Kinetic study on acid‐base catalyzed hydrolysis of azimsulfuron,a sulfonylurea herbicide |
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Authors: | M. Niyaz Khan Baki B. Bakar Fenny W. N. Yin |
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Abstract: | 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. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 253–260, 1999 |
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