Binary liquid–liquid equilibrium in the systems containing monofunctional benzene derivates and 1,2-ethanediol
Introduction
Productions of pharmaceuticals require the presence of solvents in all technological steps. Selection of proper solvents have great influence on quality of final products and on economical aspects of production. Selection of solvents for pharmaceuticals mostly relies on experience or experimental testing only. Effort of some pharmaceutical manufacturers is to select solvents for their technologies on basis of improved prediction of solubility of pharmaceuticals. Several possibilities how it can be realized were outlined in the study [1]. One of the possibilities can be an usage group contributions prediction methods for activity coefficients (e.g. UNIFAC [2]). Systematic measurement of phase equilibria in small systems containing common core structures of pharmaceuticals is very desirable for evaluation group contribution parameters.
In the work [1] 13 monofunctional benzene derivatives were selected and their availability of solubility data with 17 solvents was presented. A lack of solvent–solute experimental data was found for solvent 1,2-ethanediol.
The aim of the work was to obtain data on liquid–liquid equilibrium in binary systems containing monofunctional derivatives of benzene and 1,2-etanediol (i.e. ethylene glycol). For the study, liquid compounds showing limited miscibility with 1,2-ethanediol were selected. They were toluene, methoxybenzene (i.e. anisole), chlorobenzene and acetophenone. It was found that phenol and aniline were completely miscible with 1,2-ethanediol at ambient temperature.
1,2-Ethanediol as the solvent was chosen because its polarity is lower than that of water and higher than that of methanol. Its solubility parameter [1] (29.1 MPa1/2) is close to the solubility parameter of methanol (29.7 MPa1/2) and far of the solubility parameter of water (48.1 MPa1/2). The selected solutes are soluble in methanol but their solubilities in water are very low [3]. For chlorobenzene, toluene, methoxybenzene and acetophenone, they are in mole fractions 8 × 10−5, 1 × 10−4, 2.5 × 10−4 and 9.5 × 10−4, respectively. From this point of view, to study LLE of monofunctional derivatives of benzene and 1,2-ethanediol can bring new information. No experimental data in the specified systems (except that for toluene and 1,2-ethanediol in the temperature range of 283–333 K [4]) were found in literature.
Section snippets
Materials
Specifications of chemical used in this work are given in Table 1. Water content was determined by Karl-Fischer titration using an automatic burette and titration controller from Schott. Densities were measured by a density meter AP DMA 5000. Due to high hydrophilic behaviour of 1,2-ethanediol, an anhydrous reagent was used and all main manipulations with it were performed in a dry-box.
Experimental methods
Most of the LLE measurements were carried out by the volumetric method described in detail in the previous
Results and discussion
Experimental data on the LLE for toluene + 1,2-ethanediol, methoxybenzene + 1,2-ethanediol, chlorobenzene + 1,2-ethanediol and acetophenone + 1,2-ethanediol are summarised in Table 2 and presented in Fig. 1, Fig. 2.
The fact that liquid molar volumes of monofunctional benzene derivatives are much higher than that of 1,2-ethanediol causes asymmetrical experimental uncertainties in compositions of the conjugated phases and [6]. The experimental (i.e. compositions in the 1,2-ethanediol-rich
Conclusion
The liquid–liquid equilibrium was measured for selected monofunctional benzene derivates and 1,2-ethanediol. Majority of data was obtained by the volumetric method which allows to calculate standard deviations of results. Due to differences in molar volumes of solvent and solute, the solubilities of monofunctional benzene derivates in 1,2-ethanediol were obtained with very good precision. Reversely, the solubilities of 1,2-ethanediol in the corresponding monofunctional benzene derivates however
Acknowledgment
This work was supported by the Ministry of Education of the Czech Republic under grant number MSM 604 613 7307.
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