The vapor pressure behavior and association of mixtures of 1-hexanol and n-hexane between 293 and 373 K

Abstract

Vapor pressure isotherms for mixtures of 1-hexanol and n-hexane determined between 293 and 373 K with the usual accuracy of ∼0.03 kPa can be described satisfactorily by the Wilson equations. The initial increase and final decrease of G_max^E with increasing temperature reveal that the thermodynamic behaviors associated with the more strongly self-associated compound methanol and with the relatively weakly self-associated compound methylamine are observed for the hexanol mixtures at the extremes of the temperature range studied. Correspondingly, the values for the Wilson coefficient λ₁₂ — λ₁₁ (1 = hexanol, 2 = n-hexane) as well as the values for the activity coefficients and the association energy of hexanol lie between those determined under similar conditions for methylamine and methanol. Within series of mixtures containing homologous alcohols a decrease of the difference (λ₁₂ — λ₁₁) — (λ₁₂ — λ₂₂) = λ₂₂ — λ₁₁ with increasing chain length reveals decreasing interaction between the alcohol molecules. A decrease of the coefficient λ₁₂ — λ₂₂ indicates increasing interaction between the alcohol and hexane molecules with increasing chain length. A two-constant model of association, one for dimerization and the other for formation of higher polymers, permits numerical description of the thermodynamic behavior of solutions of simple aliphatic amines, thiols and short-chain alcohols in hexane without large errors over nearly the entire composition range. Such a description is not possible for solutions of hexanol and other long-chain alcohols in hexane.