Kinetics of carbosulfan degradation in the aqueous phase in the presence of a cosolvent

The degradation of the carbamate pesticide carbosulfan (2,3-dihydro-2,2-dim ethyl-7-benzofuranyl [(dibutylamino)thio]methylcarbamate] was investigated in aqueous buffer solutions (pH 3.0-7.0) containing low (1%, v/v) and high (10-60%, v/v) concentrations of acetonitrile. The cleavage of the carbamyl N-S bond yields carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranol methylc arbamate). The rate of carbosulfan degradation depends on pH, the initial c oncentration of carbosulfan, acetonitrile concentration, shaking speed, ion ic strength, and temperature. Carbosulfan was completely dissolved only in solutions with high acetonitrile concentrations. The concentration of aceto nitrile needed for the complete dissolution of carbosulfan depended on the initial concentration of carbosulfan. In this case, the degradation is a ps eudo-second-order reaction with respect to the concentration of carbosulfan and hydronium ion. The degradation reaction is promoted by the hydronium i on, In the case of low acetonitrile concentrations, where carbosulfan was n ot completely dissolved, the overall kinetic's depend also on the slow diss olution process. The degradation of carbosulfan probably is not a pure hydr olysis reaction, but a protonation-intermolecular rearrangement reaction. T he results indicate that the abiotic degradation of carbosulfan in natural waters is a very slow process when organic solvents and minerals are absent or present in only minor concentrations.