Toward an Understanding of the Formation and Desolvation of Methanol Solvate, and Structure of Methanolysis Product: A Case Study of Nicosulfuron

Nicosulfuron (NS) is a widely used sulfonylurea herbicide because of its high selectivity, broad spectrum of herbicide activity, and excellent performance. In this work, nicosulfuron methanol solvate (NS-MeOH) and [[3-[(Dimethylamino)carbonyl]-2-pyridinyl]sulfonyl]carbamic acid methyl ester (PCM) as a product of methanolysis of NS were obtained. Both of their structures were determined by a single crystal X-ray diffraction. A broad range of analytical techniques was applied to characterize the NS-MeOH, such as Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and hot stage microscopy (HSM). Combined with the analysis of the Independent gradient model (IGM), Atom-in-molecules (AIM), and Hirshfeld surface (HS), direct insights into the role of solvent played in the formation of NS-MeOH and the mechanism of solid-to-solid phase transformation of NS-MeOH could be obtained. In addition, the aqueous solubility of NS was improved through the formation of NS-MeOH. A systematic investigation of herbicidal activity of NS and PCM was carried out. It was found that NS and NS-MeOH had similar herbicidal activities at the experimental concentrations while PCM exhibited significantly lower activity. It was suggested that methanolysis of the sulfonylurea bridge in the NS molecule exerted a great influence on the herbicidal activity.

Abstract licence: CC BY

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