A Convenient Method for Oxidation of Organophosphorus Pesticides in Organic Solvents

Since organophosphorus pesticides can be oxidized to oxons in vivo and in the environment and their determination based on inhibition of cholinesterases can be more sensitive after their oxidation to oxons, development of an efficient method for their in vitro oxidation is important for their toxicological and analytical studies. This study demonstrated that treatment of organophosphorus pesticides with 10 molar excess bromine in acetonitrile is a rapid and efficient method for their oxidation. For the nine organophosphorus pesticides tested, the reaction was complete within a few seconds. All reactions gave the respective oxons as single major product, except that of fenthion, which gave two major products, the respective oxon and another product from further oxidation of the oxon. The yields of the oxons were 82–100%. The inhibitory power of the pesticides on acetylcholinesterase before and after oxidation was measured and, for all pesticides tested, the power after oxidation was much higher than that before oxidation. Inhibition calibration curves for both unoxidized and oxidized forms of fenitrothion and parathion were obtained. The sensitivity of the detection of these pesticides was much higher after oxidation.