Study of the Purification of Antipyrine Benzenesulfonate in a Selective Solvent
Abstract Generated abstract
This study addresses the purification of antipyrine benzenesulfonate, an intermediate in amidopyrine production, where aqueous recrystallization in batch crystallizers led to product losses and insufficient process performance. The authors experimentally determined the solubility of purified antipyrine benzenesulfonate in water, ethyl alcohol, acetone, and dioxane over a range of temperatures, using repeated thermostated measurements and constructing solubility curves from the data. Comparison of the curves and the expected impurity solubility indicated that acetone was the preferred selective solvent, since dioxane showed a sharp increase in solubility for the target compound above about 28°C.
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STUDY OF THE PURIFICATION OF ANTIPYRINE BENZENESULFONATE IN A SELECTIVE SOLVENT
M. S. Lantsman, I. P. Chapin, G. M. Khayut, N. M. Shevel, V. I. Redekop
In the production of amidopyrine, the product of the first stage is antipyrine benzenesulfonate (BSA). Under the existing batch production scheme, purification of BSA is carried out by recrystallizing it from an aqueous solution. Because of the unsatisfactory operation of batch crystallizers and the fairly high solubility of BSA in water at the crystallization end temperature, the need arose to search for a new method of purifying BSA in order to obtain a pure product with minimal losses.
One of the principal properties in selecting a purification method is the solubility of the substance in a given solvent.
Along with experimental methods, empirical expressions exist for determining solubility [1]. If, during crystallization of a substance, solvent molecules are incorporated into the crystal lattice, this is necessarily reflected in the character of the solubility curve. In the absence of a third component (impurity) in the solution, the solubility of the principal substance usually decreases, which is especially noticeable for compounds with common ions.
All the foregoing predetermined the need for an experimental determination of the solubility of BSA in certain solvents. To clarify certain factors affecting the process of selective purification, it was necessary to determine the influence of various solvents on the target product, and also to find a solvent that would dissolve impurities well without dissolving BSA, would be inexpensive and of low toxicity, and would possess certain other properties useful from a technological standpoint.
Preliminary exploratory experiments for the experiment were
the following solvents were chosen: water, ethyl alcohol, acetone, and dioxane. The solvents were selected on the basis of their properties: to dissolve the impurities to a high degree and the main substance, i.e., ABSA, to a lesser degree.
There are a number of methods for obtaining solubility curves [2], but because of a number of shortcomings, complexity, and labor-intensiveness, we adopted the following procedure, which satisfies the aims of the work.
ABSA, previously recrystallized many times from an ethyl-alcohol solution and having a melting point of \(110^\circ\mathrm{C}\), was dried to constant weight and used to determine the solubility curves. A weighed portion of ABSA of about 10 g is placed in a dried and weighed weighing bottle and is treated with a definite amount of solvent, which is determined for each temperature by preliminary experiments. The weighing bottles are placed in a thermostat and kept at the selected temperatures, with stirring, for 2 hours. Without removing the weighing bottles from the thermostat, the ABSA dissolved in the solvent is carefully decanted in order to prevent the solution from crystallizing out, i.e., from disturbing the equilibrium. The remaining undissolved ABSA, together with the weighing bottles, is dried at a temperature of \(50\text{–}60^\circ\mathrm{C}\) to constant weight, and from the difference in weights the amount of ABSA dissolved in the solvent is determined.
The experiments for each temperature were repeated five times; the experimental error lies within \(0.2\text{–}0.3\%\) by weight.
The results of the study of the solubility of ABSA in the selected solvents are presented in Table 1.
Table 1
| No. | Temperature, °C | Water | Acetone | \(n\)-Dioxane | Ethyl alcohol |
|---|---|---|---|---|---|
| 1 | 5 | 2.85 | 0.44 | 0.31 | 1.28 |
| 2 | 10 | 3.46 | 0.81 | 0.48 | 2.20 |
| 3 | 20 | 4.33 | 1.32 | 0.48 | 6.20 |
| 4 | 25 | 5.19 | 1.33 | 0.48 | 8.18 |
| 5 | 30 | 5.19 | 2.09 | 2.20 | 11.24 |
| 6 | 35 | 5.95 | 2.80 | 8.48 | 13.20 |
| 7 | 40 | 6.75 | 3.15 | 14.80 | 16.76 |
| 8 | 50 | 11.87 | 4.88 | 25.45 | 23.98 |
Average amount of dissolved ABSA in g/100 g of solvent.
On the basis of the experimental data, after processing them on the “Mir-1” electronic digital computer, solubility curves of pure ABSA were constructed, shown in Fig. 1.
Fig. 1. Solubility curves of ABSA in certain solvents: 1—ethyl alcohol; 2—dioxane; 3—water; 4—acetone.
Solubility curves can serve as a criterion for selecting a solvent. Analyzing the course of the curves and taking into account that the impurities dissolve to a greater extent in dioxane and acetone than in water and ethyl alcohol, the former may be selected; however, taking into account the large increase in the solubility of ABSA in dioxane beginning at 28°C, it is preferable to choose acetone.
Literature
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M. V. Govoin, S. I. Krasnova. Stability of supersaturated solutions of sparingly soluble salts. Ukrainian Chemical Journal, vol. 21, issue 1, 1955.