Descriptors for solutes from the solubility of solids: trans-stilbene as an example

Solubilities of trans-stilbene in 17 nonaqueous solvents are reported. Thes e may be combined with literature values for the solubility in water and fo r the vapour pressure of stilbene to give 17 values of water-solvent partit ions, P, and 17 values of gas-solvent partitions, L. Coefficients in the ge neral solvation equations (i) and (ii) are known for all 34 of these system s, together with two additional equations for gas-water partitions. In equa tions (i) and (ii), the independent variables are solute descriptors as fol lows: R-2 is an excess molar refraction, pi(2)(H) is the dipolarity/polariz ability, Sigma alpha(2)(H) and Sigma beta(2)(H) are the overall hydrogen-bo nd acidity and basicity, Vx is the McGowan characteristic volume, and log L -16 is a descriptor where L-16 is the solute L-coefficient on hexadecane at 298 K. (i) log SP = c + rR(2) + s pi(2)(H) + a Sigma alpha(2)(H) + b Sigma beta(2) (H) + nu Vx (ii) log SP = c + rR<INF>2</INF> + s pi<INF>2</INF><SUP>H</SUP> + a Sigma a lpha<INF>2</INF><SUP>H</SUP> + b Sigma beta<INF>2</INF><SUP>H</SUP> + l log L<SUP>16 </SUP>We estimate R-2 as 1.45 and calculate Vx as 1.563, and then solve the total set of 36 equations to yield pi(2)(H) = 1.04, Sigma alpha(2)(H) = 0. 00, Sigma beta(2)(H) = 0.34 and log L-16 = 7.525 units. These descriptors r eproduce the 36 observed log P and log L values with a standard deviation o f only 0.086 log units. This represents an entirely new method for determin ing solvation descriptors and is also a quite novel method for the correlat ion and estimation of solubilities.