Prediction of gas to water partition coefficients from 273 to 373 K using predicted enthalpies and heat capacities of hydration

Abstract

In previous works, we have developed methods for the prediction of gas to water partition coefficients at 298 K, log K w (298), and for the prediction of enthalpies of transfer from the gas phase to water, that is enthalpies of hydration, Δ H w ° , using the set of Abraham descriptors. In the present work we collect data on heat capacities of hydration, Δ C p w , for 321 varied compounds and obtain equations that can be used to predict this quantity, again in terms of Abraham descriptors. If the three thermodynamic input quantities, log K w (298), Δ H w ° and Δ C p w , are all available it is trivial to predict log K w at any temperature between 273 and 373 K through equations given by Plyasunov and Shock. However, if one or more of these input quantities are unavailable, we show that predictions of these input quantities using our equations based on Abraham descriptors can be used to predict log K w at any temperature between 273 and 373 K, log K w ( T). In the most rigorous test of this method, log K w (373) values were calculated using predicted values of all three input quantities, log K w (298), Δ H w ° and Δ C p w . For 40 varied compounds covering a range of 5.5 log units in log K w (373), values of log K w (373) were predicted with an average error of −0.02, and a standard deviation of 0.16 log unit. Many other examples of predictions are given. A spreadsheet is available for the prediction of log K w ( T) values; all that is required is insertion of Abraham descriptors for a compound and the temperature. We consider polyaromatic hydrocarbons and polychlorobiphenyls separately, and show that it is possible to predict log K w ( T) for these compounds as well.