Solid–liquid equilibrium and thermodynamic of 2,5-thiophenedicarboxylic acid in different organic solvents
Introduction
2,5-Thiophenedicarboxylic acid (Fig. 1, C6H4O4S, CASRN: 4282-31-9) is a kind of white powder, which is an important intermediate in the synthesis of fluorescent brightening agent, efficient agricultural fungicide and anticancer drug. Especially the 2,5-bis-benzoxazoyl-thiophene(EBF), derived from 2,5-thiophenedicarboxylic acid, is a new fluorescent dye which is widely used in terylene, chinlon, plastic, and coating, etc. In addition, 2,5-thiophenedicarboxylic acid is employed in the construction of metal–organic framework to produce a variety of properties including magnetic property, luminescent property, dielectric bistability and so on [1], [2], [3], [4], [5].
In industrial mass production, 2,5-thiophenedicarboxylic acid is synthesized by chlorinating adipic acid and thionyl chloride (Fig. 2) [6]. As purity is a significant part of a chemical substance, this work aims to provide some useful data to the recrystallization process of 2,5-thiophenedicarboxylic acid.
In this work, the solid–liquid equilibrium of 2,5-thiophenedicarboxylic acid in methanol, ethanol, i-propanol, n-butanol, acetic acid, n-hexane, acetonitrile and acetone was explored from 278.15 K to 333.15 K under atmosphere pressure. The modified Apelblat equation and λh equation were applied to correlate with the experimental data. In addition, the thermodynamic properties of the dissolution process, including enthalpy, entropy and Gibbs energy, were calculated by means of van’t Hoff analysis and Gibbs equation. We expected to find out the best solvent in crystallization process of 2,5-thiophenedicarboxylic acid from the selected solvents according to the experimental data. Besides, the analysis of thermodynamic properties would also help to determine the best temperature interval, which gave a variation tendency of solubility at different temperatures.
Section snippets
Materials and apparatus
2,5-Thiophenedicarboxylic acid with a mass fraction ≥0.980 was purchased from Aladdin Reagent Co., Ltd. All the selected organic solvents were purchased from Tianjin Chemical Industry Co., Ltd. Their mass fractions together with CAS registry numbers were listed in Table 1. Smart thermostatic bath(model: DC-2006)was provided by Ningbo Scientz Biotechnology CO., Ltd. with an uncertainty of ±0.1 K. Analytical balance (model BSA224S) was provided by Satorius Scientific Instrument (Beijing) Co., Ltd.
Solubility data and correlation models
The solubility data of 2,5-thiophenedicarboxylic acid (x) in the eight organic solvents were showed in Table 2 and pictured in Fig. 3. And standard uncertainty was calculated according to guide to the expression of uncertainty in measurement (GUM) [9]. As acetic acid would be frozen at 278.15 K and the boiling point of acetone is lower than 333.15 K, these two data were not measured.
Also we calculated the increasing rate (IR) to show the increase of solubility when raising the temperature with
Conclusions
The solubility of 2,5-thiophenedicarboxylic acid is a function of temperature and increases with increasing temperature. Between the two models, modified Apelblat shows a good agreement with solubility data, while λh equation cannot fit the data well. The van’t Hoff analysis indicates that the enthalpy increases and the entropy decreases, which means that this dissolution process is a nonspontaneous process. In addition, the main contributor is enthalpy because all %ξH are ≥50%.
In summary,
Acknowledgments
This work was financially supported by research subject of National Key Laboratory of Material Chemistry Engineering (ZK201304), the Science and technology support program—agriculture part (BE2013442), the Joint innovation and research funding-prospective joint research projects (BY2013005-02), the Doctoral fund class topics (20113221110005 and 20133221110010).
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