Electrochemical reduction of the synthetic pyrethroid insecticides tralomethrin and tralocythrin at glassy carbon and mercury electrodes

Abstract

Abstract Tralomethrin and tralocythrin may be electrochemically reduced in an initial irreversible two-electron process in the solvents acetonitrile and methanol at glassy carbon and mercury electrodes. The reduction potentials at mercury electrodes are between 600–900 mV less negative than at glassy carbon electrodes. Despite this difference, under both voltammetric and controlled potential electrolysis (CPE) conditions at either electrode surface, the overall reduction process for both compounds involves the elimination of two molecules of bromide ion to yield quantitatively the synthetic pyrethroid compounds deltamethrin (from tralomethrin) and cypermethrin (from tralocythrin) as products. The mechanism of bromide elimination therefore is highly dependent upon the electrode surface. At a glassy carbon electrode, reduction of the pyrethroid compounds is a concerted process involving bromide elimination. In contrast, the presence of the mercury electrode introduces the possibility of chemically reducing tralomethrin (or tralocythrin) to give deltamethrin (or cypermethrin) and a mercury bromide species at the electrode surface. The reaction provides a catalytic pathway for reduction and under voltammetric or CPE conditions the reduction process at the mercury electrode, therefore, is actually associated with the reduction of the mercury bromide species, present at the electrode surface, to elemental mercury and free bromide ion.