Adsorption and degradation of rimsulfuron on Al hectorite

A study was carried out to examine the interactions between a smectite (hectorite) saturated with Al3+ and a sulfonylurea herbicide, rimsulfuron [N-((4,6-dimethoxypyrimidin-2-yl)aminocarbonyl)-3-(ethylsulfonyl)-2-pyridinesulfonamide]. As rimsulfuron is extremely unstable in water, to evaluate the role of the clay surface in decomposing the herbicide, the experiments were carried out in chloroform solution. The coordination of the C=O group is initially involved in the adsorption as revealed by FT-IR analysis. The adsorbed rimsulfuron decomposes initially into N-(4,6 dimethoxypyrimidin-2-yl)-N-((3-(ethylsulfonyl)-2-pyridinyl)urea (metabolite 367). This metabolite is adsorbed onto a clay surface by coordination of the C=O group-and protonation of the pyrimidine ring. Successively, this metabolite decomposes on a clay surface to N-[(3-ethylsulfonyl)-2-pyridinyl]-4,6-dimethoxy-2-pyrimidineamine (metabolite 324). This second metabolite remains adsorbed by protonation of its pyrimidine ring.