Comparative study of the efficacy of the degradation of the organophosphorus pesticide, fenitrothion, by sodium perborate and hydrogen peroxide

This thesis reports a comparative study of the degradation of the organophosphorus pesticide, fenitrothion, by sodium perborate (SPB) and hydrogen peroxide (H 2O2) in aqueous solution over the pH range 6.0 to 10.0 at 25.0°C. All kinetic reactions were followed using UV/VIS spectroscopy. The aqueous equilibrium speciation of SPB was investigated over the pH range 7.0 to 10.0 using 11B NMR Spectroscopy.;At pH ≥ 9.0 hydrogen peroxide reacted with fenitrothion more rapidly than did sodium perborate at equivalent concentration, while at pH ≤ 8.0, hydrogen peroxide reacted with fenitrothion less rapidly than did sodium perborate at equivalent concentration.;The kinetics of degradation of fenitrothion by hydrogen peroxide is well-behaved over the pH range 6.0 to 10.0, giving linear plots of kobs versus [H2O2] with a linear pH profile of the second order rate constants. Dissection of the results revealed that there is no observable reaction between un-ionized H2O2 and fenitrothion, and degradation of fenitrothion in aqueous hydrogen peroxide occurs by nucleophilic attack at the phosphorus centre of fenitrothion (SN2(P)) by hydroperoxide anion (HOO-) with the second order rate constant, kHOO-2 , estimated to be 1.5 +/- 0.2 M-1s -1. (Abstract shortened by UMI.).