Model for the distribution of neutral organic compounds between n-hexane and acetonitrile

Partition coefficients for 69 varied compounds were determined for the n-hexane-acetonitrile partition system and combined with 74 partition coefficients for (largely) terpenes, esters and alkylaromatic compounds determined by Isidorov and coworkers and 27 extraction p-values determined by Bowman and Beroza to derive a general model for the distribution of neutral compounds in the biphasic system. The partition coefficients, log K, were correlated through the solvation parameter model giving log K-p = 0.097 (+/- 0.049) + 0.189 (+/- 0.041) E - 1.332 (+/- 0.056) S - 1.649 (+/- 0.055)A - 0.966 (+/- 0.074) B + 0.773 (+/- 0.040) V with a multiple correlation coefficient of 0.985, standard error of the estimate 0.114, and Fischer statistic 1087. The solute descriptor E is the excess molar refraction, S is the dipolarity/polarizability, A and B are the overall hydrogen-bond acidity and basicity, respectively, and V is McGowan's characteristic volume. The model is expected to be able to estimate further values of the partition coefficient to about 0.1 log units and is applicable to a wide range of compounds except for n-alkylcarboxylic acids, which have higher partition coefficients than predicted, most likely due to the formation of oligomers (e.g. dimers) in the n-hexane layer. (c) 2005 Elsevier B.V. All rights reserved.