Thermodynamic functions for solubility of 2-mercaptobenzothiazole in eleven pure organic solvents at temperatures from 273.15 K to 318.15 K and mixing properties of solutions

Abstract

The solid-liquid equilibrium of 2-mercaptobenzothiazole in eleven solvents of methanol, n-propanol, i-propanol, n-butanol, i-butanol, acetonitrile, ethyl acetate, toluene, 2-butanone, chloroform and 1,4-dioxane was investigated by the isothermal dissolution equilibrium method under atmosphere pressure of 101.2kPa, and the solubilities were determined by a high-performance liquid chromatography at T=(273.15, 275.65, 278.15, 280.65, 283.15, 285.65, 288.15, 290.65, 293.15, 295.65, 298.15, 300.65, 303.15, 305.65, 308.15, 310.65, 313.15, 315.65 and 318.15)K. For the eleven solvents, the mole fraction solubility of 2-mercaptobenzothiazole increased with increasing temperature. Thee obeyed the following order from high to low in different solvents: 2-butanone>1,4-dioxane>ethyl acetate>n-butanol>n-propanol>i-butanol>i-Propanol>methanol>chloroform>acetonitrile>toluene. The solubility values obtained for 2-mercaptobenzothiazole in the selected solvents were correlated with four models, which corresponded to modified Apelblat equation, λh equation, Wilson model and NRTL model. The largest values of relative average deviation and the root-mean-square deviation acquired with the four models were 0.59 % and 4.86×10−4, respectively. Generally, the four thermodynamic models were all acceptable for describing the solubility behaviour of 2-mercaptobenzothiazole in the solvents. In addition, based on the Wilson model, the mixing thermodynamic properties (mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient at infinitesimal concentration and reduced excess enthalpy) of solutions were derived. The results indicated that the dissolution of 2-mercaptobenzothiazole in all studied cases was spontaneous and favourable. The solubility values and thermodynamic relations of 2-mercaptobenzothiazole in selected solvents would be invoked as fundamental data and models regarding the purification process of 2-mercaptobenzothiazole.