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

Pseudo‐first‐order rate constants (k_obs) 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: k_obs =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 (k_obs) for hydrolysis of AZS within the [H⁺] range from 2.5 × 10⁻⁶ to 1.4 M follow the relationship: k_obs = (α₁K _a + B₁[H⁺] + B₂[H⁺]²)/([H⁺] + K_a) where pK_a = 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. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 253–260, 1999