Journal of Solution Chemistry, Vol. 23, No. 10, 1994 Solvent Effects on the Dissociation of Aliphatic Carboxylic Acids in Water-N,N-Dimethylformamide Mixtures: Correlation Between Acidity Constants and Solvatochromic Parameters R. J. Sindreu, 1 M. L. Moy&, 1 F. S&nchez Burgos, 1 and A. G. Gonz&lez 2 Received December 30, 1994; Revised February 18, 1994 The acid dissociation constants of nine aliphatic carboxylic acids in several N~-dimethylformamide-water mixtures were subjected to factor analysis (FA) and two solvent factors emerged. A further target factor analysis (TFA) indicated that the Kamlet and Taft general equation is re- duced in these mixtures to two terms: the independent one and that re- lated to the hydrogen bond acceptor (HBA) basicity [3 solvatochromic parameter. Accordingly, an excellent correlation is found between the logarithmic values of the acidity constants of each acid in the binary mixtures and their corresponding fl values. KEY WORDS: Binary mixtures; N,N-dimethylformamide-water; solvatochromic parameters; acidity constants; factor analysis. 1. INTRODUCTION The present study is part of our research on the solvent effects of partially aqueous mixtures on the rate or equilibrium constants of chemical processes. Aside from its intrinsic value as a solvent, N,N-dimethylfor- mamide (DMF) appears to be a suitable co-solvent since it is aprotic and fully miscible with water. DMF-water mixtures are strongly non- ideal and can act in the solute-solvation process via hydrophobic in- teractions and preferential solvation.(1-2) Recently, an effort has been 1Department of Physical Chemistry, University of Seville, 41012-Seville, Spain. 2To whom correspondence should be addressed: Department of Analytical Chemis- try, University of Seville, 41012-Seville, Spain. 1101 0095-9782/94/1000-1101507.00/0 9 I994 Plenum Publishing Corporation