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1H-NMR studies of the binary mixtures of sulfolane with ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol at 303 K
Journal of Molecular Liquids 141 (2008) 31–34
Contents lists available at ScienceDirect
Journal of Molecular Liquids j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m o l l i q
1
H-NMR studies of the binary mixtures of sulfolane with ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol at 303 K Cezary M. Kinart a,⁎, Wojciech J. Kinart b, Marta Maj a a b
Department of Chemistry, University of Łódź, 90 - 236 Łódź, Pomorska 163, Poland Department of Organic Chemistry, University of Łódź, 90 - 136 Łódź, Narutowicza 68, Poland
a r t i c l e
i n f o
Article history: Received 10 January 2008 Accepted 27 February 2008 Available online 7 March 2008 Keywords: 1 H-NMR studies Sulfolane Ethylene glycols Intermolecular interactions
a b s t r a c t 1
H-NMR spectra in binary mixtures of sulfolane with ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol have been recorded over the whole composition range at 303 K under atmospheric pressure. The experimental data have been used to calculate the deviations in chemical shifts from the additive properties, viz. Δδ, as a function of mole fractions, and values obtained are fitted to the Redlich–Kister polynomial equation to obtain the binary coefficients and the standard errors. The results are discussed in terms of intermolecular interactions and structure of studied binary mixtures. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Regarding structural studies, review of the literature shows that for the analysis of intermolecular interactions and the internal structure of mixed binary liquid mixtures it is possible to apply a wide range of spectral methods (NMR, IR), thermochemical methods, as well as studies on intensive macroscopic properties of solutions (such as relative permittivity, density, viscosity, etc.) carried out at different temperatures [1–3]. There is a large number of important effects and hence of NMR applications. There are available extensive tables of the chemical shifts for protons in various chemical environments, and the NMR spectrum of a molecule serves not only as a “fingerprint” but it usually allows to derive quite detailed conclusions regarding its isomeric structure, the influence of a solvent, formation of inter- and intramolecular hydrogen bonds, etc. [3–6]. Changes of chemical shifts visible in the 1 H-NMR spectrum are observed when molecules of a solvent and the dissolved substance form a certain type of an intermolecular complexes as a result of occurring in the mixture dipole–dipole, and van der Waals and specific interactions and as the outcome of different influence of a solvent at individual protons of molecules of the dissolved compound. The aim of the present work has been to apply experimentally obtained 1H-NMR spectral characteristics for sulfolane (SU) + ethylene glycol (EG), sulfolane + diethylene glycol (DEG), sulfolane + triethylene glycol (TEG), and sulfolane + tetraethylene glycol (TETRAEG) binary mix-
⁎ Corresponding author. E-mail address: [email protected] (C.M. Kinart). 0167-7322/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2008.02.007
tures in order to estimate qualitatively intermolecular interactions displayed in the bulk of these liquid mixed solvents. Ethylene glycols are a very interesting class of the solvents, due to the simultaneous presence of the oxy and hydroxyl groups in the same molecule, which allow their self-association via intra- and/or intermolecular hydrogen bonds and by dipole–dipole interactions. The formation of stable intermolecular hydrogen bonds is more favourable when the molecules are in the gauche conformations [7–9]. Sulfolane is a typical dipolar aprotic solvent with a low donor number of 14.81 and a large dipole moment and relative permittivity in the liquid phase (μ = 4.8 D; ε = 43.39). It is a globular molecule in which only the negative end of its large dipole moment is exposed and thus is cannot act as a proton acceptor–donor [10–13]. These solvents have found a wide variety of applications in the petroleum, cosmetics, textile, pharmaceutical, and the other industries [14–16]. 2. Experimental section 2.1. Chemicals The following materials with mole fraction purity as stated were used: sulfolane (Aldrich, purum, GC ≥ 0.98 mol fraction), ethylene glycol (Fluka, Swizerland, puriss. anhydrous, GC N 0.99 mol fraction), diethylene glycol (Fluka, Swizerland, puriss. p.a., GC ≥ 0.995 mole fraction), triethylene glycol (Fluka, Swizerland, puriss. anhydrous, GC N 0.99 mol fraction), and tetraethylene glycol (Fluka, Switzerland, purum, GC ≥ 0.99 mol fraction). All glycols were further purified by the methods described by us previously [17,18]. Sulfolane was purified according to method described by Domańska et al. [10]. The mixtures were prepared using a Sartorius balance. Conversion to molar
32
C.M. Kinart et al. / Journal of Molecular Liquids 141 (2008) 31–34
Table 1 Chemical shifts δ(–CH2–), δ(–OH), δ[(–CH2–) − (HO–)] and deviations in chemical shift Δδ, as a function of mole fraction of sulfolane (x1) for various binary mixtures at 303 K x1
dð–CH2 –Þ Hz
dð–OHÞ Hz
SU + EG 0.0000 0.0096 0.0500 0.1000 0.2000 0.3007 0.4001 0.5000 0.5999 0.7004 0.8001 0.9003 0.9501 0.9900 1.0000
355.4a 349.1 336.0 331.1 341.4 350.7 357.1 357.9 356.6 356.1 353.2 349.8 348.6 350.6 353.3a
194.5a 196.2 199.4 204.1 212.8 217.8 222.6 226.3 230.3 237.4 245.9 258.4 265.4 272.3 276.1a
160.9 152.9 136.6 127.0 128.6 132.9 134.5 131.6 126.3 118.7 107.3 91.4 83.2 78.3 77.2
0.0 −7.2 −20.1 −25.5 −15.6 −2.8 7.1 12.5 15.6 16.4 13.4 5.9 1.8 0.3 0.0
SU + DEG 0.0000 0.0102 0.0502 0.1001 0.2004 0.2999 0.3989 0.5001 0.6017 0.7004 0.8005 0.9001 0.9500 0.9908 1.0000
352.1a 347.3 330.1 323.4 333.2 345.5 352.2 352.6 350.3 348.3 346.3 344.1 345.2 347.1 349.1a
192.7a 192.4 185.6 188.4 202.4 212.5 218.6 220.3 221.5 227.6 241.9 262.2 275.2 285.1 288.7a
159.4 154.9 144.5 135.0 130.8 133.0 133.6 132.3 128.8 120.7 104.4 81.9 70.0 62.0 60.4
0.0 −3.5 −9.9 −14.5 −8.8 3.3 13.7 22.4 29.0 30.6 24.2 11.6 4.6 0.7 0.0
SU + TEG 0.0000 0.0098 0.0499 0.0992 0.2006 0.2999 0.4011 0.4989 0.6008 0.7027 0.8002 0.9031 0.9491 0.9908 1.0000
348.1a 343.6 326.5 319.4 328.4 339.2 342.2 340.1 338.2 337.1 336.7 337.9 339.3 341.5 342.4a
198.5a 196.4 187.5 187.1 200.3 208.5 208.0 204.5 206.1 212.5 226.1 252.2 266.9 283.2 287.5a
149.6 147.2 139.0 132.3 128.1 130.7 134.2 135.6 132.1 124.6 110.6 85.7 72.4 58.3 54.9
0.0 −1.5 −5.9 −7.9 −2.5 9.5 22.6 33.2 39.4 41.5 36.8 21.6 12.7 2.5 0.0
SU + TETRAEG 0.0000 0.0103 0.0507 0.1000 0.2005 0.3033 0.4009 0.5027 0.5999 0.6998 0.8003 0.9010 0.9502 0.9924 1.0000
341.2a 337.1 322.1 316.2 323.2 331.1 334.5 333.2 329.9 326.1 325.7 326.4 327.4 328.2 328.5a
200.1a 197.5 189.6 190.0 199.9 202.9 200.2 195.8 195.2 200.9 217.5 244.8 263.9 283.0 288.4a
141.1 139.6 132.5 126.2 123.3 128.2 134.3 137.4 134.7 125.2 108.2 81.6 63.5 45.2 40.1
0.0 −0.5 −3.5 −4.8 2.5 17.7 33.7 47.1 54.2 54.8 47.9 31.5 18.4 4.3 0.0
a
d½ð–CH2 –ÞðOH–Þ Hz
Dd Hz
Values extrapolated to 0 and 1.
quantities was based on the relative atomic mass table of 1985, issued by IUPAC in 1986. The maximum estimated error in the mole fractions is ±1 · 10− 4. Liquids were stored in dry-box over phosphorus pentoxide and degassed by ultrasound just before the experiment.
2.2. Measurements The 1H-NMR spectra for both the pure liquids and their mixtures were recorded using a TESLA BS 567A (100 MHz) spectrometer at 303±1 K. The proton chemical shifts were measured with an accuracy of±0.5 Hz with respect to an external standard HMDS (hexamethyldisiloxane). 3. Results and discussion 1
H-NMR spectra at 303 ± 1 K have been recorded for binary liquid mixtures of sulfolane and ethylene glycols. Chemical shifts (δ) as a function of mole fraction for sulfolane protons corresponding to –CH2– groups (C-2 and C-5) [δ(–CH2–)], –OH protons of glycols [δ(–OH)] and difference between the centers of these signals {δ[(–CH2–) − (HO–)]} are summarized in Table 1. The variations of the δ[(–CH2–) − (HO−)] values with binary composition were studied by using the following equations:
dmix ðx1Þ ¼
6 X
bj x1j ;
where : dmix ¼ d½ð–CH2 –Þ ðHO–Þ
ð1Þ
j¼0
which could be fitted to the experimental data at 303 K using a leastsquares method. The bj coefficients of this fitting procedure are listed in Table 2, along with the standard deviations σ(δmix) for each binary mixture. The goodness-of-fit of this procedure is ascertained by a mean deviaP P tion Ddmix ¼ F0:3 Hz for ðSU þ EGÞ; Ddmix ¼ F0:3 Hz for ðSU þ DEGÞ; P P Ddmix ¼ F 0:2 Hz for ðSU þ TEGÞ; and Ddmix ¼ F0:2 Hz for ðSUþ TETRAEGÞ of binary liquid mixtures. From obtained values of δmix the deviations in chemical shift difference Δδ were calculated using the relation: Dd ¼ dmix ðx1 d1 x2 d2 Þ
ð2Þ
where: δ1 and δ2 are the chemical shifts at lowest and highest mole fraction (values were obtained by extrapolating the curves from 0 to 1), x1 and x2 are mole fractions of components Eqs. (1) and (2), respectively. The values of Δδ, at T = 303.15 K, are summarized in Table 1, and were fitted by a Redlich–Kister type equation [19]: Dd=Hz ¼ x1 ð1 x1 Þ
4 X
aj ð2x1 1Þ j :
ð3Þ
j¼0
The parameters aj in Eq. (3) were evaluated by the least-squares method. The values of these parameters with standard deviation σ(Δδ), are summarized in Table 3.
Table 2 Coefficients bj and standard deviations σ(δmix) of Eq. (1) for {SU (1) + EG (2), SU (1) + DEG (2), SU (1) + TEG (2) and SU (1) + TETRAEG (2)} binary mixtures at T = 303 K T (K)
b0 · 10− 2 b1 · 10− 2
b2 · 10− 3 b3 · 10− 4
b4 · 10− 4
b5 · 10− 4
b6 · 10− 3
r(δmix)
SU + EG 303.15 1.5998
−6.6801
4.6003
−1.3943
2.1221
−1.6102
4.8087
0.6
SU + DEG 303.15 1.5941
−4.2350 2.4354
−6.9146
1.0711
−8.7444 2.8383
0.5
SU + TEG 303.15 1.4980
−2.8115
1.2799
−2.4895 2.5589
−1.5649
0.4
SU + TETRAEG 303.15 1.4146
−2.1609
6.4351
4.6999
−3.4208 3.8626
4.0193
−1.4401 0.4
C.M. Kinart et al. / Journal of Molecular Liquids 141 (2008) 31–34 Table 3 Coefficients aj and standard deviations σ(Δδ) of Eq. (3) {SU (1) + EG (2), SU (1) + DEG (2), SU (1) + TEG (2) and SU (1) + TETRAEG (2)} binary mixtures at T = 303 K T (K)
a0
a1
a2
a3
a4
r(Δδ)
SU + EG 303.15
49.3635
76.1970
−47.1352
221.3009
−313.2000
0.73
SU + DEG 303.15
91.2382
159.4549
−51.0397
28.8734
−175.5400
0.56
SU + TEG 303.15
132.1920
184.2628
−63.6392
42.9880
−23.0434
0.44
SU + TETRAEG 303.15 187.6377
214.9224
−122.0141
58.3952
103.9973
0.45
Standard deviation values were obtained from: "P r¼
Vexptl Vcalcd Np
2 #1=2 ;
ð4Þ
where N is the number of experimental points, p is the number of parameters, Vexptl and Vcalcd are the experimental and calculated properties. The variations of Δδ values as a function of the mole fraction of sulfolane (x1) for all studied mixtures are presented in the Fig. 1. For all studied mixtures sulfolane with ethylene glycols the deviations in chemical shift difference are illustrated by the S-shaped
33
curves, with minimum at ~ 0.10 and maximum ~0.75 mole fraction of sulfolane, respectively. Therefore, on the basis of the actual experimental evidence and literature information about internal structure of sulfolane and ethylene glycols [7–13], we can suggest that the addition of pure sulfolane to ethylene glycols would disrupt their self-associated structure. That structural effect is the strongest in the range of the composition corresponding to ~10% mol of sulfolane, it means where the minimum values of Δδ are observed. In this region sulfolane may play the role of an almost inert diluent (probably due to the steric hindrance of this globular molecule). These free SU, EG, DEG, TEG and TETRAEG molecules may interact by dipole–dipole forces and/or intermolecular hydrogen bonds forming the mixed intermolecular complexes. The position of the relative maxima in the plots of Δδ versus x 1, could be taken as the true composition of these intermolecular complexes [3,5,6,20]. In the analysed mixtures we observed maxima of Δδ values at ca. 0.70 mol fraction of sulfolane. The value of Δδ becomes more positive as the number of oxyethylene groups –O–CH2–CH2– in the glycol increases:Ddmax ðSU þ TETRAEGÞN Ddmax ðSU þ TEGÞNDdmax ðSU þ DEGÞNDdmax ðSU þ EGÞ. The similar structural effects in the SU + EG and SU + DEG were observed by Al-Dujaili and co-workers [21]. In this work, they have measured the density, refractive index, and relative permittivity over the entire composition range at 303.15 K for binary mixtures of sulfolane with ethylene glycol, diethylene glycol, poly(ethylene glycol) with an average molecular weight of 200, and poly(ethylene glycol) with an average molecular weight of 600. They have suggested that the specific interaction between sulfolane and glycols increases as the glycol carbon chain length increases and it is also as a result of molecular size differences.
Fig. 1. Plot of the deviation in chemical shift (Δδ) against mole fraction SU (x1) for {(♦) SU (1) + EG (2), (■) SU (1) + DEG (2), (▲) SU (1) + TEG (2), and (●)SU (1) + TETRAEG (2)} binary liquid mixtures, at T = 303 K.
34
C.M. Kinart et al. / Journal of Molecular Liquids 141 (2008) 31–34
References [1] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, Wiley-VCH, Weinheim, 2003. [2] J. Bernstein, M.C. Etter, L. Leiserowitz, in: H.-B. Burgi, J.D. Dunitz (Eds.), The Role of Hydrogen Bonding in Molecular Assemblies in Structure Correlation, VCH, Weinheim, 1994. [3] C.M. Kinart, W.J. Kinart, Phys. Chem. Liq. 38 (2000) 155. [4] P. Laszlo, in: J.W. Emsley, J. Feeney, L.H. Sctcliffe (Eds.), Progress in NMR Spectroscopy, III, 1967. [5] S. Romanowski, C.M. Kinart, W.J. Kinart, J. Chem. Soc., Faraday Trans. 9 (1995) 165. [6] M. Kr. Yadav, A. Kumar, J. Mol. Liq. 12 (2005) 194. [7] L. Kang-Jen, Macromolecules 1 (1968) 213. [8] A. Kumagai, H. Mochida, S. Takahashi, Int. J. Thermophys. 14 (1993) 45. [9] A. Pal, P.N. Halder, W. Singh, Indian J. Chem. 33A (1994) 154. [10] U. Domańska, W.C. Moollan, J. Chem. Eng. Data 41 (1996) 261.
[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
M. Della Monica, L. Janelli, U. Lamanna, J. Phys. Chem. 72 (1968) 1068. L. Jannelli, A. Inglese, A. Sacco, P. Ciani, Z. Naturforsch. 30a (1975) 87. L. Jannelli, A. Sacco, J. Chem. Thermodyn. 4 (1972) 715. R.Y. Lochhead, J.V. Gruber, Principles of Polymer Science and Technology in Cosmetics and Personal Care, Marcel Dekker, New York, 1999. G.M. Powell, Polyethylene Glycol, Handbook of water soluble gums and resins, McGraw-Hill Book Company, New York, 1980, Chapter 18. R.L. Smith, Environ. Health Perspect. 57 (1984) 1. C.M. Kinart, M. Klimczak, A. Ćwiklińska, W.J. Kinart, J. Mol. Liq. 135 (2007) 192. C.M. Kinart, M. Klimczak, A. Ćwiklińska, W.J. Kinart, J. Chem. Thermodyn. 39 (2007) 822. O. Redlich, A. Kister, Ing. Eng. Chem. 40 (1948) 345. C. Wang, H. Li, L. Zhu, S. Han, J. Solution Chem. 31 (2002) 109. A.M. Awwad, H. Amar, A.H. Al-Dujaili, E. Hameda, H.E. Salman, J. Chem. Eng. Data 47 (2002) 421.
Contents lists available at ScienceDirect
Journal of Molecular Liquids j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m o l l i q
1
H-NMR studies of the binary mixtures of sulfolane with ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol at 303 K Cezary M. Kinart a,⁎, Wojciech J. Kinart b, Marta Maj a a b
Department of Chemistry, University of Łódź, 90 - 236 Łódź, Pomorska 163, Poland Department of Organic Chemistry, University of Łódź, 90 - 136 Łódź, Narutowicza 68, Poland
a r t i c l e
i n f o
Article history: Received 10 January 2008 Accepted 27 February 2008 Available online 7 March 2008 Keywords: 1 H-NMR studies Sulfolane Ethylene glycols Intermolecular interactions
a b s t r a c t 1
H-NMR spectra in binary mixtures of sulfolane with ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol have been recorded over the whole composition range at 303 K under atmospheric pressure. The experimental data have been used to calculate the deviations in chemical shifts from the additive properties, viz. Δδ, as a function of mole fractions, and values obtained are fitted to the Redlich–Kister polynomial equation to obtain the binary coefficients and the standard errors. The results are discussed in terms of intermolecular interactions and structure of studied binary mixtures. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Regarding structural studies, review of the literature shows that for the analysis of intermolecular interactions and the internal structure of mixed binary liquid mixtures it is possible to apply a wide range of spectral methods (NMR, IR), thermochemical methods, as well as studies on intensive macroscopic properties of solutions (such as relative permittivity, density, viscosity, etc.) carried out at different temperatures [1–3]. There is a large number of important effects and hence of NMR applications. There are available extensive tables of the chemical shifts for protons in various chemical environments, and the NMR spectrum of a molecule serves not only as a “fingerprint” but it usually allows to derive quite detailed conclusions regarding its isomeric structure, the influence of a solvent, formation of inter- and intramolecular hydrogen bonds, etc. [3–6]. Changes of chemical shifts visible in the 1 H-NMR spectrum are observed when molecules of a solvent and the dissolved substance form a certain type of an intermolecular complexes as a result of occurring in the mixture dipole–dipole, and van der Waals and specific interactions and as the outcome of different influence of a solvent at individual protons of molecules of the dissolved compound. The aim of the present work has been to apply experimentally obtained 1H-NMR spectral characteristics for sulfolane (SU) + ethylene glycol (EG), sulfolane + diethylene glycol (DEG), sulfolane + triethylene glycol (TEG), and sulfolane + tetraethylene glycol (TETRAEG) binary mix-
⁎ Corresponding author. E-mail address: [email protected] (C.M. Kinart). 0167-7322/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2008.02.007
tures in order to estimate qualitatively intermolecular interactions displayed in the bulk of these liquid mixed solvents. Ethylene glycols are a very interesting class of the solvents, due to the simultaneous presence of the oxy and hydroxyl groups in the same molecule, which allow their self-association via intra- and/or intermolecular hydrogen bonds and by dipole–dipole interactions. The formation of stable intermolecular hydrogen bonds is more favourable when the molecules are in the gauche conformations [7–9]. Sulfolane is a typical dipolar aprotic solvent with a low donor number of 14.81 and a large dipole moment and relative permittivity in the liquid phase (μ = 4.8 D; ε = 43.39). It is a globular molecule in which only the negative end of its large dipole moment is exposed and thus is cannot act as a proton acceptor–donor [10–13]. These solvents have found a wide variety of applications in the petroleum, cosmetics, textile, pharmaceutical, and the other industries [14–16]. 2. Experimental section 2.1. Chemicals The following materials with mole fraction purity as stated were used: sulfolane (Aldrich, purum, GC ≥ 0.98 mol fraction), ethylene glycol (Fluka, Swizerland, puriss. anhydrous, GC N 0.99 mol fraction), diethylene glycol (Fluka, Swizerland, puriss. p.a., GC ≥ 0.995 mole fraction), triethylene glycol (Fluka, Swizerland, puriss. anhydrous, GC N 0.99 mol fraction), and tetraethylene glycol (Fluka, Switzerland, purum, GC ≥ 0.99 mol fraction). All glycols were further purified by the methods described by us previously [17,18]. Sulfolane was purified according to method described by Domańska et al. [10]. The mixtures were prepared using a Sartorius balance. Conversion to molar
32
C.M. Kinart et al. / Journal of Molecular Liquids 141 (2008) 31–34
Table 1 Chemical shifts δ(–CH2–), δ(–OH), δ[(–CH2–) − (HO–)] and deviations in chemical shift Δδ, as a function of mole fraction of sulfolane (x1) for various binary mixtures at 303 K x1
dð–CH2 –Þ Hz
dð–OHÞ Hz
SU + EG 0.0000 0.0096 0.0500 0.1000 0.2000 0.3007 0.4001 0.5000 0.5999 0.7004 0.8001 0.9003 0.9501 0.9900 1.0000
355.4a 349.1 336.0 331.1 341.4 350.7 357.1 357.9 356.6 356.1 353.2 349.8 348.6 350.6 353.3a
194.5a 196.2 199.4 204.1 212.8 217.8 222.6 226.3 230.3 237.4 245.9 258.4 265.4 272.3 276.1a
160.9 152.9 136.6 127.0 128.6 132.9 134.5 131.6 126.3 118.7 107.3 91.4 83.2 78.3 77.2
0.0 −7.2 −20.1 −25.5 −15.6 −2.8 7.1 12.5 15.6 16.4 13.4 5.9 1.8 0.3 0.0
SU + DEG 0.0000 0.0102 0.0502 0.1001 0.2004 0.2999 0.3989 0.5001 0.6017 0.7004 0.8005 0.9001 0.9500 0.9908 1.0000
352.1a 347.3 330.1 323.4 333.2 345.5 352.2 352.6 350.3 348.3 346.3 344.1 345.2 347.1 349.1a
192.7a 192.4 185.6 188.4 202.4 212.5 218.6 220.3 221.5 227.6 241.9 262.2 275.2 285.1 288.7a
159.4 154.9 144.5 135.0 130.8 133.0 133.6 132.3 128.8 120.7 104.4 81.9 70.0 62.0 60.4
0.0 −3.5 −9.9 −14.5 −8.8 3.3 13.7 22.4 29.0 30.6 24.2 11.6 4.6 0.7 0.0
SU + TEG 0.0000 0.0098 0.0499 0.0992 0.2006 0.2999 0.4011 0.4989 0.6008 0.7027 0.8002 0.9031 0.9491 0.9908 1.0000
348.1a 343.6 326.5 319.4 328.4 339.2 342.2 340.1 338.2 337.1 336.7 337.9 339.3 341.5 342.4a
198.5a 196.4 187.5 187.1 200.3 208.5 208.0 204.5 206.1 212.5 226.1 252.2 266.9 283.2 287.5a
149.6 147.2 139.0 132.3 128.1 130.7 134.2 135.6 132.1 124.6 110.6 85.7 72.4 58.3 54.9
0.0 −1.5 −5.9 −7.9 −2.5 9.5 22.6 33.2 39.4 41.5 36.8 21.6 12.7 2.5 0.0
SU + TETRAEG 0.0000 0.0103 0.0507 0.1000 0.2005 0.3033 0.4009 0.5027 0.5999 0.6998 0.8003 0.9010 0.9502 0.9924 1.0000
341.2a 337.1 322.1 316.2 323.2 331.1 334.5 333.2 329.9 326.1 325.7 326.4 327.4 328.2 328.5a
200.1a 197.5 189.6 190.0 199.9 202.9 200.2 195.8 195.2 200.9 217.5 244.8 263.9 283.0 288.4a
141.1 139.6 132.5 126.2 123.3 128.2 134.3 137.4 134.7 125.2 108.2 81.6 63.5 45.2 40.1
0.0 −0.5 −3.5 −4.8 2.5 17.7 33.7 47.1 54.2 54.8 47.9 31.5 18.4 4.3 0.0
a
d½ð–CH2 –ÞðOH–Þ Hz
Dd Hz
Values extrapolated to 0 and 1.
quantities was based on the relative atomic mass table of 1985, issued by IUPAC in 1986. The maximum estimated error in the mole fractions is ±1 · 10− 4. Liquids were stored in dry-box over phosphorus pentoxide and degassed by ultrasound just before the experiment.
2.2. Measurements The 1H-NMR spectra for both the pure liquids and their mixtures were recorded using a TESLA BS 567A (100 MHz) spectrometer at 303±1 K. The proton chemical shifts were measured with an accuracy of±0.5 Hz with respect to an external standard HMDS (hexamethyldisiloxane). 3. Results and discussion 1
H-NMR spectra at 303 ± 1 K have been recorded for binary liquid mixtures of sulfolane and ethylene glycols. Chemical shifts (δ) as a function of mole fraction for sulfolane protons corresponding to –CH2– groups (C-2 and C-5) [δ(–CH2–)], –OH protons of glycols [δ(–OH)] and difference between the centers of these signals {δ[(–CH2–) − (HO–)]} are summarized in Table 1. The variations of the δ[(–CH2–) − (HO−)] values with binary composition were studied by using the following equations:
dmix ðx1Þ ¼
6 X
bj x1j ;
where : dmix ¼ d½ð–CH2 –Þ ðHO–Þ
ð1Þ
j¼0
which could be fitted to the experimental data at 303 K using a leastsquares method. The bj coefficients of this fitting procedure are listed in Table 2, along with the standard deviations σ(δmix) for each binary mixture. The goodness-of-fit of this procedure is ascertained by a mean deviaP P tion Ddmix ¼ F0:3 Hz for ðSU þ EGÞ; Ddmix ¼ F0:3 Hz for ðSU þ DEGÞ; P P Ddmix ¼ F 0:2 Hz for ðSU þ TEGÞ; and Ddmix ¼ F0:2 Hz for ðSUþ TETRAEGÞ of binary liquid mixtures. From obtained values of δmix the deviations in chemical shift difference Δδ were calculated using the relation: Dd ¼ dmix ðx1 d1 x2 d2 Þ
ð2Þ
where: δ1 and δ2 are the chemical shifts at lowest and highest mole fraction (values were obtained by extrapolating the curves from 0 to 1), x1 and x2 are mole fractions of components Eqs. (1) and (2), respectively. The values of Δδ, at T = 303.15 K, are summarized in Table 1, and were fitted by a Redlich–Kister type equation [19]: Dd=Hz ¼ x1 ð1 x1 Þ
4 X
aj ð2x1 1Þ j :
ð3Þ
j¼0
The parameters aj in Eq. (3) were evaluated by the least-squares method. The values of these parameters with standard deviation σ(Δδ), are summarized in Table 3.
Table 2 Coefficients bj and standard deviations σ(δmix) of Eq. (1) for {SU (1) + EG (2), SU (1) + DEG (2), SU (1) + TEG (2) and SU (1) + TETRAEG (2)} binary mixtures at T = 303 K T (K)
b0 · 10− 2 b1 · 10− 2
b2 · 10− 3 b3 · 10− 4
b4 · 10− 4
b5 · 10− 4
b6 · 10− 3
r(δmix)
SU + EG 303.15 1.5998
−6.6801
4.6003
−1.3943
2.1221
−1.6102
4.8087
0.6
SU + DEG 303.15 1.5941
−4.2350 2.4354
−6.9146
1.0711
−8.7444 2.8383
0.5
SU + TEG 303.15 1.4980
−2.8115
1.2799
−2.4895 2.5589
−1.5649
0.4
SU + TETRAEG 303.15 1.4146
−2.1609
6.4351
4.6999
−3.4208 3.8626
4.0193
−1.4401 0.4
C.M. Kinart et al. / Journal of Molecular Liquids 141 (2008) 31–34 Table 3 Coefficients aj and standard deviations σ(Δδ) of Eq. (3) {SU (1) + EG (2), SU (1) + DEG (2), SU (1) + TEG (2) and SU (1) + TETRAEG (2)} binary mixtures at T = 303 K T (K)
a0
a1
a2
a3
a4
r(Δδ)
SU + EG 303.15
49.3635
76.1970
−47.1352
221.3009
−313.2000
0.73
SU + DEG 303.15
91.2382
159.4549
−51.0397
28.8734
−175.5400
0.56
SU + TEG 303.15
132.1920
184.2628
−63.6392
42.9880
−23.0434
0.44
SU + TETRAEG 303.15 187.6377
214.9224
−122.0141
58.3952
103.9973
0.45
Standard deviation values were obtained from: "P r¼
Vexptl Vcalcd Np
2 #1=2 ;
ð4Þ
where N is the number of experimental points, p is the number of parameters, Vexptl and Vcalcd are the experimental and calculated properties. The variations of Δδ values as a function of the mole fraction of sulfolane (x1) for all studied mixtures are presented in the Fig. 1. For all studied mixtures sulfolane with ethylene glycols the deviations in chemical shift difference are illustrated by the S-shaped
33
curves, with minimum at ~ 0.10 and maximum ~0.75 mole fraction of sulfolane, respectively. Therefore, on the basis of the actual experimental evidence and literature information about internal structure of sulfolane and ethylene glycols [7–13], we can suggest that the addition of pure sulfolane to ethylene glycols would disrupt their self-associated structure. That structural effect is the strongest in the range of the composition corresponding to ~10% mol of sulfolane, it means where the minimum values of Δδ are observed. In this region sulfolane may play the role of an almost inert diluent (probably due to the steric hindrance of this globular molecule). These free SU, EG, DEG, TEG and TETRAEG molecules may interact by dipole–dipole forces and/or intermolecular hydrogen bonds forming the mixed intermolecular complexes. The position of the relative maxima in the plots of Δδ versus x 1, could be taken as the true composition of these intermolecular complexes [3,5,6,20]. In the analysed mixtures we observed maxima of Δδ values at ca. 0.70 mol fraction of sulfolane. The value of Δδ becomes more positive as the number of oxyethylene groups –O–CH2–CH2– in the glycol increases:Ddmax ðSU þ TETRAEGÞN Ddmax ðSU þ TEGÞNDdmax ðSU þ DEGÞNDdmax ðSU þ EGÞ. The similar structural effects in the SU + EG and SU + DEG were observed by Al-Dujaili and co-workers [21]. In this work, they have measured the density, refractive index, and relative permittivity over the entire composition range at 303.15 K for binary mixtures of sulfolane with ethylene glycol, diethylene glycol, poly(ethylene glycol) with an average molecular weight of 200, and poly(ethylene glycol) with an average molecular weight of 600. They have suggested that the specific interaction between sulfolane and glycols increases as the glycol carbon chain length increases and it is also as a result of molecular size differences.
Fig. 1. Plot of the deviation in chemical shift (Δδ) against mole fraction SU (x1) for {(♦) SU (1) + EG (2), (■) SU (1) + DEG (2), (▲) SU (1) + TEG (2), and (●)SU (1) + TETRAEG (2)} binary liquid mixtures, at T = 303 K.
34
C.M. Kinart et al. / Journal of Molecular Liquids 141 (2008) 31–34
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