducing agents (such as Cl
, Tl2+, SO
and (CH3)2COH, CO
, respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e
was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·109 and 3.2·109 dm3·mol–1·s–1, respectively.
Using the pulse radiolysis competition kinetic technique, OH radical rate constants with 12 metal DTPA complexes were determined in neutral aerated aqueous solutions. They are in the range of /1.3–5.9/×109 dm3 mol–1s–1. To a first approximation, the rate constant was found to decrease linearly with an increase in the field strength of the metal ion (q/r2).
Authors:G. Dey, D. Naik, K. Kishore, and P. Moorthy
Rate constants for the reaction of the primary species of water radiolysis, viz. e
, H and OH, with picolinic acid have been determined at various pHs. The semi-reduced species exhibits
max at 305 and 350 nm. It is a strong reductant and has two pKa values of 1 and 5.7. The OH adduct of this compound also exhibits two pKa s at 2.1 and 5.2. H-atom reaction with picolinic acid gives rise to a mixture of species.