Solubilities and partition coefficients of semi-synthetic antibiotics in water+1-butanol systems

In this contribution, experimental data are presented on the solubilities a nd partition coefficients of two semi-synthetic antibiotics (amoxicillin, a mpicillin) and their precursors (D-phenylglycine, D-(p -hydroxy)phenylglyci ne, 6-aminopenicillanic acid) in water + 1-butanol mixtures at a constant t emperature of 298 K. In the aqueous phase, the solubility of amoxicillin an d ampicillin increases with increasing butanol concentration. For the other components, the solubility decreases. In the organic phase, the solubility of all components is less than that in the aqueous phase. The partition co efficients are approximately constant for all components and less than unit y, indicating the higher solubility in the aqueous phase. No influence of t he solutes on the phase behavior of the solvent system is detected. The pha se behavior is described with the g(ex) model, as suggested by Gude et al. (Gude,M. T.; Meeuwissen, H. H. J.; Van der Wielen, L. A. M.; Luyben, K. Ch. A. M. Ind. Eng. Chem. Res. 1996, 35, 4700. Gude, M. T.; Van der Wielen, L. A. RI.; Luyben, K. Ch. A. M. Fluid Phase Equilib. 1996, 116, 110), in its o riginal and in a modified version. This model, based on an excess solubilit y approach, contains a single adjustable interaction parameter that correla tes with the hydrophobicity of the solute. The description by the original model is reasonable but cannot reproduce the phase behavior in the aqueous phase of the systems containing amoxicillin and ampicillin. The modified ve rsion of the model gives a better representation of the experimentally foun d phase behavior. Unfortunately, neither model describes solubilities and p artitioning simultaneously in a quantitatively correct fashion.