Study On The Structure And Property Of The Solvate And Cocrystal Of Nicosulfuron

Nicosulfuron（NS）is a kind of sulfonylurea herbicide that can effectively getting rid of the weeds in crops.Currently,The NS on sale is the crystal form Ia with a low solubility in aqueous.In order to enhance the solubility of NS in aqueous,the solid forms of NS,solvate and cocrystal,were screened experimentally.The structures and properties of solvate and cocrystal obtained were systematically studied.In this study,NS methanol solvate（NS-Me OH）and ethanol solvate（NS-Et OH）were screened by solventing-out crystallization and low-temperature suspension meth-ods,respectively.Both solvates were characterized by powder X-ray diffraction（PXRD）,thermogravimetric analysis（TGA）and differential scanning calorimetry（DSC）.The results showed that the T_onset of desolvation of two solvates were both higher than the boiling point of the corresponding solvents.In addition,the study of the dissolution behavior of NS and NS-Me OH indicated that the formation of NS-Me OH enhanced the solubility of nicosulfuron in aqueous.Moreover,single crystal X-ray diffraction（SCXRD）was successfully used to ob-tain the structures of NS-Me OH and NS-Et OH.The results showed that the theoretical stoichiometric ratios were both 1:1,and the NS-Me OH crystallized in a triclinic crystal system with the group of P-1,while the NS-Et OH crystallized in a triclinic crystal sys-tem with the group of C2/c.The roles of solvent molecules on the formation of solvates were also explored.The results indicated that the solvent molecules bonded with NS molecules through hydrogen bonds in solvates.Due to the different physicochemical properties of the methanol and ethanol,the NS molecules in two solvates exhibited different molecular conformations.As a result,the network structures of the two solv-ates formed by hydrogen bonds were stacked and arranged in different directions.In addition,the model-free method combined with the model-fitting method was applied to investigate the non-isothermal desolvation process of NS-Me OH and NS-Et OH at three different heating rates.The results showed that the desolvation of two solvates in the initial stage included multiple reaction mechanisms,while the desolva-tion in the later stage followed the nucleation-and-growth mechanism.In this end,the Nicosulfuron-Urea cocrystal（NS-Urea）was screened by liquid-assisted grinding method.The cocrystal was characterized by powder X-ray diffraction（PXRD）,thermogravimetric analysis（TGA）and differential scanning calorimetry（DSC）.The results showed that the decomposition reactions of the cocrystal occurred at 170.8℃.The single-crystal-structure analysis indicated the cocrystal crystallized in a triclinic crystal system with the group of P-1,and the theoretical stoichiometric ratio was 1:1.In addition,dissolution and herbicidal activities of NS-Urea were also meas-ured.The results showed that the formation of cocrystal had little influences on herbi-cidal activities,but it greatly enhanced the solubility of NS in aqueous.