The Electrostatic and Non-Electrostatic Interaction Affect on Acidity Constants of Bromocresol Purple in Aqueous Ethanolic Media

Abstract This work aimed to the study effect of ethanol ratios on the acidity constants of bromocresol purple. The acidity constants of BCP were determined in binary mixtures of water with ethanol containing 0, 30, 40, 50, 60, and 70% (v/v) using spectrophotometric methods. The results indicate the dependence of acidity constants on the ratio of ethanol. The values of logKa1 and logKa2 were correlated with the macroscopic (relative permittivity, ε) and microscopic Kamlet-Taft parameters (α, β, and π*) of binary mixtures. The influence of solvent on the acidity constants was analyzed in terms of the KAT parameters in order to study the solvent-solute interaction. Multiple linear regression was used to find the contribution of the microscopic parameters containing α (acidity), π* (dipolarity/polarizability), and β (basicity). It was found that α and β were the most predominant descriptors. Also, a relationship with reciprocal relative permittivity was obtained based on Born’s model, showing the significance of specific solute-solvent interactions. Therefore, the hydrogen bonding interactions between solute and solvent components are mainly responsible for the change in acidity constants of bromocresol purple of binary mixtures.