Reactions of Sulphate Radicals with Substituted Pyridines: A Structure–Reactivity Correlation Analysis

Abstract

The kinetics of the oxidation of pyridine, 3-chloropyridine, 3-cyanopyridine, 3-methoxypyridine and 3-methylpyridine mediated by SO4 (<M->) radicals are studied by flash photolysis of peroxodisulphate, S2O8(2-), 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.

Initial stage of the degradation of three common neonicotinoids: theoretical prediction of charge transfer sites

“…Another important conclusion obtained from this table, is the fact that for the three neonicotinoids, the N3 atom shows small condensed ω − (r) values, for this reason the pyridine is not susceptible to react with oxidant agents 69 in an charge transfer process.…”

Reaction kinetics and mechanisms of organosilicon fungicide flusilazole with sulfate and hydroxyl radicals

“…Nitrogen-centered radical cations do not efficiently react with molecular oxygen, as observed in other organic transients (Bosio et al, 2005;Dell'arciprete et al, 2007). It is discussed in literature that a-aminoalkyl radicals are formed after the elimination of H þ from nitrogen-centered radical cations; this a-aminoalkyl radicals are highly stabilized by the free electronic pair of the vicinal nitrogen (Padmaja et al, 1993;Luke et al, 2003;Ito et al, 2009).…”

Oxidation of ophthalmic drugs photopromoted by inorganic radicals

“…Finally, each whole spectrum was obtained by summing over all computed transitions [29]. As a previous work from this laboratory [25] a Gaussian bandwidth of 0.2 eV (1613 cm −1 ) was used to interpret the experimental spectra. The slopes of the experimental linear plots yield the bimolecular rate constants k 1 shown in Table 1.…”

“…Afterwards, the time-dependent density functional theory was employed to estimate the absorption spectra of the possible radical and radical cation transients [21][22][23]. To characterize the position and the intensity of the bands, the energies of the first twenty doublet-doublet electronic transitions and their associated oscillator strengths were calculated at the CPCM-TD-O3LYP/6-311++G(d,p) level of theory [24][25][26][27]. For all quantum-chemical calculations the Gaussian 09 package was employed [28].…”