Electrochemical reduction of pyrethroid insecticides in non-aqueous solvents

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Abstract

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 contrastm no well-defined electrochemical processes were observed for phenothrin, bioresmethrin 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 allehtrin in an insecticide formulation containingpermethrin was developed using the reduction response at a glassy carbon electrode and the technique of differential pulse voltemmetry, 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.

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      2004, Analytica Chimica Acta
      Citation Excerpt :

      These results demonstrate that no adsorption of lambda-cyhalothrin in the tests solutions occurred and the mass transport of electroactive species to the mercury electrode is diffusion-controlled at the three pH values tested. A study of the molecular structure of lambda-cyhalothrin together with the previous knowledge of the voltammetric behaviour of cypermethrin and deltamethrin, two pyrethroids with similar structures [12], led us to attribute the electroactivity of these insecticides in pH range 2.0–10.5 to the two-electron reduction of the double bond in the pyrethroid [16,17]. In alkaline medium (pH>10.5), the hydrolysis of the ester group in lambda-cyhalothrin [11,12] gives rise to chrysanthemum acid and 3-phenoxybenzaldehyde.

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    1

    Present address: Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QT, UK.

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