THE AQUEOUS HYDROLYSIS OF TRIBENURON METHYL

Ware , Douglas Russell

MS

University Of Delaware

1997

The research contained in this thesis investigates the kinetics of the chemical hydrolysis of tribenuron methyl, a sulfonylurea herbicide, in sterile aqueous solution. The reaction was studied at pH ranging from 3 to 10, and temperature ranging from 295 to 328 Kelvin. High pressure liquid chromatography (HPLC) was used for the analysis of tribenuron methyl concentration. A general mechanistic model which describes the kinetics of sulfonylurea herbicide hydrolysis as a function of temperature and pH was applied to the data and kinetic parameters of hydrolysis were determined from the fit. The data suggest that three mechanistic reactions are responsible for the overall hydrolysis of tribenuron methyl. These are the hydrolysis of the neutral species, the hydrolysis of the anionic species, and the hydrolytic cleavage of the anionic species by OH-. The energies of activation, Ea, for these reactions as determined by the model fit are 98 +/-2 kJmol-1, 59 +/-9 kJmol-1, and 84 +/-15 kJmol-1, respectively. The frequency factors, lnA, are 39.5 +/-0.7, 16 +/-4, and 35 +/-6, respectively. From the energies of activation and frequency factors thermodynamic parameters of the activated complexes have been calculated.