THERMODYNAMICS OF BINARY-MIXTURES CONTAINING THIAALKANES - EXCESS-ENTHALPIES OF THIAALKANES AND POLYTHIAALKANES PLUS N-ALKANES OR CYCLOHEXANE

An LKB flow microcalorimeter has been used to determine excess enthalp ies, H(E), of mixtures of thiaalkanes, dithiaalkanes and polythiaalkan es + n-alkanes or + cyclohexane. These data, the previously measured e xcess Gibbs energies, G(E), and the data available in the literature o n G(E), H(E) and activity coefficients at infinite dilution, gamma(i)i nfinity, are examined on the basis of the DISQUAC group contribution m odel. The interaction parameters, quasi-chemical and dispersive, depen d on the environment of the S atom. There is a clear evidence for the S...S proximity effect, which produces a regular decrease in both the quasi-chemical and the dispersive interaction parameters. The model co nsistently describes the excess functions G(E) and H(E) of the investi gated thiaalkanes + n-alkanes or cyclohexane mixtures. Characteristic deviations between predicted and experimental gamma(i)infinity data ar e observed in mixtures containing molecules of widely different sizes. The present study confirms the conclusions of other authors that the replacement of one or several CH2 groups in n-alkanes by S atoms does not break the ''orientational order'' related to molecular conformatio n.