Partitioning of oxytetracycline between aqueous and organic solvents: Effect of hydrogen bonding

Abstract

Phase equilibrium behavior of antibiotics is important in drug design and for optimization of the recovery process in manufacturing. Aqueous/organic partitioning behavior of a clinically important antibiotic, oxytetracycline is measured. The organic phase includes pure solvent n-hexane, chloroform, diethyl ether and ethyl acetate. In addition, measurements are also made for mixed organic phase composed of n-hexane+ethyl acetate. Organic-phase partitioning increases with the hydrogen bonding (H-bonding) tendency of the solvent in the order n-hexane<chloroform<diethyl ether<ethyl acetate. An activity coefficient model that includes H-bonding, UNIQUAC-HB (Gupta, R.B., Kumar, R., Betageri, G.V., 1997. Ind. Eng. Chem. Res., 36, 3954–3959), is used to model the partitioning behavior between aqueous and organic phases. Single solvent-organic-phase data are correlated using the model to obtain the free-energy-of-H-bonding parameters for H-bonding between antibiotic and solvent. Predictions made for mixed-solvent-organic-phase systems agrees well with the experimental data without using any adjustable parameter.