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

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 log10Ka1 and log10Ka2 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 α (acidity), π* (dipolarity/polarizability), and β (basicity). It was found that hydrogen bond donating and hydrogen bond accepting abilities were the most predominant to change the acidity constants. Also, a relationship with the reciprocal relative permittivity was obtained based on Born's model. The hydrogen bonding interactions between solute and solvent components are mainly responsible for the change in acidity constants of bromocresol purple of binary mixtures. [ABSTRACT FROM AUTHOR]