Kinetic study of the degradation of ethiofencarb in aqueous solutions

Zusammenfassung

A kinetic study of the hydrolysis of ethiofencarb (α-ethylthio-o-tolyl methylcarbamate) in pure water and in aqueous solutions at pH 2, 6, 9 and 12 and at three different temperatures (4, 20 and 50(± 1)°C) has been carried out using a gas chromatographic nitrogen-phosphorus detection method. The values of the first-order rate constants (k) for the degradation reaction were calculated. The values for k were found to be dependent on pH and temperature. No acid hydrolysis was observed in any case. Complete degradation of ethiofencarb was observed at pH 12 at all three temperatures; it was practically instantaneous at room temperature. Ethiofencarb was also completely degraded at pH 9 at 20 and 50°C, while in pure water (pH 6) degradation took place at 50°C but not at 2°C. Ethiofencarb was not degraded in pure water at lower temperatures and, due to the reversible nature of the reaction, at equilibrium about 80% of the pesticide remained undegraded at room temperature.