Thiamethoxam in aqueous co-solvent mixtures of 1,4-dioxane, N,N-dimethylacetamide, dimethyl sulfoxide and acetonitrile: Solubility solute-solvent and solvent-solvent interactions, and preferential solvation analysis

Abstract

The determination of equilibrium solubilities of thiamethoxam in solutions of 1,4-dioxane (1) + water (2), N,N-dimethylacetamide (DMAC, 1) + water (2), dimethyl sulfoxide (1) + water (2) and acetonitrile (1) + water (2) was carried out through the shake-flask method from 278.15 to 323.15 K under 101.2 kPa. The relative contributions of solvent–solvent and solute–solvent interactions on the drug solubility variation were studied via the analysis of linear solvation energy relationships. The significant contributions to the solubility variation were the cavity term and dipolarity-polarizability term in aqueous solution of 1,4-dioxane; and cavity term in aqueous solutions of DMAC/DMSO/acetonitrile. The inverse Kirkwood–Buff integrals were employed to investigate the preferential solvation in light of several solution thermodynamic properties. The preferential solvation parameters for 1,4-dioxane, DMAC and acetonitrile presented positive values in the three aqueous solutions within intermediate and 1,4-dioxane/DMAC/acetonitrile-rich compositions, demonstrating that the drug thiamethoxam was solvated preferentially by 1,4-dioxane/DMAC/acetonitrile. It is conjectured that in these regions thiamethoxam serves as a Lewis acid with the 1,4-dioxane and DMAC molecules; while for the (acetonitrile + water) mixture, the preferential solvation could be attributed to polarization effects. Moreover, the solubility data in mole fraction was mathematically described by the van’t Hoff–Jouyban-Acree model and Jouyban-Acree model attaining the average relative deviations no more than 6.67%.