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This paper presents an interpretation on the behaviour of mixtures containing alkyl methanoates with n-alkanes from a structural point of view. New experimental data of molar excess properties, hE and vE, are measured at 298.15 K and 101.32 kPa for this work to complete the existing information. Mixtures corresponding to methyl methanoate ] n-alkanes showed excess quantities higher than expected because of the self-association of methyl methanoates, which decreases as the chain length/molar mass of alkyl methanoates increases. The consideration of autoassociation in methanoates, presented in this paper as an empirical relationship for its characterization as a function of number of carbon atoms of alkyl methanoate, was included as a speciÐc term in the UNIFAC model that gave excellent results in the predictions of HE, with mean di †erences smaller than 2%. In the Nitta model the association in methanoates was considered employing di †erent forms of molecular interactions but the results were not so good.

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Thermodynamic study of (alkyl esters + a,x-alkyl dihalides) II:H E m and V E m for 25 binary mixtures {xC u À 1 H 2u À 1 CO 2 C 2 H 5 + (1 À x)a,x-BrCH 2 (CH 2 ) v À 2 CH 2 Br}, where u = 1 to 5, a = 1 and v = x = 2 to 6 Abstract Excess molar enthalpies H E 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 H E 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.