Equilibrium Solubility and Mathematical Correlation of (2-Naphthylthio)acetic Acid in Four Aqueous Cosolvency Systems at 278.15–323.15 K

Abstract

Pure solvents are often single in nature and often cannot meet the dissolution requirements of (2-naphthylthio)acetic acid. The method of adding a solvent into another solvent to form a mixed solvent improves this situation. As a common solvent, water cannot dissolve the solute in this study well, so methanol was added into water to form a liquid mixture of different compositions. At first, the ratio of methanol mass is 90% and then decreases by 10% until the methanol content is 10%. According to the above method, ethanol, isopropanol, and N,Ndimethylformamide (DMF) are made into corresponding mixed solvents. Under a pressure of 101.2 kPa, the temperature of (2-naphthylthio)acetic acid and the solvent is kept at 278.15 K. Based on the basic principle of the static gravimetric method, the amount of solute diffusion in the above four mixed solvents is obtained. Other conditions remain unchanged, but the temperature increases by 5 K and the above steps are repeated until the temperature is 323.15 K. Generally speaking, there are two variables in the experiment, one is the temperature variable and the other is the organic solvent ratio variable. Other variables remain the same, but the temperature changes to a higher level, and more (2-naphthylthio)acetic acid can be detected in the solution. Regardless of the change in the temperature variable, the larger the mass of the organic solvent, the more the solute in the solution. The above rules are applicable to the four groups of mixed solvents, but under the same conditions, the combination of DMF and water is superior in terms of dissolution. The Jouyban−Acree model, van't Hoff−Jouyban−Acree model, and modified Apelblat−Jouyban−Acree model were employed to correlate the obtained solubility. In all models, the relative average deviation (RAD) and root-mean-square deviation (RMSD) were not more than 5.30% and 6.40 × 10 −5 , respectively. The poor water solubility not only makes the (2-naphthylthio)acetic acid production process more difficult but also suffers many limitations in application because it cannot be prepared into a liquid dosage form and is inconvenient to use on many occasions.