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J. Chem. Inf Model. 2007, 47, 115-121
Enthalpy of Solvation Correlations for Gaseous Solutes Dissolved in Water and in
1-Octanol Based on the Abraham Model
Christina Mintz,t Michael Clark,% William E. Acree, Jr.,*,t and Michael H. Abraham
Department of Chemistry, P.O. Box 305070, University of North Texas, Denton, Texas 76203-5070,
Department of Research and Statistical Support, P.O. Box 305398, University of North Texas,
Denton, Texas 76203-5070, Department of Chemistry, University College London, 20 Gordon Street,
London, WC1H OAJ, United Kingdom
Received September 15, 2006
Data have been assembled on the enthalpies of solvation of 373 compounds in water and 138 compounds
in 1-octanol. It is shown that an Abraham solvation equation with five descriptors can be used to correlate
the experimental solvation enthalpies to within standard deviations of 3.68 kJ/mol (water) and 2.66 kJ/mol
(1-octanol). The derived correlations provide very accurate mathematical descriptions of the observed
enthalpies of solvation, which in the case of water span a range of 150 kJ/mol. Division of the experimental
values into a training set and a test set shows that there is no bias in predictions and that the predictive
capability of the correlations is better than 4 kJ/mol.
INTRODUCTION
The air-to-water and air-to-octanol partition coefficients,
Kw and KOTOH, as well as their temperature dependence, are
used in predicting the fate and transport of volatile organic
compounds (VOCs) in the environment. Of particular interest
are the processes involving the partition of VOCs from the
gas phase into natural water systems and water droplets, and
into systems containing natural organic matter. Measured air-
to-octanol partition coefficient data have been used with
success to describe the partitioning behavior of organic
compounds between the gas phase and soils,12 plants,3-7
aerosols,8-11 and human faeces.12 Temperature dependence
of Kw and KOTOH is needed to predict the effect of ambient
temperature changes on environmental phase distribution, to
explain the accumulation of VOCs in remote mountainous
regions and cold arctic climates, and to describe the release
of organic contaminants from melting ice and snow. A recent
paper13 addressed the misinterpretations that can result
whenever the temperature dependence is not taken into
account.
In order to improve the quality of experimental data used
in environmental modeling computations, Cole and Mackay'4
have developed procedures for evaluating the consistency
of experimental solubility data, air-to-water and air-to-organic
partition coefficients using known thermodynamic relation-
ships. Their "three-solubility" approach allows missing
property data to be estimated. The approach also identifies
inconsistencies in reported values. Knowledge of the tem-
perature dependence of Kw and KOTOH helps in establishing
part of the evaluation criteria.
* Corresponding author fax: (940) 565-4318; e-mail: acree@unt.edu.
t Department of Chemistry, University of North Texas.
D .epartment of Research and Statistical Support, University of North
Texas.
University College London.
To date, we have developed linear free energy correlations
for the gas-to-water coefficients:'5
log Kw = -1.271 + 0.822E 2.743S + 3.904A +
4.814B - 0.213L (1)
and gas-to-octanol partition coefficients:16
log KOTOH = -0.119 - 0.203E + 0.560S + 3.576A +
0.702B + 0.940L (2)
based on the Abraham solvation parameter model. Both
correlations pertain to a temperature of 298.15 K. The
independent variables, or descriptors, in eqs 1 and 2 are solute
properties, as we have discussed before several times.17-20
E is the solute excess molar refractivity in units of (dm3
mol-1)/10; S is the solute dipolarity/polarizability; A and B
are the solute overall or summation hydrogen bond acidity
and basicity, and L is the logarithm of the solute gas-
hexadecane partition coefficient at 298.15 K The regression
coefficients and constants (c, e, s, a, b, and l) are obtained
by regression analysis of experimental results for a given
process (i.e., a given partitioning process and so forth). For
partition coefficients involving two condensed phases, the
c, e, s, a, b, and l coefficients represent differences in the
solvent phase properties. Note that, for the gas-to-water
partition, an alternative equation in which the descriptor V
replaces L yields a slightly better correlation. ' V is the
McGowan volume in units of (dm3 mol-1)/100.
In the present study, we are expanding our considerations
to other temperatures and properties by developing Abraham
model correlations for the enthalpies of solvation of gaseous
solutes, Aso01H , in both water and 1-octanol. The derived
enthalpic correlations, when combined with eqs 1 and 2,
allow one to estimate the gas-to-water and gas-to-octanol
10.1021/ci600402n CCC: $37.00 2007 American Chemical Society
Published on Web 12/15/2006
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