Investigation on florasulam in aqueous blends including solubility, preferential solvation, thermodynamic properties and enthalpy-entropy compensation

The equilibrium solubility of florasulam in solvent mixtures (methanol/ethanol /n-propanol/propylene glycol (PG) + water) was determined experimentally by isothermal saturation method at 278.15 K to 323.15 K under 101.2 kPa. Both high temperature and low water content of solvent promoted the dissolution of florasulam. Under given conditions, the mole fraction of florasulam was greater in (n-propanol + water) than other three solvent mixtures. Besides, the solubility of florasulam was correlated with the Jouyban-Acree (J-A) model and van't Hoff-Jouyban-Acree (V-J-A) model. The obtained average relative deviations (RAD) and root mean square deviations (RMSD) were no >4.04 % and 1.73 x 10-4. The calculated preferential solvation parameter & delta;x1,3 was used to analyze the preferential dissolution of florasulam between water and alcohols from the molecular perspective. The result is that in the intervals 1 > xmethanol > 0.32, 1 > xethanol > 0.23 and 1 > xn-propanol > 0.19, the florasulam was preferentially dissolved by methanol/ethanol/n-propanol. In other concentration ranges, the florasulam was preferentially dissolved by water. The reason for the special existence of PG + water is that |& delta;x1,3| < 1 x 10-2 and the dissolution of florasulam in it conformed to the uncertainty propagation rather than preferential solvation theory. The parameters (& UDelta;solHo, & UDelta;solGo, & UDelta;solSo, & UDelta;trGo, & UDelta;trHo and & UDelta;trSo) that could reflect the apparent and transfer thermodynamic properties were obtained. It was concluded that the solubility change of florasulam was dominated by entropy and the transfer of florasulam from pure water to mixtures was an exothermic process. Finally, the enthalpy-entropy compensation analysis further studied the mechanism of enthalpy and entropy in the dissolution process.