Thermodynamic study of the solubility of 2,4′-dihydroxydiphenyl sulfone in nine organic solvents from T = (278.15 to 313.15) K and thermodynamic properties of dissolution
Graphical abstract
Introduction
2,4′-Dihydroxydiphenyl sulfone (CAS Reg. No. 5397-34-2; chemical structure shown in Fig. 1) is an important compound which is employed as a developer for heat-sensitive recording materials and provides excellent heat-sensitive recording paper showing excellent colouring property, causing little fog on the back-ground and stored with stability [1], [2], [3]. It is also commonly used as raw material to synthesize lubricant to metal working [4], antibacterial and antifungal agents [5]. 2,4′-Dihydroxydiphenyl sulfone is prepared by the reaction of 2 mol of phenol with 1 mol of sulfuric acid [2], [6], [7]. However, the reaction product of phenol and sulfuric acid is a mixture of 4,4′-dihydroxydiphenylsulfone and 2,4′-dihydroxydiphenylsulfone. The presence of the product 4,4′-isomer greatly restricts the application field of such contaminated 2,4′-dihydroxy diphenyl sulfone. Thus, it is necessary for acquiring highly pure 4,4′-dihydroxydiphenylsulfone or 2,4′-dihydroxydiphenylsulfone which are separated from each other.
It is a common sense that crystallization is the critical step in purifying a solid compound. Thermodynamic parameters, especially solubility, play an important role during the separation process and determination of proper solvents via solvent crystallization. In the previous works, several crystallization methods have been proposed to separate 2,4′-dihydroxydiphenyl sulfone from the dihydroxydiphenyl sulfone isomers. It can be obtained via crystallization in pure solvents of isopropyl acetate [8], water [9] and trichlorobenzene [10]. Many separation processes are made via crystallization in mixed solvents of {methanol (acetone) + di-isopropyl ether (di-n-butyl ether, di-n-hexyl ether, anisole)} [11], (phenol + water) [6], [12], {methanol (ethanol, propanol) + o-dichlorobenzene} [13], [14], (methanol + water) [15], [16], {methanol (ethanol) + acetone (methyl ethyl ketone)} [17], (methanol + benzene) [18], (DMSO + water) [19], (o-dichlorobenzene + ethyl acetate) [20] and (o-dichlorobenzene + acetic acid) [21]. However, values of solubility of 2,4′-dihydroxydiphenyl sulfone are very scarce in previous publications. Only the 2,4′-dihydroxydiphenyl solubility in water and aqueous of phenol appears in the literature [6]. In order to understand the solvent crystallization process of 2,4′-dihydroxydiphenyl sulfone and to obtain the product with high purity and yield, the solubility of 2,4′-dihydroxydiphenyl sulfone in different solvents at various temperatures and the associated thermodynamic properties of solution must be known in advance.
The aims of this work are to (1) determine the solubility of 2,4′-dihydroxydiphenyl sulfone in nine pure solvents (methanol, ethanol, acetone, acetonitrile, ethyl acetate, n-butanol, isopropanol and 2-butanone); (2) correlate the 2, 4′-dihydroxydiphenyl sulfone solubility in pure solvents by using the modified Apelblat equation, λh equation, Wilson model and NRTL model; and (3) calculate the thermodynamic properties for the dissolution process of 2,4′-dihydroxydiphenyl sulfone in different solvents.
Section snippets
Thermodynamic modelling
With the purpose of selecting the proper model to describe the 2,4′-dihydroxydiphenyl sulfone solubility in different solvents in this work, the solubility of 2,4′-dihydroxydiphenyl sulfone in the studied solvents are correlated with four models, which are the modified Apelblat equation [22], [23], λh equation [24], Wilson model [25] and NRTL model [26].
Materials and apparatus
2,4′-Dihydroxydiphenyl sulfone purchased from Tokyo Chemical Industry Co., Ltd had a mass fraction of 0.984. It was recrystallized in 20% (volume fraction) aqueous solutions of methanol. The final content of 2,4′-dihydroxydiphenyl sulfone used for solubility determination was 0.993 in mass fraction, which was determined by a high-performance liquid chromatography (HPLC). The solvents, including methanol, ethanol, acetone, acetonitrile, ethyl acetate, 1,4-dioxane, n-butanol, isopropanol and
Property of the pure component
Fig. 3 contains the DSC scan for 2,4′-dihydroxydiphenyl sulfone. Shown are the transition temperature of 455.35 K and enthalpy 42.80 kJ mol−1, respectively. The value of melting temperature Tm determined in this work as the mean extrapolated onset temperature (455.35 K) is a little lower than those [30], [31] presented in Table 1. The deviation is perhaps due to the difference in equipment, purity and purification method.
According to the classical thermodynamic property (Eq. (16)), the melting
Conclusion
The solubility of 2,4′-dihydroxydiphenyl sulfone in nine pure organic solvents was determined experimentally at temperatures ranging from (278.15 to 313.15) K under 101.2 kPa by using the high-performance liquid chromatography (HPLC). For all the solvents studied, the solubility of 2,4′-dihydroxydiphenyl sulfone increases with the increase in temperature. At a specific temperature, the mass fraction solubility of 2,4′-dihydroxydiphenyl sulfone in solvents except for 1,4-dioxane follows the
Acknowledgments
This work is financial supported by the Natural Science Foundation of the Anhui Province (Project numbers: 1408085MB40 and KJ2016A888), the National Natural Science Foundation of China (Project number: 21406192) and the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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