- Adsorption and degradation of rimsulfuron on Al hectorite
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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.
- Pantani, Ottorino,Pusino, Alba,Calamai, Luca,Gessa, Carlo,Fusi, Paolo
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- Soil Metabolism of the Herbicide Laboratory and Field Conditions
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Procedures were developed for soil analysis of rimsulfuron and its metabolites by means of GC-ECD, GC-FPD and GC-MS with a detection limit of 1 μg of rimsulfuron equivalents per kilogram of dry soil, after purification of the soil extracts by TLC. Soil containing an exaggerated rimsulfuron concentration was incubated in the laboratory, in order to adjust the analytical procedures. To evaluate the role of different manuring managements, rimsulfuron was applied postemergence (10 g ha-1 on a corn field in 1994 and 1995) on plots treated with (1) green manure, pig slurry applied in (2) November and (3) March, and cow manure applied in (4) November and (5) March and (6) untreated control plots without organic fertilizer. Neither rimsulfuron nor its metabolites were detected at soil depths lower than 8 cm. The results show that manure managements prolong rimsulfuron half-life in the 0-8 cm surface soil layer from a minimum of 14 days (control) to a maximum of 46 days (pig slurry in March). At corn harvest, rimsulfuron and its metabolites were not detected in soil. Similar soil degradation pathways were observed in the field as in the laboratory. N-(4,6-Dimethoxypyrimidin-2-yl)-N-[3-(ethylsulfonyl)-2-pyridinyl]urea 2 was a transient soil degradation product. N-[3-(ethylsulfonyl)-2-pyridinyl]-4,6-dimethoxy-2-pyrimidineamme 3 attained a maximum soil concentration after 20 days of incubation and then progressively disappeared and could not be detected after 40 days. The high-molecular weight amine 3 did not accumulate in soil, eliminating the concern for potential formation of nitroso amino compounds. 2-Hydroxy-3-(ethylsulfonyl)pyridine 4 became the major rimsulfuron soil degradation product. The soil concentrations increased and attained a maximum after 40 days of incubation and then decreased; its isomerization into 2-pyridone, followed by hydrolysis, could transform it into low molecular weight nontoxic products. The concentrations of 2-amino-4,6-dimethoxypyrimidine 5 were somewhat lower than those of compound 4.
- Rouchaud, Jean,Neus, Olivier,Callens, Dany,Bulcke, Robert
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- Intramolecular and bimolecular nucleophilic substitutions of rimsulfuron sulfonylurea
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The sulfonylurea herbicide rimsulfuron 1 (N-((4,6-dimethoxypyrimidin-2-yl)aminocarbonyl)-3-(ethylsulfonyl)-2-pyridinesulfonamide) in aqueous solutions of KOH, NaOH, NH4OH, or dilute HCl, and thermally (rimsulfuron or monomethylated rimsulfuron at the sulfonamide hydrogen) was transformed by SO2 extrusion and intramolecular nucleophilic substitution into 2-(N-(4,6-dimethoxy)pyrimidin-2-yl)amino-3-ethylsulfonylpyridine 3.In mild methanol + HCl conditions, the intermediate rearranged urea N-(4,6-dimethoxypyrimidin-2-yl)-N-(3-(ethylsulfonyl)-2-pyridinyl)urea 2 was isolated.In concentrated hydrochloric acid, rimsulfuron 1 was transformed by bimolecular nucleophilic substitution successively into 2-chloro-3-ethylsulfonylpyridine 6 and 2-hydroxy-3-ethylsulfonylpyridine 4.Sodium sulfite transformed rimsulfuron 1 into a mixture of 2-sodiumsulfonate-3-ethylsulfonylpyridine 7 and amine 3.
- Rouchaud, J.,Neus, O.,Moulard, C.
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