Thermodynamic study of (alkyl esters+α,ω-alkyl dihalides) II: and for 25 binary mixtures {xCu−1H2u−1CO2C2H5+(1−x)α,ω-BrCH2(CH2)v−2CH2Br}, where u=1 to 5, α=1 and v=ω=2 to 6

Abstract

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.

Thermodynamic study of (alkyl esters+α,ω-alkyl dihalides) IV: for 25 binary mixtures {xCu−1H2u−1CO2CH3+(1−x)α,ω-BrCH2(CH2)v−2CH2Br}, where u=1 to 5, α=1 and v=ω=2 to 6

“…Another relevant aspect that should be taken into account when analysing the results, is the increase in H E m and the reduction of the effects on V E m with increased chain length v of the dibromoalkane, a,x-BrCH 2 (CH 2 ) vÀ2 CH 2 Br, see figure 3(a), for a same ester. All this is consistent with the results of a previous work [1] for ethyl esters. The reduction in H E m would be explained by the overall decreasing in the contact surfaces between the molecules of the initial substances and of the substances in the mixture; since the increase in v stabilizes the dibromoalkane by the attractions of van der Waals.…”

“…The values of both quantities obtained for methyl esters are shown in table 1, while, those obtained for a,x-dibromoalkanes were very similar to those of a previous publication [1], so have not been reported here. The comparison of experimental values for methyl esters and those published in the literature is acceptable in all cases.…”

“…The enthalpies, which were almost all endothermic at low ester concentrations, diminished quasi-exponentially with the length of the methyl ester chain, giving rise to greater net values than those corresponding to the mixtures with ethyls. This is only to be expected, taking into account the previously known [1,[5][6][7] behaviour of esters in solution.…”

“…In a previous study [1], experimental data of H E m and V E m were measured at a constant temperature of 298.15 K for mixtures of the same dibromoalkanes used in this study and the first five ethyl esters (methanoate to pentanoate). In the current literature, there are a series of studies on mixtures of mono and dibromoalkanes with other compounds [2][3][4][5][6][7].…”

“…Hence, the values of excess enthalpies H E m , and excess volumes V E m , are presented as a function of the ester composition, at T = 298.15 K, of the following set of systems {methyl esters (methanoate to pentanoate)(1) + a,x-dibromoalkanes (a = 1, x = 2 to 6)}. For a better analysis of experimental values these will be correlated with a polynomial equation, on the basis of the so-called in previous papers [1] the active fraction z of compounds 1 and 2 involved. This, in turn, will depend on the surfaces or volumes in contact, depending on whether these are to be applied to H E m or V E m , respectively.…”