Thermodynamics of mixtures containing amines. XI. Liquid + liquid equilibria and molar excess enthalpies at 298.15 K for N-methylaniline + hydrocarbon systems. Characterization in terms of DISQUAC and ERAS models
Highlights
► We report LLE for N-methylaniline + n-C14 or +n-C16. ► We report at 298.15 K for N-methylaniline + n-C7, +n-C8, +n-C10, +C6H12, +C7H8. ► DISQUAC and ERAS interaction parameters are given for the studied mixtures. ► Physical interactions are more relevant than those of association/solvation effects.
Introduction
The study of mixtures with amines makes possible to examine the influence of some interesting effects on their thermodynamic properties. For example, the treatment of systems with primary or secondary linear amines allows the study of the size and steric effects produced by the alkyl groups attached to the amine group. Effects related to the quasi globular shape of small N,N,N-trialkylamines can be analyzed through solutions containing these amines. On the other hand, effects related to the ring strain or to the influence of an aromatic ring may be investigated through systems containing cyclic or aromatic amines, respectively.
N-methylaniline is an aromatic secondary amine, which is weakly self-associated, as its Trouton’s constant indicates (91.1 J · mol−1 · K−1; enthalpy of vaporization, 42.8 J · mol−1 [1] at the boiling point, 469.6 K [2]). In fact, the Trouton’s constant of non-associated species is 92.05 J · mol−1 · K−1 [3], while that for 1-alkanols is 110.88 J · mol−1 · K−1 [3]. N-methylaniline is an important intermediate for dyes or agrochemical manufacturing. Interestingly, aniline polymers are widely studied due their high stability and wide range of conductivity. They are used in transistors, solar cells or light emitting diodes [4]. N-substituted polymers (Poly (N-methylaniline), e.g.) provide better solubility and processability, which is of importance in printable electronics. Poly (N-methylaniline) has been studied as cathode active material in aqueous rechargeable batteries [5].
This work is part of a series devoted to the experimental and theoretical characterization of mixtures containing amines. We have provided excess molar volumes of N,N,N-trialkylamine [6], [7], or methyl butyl amine [8] +alkane mixtures, as well as liquid + liquid and/or solid + liquid equilibrium temperatures for 2-methylaniline [9], imidazoles [10] or quinoline [11] +hydrocarbon systems. Mixtures with aniline [12], 2-methylaniline [9], pyridines [13], [14], [15], [16], quinoline [11] or imidazoles [10] or cyclic amines [17] with various solvents have been studied using different models: DISQUAC [18], [19], ERAS [20], Kirkwood–Buff integrals [21], or the formalism of the concentration-concentration structure factor [16]. As continuation of these works, we report here liquid + liquid equilibrium temperatures for N-methylaniline + tetradecane, or +hexadecane systems and molar excess enthalpies at 298.15 K and at atmospheric pressure for the mixtures N-methylaniline + heptane, +octane, +decane, +cyclohexane, or +toluene. data for systems with toluene [22] or cyclohexane [23] at T ≠ 298.15 K are available in the literature. In order to gain insight into the interactions and structure of systems formed by N-methylaniline and alkane, aromatic compound or 1-alkanol, they are studied through the application of the DISQUAC [18], [19] and ERAS [20] models. In the framework of UNIFAC (Dortmund version) [24], aniline, is a main group by itself [25], but no specific group has been defined for N-methylaniline [25], [26], [27], [28].
Section snippets
Materials
Prior to the measurements, the chemicals were stored over molecular sieves (Union Carbide Type 4 Å from Fluka). All the chemicals were used without further purification. Table 1 contains information about the source, purity, water content, determined by Karl-Fischer method, and densities, , of the pure compounds, measured using a vibrating-tube densimeter and a sound analyser, Anton Paar model DSA-5000. The uncertainty for the values is ±1·10−2 kg · m−3, while the corresponding precision is ±1·10
Experimental results
TABLE 2, TABLE 3 list the direct experimental results of and of , respectively, vs. the mole fraction of the amine, , for the investigated mixtures (see FIGURE 1, FIGURE 2, FIGURE 3, FIGURE 4). At equimolar composition, the values (toluene, 303.15 K) = 520 J · mol−1 [22] and (cyclohexane, 323.15 K) = 1780 J · mol−1 [23] are more or less consistent with those determined in this work at 298.15 K (497 and 1617 J · mol−1). The LLE coexistence curves show an UCST and have a rather flat horizontal
DISQUAC
This is a group contribution model based on the rigid lattice theory developed by Guggenheim [43]. A brief summary of the main features of DISQUAC follows. (i) The total molecular volumes, ri, surfaces, qi, and the molecular surface fractions, αi, of the compounds present in the mixture are calculated additively on the basis of the group volumes RG and surfaces QG recommended by Bondi [44]. As volume and surface units, the volume RCH4 and surface QCH4 of methane are taken arbitrarily [45]. The
Adjustment of DISQUAC interaction parameters
In the framework of DISQUAC, N-methylaniline + organic solvent mixtures are regarded as possessing the following five types of surface: (i) type a, aliphatic (CH3, CH2, in N-methylaniline, n-alkanes, toluene, or 1-alcohols); (ii) type b, aromatic (C6H6 in benzene; C6H5 in toluene or N-methylaniline); (iii) type c, c-CH2 in cyclohexane (iv) type h, OH in 1-alcohols; (v) type n, NH in N-methylaniline.
The general procedure applied in the estimation of the interaction parameters has been explained in
Theoretical results
Results from DISQUAC for LLE are compared with experimental data in figure 1. As, usually [12], [53], the coordinates of the critical points are represented by DISQUAC in the correct range of composition and temperature (table 4). Note that calculations are developed under the assumption that the excess functions are analytical close to the critical points, while the thermodynamic properties are, really, expressed in terms of scaling laws with universal critical exponents and universal scaling
Discussion
Below, we are referring to values of the excess functions at 298.15 K and equimolar composition. Inspection of table 9 shows that the values of the N-methylaniline solutions are positive. Consequently, the main contribution to comes from the disruption, upon mixing, of the interactions between like molecules.
The UCST of mixtures containing an aromatic amine and heptane decreases in the sequence: aniline (343.11 K [59]) >2-methylaniline (292.86 K [9]) >N-methylaniline (273.15 K [60]) >255.2
Conclusions
The liquid + liquid equilibrium curves have been reported for N-methylaniline + tetradecane, or +hexadecane systems. values at 298.15 K have been measured for the N-methylaniline + heptane, +octane, +decane, +cyclohexane, or +toluene mixtures. These systems together with those including 1-alkanols or benzene have been investigated by means of the DISQUAC and ERAS models. The corresponding interaction parameters have been determined. The (l = 1, 3; s = a, b, c, h) interchange coefficients are
Acknowledgements
The authors gratefully acknowledge the financial support received from the Ministerio de Ciencia e Innovación, under the Project FIS2010-16957. I.A. acknowledges the grant financed jointly by the Junta de Castilla y León and Fondo Social Europeo.
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2019, Journal of Molecular LiquidsCitation Excerpt :That is, intramolecular effects lead to enhanced interactions between like polar molecules, while intermolecular effects make usually more favourable interactions between unlike molecules (see below). With this idea, we have studied, both experimental and theoretically, intramolecular effects, also termed proximity effects, in mixtures containing aromatic amines [3–10] (anilines, 2-amino-1-methylbenzene, 1-phenylmethanamine, 1H-pyrrole, quinoline or imizadoles); phenylmethanal, 1-phenylethanone, 4-phenyl-2-butanone, benzyl ethanoate [11–14], benzonitrile, phenyl-acetonitrile, 3-phenylpropionitrile [15], 2-phenoxyethanol [16], or aromatic alkanols (phenol; phenylmethanol, 2-phenylethan-1-ol) [17–19]. As a continuation, we provide now liquid-liquid equilibria data for alkane systems involving 2-ethoxy-benzenamine (o-phenetidine) or 4-ethoxy-benzenamine (p-phenetidine).