JOURNAL of the Tunisian Chemical Society

This paper describes the analysis and rates of hydrolysis of N,N-dialkyl carbamate insecticide, Pirimicarb in aqueous media. This work is carried out by reversed phase Liquid Chromatography and UV Spectrophotometry. Pirimicarb was found to be stable towards hydrolysis in buffered solutions in the pH range of 9-12. The N,N-dialkyl carbamates were more stables to alkaline hydrolysis than the N-monoalkyl carbamates. The rates of hydrolysis with different hydroxide ion concentrations, ranging from 0,2M to 1M, (ionic strength µ = 1, T = 40°C) were measured. Pseudo-first order rate constants for alkaline hydrolysis of Pirimicarb were found to be 4,9 10-3 min^-1 for [OH^-] = 0,2 M and 2,4 10^-2 min^-1 for [OH^-] = 1M. The effect of temperature on the rates of hydrolysis was also investigated. The obtained negative activation entropy ΔS = - 98,096 J mol^-1 K^-1, indicates a B_Ac2 hydrolytic mechanism involving the addition of hydroxide ion to the carbonyl group of the carbamate to form a tetrahedral intermediate, followed by decomposition of this intermediate to give the dimethylamine and the 4-hydroxy-2-dimethylamino-5,6-dimethylpyrimidine.

R. Ouertani, A. Gadhgadhi, N. Ben Hamida

Pirimicarb, kinetic, mechanism, HPLC, spectrophotometric UV

Pages 29-38