ELECTROCHEMICAL REDUCTION OF THE SYNTHETIC PYRETHROID INSECTICIDES TRALOMETHRIN AND TRALOCYTHRIN AT GLASSY-CARBON AND MERCURY-ELECTRODES

Tralomethrin and tralocythrin may be electrochemically reduced in an i nitial irreversible two-electron process in the solvents acetonitrile and methanol at glassy carbon and mercury electrodes. The reduction po tentials at mercury electrodes are between 600-900 mV less negative th an at glassy carbon electrodes. Despite this difference, under both vo ltammetric and controlled potential electrolysis (CPE) conditions at e ither electrode surface, the overall reduction process for both compou nds involves the elimination of two molecules of bromide ion to yield quantitatively the synthetic pyrethroid compounds deltamethrin (from t ralomethrin) and cypermethrin (from tralocythrin) as products. The mec hanism of bromide elimination therefore is highly dependent upon the e lectrode surface. At a glassy carbon electrode, reduction of the pyret hroid compounds is a concerted process involving bromide elimination. In contrast, the presence of the mercury electrode introduces the poss ibility of chemically reducing tralomethrin (or tralocythrin) to give deltamethrin (or cypermethrin) and a mercury bromide species at the el ectrode surface. The reaction provides a catalytic pathway for reducti on and under voltammetric or CPE conditions the reduction process at t he mercury electrode, therefore, is actually associated with the reduc tion of the mercury bromide species, present at the electrode surface, to elemental mercury and free bromide ion. (C) 1998 Elsevier Science S.A. All rights reserved.