Preferential solvation in mixed solvents. 16. Mixtures of N,N-dimethylformamide or propylene carbonate with organic solvents

J. Chem. Thermodynamics 140 (2020) 105903

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Preferential solvation in mixed solvents. 16. Mixtures of N,Ndimethylformamide or propylene carbonate with organic solvents Yizhak Marcus Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

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Article history: Received 2 July 2019 Received in revised form 12 August 2019 Accepted 13 August 2019 Available online 14 August 2019 Keywords: N,N-dimethylformamide Propylene carbonate Binary liquid mixtures Preferential solvation Self-association

a b s t r a c t The preferential solvation parameters for the self-association and the mutual association of each of N,Ndimethylformamide and propylene carbonate with a co-solvent in their binary mixtures as well as the self-association of each of these components at infinite dilution in the other component as solvent have been calculated from previously reported experimental data, using the inverse Kirkwood-Buff integrals approach. Ó 2019 Elsevier Ltd.

1. Introduction N,N-dimethylformamide (henceforth denoted as DMF) and propylene carbonate (henceforth denoted as PC) are very useful solvents, but certain processes are carried out advantageously in their completely miscible mixtures with other solvents. In such cases the components of the solvent mixture generally solvate solutes preferentially, but even without added solutes, the preferential solvation of the components of the binary solvent mixtures are of interest. The method best applicable to the study of the preferential solvation in binary solvent mixtures is that using the Inverse Kirkwood-Buff Integrals [1]. These integrals of the pair correlation functions denote the probabilities of finding in the binary solvent mixture, in the present case involving each of DMF or PC, denoted by A, and the co-solvent, denoted by B, a molecule of one of the components, say A, in a specified volume around another molecule of A or a molecule of B. That is, the integrals are related to the selfor the mutual interactions of the molecules of the two components, but also to the relative sizes of these molecules. The local mole fractions, xLA|(B), for the surroundings of a cosolvent molecule B by the molecules of A and vice versa are obtained from the Kirkwood-Buff integrals GAA, GBB, and GAB and the correlation volumes Vcor A and Vcor B as described below. The difference between the local mole fraction of A, xLA(B)), and its bulk mole fraction xA yields the preferential solvation parameter: E-mail address: [email protected] https://doi.org/10.1016/j.jct.2019.105903 0021-9614/Ó 2019 Elsevier Ltd.

dxAðBÞ ¼ xLAðBÞ  xA ¼  dxBðBÞ

ð1Þ

Similarly, for the self-interaction of solvent A:

dxAðAÞ ¼ xLAðAÞ  xA ¼  dxBðAÞ

ð2Þ

2. Calculation method The Kirkwood-Buff integrals GAA, GBB, and GAB are obtained from thermodynamic data pertaining to the solvents and to their mixtures. The required thermodynamic data include the molar volumes VoA and VoB of the pure components and their isothermal compressibilities joTA and joTB. Also required as functions of the mole fractions of one of the components of the binary mixture, say xB, are the excess Gibbs energies of mixing GE = f(xB), and the excess molar volumes VE = f(xB) at the temperature of application, generally prescribed by the availability of the GE = f(xB) data. The expressions used for the calculation of the Kirkwood-Buff integrals GAA, GBB, and GAB have been recently described [2]. Another quantity that is required for obtaining the preferential solvation parameters for the binary mixed solvent is the correlation volume, Vcor, i.e., the extent in space where the local mole fractions are pertinent and the preferential solvation of a given molecule by the components of the mixture takes place. The correlation volume involves the hard sphere diameters of the solvent molecules that can be calculated according to [3]. The correlation volumes Vcor A and Vcor B around the component solvent molecules have also recently been prescribed [2].

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Y. Marcus / J. Chem. Thermodynamics 140 (2020) 105903

Finally, the preferential solvation parameters and local compositions, dxij and xLij, are related to the Kirkwood-Buff integrals and to the correlation volumes Vcor as follows:

dxAA ¼ xLAA  xA ¼ xA xB ðGAA  GAB Þ=½xA GAA þ xB GAB þ V cor A 

ð3Þ

dxAB ¼ xLAB  xA ¼ xA xB ðGAB  GBB Þ=½xA GAB þ xB GBB þ V cor B 

ð4Þ

3. Sources of the required data DMF (A) and ethyl-, chloro-, and bromobenzene and aniline (B): the GE = f(xB) data at 298.15 K are from [4] and the VE = f(xB) data are from [5].

Fig. 1. The preferential solvation parameters dx11 (filled symbols) and dx12 (empty symbols) for DMF and toluene (triangles), chlorobenzene (circles) and bromobenzene (squares).

Fig. 2. The preferential solvation parameters dx11 (filled symbols) and dx12 (empty symbols) for DMF and methanol (circles), ethanol (triangles) and 1-propanol (squares).

DMF (A) and methanol (B): the GE = f(xB) data at 313.15 K are from [6] and the VE = f(xB) data are from [7]. DMF (A) and ethanol (B): the GE = f(xB) data at 313.15 K are from [8] and the VE = f(xB) data are from [9]. DMF (A) and 1-propanol (B): the GE = f(xB) data at 313.15 K are from [10] and the VE = f(xB) data are from [11]. DMF (A) and ethyl acetate (B): the GE = f(xB) data at 298.15 K are from [12] but no VE = f(xB) data could be found, so the approximation VE = 0 and the molar volumes of the components were employed. DMF (A) and nitrobenzene (B): the GE = f(xB) data at 450 ± 18 K (isobaric data) are from [13] and the VE = f(xB) data are from [9]. PC (A) and benzene, toluene, and p-xylene (B): the GE = f(xB) data at 298.15 K are from [14] and the VE = f(xB) data are from [15].

Fig. 3. The preferential solvation parameters dx11 (filled symbols) and dx12 (empty symbols) for DMF and aniline (circles), nitrobenzene (triangles) and ethyl acetate (squares).

Fig. 4. The preferential solvation parameters dx11 (filled symbols) and dx12 (empty symbols) for PC and benzene (circles), toluene (triangles) and p-xylene (squares).

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Fig. 5. The preferential solvation parameters dx11 (filled symbols) and dx12 (empty symbols) for PC and methyl propyl ether (circles), methyl acetate (triangles) and ethyl acetate (squares).

PC (A) and dimethyl-, diethyl-, and ethylene carbonate (B): the GE = f(xB) data at 298.15 K are from [16] and the VE = f(xB) data for dimethyl- and diethyl carbonate are from [17], and those for ethylene carbonate are from [18]. PC (A) and methyl acetate, ethyl acetate and methyl propanoate (B): the GE = f(xB) data at 298.15 K are from [19] but no VE = f(xB) data could be found, so the approximation VE = 0 and the molar volumes of the components were employed. The molar volumes and the isothermal compressibilities of the pure liquid components were taken from [20]. 4. Results The preferential solvation parameters for DMF and toluene, chlorobenzene, and bromobenzene are shown in Fig. 1. Toluene tends to self-associate at large concentrations in DMF, whereas chlorobenzene and bromobenzene associate preferentially with the DMF. On the contrary, the three alkanols: methanol. ethanol, and 1-propanol, do associate preferentially with the DMF (in

Fig. 6. The preferential solvation parameters dx11 (filled symbols) and dx12 (empty symbols) for PC and dimethyl carbonate (circles), diethyl carbonate(triangles) and ethylene carbonate (squares).

decreasing order) than self-associate, as shown in Fig. 2. The preferential solvation parameters for DMF and three additional cosolvents: aniline, nitrobenzene, and ethyl acetate, are shown in Fig. 3. Aniline tends to associate with the DMF rather than selfassociate and nitrobenzene does so too, but to a lesser extent. On the contrary, ethyl acetate self-associates preferentially in DMF and does not associate with the DMF. The preferential solvation parameters for PC and benzene, toluene, and p-xylene are shown in Fig. 4. The aromatic hydrocarbons tend to self-associate rather than associate with the PC, the more so for the slightly polar toluene than the non-polar benzene and p-xylene. Fig. 5 shows the preferential solvation parameters for PC and methyl propyl ether, methyl acetate, and ethyl acetate. All the values of these parameters are rather small, in particular for the two esters in PC, but the ether does tend to self-associate at large concentrations rather than interact with the propylene carbonate. The preferential solvation parameters for PC and other carbonate esters are more interesting, in that fairly large values are attained in some combinations and rather nearly ideal interactions are seen in others in Fig. 6.

Table 1 1 1 The infinite dilution KB integrals indicating the mutual (if negative) or the self-association (if positive) of the co-solvent (G1 SS) and of DMF (GDD) and of PC (GPP). Co-solvent S

Mixed with DMF 3 1 G1 ) SS/(cm ∙mol

Benzene Toluene p-Xylene Ethylbenzene Chlorobenzene Bromobenzene Methanol Ethanol 1-Popanol Methyl propyl ether Methyl acetate Ethyl acetate Aniline Nitrobenzene Dimethyl carbonate Diethyl carbonate Ethylene carbonate

167 34 284 66 84 106

48 485 160

Mixed with PC 3 1 G1 ) DD/(cm ∙mol

3 1 G1 ) SS/(cm ∙mol

3 1 G1 ) PP/(cm ∙mol

11 142 239

341 432 432

59 66 131

12 80 95

22 52 610

96 –657 420

70 62 892 155 102 98

93 78 199

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Y. Marcus / J. Chem. Thermodynamics 140 (2020) 105903

The infinite dilution values of the Kirkwood-Buff integrals indicate the mutual- (if negative) or the self-association (if positive) of the co-solvent and of DMF and of PC as shown in Table 1.

5. Discussion In these binary solvent mixtures the main interactions are of the dispersion type with dipole-(induced)dipole interactions superimposed on them. Both DMF and PC are highly polar, their dipole moments are 3.82 and 4.94 D (1 D = 3.33564C∙m), respectively [20]. Therefore, these two solvents tend to self-associate by dipole-dipole interactions when mixed with non-polar solvents. This is shown in Table 1 in the case of PC with aromatic hydrocarbons. When mixed with polar solvents the mutual- and selfassociation compete with each other. However, self-association of the DMF is seen also in some mixtures with polar solvents (chlorobenzene, ethyl acetate and aniline) and the mutual association is not pronounced. Generally, however, both DMF and PC at infinite dilution in polar solvents are well solvated by the latter and the mutual interactions are appreciable.

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