Solubility measurements of amoxicillin in mixtures of water and ethanol from 283.15 to 298.15 K

Among the various types of existing antibiotics, amoxicillin stands out as a semi synthetic penicillin widely used on a world scale. The enzymatic synthesis of amoxicillin has arisen as an alternative to the drawbacks of conventional chemical synthesis. Nevertheless, to make it feasible a wide data basis of solubility is required in different conditions of industrial interest, aiming at crystallization and subsequent purification of the antibiotic. In this case, the variables such as temperature, pH and solvent composition are of fundamental importance. This work presents solubility data of amoxicillin in aqueous media using an analytical method. The solubility measurements were carried out at 283.15–298.15 K, varying the pH between 2 and 8, and ethanol composition up to 70 wt%. Dissociation constants have also been measured at the studied values of temperature and ethanol composition, using potentiometric titration. The values of pKa demonstrated to be in agreement with the solubility behavior observed experimentally. Thus, the ideal model based on pKa values has been applied as reference for the representation of the solubility data. Furthermore, the experimental solubility and pKa data sets can be used for correlation and thermodynamic modeling purposes.