The factors that influence solubility in perfluoroalkane solvents

• Data on solvation of solutes in perfluoroalkane solvents collected.
• Gas-perfluoroalkane partition coefficients, K, analysed.
• The main influence on log K is a solute size effect.
• The size effect is a combination of cavity and interaction effects.
• Cavity effects calculated by Scaled Particle Theory.

Data on the solubility of neutral compounds in perfluoro-hexane, -heptane, and –octane have been obtained from the literature. It is shown that water-solvent and gas-solvent partition coefficients, P and K respectively, are effectively the same for all three perfluoroalkanes. Linear free energy relationships, LFERs, have been set up for these partition coefficients, as log P and log K. Comparison of the LFER coefficients in the log K equation for perfluoroheptane with those for a large number of other solvents shows that perfluoroheptane is an unusual solvent, in that small nonpolar solutes are more soluble than in other solvents. The comparative solubility of small nonpolar gaseous compounds in perfluoroheptane is due to a combination of cavity and interaction terms. Calculations using Pierotti's version of Scaled Particle Theory indicates that the solute-perfluoroheptane unfavourable cavity term is always smaller than that for solution in other solvents, which by itself would lead to enhanced solubilities in perfluoroheptane, as shown by small nonpolar solutes. As the solute becomes larger and more polar, the favourable interaction terms in other organic solvents become much larger than the corresponding interaction terms in perfluoroheptane. This results in the larger and/or more polar gaseous solutes being much more soluble in other organic solvents than in perfluoroheptane.