Determination of some thiophosphorus insecticides based on coulometric titration with the anodically generated chlorine: a further insight in the reaction mechanism in aqueous medium

A new method of analytical determination of some thiolo (P-S) and thiono (P=S) group containing phosphorus insecticides using a coulometric titration with the anodically generated chlorine and biamperometric end-point detection was described. The method worked well for compounds containing one (methamidophos) or two P-S bonds (iso-malathion) or one P=S bond (fenitrothion) but failed for compounds containing both P-S and P=S bonds (malathion, dimethoate) or additional sterically hindered C-S-C bond (fenthion). Based on the found number z of electrons transferred per mol of oxidized compounds, mechanistic pathways for chlorination of P-S and P S containing thiophosphorus insecticides with molecular chlorine in aqueous, acidic medium were proposed. (C) 2003 Elsevier Science B.V. All rights reserved.