Experimental and statistical mechanical studies of heats of dilution of alkanols in pyridine derivatives based on ab initio calculations of hydrogen bonding energies

Experimental data of the heat of dilution of methanol and tert-butanol in 2,6-di-tert-butyl-pyridine are reported. Together with corresponding data of these alcohols in pyridine and 2,6-dimethylpyridine taken from previous work the molar heat of mixing of all six systems has been calculated in the diluted region of the alcohols. in purpose of this paper is the application of an improved version of the so-called ERAS model which is able to describe thermodynamic properties of mixtures containing selfassociating components including cross association with other components. Stepwise association of linearly associated alcohol molecules have been accounted for by differentiating between dimerization and higher associated clusters also including cyclic species, in particular tetramers. association between free OH-groups of alcohol associated with pyridine derivatives are also included into the refined model. Hydrogen bonding energies needed as parameters in the theory have been obtained from high level ab initio calculations, association constants are taken from previous work with alcohol + alkane mixtures. Finally only two parameters have to be adjusted to the experiments. The results are satisfying and clearly reveal how special steric effects of the cross association dominate the thermodynamics of the mixtures studied.