Solubility modelling and thermodynamic dissolution functions of phthalimide in ten organic solvents
Graphical abstract
Introduction
Phthalimide is an important chemical intermediate. The use of phthalimide and its derivatives is widely spread in dyestuffs, agriculture, medicine, and many other fields [1], [2], [3], [4], [5]. In industry, phthalimide can be prepared by treating phthalic anhydride with ammonia [6], [7], [8] or by treating the anhydride with ammonium carbonate or urea [9], [10] and or by ammoxidation of ortho-xylene [11]. At present, the commercial preparation method of phthalimide is using phthalic anhydride as raw material. Although the yield of phthalimide is relatively high by this method, the crude product usually contains some unreacted phthalic anhydride. Extreme difficulty is encountered in separating the phthalimide of high purity from the reaction mixture because of the extremely poor solubility of phthalimide in water. With the development of industry, the requirements for product purity are becoming greater. The crude phthalimide restricts its applications in many aspects.
It is well-known that crystallization is an important process during purifying a solid compound. Knowledge of solubility is of significance in designing chemical and pharmaceutical industrial processes. In previous works, some purification methods have been proposed to separate the phthalimide directly with high purity [12], [13], however, the cost of these processes is relatively high. To the best of the authors’ knowledge, crystallization is an effective method in phthalimide purification. Unfortunately, values of the solubility of phthalimide in solvents are very scare in previous publications. Solubility may be employed to optimise the basic design of the crystallization process and improve the purity of phthalimide which is of great significance in the purification procedure of phthalimide via the method of solvent crystallization. Thus, in order to obtain the product with high purity, investigation of the phthalimide solubility in different solvents at various temperatures and the thermodynamic properties of solution are especially necessary in industry.
The purposes of the work are to (1) determine the solubility of phthalimide in methanol, isopropanol, n-propanol, ethyl acetate, acetonitrile, i-butanol, n-butanol, toluene, acetone and ethanol at temperatures ranging from (283.15 to 318.15) K by high performance liquid chromatography (HPLC), (2) correlate solubility data using the Apelblat equation, λh equation, Wilson model and NRTL model, and (3) evaluate the thermodynamic properties for the solutions of phthalimide in different solvents.
Section snippets
Materials
Phthalimide having a mass fraction of 0.980 was purchased from Taixing Haoshen Chemical Co., Ltd. It was recrystallized three times in acetone. The content of phthalimide employed in solubility determination was 0.994 in mass fraction, which was further analysed by a high performance liquid chromatography (HPLC). The solvents were of analytical grade and used without additional purification. The detailed information of the materials employed in this work is tabulated in table 1.
Solubility determination
In the present
Solubility values
The mole fraction solubilities determined in this work for phthalimide in methanol, isopropanol, n-propanol, ethyl acetate, acetonitrile, i-butanol, n-butanol, toluene, acetone and ethanol within the temperature range from (283.15 to 318.15) K are tabulated in table 2, and plotted in FIGURE 1, FIGURE 2. Furthermore, the van’t Hoff plots of ln (x) versus inverse of absolute temperature in different solvents are graphically shown in figure 3. We can find from table 2 and FIGURE 1, FIGURE 2 that,
Conclusions
The equilibrium solubility data of phthalimide in ten organic solvents were determined experimentally at the temperatures between (283.15 and 318.15) K under 0.1 MPa by means of the high performance liquid chromatography (HPLC). The solubility values of phthalimide in the pure solvents increase with increasing temperature, but the increments are different for different solvents. At a certain temperature, the solubilities rank as acetone > ethyl acetate > (methanol, isopropanol, n-propanol,
Acknowledgements
We thank the National Natural Science Foundation of China for their support (Project number: 21406192). Furthermore, the Yangzhou City Science and Technology Bureau, China (Project number: 2012038-3 and YZ2011139), are also appreciated.
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