Solvent Effect on Protonation Constants of Erythromycin in Different Aqueous Solutions of Methanol and Ethanol

The protonation constants of erythromycin were measured in binary mixtures of water+metanol and water+etanol containing 0, 10, 20, 30, 40 and 50% (v/v). These measurments were done using the potentiometric method at T = 25 °C and constant ionic strength (0.1 mol.dm-3 of sodium perchlorate). The protonation constants were analyzed using Kamlet-Abboud-Taft (KAT) and normalized polarity parameters (ETN). Dual-parameter correlation of pKa versus π* (dipolarity/polarizability) and α (hydrogen-bond donor acidity) as well as pKa versus π* and β (hydrogen-bond acceptor basicity) gave a good results in mixed solvents of water+methanol and water+ethanol. There is a linear relationship between acidic dissociation constants and mole fraction of alcohol in solvent mixture water+methanol. In this research work, we discussed the solvent effect and dielectric of the area on the acidic dissociation constants of erythromycin.