Linear alkyl–alkanoates+cyclohexane mixtures. Excess enthalpies measurements and DISQUAC analysis of thermodynamic properties

Abstract

The molar excess enthalpies ( H E), at 298.15 K and atmospheric pressure, of fourteen mixtures of alkyl–alkanoates with cyclohexane have been measured using a flow calorimeter LKB. These data along with the literature data on molar excess enthalpies, H E, and molar excess Gibbs energies, G E, of mixtures in cyclohexane of alkyl–alkanoates of general formula, H(CH 2) u –COO–(CH 2) v−1 CH 3 are treated in the framework of DISQUAC, an extended group contribution model. The systems are characterized by three types of contact surfaces: carboxylate (COO group), aliphatic (CH 3 or CH 2 groups) and cyclohexane (c-CH 2, group). The three types of surface, a, c, k generate three pairs of contacts (ac), (ak) and (ck). The interchange energies parameters of the aliphatic/cyclohexane and aliphatic/carboxylate contacts were determined previously, the interaction parameters of the cyclohexane/carboxylate contacts are reported in this work. The interchange energy parameters depend on the environment of the carboxylate group, the number of alkyl groups adjacent to the COO group. The dispersive parameters increase or remain constant whereas the quasi-chemical parameters decrease with the n-alkyl chain of the alkyl–alkanoate. The model provides a fairly consistent description of the experimental data as a function of concentration.