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Enthalpy of solution of hexaglyme in mixtures of water with N,N-dimethylformamide at 298.15 K
Journal of Molecular Liquids 199 (2014) 224–226
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Short Communication
Enthalpy of solution of hexaglyme in mixtures of water with N,N-dimethylformamide at 298.15 K Małgorzata Jóźwiak a,⁎, Andrzej Jóźwiak b a b
University of Lodz, Faculty of Chemistry, Department of Physical Chemistry, Pomorska 165, 90-236 Lodz, Poland University of Lodz, Faculty of Chemistry, Department of Organic Chemistry, Tamka 12, 91-403 Lodz, Poland
a r t i c l e
i n f o
Article history: Received 2 July 2014 Received in revised form 29 August 2014 Accepted 8 September 2014 Available online 11 September 2014
a b s t r a c t The enthalpies of solution of hexaglyme in water–N,N-dimethylforamide mixtures have been measured at 298.15 K. To analyze the process of hydrophobic hydration the cage model proposed by Mastroianni, Pical and Lindenbaum was used. The enthalpic effect of hydrophobic hydration of hexaglyme in water has been calculated. © 2014 Elsevier B.V. All rights reserved.
Keywords: Hexaglyme Water–N,N-dimethylforamide mixtures Enthalpy of solution Hydrophobic hydration
1. Introduction Linear polyethers known as glymes with their general formula CH3O(CH2CH2O)nCH3 constitute an interesting class of compounds. They are used in many areas of science and industry, mainly as a solvent but also as ligands in complexes [1–9]. Glymes have hydrophilic and hydrophobic groups in the molecules. Therefore, in water or in mixed aqueous-organic solvents, they are hydrophobically hydrated by water. The process of hydrophobic hydration plays a very important role in nature and has not yet been fully investigated. Therefore, the study of this process is of great importance. The literature offers just few publications on the hydrophobic hydration of glymes [9,10]. In our previous paper [10], the process of hydrophobic hydration of monoglyme, diglyme, triglyme, tetraglyme and pentaglyme in the mixtures of water and N,N-dimethylformamide (DMF + W) at 298.15 K was examined and the enthalpic effect of hydrophobic hydration of these compounds was calculated using the cage model of hydrophobic hydration [11,12]. It seemed appropriate to investigate the hexaglyme (Fig. 1), the next glyme of homologous series and compare the results with those given in previous publications. In this paper we present the solution enthalpy of hexaglyme in DMF + W at 298.15 K. As before, for our studies we chose a mixture of DMF with water as a solvent. DMF is a neutral solvent from the point of view of the hydrophobic and hydrophilic properties; these properties almost undergo compensation. Thus, this solvent in the mixture with water meets the ⁎ Corresponding author. E-mail address: [email protected] (M. Jóźwiak).
http://dx.doi.org/10.1016/j.molliq.2014.09.017 0167-7322/© 2014 Elsevier B.V. All rights reserved.
assumptions of Mastroianni et al.'s cage model of hydrophobic hydration [11,12] used in the presented paper. The DMF + W mixture can be used to study the pure effect of hydrophobic hydration of compounds showing hydrophobic properties [13]. 2. Experimental section 2.1. Materials 2,5,8,11,14,17,20-Heptaoxahenicosane (hexaethylene glycol dimethyl ether) was prepared from 2-methoxyethanol and tetraethylene glycol ditosylate. 2-Methoxyethanol (5.33 g, 0.07 mol, Aldrich) was added to a stirred suspension of sodium hydroxide (6.00 g, 0.15 mol) in THF (300 ml) under argon atmosphere. After 1 h, tetraethylene glycol ditosylate was added to the mixture (obtained as described previously [14] 15.08 g, 0.03 mol) in THF (150 ml) dropwise over 1 h and stirring was continued for 50 h at 66 °C. The precipitate was separated and washed with THF (3 × 50 ml). The filtrate was concentrated under a reduced pressure to obtain crude hexaethylene glycol dimethyl ether that was then purified by Kugelrohr distillation (oil bath 215–220 °C, 2.0 Torr; ref. [15], 145–149 °C 0.6 Torr; 5.22 g, yield 56%). 1H NMR (CDCl3, 600 MHz): δ = 3.65–3.52 (24H, m, \OCH2CH2\), 3.36 (6H, s, \OCH3). 1H NMR spectra were recorded on a Bruker Advance III spectrometer at 600 MHz and referenced to the residual CDCl3 signal at 7.26 ppm. The purity of the compound is 0.99 mole fraction and was determined with a TG DSC 111 (SETARAM) with indium as a standard. N,N-dimethylformamide (Aldrich, anhydrous, 99.8%) was purified and dried according to the procedures described in the literature [16, 17]. To prepare the aqueous solutions doubly distilled water was used.
M. Jóźwiak, A. Jóźwiak / Journal of Molecular Liquids 199 (2014) 224–226
225
Fig. 1. The molecule of hexaglyme.
The enthalpy of solution of hexaglyme in the DMF + W mixtures was performed at (298.15 ± 0.01) K using an “isoperibol” type calorimeter as described in the literature. [18]. The calorimeter was verified on the basis of the standard enthalpy of solution of urea and KCl (Calorimetric standard US, NBS) in water at (298.15 ± 0.005) K [19,20] as was described in our recent publication [21]. The concentration of hexaglyme in the mixtures was from 0.00168 to 0.00416 mol kg− 1 (the mole per kilogram of solvent). Six to eight independent measurements were performed for each investigation system. The uncertainties in the measured enthalpies did not exceed ± 0.5% of the measured value. No concentration dependence (outside the error limits) of the measured enthalpies of solution was observed within the examined range of hexaglyme content. For this reason, the standard solution enthalpy ΔsolHo was calculated as a mean value of the measured enthalpies (Table 1).
Δ
2.2. Methods
3. Results and discussion The transfer enthalpies of hexaglyme from water to DMF + W mixtures are presented in Fig. 2 as a mole fraction of water (xw) in the mixture. For comparison, Fig. 2 shows the transfer enthalpies of monoglyme, diglyme, triglyme, tetraglyme and pentaglyme from water to DMF + W mixtures. As seen in Fig. 2, the dissolution enthalpy curves of glymes run according to a similar course. It is characterized by an almost linear course of the function (ΔsolHo) from the value in pure organic solvent, and then, beyond the maximum, strong decrease of ΔsolHo values within the water-rich region. The drop in the exothermic dissolution effect along with the increase of the water content in the mixed solvent is connected with the hydrophobic hydration of glymes. The maximum at xw ≈ 0.5 is connected with the structure of mixed solvent DMF + W. In this region of mixture composition the interactions between molecules being mixture components are the strongest. DMF molecules react with water molecules through the formation of weak hydrogen bonds, but the structures formed are not characterized in detail. The wider discussion on this topic is presented in our previous papers [22,23].
Table 1 Standard dissolution enthalpy of hexaglyme in DMF + W mixtures at 298.15 K. xw
ΔsolHo/kJ mol−1
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.92 0.94 0.96 0.98 1.00
−3.18 −1.77 −0.38 1.00 2.02 2.46 0.98 −5.10 −17.00 −34.82 −39.25 −43.39 −48.27 −54.05 −60.52
xw — the mole fraction of water in the mixtures. ± is the standard deviation.
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.04 0.06 0.08 0.07 0.05 0.05 0.08 0.05 0.03 0.03 0.03 0.03 0.02 0.02 0.02
Fig. 2. The transfer enthalpy of glymes: monoglyme, ■; diglyme, ●; triglyme, ▲; tetraglyme, ▼; pentaglyme, ♦; and hexaglyme,◄ from water to DMF + W mixtures at 298.15 K as a function of the mole fraction of water (xw) at 298.15 K.
Fig. 2 analysis showed that for each mixed solvent composition transfer enthalpy of glymes from water to the mixed solvent depends linearly on the number of n—CH2 CH2 — groups (n—CH2 CH2 — is the number of \CH2CH2\ groups in the glyme molecules) with high regression coefficient. However, the analysis of coefficients of linear functions, as well as the regression coefficient and the standard deviation does not give interesting conclusions. Using the standard molar enthalpies of solution of hexaglyme in DMF + W, ΔsolHo, and the cage model of hydrophobic hydration [11, 12], the enthalpic effect of hydrophobic hydration, Hb(W), of hexaglyme was determined. As described in our earlier publications [24], using the diagrams of the standard dissolution enthalpies of hexaglyme, the values of dissolution enthalpy of the hypothetical substances with no hydrophobic hydration were determined graphically, ΔsolHo(W*) [25]. The enthalpic effect of hydrophobic hydration in water, Hb(W) was calculated using Eq. (1).
o
o
HbðWÞ ¼ Δsol H ðWÞ−Δsol H W
ð1Þ
where ΔsolHo(W) is the standard enthalpy of solution in water and ΔsolHo(W*) is the solution enthalpy of the solute in water when hydrophobic effect is absent. The value of the enthalpic effect of hydrophobic hydration of hexaglyme in water calculated in this way, Hb(W), is equal to (− 71.28 ± 0.06) kJ mol−1. Using analogous values for monoglyme, diglyme, triglyme, tetraglyme and pentaglyme, the function Hb(W) = f(n—CH2 CH2 — ) is presented in Fig. 3. As shown in Fig. 3, the relationship
226
M. Jóźwiak, A. Jóźwiak / Journal of Molecular Liquids 199 (2014) 224–226
References
Fig. 3. The enthalpic effect of hydrophobic hydration of glymes in water, Hb(W), as a function of number of \CH2CH2\ groups in the molecules.
is linear (Eq. (2)) with regression coefficient, R2, and standard deviation, SD. HbðWÞ ¼ –18:94ð0:42Þ–8:68ð0:11Þ n—CH2 CH2 —
ð2Þ
2
R ¼ 0:99938 SD ¼ 0:45423 This indicates that with the increase in the polyether chain, the enthalpic effect of hydrophobic hydration increases. Moreover, the interaction of glyme molecules with DMF molecules in pure DMF and with water molecules in pure water is also linearly dependent on the chain length of glymes. This is illustrated by the linear relationship of the dissolution enthalpy of glymes as a function of oxygen atoms in the glyme molecules, Eqs. (3) and (4), respectively. o
Δsol H ðDMFÞ ¼ 0:19ð0:05Þ–0:56ð0:01Þ n—CH2 CH2 — 2
R ¼ 0:99810
ð3Þ
SD ¼ 0:05111
o
Δsol H ðWÞ ¼ –14:98ð0:65Þ–7:68ð0:17Þ n—CH2 CH2 —
ð4Þ
2
R ¼ 0:99812 SD ¼ 0:69769 It is known that glyme molecules can form hydrogen bonds with water molecules [25]. The contribution of these interactions is important in the analysis of the solvation enthalpy. Barannikov et al. [9] discussed in their publication the participation of hydrogen bonds between the oxygen atoms in the glyme molecules and water and hydrophobic hydration in the enthalpy of solvation. According to the authors, the role of these contributions is debatable. 4. Conclusion Enthalpic effects of the hydrophobic hydration of monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme are directly proportional to the length of the chain in the glyme molecules. The interactions between glyme molecules (monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme) and water molecules as well as glyme molecules and DMF molecules are dependent on the length of the chain in the glyme molecules.
[1] D. Salavera, K.R. Patil, A. Coronas, Thermal conductivity measurement of polyglycol alkyl ethers at temperatures from (303.15 to 393.15) K, J. Chem. Eng. Data 55 (2010) 1440–1452. [2] N.R. Dhumal, S.P. Gejji, Theoretical studies in local coordination and vibrational spectra of M+CH3O(CH2CH2O)nCH3 (n = 2–7) complexes (M = Na, K, Mg and Ca), Chem. Phys. 323 (2006) 595–605. [3] H.J. Buschmann, E. Schollmeyer, The complex formation of non-cyclic polyethers and crown ethers with Ag+ in acetone and propylene carbonate studied by potentiometric and calorimetric methods, J. Electroanal. Chem. 474 (1999) 188–191. [4] K. Hayamizu, E. Akiba, T. Bando, Y. Aihara, 1H, 7Li and 19F nuclear magnetic resonance and ionic conductivity studies for liquid electrolytes compound of glymes and polyetheneglycol dimethyl ethers of CH3O(CH2CH2O)nCH3 (n = 3–50) moped with Lin(SO2CF3)2, J. Chem. Phys. 117 (2002) 5929–5939. [5] K. Kusano, J. Suurkuusk, I. Wadsö, Thermochemistry of solutions of biochemical model compounds. 2. Alkoxyethanols and 1,2-dialkoxyethanes in water, J. Chem. Thermodyn. 5 (1973) 757–767. [6] K. Ng, A. Rosenberg, M. Bartos, I. Wadsö, Heat capacity of poly(ethylene glycol)– water mixtures: poly(ethylene glycol)–water interactions, Thermochim. Acta 169 (1990) 339–346. [7] G. Nichols, J. Orf, S.M. Reiter, J. Chickos, G.W. Gokel, The vaporization enthalpies of some crown and polyethers by correlation gas chromatography, Thermochim. Acta 346 (2000) 15–28. [8] R.B. Sharma, A.T. Blades, P. Kebarle, Protonation of polyethers, glymes and crown ethers, in the gas phase, J. Am. Chem. Soc. 106 (1984) 510–516. [9] V.P. Barannikov, S.S. Guseynov, A.I. Vyugin, Thermochemical behaviour of straightchain ethers CH3O(CH2CH2O)nCH3 (n = 1–4) in aqueous and tetrachlormethane solutions, Thermochim. Acta 469 (2008) 23–27. [10] M. Jóźwiak, M.A. Kosiorowska, A. Jóźwiak, Enthalpy of solvation of monoglyme, diglyme, triglyme, tetraglyme and pentaglyme in the mixtures of water with N,Ndimethylformamide at 298.15 K, J. Chem. Eng. Data 55 (2010) 5941–5945. [11] M.J. Mastroianni, M.J. Pikal, S. Lindenbaum, Effect of dimethyl sulfoxide, urea, guanidine hydrochloride, and sodium chloride on hydrophobic interactions. Heats of dilution of tetrabutylammonium bromide and lithium bromide in mixed aqueous solvent systems, J. Phys. Chem. 76 (1972) 3050–3057. [12] R.W. Balk, G. Somsen, Preferential solvation and hydrophobic hydration of polyols in mixtures of water and N,N-dimethylformamide, J. Phys. Chem. 89 (1985) 5093–5097. [13] C. de Visser, G. Somsen, Hydrophobic interactions in mixtures of N,Ndimethylformamide and water. model calculations and enthalpies of solution, J. Phys. Chem. 78 (1974) 1719–1722. [14] M. Ouchi, Y. Inoue, T. Kanzaki, T. Hakushi, Molecular design of crown ethers. 1. Effects of methylene cain length: 15- to 17-crown-5 and 18- to 22 crown-6, J. Org. Chem. 49 (1984) 1048–1412. [15] G. Chaput, G. Jeminet, J. Juillard, Constantes d'association de quelques ethers de polyethylene glycols avec Na+, K+, Cs+ et Tl+, Can. J. Chem. 53 (1975) 2240–2246. [16] S.C. Chan, J.P. Valleau, Ultrasonic study of hydrochloric acid association in N,Ndimethylformamide, Can. J. Chem. 46 (1968) 853–858. [17] C.D. Schmulbach, R.S. Drago, Molecular addition compounds of iodine. III. An infrared investigation of the interaction between dimethylacetamide and iodine, J. Am. Chem. Soc. 82 (1960) 4484–4487. [18] H. Piekarski, D. Waliszewski, Hydration effect on urea-non-electrolyte enthalpic pair interaction coefficients. Dissolution enthalpies of urea in aqueous solution of alkoxyethanols at 298.15 K, Thermochim. Acta 258 (1995) 67–76. [19] R. Sabbah, A. Xu-wu, J.S. Chickos, M.L. Planas Leitão, M.V. Roux, L.A. Torres, Reference materials for calorimetry and differential thermal analysis, Thermochim. Acta 331 (1999) 93–204. [20] I. Wadsö, R.N. Goldberg, Standards in isothermal microcalorimetry (IUPAC technical report), Pure Appl. Chem. 73 (2001) 1625–1639. [21] M. Jóźwiak, L. Madej-Kiełbik, Effect of temperature on the process of complex formation crown ether 15C5 with Na+ in the (water + ethanol) mixture at temperatures from (293.15 to 308.15)K, Thermochim. Acta 580 (2014) 13–19. [22] M. Jóźwiak, M. Tyczyńska, Volumetric properties of urea in the mixture of N,Ndimethylformamide with water, J. Chem. Eng. Data 57 (2012) 2067–2075. [23] M. Tyczyńska, M. Jóźwiak, Apparent and partial molar volumes of 18-crown-6 in the mixture of N,N-dimethylformamide with water, J. Mol. Liq. 195 (2014) 80–86. [24] M. Jóźwiak, Thermal behaviour of crown ethers in the mixtures of water with organic solvents. Part II. Enthalpy of solution of benzo-15-crown-5 ether in the mixtures of water and DMSO, DMF, DMA and HMPA at 298.15 K, J. Mol. Liq. 81 (1999) 261–268. [25] P. Bernal, A. Bunn, J. Logan, J. McCluan, Apparent molar volumes and adiabatic compressibilities of crown ethers and glymes in aqueous solutions at various temperatures, J. Solut. Chem. 29 (2000) 651–663.
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Short Communication
Enthalpy of solution of hexaglyme in mixtures of water with N,N-dimethylformamide at 298.15 K Małgorzata Jóźwiak a,⁎, Andrzej Jóźwiak b a b
University of Lodz, Faculty of Chemistry, Department of Physical Chemistry, Pomorska 165, 90-236 Lodz, Poland University of Lodz, Faculty of Chemistry, Department of Organic Chemistry, Tamka 12, 91-403 Lodz, Poland
a r t i c l e
i n f o
Article history: Received 2 July 2014 Received in revised form 29 August 2014 Accepted 8 September 2014 Available online 11 September 2014
a b s t r a c t The enthalpies of solution of hexaglyme in water–N,N-dimethylforamide mixtures have been measured at 298.15 K. To analyze the process of hydrophobic hydration the cage model proposed by Mastroianni, Pical and Lindenbaum was used. The enthalpic effect of hydrophobic hydration of hexaglyme in water has been calculated. © 2014 Elsevier B.V. All rights reserved.
Keywords: Hexaglyme Water–N,N-dimethylforamide mixtures Enthalpy of solution Hydrophobic hydration
1. Introduction Linear polyethers known as glymes with their general formula CH3O(CH2CH2O)nCH3 constitute an interesting class of compounds. They are used in many areas of science and industry, mainly as a solvent but also as ligands in complexes [1–9]. Glymes have hydrophilic and hydrophobic groups in the molecules. Therefore, in water or in mixed aqueous-organic solvents, they are hydrophobically hydrated by water. The process of hydrophobic hydration plays a very important role in nature and has not yet been fully investigated. Therefore, the study of this process is of great importance. The literature offers just few publications on the hydrophobic hydration of glymes [9,10]. In our previous paper [10], the process of hydrophobic hydration of monoglyme, diglyme, triglyme, tetraglyme and pentaglyme in the mixtures of water and N,N-dimethylformamide (DMF + W) at 298.15 K was examined and the enthalpic effect of hydrophobic hydration of these compounds was calculated using the cage model of hydrophobic hydration [11,12]. It seemed appropriate to investigate the hexaglyme (Fig. 1), the next glyme of homologous series and compare the results with those given in previous publications. In this paper we present the solution enthalpy of hexaglyme in DMF + W at 298.15 K. As before, for our studies we chose a mixture of DMF with water as a solvent. DMF is a neutral solvent from the point of view of the hydrophobic and hydrophilic properties; these properties almost undergo compensation. Thus, this solvent in the mixture with water meets the ⁎ Corresponding author. E-mail address: [email protected] (M. Jóźwiak).
http://dx.doi.org/10.1016/j.molliq.2014.09.017 0167-7322/© 2014 Elsevier B.V. All rights reserved.
assumptions of Mastroianni et al.'s cage model of hydrophobic hydration [11,12] used in the presented paper. The DMF + W mixture can be used to study the pure effect of hydrophobic hydration of compounds showing hydrophobic properties [13]. 2. Experimental section 2.1. Materials 2,5,8,11,14,17,20-Heptaoxahenicosane (hexaethylene glycol dimethyl ether) was prepared from 2-methoxyethanol and tetraethylene glycol ditosylate. 2-Methoxyethanol (5.33 g, 0.07 mol, Aldrich) was added to a stirred suspension of sodium hydroxide (6.00 g, 0.15 mol) in THF (300 ml) under argon atmosphere. After 1 h, tetraethylene glycol ditosylate was added to the mixture (obtained as described previously [14] 15.08 g, 0.03 mol) in THF (150 ml) dropwise over 1 h and stirring was continued for 50 h at 66 °C. The precipitate was separated and washed with THF (3 × 50 ml). The filtrate was concentrated under a reduced pressure to obtain crude hexaethylene glycol dimethyl ether that was then purified by Kugelrohr distillation (oil bath 215–220 °C, 2.0 Torr; ref. [15], 145–149 °C 0.6 Torr; 5.22 g, yield 56%). 1H NMR (CDCl3, 600 MHz): δ = 3.65–3.52 (24H, m, \OCH2CH2\), 3.36 (6H, s, \OCH3). 1H NMR spectra were recorded on a Bruker Advance III spectrometer at 600 MHz and referenced to the residual CDCl3 signal at 7.26 ppm. The purity of the compound is 0.99 mole fraction and was determined with a TG DSC 111 (SETARAM) with indium as a standard. N,N-dimethylformamide (Aldrich, anhydrous, 99.8%) was purified and dried according to the procedures described in the literature [16, 17]. To prepare the aqueous solutions doubly distilled water was used.
M. Jóźwiak, A. Jóźwiak / Journal of Molecular Liquids 199 (2014) 224–226
225
Fig. 1. The molecule of hexaglyme.
The enthalpy of solution of hexaglyme in the DMF + W mixtures was performed at (298.15 ± 0.01) K using an “isoperibol” type calorimeter as described in the literature. [18]. The calorimeter was verified on the basis of the standard enthalpy of solution of urea and KCl (Calorimetric standard US, NBS) in water at (298.15 ± 0.005) K [19,20] as was described in our recent publication [21]. The concentration of hexaglyme in the mixtures was from 0.00168 to 0.00416 mol kg− 1 (the mole per kilogram of solvent). Six to eight independent measurements were performed for each investigation system. The uncertainties in the measured enthalpies did not exceed ± 0.5% of the measured value. No concentration dependence (outside the error limits) of the measured enthalpies of solution was observed within the examined range of hexaglyme content. For this reason, the standard solution enthalpy ΔsolHo was calculated as a mean value of the measured enthalpies (Table 1).
Δ
2.2. Methods
3. Results and discussion The transfer enthalpies of hexaglyme from water to DMF + W mixtures are presented in Fig. 2 as a mole fraction of water (xw) in the mixture. For comparison, Fig. 2 shows the transfer enthalpies of monoglyme, diglyme, triglyme, tetraglyme and pentaglyme from water to DMF + W mixtures. As seen in Fig. 2, the dissolution enthalpy curves of glymes run according to a similar course. It is characterized by an almost linear course of the function (ΔsolHo) from the value in pure organic solvent, and then, beyond the maximum, strong decrease of ΔsolHo values within the water-rich region. The drop in the exothermic dissolution effect along with the increase of the water content in the mixed solvent is connected with the hydrophobic hydration of glymes. The maximum at xw ≈ 0.5 is connected with the structure of mixed solvent DMF + W. In this region of mixture composition the interactions between molecules being mixture components are the strongest. DMF molecules react with water molecules through the formation of weak hydrogen bonds, but the structures formed are not characterized in detail. The wider discussion on this topic is presented in our previous papers [22,23].
Table 1 Standard dissolution enthalpy of hexaglyme in DMF + W mixtures at 298.15 K. xw
ΔsolHo/kJ mol−1
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.92 0.94 0.96 0.98 1.00
−3.18 −1.77 −0.38 1.00 2.02 2.46 0.98 −5.10 −17.00 −34.82 −39.25 −43.39 −48.27 −54.05 −60.52
xw — the mole fraction of water in the mixtures. ± is the standard deviation.
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.04 0.06 0.08 0.07 0.05 0.05 0.08 0.05 0.03 0.03 0.03 0.03 0.02 0.02 0.02
Fig. 2. The transfer enthalpy of glymes: monoglyme, ■; diglyme, ●; triglyme, ▲; tetraglyme, ▼; pentaglyme, ♦; and hexaglyme,◄ from water to DMF + W mixtures at 298.15 K as a function of the mole fraction of water (xw) at 298.15 K.
Fig. 2 analysis showed that for each mixed solvent composition transfer enthalpy of glymes from water to the mixed solvent depends linearly on the number of n—CH2 CH2 — groups (n—CH2 CH2 — is the number of \CH2CH2\ groups in the glyme molecules) with high regression coefficient. However, the analysis of coefficients of linear functions, as well as the regression coefficient and the standard deviation does not give interesting conclusions. Using the standard molar enthalpies of solution of hexaglyme in DMF + W, ΔsolHo, and the cage model of hydrophobic hydration [11, 12], the enthalpic effect of hydrophobic hydration, Hb(W), of hexaglyme was determined. As described in our earlier publications [24], using the diagrams of the standard dissolution enthalpies of hexaglyme, the values of dissolution enthalpy of the hypothetical substances with no hydrophobic hydration were determined graphically, ΔsolHo(W*) [25]. The enthalpic effect of hydrophobic hydration in water, Hb(W) was calculated using Eq. (1).
o
o
HbðWÞ ¼ Δsol H ðWÞ−Δsol H W
ð1Þ
where ΔsolHo(W) is the standard enthalpy of solution in water and ΔsolHo(W*) is the solution enthalpy of the solute in water when hydrophobic effect is absent. The value of the enthalpic effect of hydrophobic hydration of hexaglyme in water calculated in this way, Hb(W), is equal to (− 71.28 ± 0.06) kJ mol−1. Using analogous values for monoglyme, diglyme, triglyme, tetraglyme and pentaglyme, the function Hb(W) = f(n—CH2 CH2 — ) is presented in Fig. 3. As shown in Fig. 3, the relationship
226
M. Jóźwiak, A. Jóźwiak / Journal of Molecular Liquids 199 (2014) 224–226
References
Fig. 3. The enthalpic effect of hydrophobic hydration of glymes in water, Hb(W), as a function of number of \CH2CH2\ groups in the molecules.
is linear (Eq. (2)) with regression coefficient, R2, and standard deviation, SD. HbðWÞ ¼ –18:94ð0:42Þ–8:68ð0:11Þ n—CH2 CH2 —
ð2Þ
2
R ¼ 0:99938 SD ¼ 0:45423 This indicates that with the increase in the polyether chain, the enthalpic effect of hydrophobic hydration increases. Moreover, the interaction of glyme molecules with DMF molecules in pure DMF and with water molecules in pure water is also linearly dependent on the chain length of glymes. This is illustrated by the linear relationship of the dissolution enthalpy of glymes as a function of oxygen atoms in the glyme molecules, Eqs. (3) and (4), respectively. o
Δsol H ðDMFÞ ¼ 0:19ð0:05Þ–0:56ð0:01Þ n—CH2 CH2 — 2
R ¼ 0:99810
ð3Þ
SD ¼ 0:05111
o
Δsol H ðWÞ ¼ –14:98ð0:65Þ–7:68ð0:17Þ n—CH2 CH2 —
ð4Þ
2
R ¼ 0:99812 SD ¼ 0:69769 It is known that glyme molecules can form hydrogen bonds with water molecules [25]. The contribution of these interactions is important in the analysis of the solvation enthalpy. Barannikov et al. [9] discussed in their publication the participation of hydrogen bonds between the oxygen atoms in the glyme molecules and water and hydrophobic hydration in the enthalpy of solvation. According to the authors, the role of these contributions is debatable. 4. Conclusion Enthalpic effects of the hydrophobic hydration of monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme are directly proportional to the length of the chain in the glyme molecules. The interactions between glyme molecules (monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme) and water molecules as well as glyme molecules and DMF molecules are dependent on the length of the chain in the glyme molecules.
[1] D. Salavera, K.R. Patil, A. Coronas, Thermal conductivity measurement of polyglycol alkyl ethers at temperatures from (303.15 to 393.15) K, J. Chem. Eng. Data 55 (2010) 1440–1452. [2] N.R. Dhumal, S.P. Gejji, Theoretical studies in local coordination and vibrational spectra of M+CH3O(CH2CH2O)nCH3 (n = 2–7) complexes (M = Na, K, Mg and Ca), Chem. Phys. 323 (2006) 595–605. [3] H.J. Buschmann, E. Schollmeyer, The complex formation of non-cyclic polyethers and crown ethers with Ag+ in acetone and propylene carbonate studied by potentiometric and calorimetric methods, J. Electroanal. Chem. 474 (1999) 188–191. [4] K. Hayamizu, E. Akiba, T. Bando, Y. Aihara, 1H, 7Li and 19F nuclear magnetic resonance and ionic conductivity studies for liquid electrolytes compound of glymes and polyetheneglycol dimethyl ethers of CH3O(CH2CH2O)nCH3 (n = 3–50) moped with Lin(SO2CF3)2, J. Chem. Phys. 117 (2002) 5929–5939. [5] K. Kusano, J. Suurkuusk, I. Wadsö, Thermochemistry of solutions of biochemical model compounds. 2. Alkoxyethanols and 1,2-dialkoxyethanes in water, J. Chem. Thermodyn. 5 (1973) 757–767. [6] K. Ng, A. Rosenberg, M. Bartos, I. Wadsö, Heat capacity of poly(ethylene glycol)– water mixtures: poly(ethylene glycol)–water interactions, Thermochim. Acta 169 (1990) 339–346. [7] G. Nichols, J. Orf, S.M. Reiter, J. Chickos, G.W. Gokel, The vaporization enthalpies of some crown and polyethers by correlation gas chromatography, Thermochim. Acta 346 (2000) 15–28. [8] R.B. Sharma, A.T. Blades, P. Kebarle, Protonation of polyethers, glymes and crown ethers, in the gas phase, J. Am. Chem. Soc. 106 (1984) 510–516. [9] V.P. Barannikov, S.S. Guseynov, A.I. Vyugin, Thermochemical behaviour of straightchain ethers CH3O(CH2CH2O)nCH3 (n = 1–4) in aqueous and tetrachlormethane solutions, Thermochim. Acta 469 (2008) 23–27. [10] M. Jóźwiak, M.A. Kosiorowska, A. Jóźwiak, Enthalpy of solvation of monoglyme, diglyme, triglyme, tetraglyme and pentaglyme in the mixtures of water with N,Ndimethylformamide at 298.15 K, J. Chem. Eng. Data 55 (2010) 5941–5945. [11] M.J. Mastroianni, M.J. Pikal, S. Lindenbaum, Effect of dimethyl sulfoxide, urea, guanidine hydrochloride, and sodium chloride on hydrophobic interactions. Heats of dilution of tetrabutylammonium bromide and lithium bromide in mixed aqueous solvent systems, J. Phys. Chem. 76 (1972) 3050–3057. [12] R.W. Balk, G. Somsen, Preferential solvation and hydrophobic hydration of polyols in mixtures of water and N,N-dimethylformamide, J. Phys. Chem. 89 (1985) 5093–5097. [13] C. de Visser, G. Somsen, Hydrophobic interactions in mixtures of N,Ndimethylformamide and water. model calculations and enthalpies of solution, J. Phys. Chem. 78 (1974) 1719–1722. [14] M. Ouchi, Y. Inoue, T. Kanzaki, T. Hakushi, Molecular design of crown ethers. 1. Effects of methylene cain length: 15- to 17-crown-5 and 18- to 22 crown-6, J. Org. Chem. 49 (1984) 1048–1412. [15] G. Chaput, G. Jeminet, J. Juillard, Constantes d'association de quelques ethers de polyethylene glycols avec Na+, K+, Cs+ et Tl+, Can. J. Chem. 53 (1975) 2240–2246. [16] S.C. Chan, J.P. Valleau, Ultrasonic study of hydrochloric acid association in N,Ndimethylformamide, Can. J. Chem. 46 (1968) 853–858. [17] C.D. Schmulbach, R.S. Drago, Molecular addition compounds of iodine. III. An infrared investigation of the interaction between dimethylacetamide and iodine, J. Am. Chem. Soc. 82 (1960) 4484–4487. [18] H. Piekarski, D. Waliszewski, Hydration effect on urea-non-electrolyte enthalpic pair interaction coefficients. Dissolution enthalpies of urea in aqueous solution of alkoxyethanols at 298.15 K, Thermochim. Acta 258 (1995) 67–76. [19] R. Sabbah, A. Xu-wu, J.S. Chickos, M.L. Planas Leitão, M.V. Roux, L.A. Torres, Reference materials for calorimetry and differential thermal analysis, Thermochim. Acta 331 (1999) 93–204. [20] I. Wadsö, R.N. Goldberg, Standards in isothermal microcalorimetry (IUPAC technical report), Pure Appl. Chem. 73 (2001) 1625–1639. [21] M. Jóźwiak, L. Madej-Kiełbik, Effect of temperature on the process of complex formation crown ether 15C5 with Na+ in the (water + ethanol) mixture at temperatures from (293.15 to 308.15)K, Thermochim. Acta 580 (2014) 13–19. [22] M. Jóźwiak, M. Tyczyńska, Volumetric properties of urea in the mixture of N,Ndimethylformamide with water, J. Chem. Eng. Data 57 (2012) 2067–2075. [23] M. Tyczyńska, M. Jóźwiak, Apparent and partial molar volumes of 18-crown-6 in the mixture of N,N-dimethylformamide with water, J. Mol. Liq. 195 (2014) 80–86. [24] M. Jóźwiak, Thermal behaviour of crown ethers in the mixtures of water with organic solvents. Part II. Enthalpy of solution of benzo-15-crown-5 ether in the mixtures of water and DMSO, DMF, DMA and HMPA at 298.15 K, J. Mol. Liq. 81 (1999) 261–268. [25] P. Bernal, A. Bunn, J. Logan, J. McCluan, Apparent molar volumes and adiabatic compressibilities of crown ethers and glymes in aqueous solutions at various temperatures, J. Solut. Chem. 29 (2000) 651–663.