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Investigation of a linear solvation free energy relationship between pKas of PAR and solvatochromic parameters of binarymixture ofwater-nonaqueous solvents

Jahan B.Ghasemi, Noushin Mandoumi

A linear solvation free energy relationship has been conducted to study the effects of solvent and solute properties on the acidity constants of 4- (2-pyridylazo) resorcinol (PAR) in different solvent mixtures. Dissociation constant values of PARwere collected fromthe literature in 90-0.0 (wt.%) of methanol, 70-0.0 (wt.%) of dioxane, 80-0.0(wt.%) of acetonitrile (AN) and 80-0.0 (wt.%) of dimethylformamide (DMF)mixedwithwater at 298.5K. The data set were gathered in a matrix submitted to multiple linear regression analysis in order to obtain the number of factors which affects the variation of the whole data sets. The SPSS software was used for the selection of the variables that resulted in the best-fittedmodels. Tomodel the solvatochromic parameters multiple linear regression (MLR) was applied to identify the important factors. The pKa values were correlated with just one of the Kamlet and Taft solvatochromic parameters (*) of mixtures of methanol, dioxane, acetonitrile and DMF with water. The proposed equation allows prediction of pKa values of PARin anymixture ofmethanol-water, dioxanewater, acetonitrile-water and DMF-water.