Solubility determination and thermodynamic modeling of paclobutrazol in nine organic solvents from T = (278.15 to 318.15) K and mixing properties of solutions

The mole fraction solubility of paclobutrazol ((R,R) and (S,S)) mixture in nine pure solvents including ethanol, isopropanol, n-propanol, 1-butanol, ethyl acetate, toluene, acetone, acetonitrile and 1,4-dioxane was determined experimentally by using the isothermal saturation method over a temperature range from (278.15 to 318.15) K under atmospheric pressure. The mole fraction solubility of paclobutrazol in the selected solvents increased with a rise of temperature. In general, at a certain temperature, they decreased according to the following order in different solvents except for ethyl acetate: toluene > 1,4-dioxane > acetone > 1-butanol > n-propanol > ethanol > isopropanol > acetonitrile. The paclobutrazol solubility showed stronger dependency on temperature in ethyl acetate than in the other solvents. The solubility determined for paclobutrazol in the selected solvents was correlated with the modified Apelblat equation, λh equation, Wilson model and NRTL model. The maximum values of root-mean-square deviation (RMSD) and relative average deviation (RAD) were 3.98 × 10−4 and 1.53%, respectively. On the whole, the four thermodynamic models were all acceptable for describing the systems of paclobutrazol in these solvents. Furthermore, the mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient at infinitesimal concentration (γ1∞) and reduced excess enthalpy (H1E,∞) were obtained. The mixing process of paclobutrazol was spontaneous and exothermic in the solvents studied. The solubility determined and the thermodynamic properties derived should be very helpful for optimizing the purification process of paclobutrazol.