Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Excess molar enthalpies HE m, and excess molar volumes V E m, have been determined experimentally at constant conditions of atmospheric pressure and a temperature of T = 298.15 K, for a set of 25 binary mixtures, composed of ethyl alkanoate (methanoate to pentanoate) with each of the a,x-dibromoalkanes (1,2-dibromoethane to 1,6-dibromohexane), presenting the values of excess quantities Y E m as a function of the ester composition x. Most of the mixtures presented V E m > 0, except those formed by 1,5-dibromopentane and 1,6-dibromohexane with propanoate, butanoate and ethyl pentanoate, for which V E m < 0. The five mixtures of (ethyl methanoate + a,x-dibromoalkanes) are all endothermic, although, in the other systems this endothermicity decreases slightly with the increase in the ester acid chain length, producing sigmoidal curves that reflect exo/endothermic effects in the mixing process. The results are explained on the basis of a structural model that considers the existence of several effects, some positive and some negative, which produce the previously mentioned variations in excess quantities. In all cases, the experimental values are correlated with a suitable polynomial equation. Finally, predictions of HE m are made using two versions of the UNIFAC group contribution model. The version proposed by Dang and Tassios produces unacceptable estimations, while the version of Gmehling et al. produces results closer to experimentals.