Thermodynamic study of (alkyl esters + α,ω-alkyl dihalides) VI. HmE and VmE for 20 binary mixtures {xCu−1H2u−1CO2(CH2)3CH3 + (1  x)α,ω-BrCH2(CH2)v−2CH2Br}, where u = 1 to 5, α = 1, and v = ω = 2 to 6

https://doi.org/10.1016/j.jct.2009.05.006Get rights and content

Abstract

This work shows the experimental values obtained for HmE and VmE at the temperature of 298.15 K and atmospheric pressure, for a set of 20 binary mixtures comprised of the first four butyl esters (methanoate to butanoate) with five α,ω-dibromoalkanes (1,2-dibromoethane to 1,6-dibromohexane). The HmE are endothermic for mixtures with butyl methanoate, while for the other esters the HmE adopt a sigmoidal shape. The VmE are positive for mixtures with low molecular weight dibromoalkanes, becoming negative with contractive effects in the final mixture, as the dihalide chain increases. The results indicate that the mixtures present specific interactions, with simultaneous expansion/contraction and exothermic/endothermic effects, and an explanation is given for the different types of interaction taking place. Experimental data are correlated with a polynomial equation used in previous works with satisfactory results.

Modelling of the experimental results of the mixtures is carried out on the HmE values, giving rise to an adequate definition of the different interactions taking place. Two versions of the UNIFAC method were used, and for Dang and Tassios’ version different possibilities were considered for the interaction parameters of the ester (G)/dibromide (G′). The best estimations were obtained when the pair of interaction parameters, type aG/G, depended on the number of carbon atoms in the compounds constituting the mixture.

Introduction

In this work, we present data for enthalpies HmE and volumes VmE for a group of twenty mixtures of butyl alkanoates (metanoate to butanoate) with five α,ω-dibromoalkanes (α = 1, ω = 2 to 6) at a temperature of 298.15 K. Experimental data are provided for these binary systems for which no data had been previously published in the literature, in order to expand on the data obtained in previous works for similar mixtures with ethyl [1] and methyl alkanoates [2]. All this information will help to explain the behaviour and the specific interactions of dihalide mixtures. Similarly, the systematic study we present verifies the utility of the UNIFAC group contribution model in estimating the mixing properties. Two versions of the model were used, the original version [3], a specific version to estimate the HmE, and the version modified by Gmehling et al. [4], with a greater predictive capacity, but neither gave acceptable results. Recalculation of the interaction parameters with the first of the versions gave good results for the mixtures of methanoates and ethanoates, treated separately. However, when the acidic part of the alkanoate presents more carbon atoms, Cu−1H2u−1COO–, u  3, the model does not estimate enthalpic behaviour, becoming increasingly distant from experimental values as the dibromoalkane chain length increases. This loss of precision of the UNIFAC method with the increased chain length of the compounds in the mixtures has already been demonstrated in previous works.

Therefore, additional experimental data can improve not only our understanding of how these mixtures behave but can, also, provide us with a broader database in the modelling process that will permit us to verify the interaction parameters obtained for the groups characterizing the carboxylate/bromide interaction, or a mathematical formalism to be introduced that precisely represents the specificity of these systems.

Section snippets

Experimental

The products used were manufactured by Fluka or Aldrich, and were all of maximum purity. Before use, they were degasified with ultrasounds for several hours and then left for several days in the dark on a molecular Fluka 0.3 nm sieve to remove any moisture. Verification by GC gave similar values to those presented by the corresponding manufacturer. Moreover, for all the pure substances, refractive indices nD and densities ρ of the butyl esters and the α,ω-dibromoalkanes were measured at

Results and discussion

The values measured for each point of the properties (x1,HmE)and(x1,VmE) at T = 298.15 K and atmospheric pressure, are presented, respectively, in TABLE 1, TABLE 2 for the 20 mixtures studied in this work, a set of mixtures that can be represented empirically by x1Cu−1H2u−1COO(CH2)3CH3 (u = 1 to 4) + x2α,ω-BrCH2(CH2)v−2 CH2Br (v = 2 to 6). Experimental data were correlated with a simple polynomial equation, a function of the so-called active fraction, z, referring to one of the components of the

Application of the UNIFAC model

An important aspect of this broad project with alkyl dihalides, consists in analysing the efficacy of the UNIFAC group contribution model and its subsequent modification. To do this, it was considered appropriate to analyse the two main versions of the model, that of Dang and Tassios [3] to estimate the HmE and the one of Gmehling et al. [4], with a wider predictive capacity, but which usually gives reasonably acceptable results. The application of both versions of the model was done

Acknowledgement

The authors thank to Spanish Ministry of Education the support conceded to the research project PPQ2006-12027.

References (15)

  • J. Ortega et al.

    J. Chem. Thermodyn.

    (2006)
  • J. Ortega et al.

    J. Chem. Thermodyn.

    (2007)
  • J. Ortega et al.

    J. Chem. Thermodyn.

    (2006)
  • J. Ortega et al.

    J. Chem. Thermodyn.

    (2005)
  • J. Ortega et al.

    J. Chem. Thermodyn.

    (2007)
  • J. Ortega et al.

    Fluid Phase Equilibr.

    (1995)
  • J. Dang et al.

    Ind. Eng. Chem. Process Des. Dev.

    (1986)
There are more references available in the full text version of this article.
View full text