Hydrogen bonding. Part 45.† The solubility of gases and vapours in methanol at 298 K: an LFER analysis

Abstract

Values of the Ostwald solubility coefficient of gases and vapours in methanol solvent, L^MeOH, at 298 K have been determined for 23 solutes by an indirect method in which experimental partition coefficients between methanol and hexadecane were combined with literature data on Ostwald solubility coefficients in hexadecane. Another 70 L^MeOH values were obtained from literature data and the total 93 values were correlated by the Abraham equation to give the regression, where n = 93, r² = 0.9952, sd = 0.13 and F = 3681.

The solute descriptors in eqn. (i) are: R₂ an excess molar refraction, π₂^H the dipolarity/polarisability, Σα₂^H the overall hydrogen-bond acidity, Σβ₂^H the overall hydrogen-bond basicity and log L¹⁶, where L¹⁶ is the Ostwald solubility coefficient on hexadecane at 298 K. The number of data points, or solutes, is n, the correlation coefficient is r, the standard deviation is sd and F is the F-statistic. Just as for the case of water solvent, solute dipolarity/polarisability, hydrogen-bond acidity and hydrogen-bond basicity all lead to an increase in log L, although methanol is much less acidic than water. However, contrary to the solubility of vapours in water, the log L¹⁶ descriptor now also leads to an increase in log L. Explanations for the different behaviour of water and methanol are given.

An analysis of log P values for the transfer of solutes from water to methanol also shows that bulk methanol is as strong a hydrogen-bond base as bulk water but is a much weaker hydrogen-bond acid.

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