Kinetic study on acid-base catalyzed hydrolysis of azimsulfuron, a sulfonylurea herbicide

Pseudo-first-order rate constants (kobs) for hydrolysis of a sulfonylurea herbicide, azimsulfuron, AZIM®, {N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbony]-1-methyl-4-(2-methyl-2H-tetrazol-5-yl)-1H-pyrazole-5-sulfonamide} (AZS) follow an empirical relationship: kobs =α1 + α2[−OH] + α3[−OH]2 within the [NaOH] range of 0.1–2.0 M at different temperatures ranging from 40 to 55°C. The contribution of α3[−OH]2 term is small compared with α2[−OH] term and this turns out to be zero at 60°C. Pseudo-first-order rate constants (kobs) for hydrolysis of AZS within the [H+] range from 2.5 × 10−6 to 1.4 M follow the relationship: kobs = (α1K a + B1[H+] + B2[H+]2)/([H+] + Ka) where pKa = 4.37 at 50°C. The value of B1 is nearly 25 times larger than that of α1. The rate of alkaline hydrolysis of AZIM is weakly sensitive to ionic strength.