The Reactions of Sulphate Radicals with Substituted Pyridines Studied by Time-Resolved Spectroscopy. A structure- reactivity correlation analysis.

MARÍA L. DELL’ARCIPRETE; CARLOS J. COBOS; JORGE P. FURLONG; DANIEL O. MÁRTIRE; MÓNICA C. GONZALEZ

Chemphyschem

Wiley-VCH Verlag

Año: 2007 vol. 8 p. 2498 - 2505

1439-4235

The kinetics of the oxidation of pyridine, 3-chloropyridine, 3-cyanopyridine,3-methoxypyridine and 3-methylpyridine mediated by SO4.- radicals are studied by flash photolysis of peroxodisulphate, S2O82-, at pH 2.5 and 9. The absolute rate constants for the reactions of both, the basic and acid forms of the pyridines, are determined and discussed in terms of the Hammett correlation. The monosubstituted pyridines react about 10 times faster with sulphate radicals than their protonated forms, the pyridine ions. The organic intermediates are identified as the corresponding hydroxypyridine radical adducts and their absorption spectra compared with those estimated employing the time-dependent density functional theory with explicit account for bulk solvent effects. A reaction mechanism which accounts for the observed intermediates and the pyridinols formed as products is proposed.