JOURNAL of the Tunisian Chemical Society

Anthropogenic compounds used as pesticides often persist in the environment and can cause toxicity to humans and wildlife. Some of them are easily degraded, whereas others are degraded very slowly or only partially, leading to accumulation of toxic products. This review examines the physico-chemical factors that affect the degradation of pesticides and the mechanisms by which new pathways emerge in nature. The present work deals with the degradation mechanism of an insecticide, Isoprocarb or 2-isopropylphenyl-N-methylcarbamate in aqueous media. It may result in the inhibition of the vital enzyme acetyl-cholinesterase. The reaction kinetics has been investigated using UV Spectrophotometry. The determination of 2-isopropylphénol, as the main degradation product of Isoprocarb hydrolysis gives evidence for the significant reactivity of this insecticide in alkaline solution. The rate constants were determined following a first order kinetic model. The obtained positive activation entropy ΔS^≠ = +21.78 J mol^-1 K^-1 and the absence of basic general catalysis indicate an E1cB mechanism involving unimolecular collapse of the Isoprocarb via a methylisocyanate intermediate. This elimination process is confirmed by the position of the point corresponding to the Isoprocarb on the Brönsted and Hammett plots, determined for a serie of substituted N-methylcarbamate which the decomposition mechanism in aqueous media proceede via E1cB.

H. Bakhti, N. Ben Hamida

Isoprocarb, carbamate, kinetic, mechanism, spectrophotometric UV

Pages: 35-43