Solubility and thermodynamic functions of tebuconazole in nine organic solvents from T = (278.15 to 313.15) K and mixing properties of solutions
Graphical abstract
Introduction
Tebuconazole (CAS NO. 107534-96-3; IUPAC Name: 1-(4-chlorophenyl)-4,4-dimethyl-3-(1,2,4-triazol-1-ylmethyl)pentan-3-ol; chemical structure shown in Fig. 1) is a high-effect fungicide. The fungicidal effectiveness of tebuconazole against the Fusarium, Penicillium, Botrytis and Melampsora lini is great [1]. It can effectively control many rust diseases for cereal crop. So tebuconazole is widely used for important economic crop seed treatment or foliar spraying. In recent years, the study of tebuconazole has never been stopped, especially for the study of synthesis of prothioconazole and tebuconazole suspending agent, which has become hotter and hotter [2], [3], [4], [5]. To date, many methods have been proposed to produce tebuconazole in the previous publications [6], [7], [8]. Tebuconazole is commonly prepared by treating 2-[2-(4-Chlorophenyl)ethyl]-2-(1,1-dimethylethyl)oxirane with 1-H-1,2,4-Triazole. However, the reaction product contains some unreacted reactants and some unknown by-product. With the development of chemical industry, the requirement for product purity is becoming higher and higher. The crude tebuconazole restricts its applications in many aspects. It must be purified before use.
Solvent crystallization is commonly employed as an important separation and purification step in the production procedure. The solid solubility in different solvents is an essential physicochemical property which plays an important role for understanding the (solid + liquid) phase equilibrium (SLE) in the development of a crystallization process. More particularly, the knowledge of accurate solubility is required for the design of crystallization process. Solvent crystallization is an effective method for tebuconazole purification. In previous publications, the purification method of tebuconazole is recommended via recrystallization from petroleum ether and acetic ether [9]. Although the solubility values are of great significance in the purification process of tebuconazole via the solvent crystallization where the accurate solubility results for tebuconazole are essential, to the best of the authors’ present knowledge, no solubility data are reported in the previous works. In order to acquire high purity tebuconazole, the knowledge of solubility of tebuconazole in different solvents at various temperatures and the thermodynamic properties of solution is a necessary procedure.
The purification of tebuconazole is often made in organic solvents [9]. From many species of organic solvents, we chose nine commonly used organic solvents (methanol, ethanol, isopropanol, n-propanol, ethyl acetate, toluene, acetone, 2-butanone and acetonitrile) in industrial purification processes. In order to select an appropriate solvent to purify tebuconazole, the objectives of the work are to (1) determine the solubility of tebuconazole in the selected solvents at temperatures ranging from (278.15 to 313.15) K by using the isothermal saturation method; (2) correlate the solubility data with different thermodynamic models; and (3) evaluate the mixing properties for the solution process of tebuconazole in these solvents. Specifically, the temperature of solvent-assisted crystallization of tebuconazole is almost in the temperature range from 273 K to 320 K, the selected temperatures are within the range from T = 278.15 K to T = 313.15 K.
Section snippets
Solid-liquid phase equilibrium models
So as to select suitable models to describe the solubility behaviour of tebuconazole in the studied solvents, in this work, four models are employed to correlate the solubility results, which correspond to the modified Apelblat equation [10], [11], Buchowski–Ksiazaczak λh equation [12], Wilson model [13] and NRTL model [14].
Materials and apparatus
Tebuconazole having a mass fraction of 0.982 was provided by Beijing Ouhe Chemical Technology Co., Ltd. It was purified via recrystallization in acetone. The recrystallized sample had a mass fraction purity of 0.993, which was determined by a high-performance liquid phase chromatograph (HPLC, Agilent-1260). Moreover, the (S, S) and (R, R) enantiomer ratio for the purified tebuconazole was determined in our laboratory on CDMPC (Cellulose-tris(3,5-dimethylphenylcarbamate) chiral stationary phase by
Melting properties of pure component
The determined DSC curve of tebuconazole is shown in Fig. 3. On the basis of the DSC analysis, the melting temperature Tm and melting enthalpy ΔfusH of tebuconazole are 373.47 K and 28.95 kJ·mol−1, respectively. The value of melting enthalpy Tm determined in the present work as the mean extrapolated onset temperature (373.47 K) is a little smaller than that reported in the literature [20]. The deviation is perhaps due to the difference in equipment, purity and purification method.
Based on the
Conclusions
In this work, the equilibrium solubility was acquired experimentally for tebuconazole in a total of nine pure organic solvents within the temperature range from (278.15 to 313.15) K under 101.2 kPa. The mole fraction solubility of tebuconazole in the selected pure solvents increases with the increase in temperature. At a certain temperature, they rank as 2-butanone > acetone > (ethyl acetate, toluene) > methanol > ethanol > isopropanol > n-propanol > acetonitrile. Values of the experimental solubility were
Acknowledgments
This work was supported by the National Natural Science Foundation of China (51403053). This work was also supported by the Science and technology research key project of the Education Department of Henan Province (No. 14B530005) and the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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