Electrochemical reduction of pyrethroid insecticides in non-aqueous solvents

The pyrethrins (as pyrethrum extract), pyrethrin I, pyrethrin II, allethrin and tetramethrin may be reduced in acetonitrile and methanol at mercury and glassy carbon electrodes. In contrast, no well-defined electrochemical processes were observed for phenothrin, bionsmethrin or permethrin. With the exception of the initial, reversible reduction response of tetramethrin in acetonitrile, the reduction processes are irreversible on the voltammetric timescale. Under conditions of controlled potential electrolysis (CPE) and in acetonitrile, the initial reduction of tetramethrin to the anion radical is followed by ester cleavage to yield the chrysanthemate anion as the major product. Evidence is also observed in acetonitrile for ester cleavage following reductive bulk electrolysis of allethrin and pyrethrum extract. In methanol and acetonitrile solutions containing phenol, tetramethrin is reduced in an irreversible two-electron process on both voltammetric and CPE timescales, and cyclohexane-1,2-dicarboximide chrysanthemate is obtained as the major product. No products were identified following CPE of allethrin or pyrethrum extract in methanol. A method for the determination of allethrin in an insecticide formulation containing permethrin was developed using the reduction response at a glassy carbon electrode and the technique of differential pulse voltammetry, after simple dilution of the formulation in acetonitrile. An allethrin concentration of 2.8 +/- 0.2 gl(-1) was obtained compared with the manufacturer's stated value of 3.0 gl(-1).(C) 1997 Elsevier Science S.A.