Studies of partial molar volumes of alkylamine in non-electrolyte solvents: I. Alkylamines in hydrocarbons at 303.15 and 313.15 K
Introduction
We are engaged in systematic studies of thermodynamic and transport properties of solutions involving alkylamine, as they are important organic bases because of their strong electron donating capability. Transport and volumetric properties of binary liquid mixtures have been extensively studied in order to know the nature and extent of various intermolecular interactions existing between different species present in solution [1], [2], [3], [4], [5], [6], [7], [8], [9]. Much effort has gone into determination of partial molar volume and transport properties of dilute solutions in non-polar non-interacting solvent [10], [11], [12], [13], [14], [15], [16], [17]. These properties can contribute to the comprehension of liquid solutions in numerous ways, some of which will be presented below.
Many investigators [18], [19], [20], [21], [22], [23], [24], [25] have applied the widely used additivity rule at 298.15 K, not only to predict new values of partial molar volumes but also to understand the molecular basis of exhibited volumetric behaviour. Information on specific interactions, conformational effects and packing efficiencies can be extracted by the use of such simple relations.
As the hard sphere mixture is the simplest system we can deal with, we have considered this model to describe the main contribution to be considered in partial molar volumes. We used the expression derived by Lee [26] for the partial molar volume of a solute in infinitely dilute hard sphere binary mixtures. The expression was obtained from a very accurate equation of state for hard sphere mixtures [27] and only takes into account the geometrical aspect of partial molar volume. The differences calculated from experimental values were attributed to the non-sphericity of the molecules and to interactions in the solution.
Another approach consists of imagining the partial molar volume as derived from the process of making a cavity in a solvent, of a suitable size to accommodate a solute molecule, and then allowing the solute to interact with the solvent. The statistical mechanical scaled particle theory (SPT) [28], [29] produced an expression for such a volumetric cavity term that has been extensively mentioned in the literature.
A theoretical model based on a statistical mechanical derivation, which accounts for self-association and cross-association in unlike components is Extended Real Associated Solution (ERAS) model due to Heintz et al. [30], [31]. It combines the effect of association with non-associative intermolecular interaction occurring in liquid mixtures based on equation of state developed originally by Flory et al. [32]. The ERAS model has subsequently being successfully applied by many investigators to describe the excess thermodynamic properties and apparent molar volumes of associated component in polar and non-polar components [33], [34], [35], [36], [37], [38], [39], [40]. In this paper we have also applied the Flory theory/the ERAS model to estimate apparent molar volumes of mono-, di- and tri-n-alkylamines in cyclohexane and benzene solutions.
As a part of our systematic studies, in previous papers [41], [42] measurements of viscosities of dilute solutions of n-propylamine (PA), n-butylamine (BA), di-n-propylamine (DPA), di-n-butylamine (DBA), triethylamine (TEA), tri-n-propylamine (TPA), and tri-n-butylamine (TBA) in hydrocarbons and chloroalkanes have been reported. As an extension of our studies in this paper we report volumetric properties of PA, BA, DPA, DBA, TEA, TPA, and TBA in cyclohexane and benzene at 303.15 and 313.15 K.
The partial molar properties reported in the literature usually refer to standard conditions of 298.15 K and 1 atm. In this paper the contribution to partial molar volumes of the methyl, methylene, and primary, secondary, and tertiary amine groups at 303.15 and 313.15 K in cyclohexane and benzene solutions and in pure compounds have been calculated using simple additive schemes [25]. The contributions of the specific interactions to partial molar volume of presently investigated amines in benzene were then calculated using Teresawa model [20], hard sphere theory [26] and scaled particle theory [29].
Section snippets
Method
Densities ρ at 303.15 and 313.15 K were measured with Anton Paar (60/602) vibrating tube digital densimeter, thermostatted within ±0.01 K using a Heto Birkeroad ultra-thermostat. Before each series of measurements the reference samples used for calibration were redistilled degassed water and air. Accurate densities of water and air were taken from literature [43], [44]. The details of the methods and techniques used to determine densities ρ have been describe previously [5]. The results of
Results and discussion
The experimentally determined values of densities ρ for dilute solutions of amines in different solvents at different concentrations and at 303.15 and 313.15 K were fitted to polynomial equation of type
The values of A, B, and C coefficients along with standard deviations values (σ) are given in Table 2. The apparent molar volumes Vϕ,B of all solutes were calculated in the usual waywhere MB is the molar mass of solute (amine) and m the concentration of amine in
Group contributions
The focus has been placed on to estimate contributions of different groups in organic molecules at 298.15 K only [19], [24], [25]. We have studied amine solutions in cyclohexane and benzene at 303.15 and 313.15 K. Therefore, it is essential first to determine contributions to partial molar volumes of the methyl, methylene, and amine (primary, secondary and tertiary) groups at 303.15 and 313.15 K in cyclohexane and benzene solutions and in pure compounds using simple additive scheme. Different
Conclusions
- (i)
The partial molar volumes and excess partial molar volumes of amines in cyclohexane are more than that in benzene indicating specific interactions between benzene and amine molecules.
- (ii)
The partial molar volumes at infinite dilution of transference from cyclohexane to benzene, (C6H12 → C6H6) are negative.
- (iii)
The values of group contributions of NH2, NH, and N in cyclohexane and benzene are 20.33, 8.33, −5.28 cm3 mol−1 and 15.64, 5.20, −7.75 cm3 mol−1, at 303.15 K, respectively.
- (iv)
The scaled particle
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