The determination of air/water partition coefficients for alkyl carboxylic acids by a new indirect method

Abstract

The air/water partition coefficients of carboxylic acids, K_w, especially those of high molecular weight, are very difficult to determine directly. Values of K_w can be obtained by an indirect method as K_w = K/P where K is an air/solvent partition coefficient and P is the corresponding water/solvent partition coefficient. In the present method, gas–liquid chromatographic data and water/solvent partition data are used to obtain ‘descriptors’ of carboxylic acids that can then be used to determine the required K, P, and thus K_w values. These are reported for all the 24 n-alkyl carboxylic acids from formic acid to n-tetracosanoic acid, and for seven branched chain alkyl carboxylic acids. There is good agreement with literature values of K_w, where available, although the present data on the n-alkyl carboxylic acids is much more self consistent than the literature data.