Thermodynamic studies of thiamethoxam in nine pure solvents and one mixed solvent, solubility and correlation ranged from 278.15 to 323.15 K

Abstract The solubility of thiamethoxam in nine single solvents (acetic acid, methanol, acetonitrile, 2-methoxyethanol, 2-ethoxyethanol, propionic acid, DMSO, 1,4-dioxane, DMA) and binary mixed solvents (methanol + acetonitrile) was measured by dynamic laser method from 278.15 K to 323.15 K under pressure of 101.2 kPa. Modified Apelblat equation, λh equation, NRTL model, and Wilson model were used to fit the experimental data of pure solvents; for mixed solvents, Modified Apelblat equation, λh equation, Jouyban-acree model and Wilson model were used for solubility data correlation. The results showed that the fitting value is in good agreement with the experimental value, the solubility of thiamethoxam in selected solvents increased with the increase of temperature. It was found that the solubility of thiamethoxam in mixtures with different proportions of methanol and acetonitrile was higher than that of two single solvent, which might be related to the bipolarity/polarizability of the solvent. What’s more, the mixing enthalpy, entropy, and Gibbs free energy in pure and mixed solvents were obtained according to the Wilson model, the value of ΔmixG is negative in the dissolution, the value of ΔmixS is positive, indicating that the mixing process in selected solvents was entropy-driven. When thiamethoxam dissolved in methanol, acetic acid, propionic acid, the value of ΔmixH is positive, which showed that thiamethoxam was endothermic during dissolution, When thiamethoxam dissolved in acetonitrile, 2-methoxyethanol, 2-ethoxyethanol, DMSO, 1, 4-dioxane, DMA and mixed solvents the value of ΔmixH is negative ,which showed that thiamethoxam was exothermic during dissolution. The solubility data, solubility model and thermodynamic parameters of thiamethoxam are of great significance to the application of thiamethoxam industrial production and crystallization.