Equations for the transfer of neutral molecules and ionic species from water to organic phases

Abstract

Equations that can be used for partition coefficients of both neutral molecules and ions have been revised, and the term that is specific to ions has been re-evaluated. A new method has been devised for the determination of partition coefficients from water to organic solvents for carboxylate anions that is based on the variation of pK(a) for carboxylic acids with solvent. Using these partition coefficients, descriptors for carboxylate anions, on the same scale as descriptors for neutral molecules, have been obtained for 71 such anions. For 13 carboxylate anions in a test set, descriptors could be predicted that in turn led to predictions of 78 log P values over six water-solvent systems with an absolute error of 0.13 and a standard deviation of only 0.55 log units. Descriptors have been obtained for 26 protonated amines as a training set and descriptors predicted for 17 protonated amines as a test set. The predicted descriptors in turn led to the prediction of 18 log P values for protonated amines with an absolute error of 0.09 and a standard deviation of 0.39 log units. The carboxylate anions are the strongest monofunctional hydrogen bond bases, and the protonated amines are the strongest monofunctional hydrogen bond acids that we have studied.