CHEM. RES. CHINESE UNIVERSITIES 2010, 26(2),

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1 CHEM. RES. CHINESE UNIVERSITIES 21, 26(2), Apparent Molar Volumes and Solvation Coefficients in Ternary-pseudo-binary Mixtures [(Styrene+Ethyl Acetate or enzene)+(n-methyl-2-pyrrolidone+ethyl Acetate or enzene)] HOU Hai-yun 1, PENG San-jun 2, WANG Sheng-ze 1 and GENG Xing-peng 1 1. College of Environmental and Chemical Engineering, Xi an Polytechnic University, Xi an 7148, P. R. China; 2. College of Chemistry and iological Engineering, Changsha University of Science and Technology, Changsha 414, P. R. China Abstract Over the full range of compositions, in the ternary-pseudo-binary mixtures of x[(1-y)c 6 H 5 CH=CH 2 + ych 3 COOC 2 H 5 (or C 6 H 6 )]+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 (or C 6 H 6 )], the apparent molar volumes of each pseudo-pure component at different y values were calculated from the density data at K and atmospheric pressure. The results show that the four parameters cubic polynomial can correlate the apparent molar volume with the molar fraction well over the full molar fraction range. The limiting partial molar volumes and the molar volumes of each pseudo-pure component were evaluated with different methods. ased on the limiting partial molar volume and molar volume at a certain y value, a new universal coefficient termed as solvation coefficient γ was defined to describe quantitatively the solvation degree of pseudo-pure solute and the interactions of solute-solvent molecules from the macroscopical thermodynamics viewpoint. The results demonstrate the solvation coefficients decrease with the amount of the third component increasing for each pseudo-pure solute, irrespective of the pseudo-pure solvent. Then the solvation degrees of each pseudo-pure component, the specific interactions between the solute molecule and the solvent one were discussed in terms of the solvation coefficient. Keywords Apparent molar volume; Ternary-pseudo-binary mixture; Solvation coefficient Article ID 15-94(21) Introduction A detailed understanding of the solution behavior of non-electrolyte solutes requires information on a variety of chemical and physical parameters. The volumetric properties are very useful in the study of molecular interactions in solution. oth the excess molar volume and the limiting apparent molar volume at infinite dilution which equals the limiting partial molar volume are important thermodynamic volumetric properties and are very helpful to the identification of solvent-solute and solute-solute interactions. Liquid mixtures containing styrene and N-methyl-2-pyrrolidone(NMP) seem to be very interesting from a practical point of view, due to their increased application in organic synthesis. Wang et al. [1] reported the excess molar volume of binary mixtures of styrene with NMP at K. A detailed understanding of the effect of the third component, such as ethyl acetate or benzene, on the excess thermodynamic properties and the corresponding behavior of liquid mixtures is thus an important topic for study from both practical and fundamental viewpoints. Peng et al. [2] reported the influences of the third component, ethyl acetate or benzene on the excess molar volumes of binary mixtures of styrene with NMP at K. However, the apparent molar volumes, the method to describe the macroscopical interactions of solute-solvent molecules, the quantitative solvation degrees of solutes are still remained unknown. The present work is a further investigation of our study of volumetric properties and solute-solvent molecules interactions of liquid pseudo-binary mixtures [2]. This study builds upon and expands on the present literature. 2 Experimental enzene used in these experiments was purchased from the Third Shanghai Chemicals Factory, China; its molar fraction purity was >.99. Styrene *Corresponding author. houhaiyun77@126.com Received February 9, 29; accepted June 12, 29. Supported by the National Natural Science Foundation of China(No.26738) and the Scientific Research Fund of Xi an Polytechnic University of China(No.S74).

2 31 CHEM. RES. CHINESE UNIVERSITIES Vol.26 was purchased from Tianjin Chemical Factory(China), extra pure with molar fraction >.99. Ethyl acetate and NMP were also purchased from Tianjin Chemicals Factory, extra pure with molar fraction >.99. The method of purification was described elsewhere [3]. All of the chemicals were stored in the dark in brown bottles and protected against atmospheric moisture and CO 2. Prior to the measurement, all the chemicals were stored with 4A molecular sieves added for one week to reduce any trace amounts of water that might be present, and were partially degassed under vacuum. Gas chromatographic studies(using a HP Series II, Model 589 chromatograph with a capillary column type 199 iz-413e and f.i.d., column temperature 4 K, and He flow rate cm 3 /s) show no evidence of appreciable impurities. The purchased styrene, containing a stabilizer(hydroquinone), was distilled under reduced pressure and then immediately used for experiments, in order to prevent the possible partial polymerization of styrene. The purity of the liquid was checked by measuring and comparing the density and refractive index with its corresponding literature values [4] as shown in Table 1. The densities of the pure compounds and mixture samples were measured by means of an Anton Parr DMA 45 vibrating-tube densimeter with an estimated accuracy of ±6 1 5 g/cm 3, and were thermostatted at (298.15±.1) K and atmospheric pressure. Table 1 Densities and refractive index values of the pure components at temperature K, and comparison with the literature Component This work Ref.[4] ρ/(g.cm 3 ) 25 n D ρ/(g.cm 3 ) 25 n D enzene Styrene N-Methyl-2-pyrrolidone Ethyl acetate Apparent molar volumes were calculated from the density measurements. efore each series of measurements, the densimeter was calibrated at atmospheric pressure using dried air and the triply distilled and degassed water with an electrical conductivity of Ω 1 m 1. All measurements were made at temperature constant to better than ±.1 K. The temperature was measured with a standard platinum resistance thermometer(wzp-1, Yunnan Instrument Factory, China), a precision bridge(qj69, Shanghai Electrical Instrument Works, China), and a null detector(acii-ac15/2, Shanghai Electric Meter Works, China). The precision of the temperature was determined with a 1/1 eckmann thermometer. The accuracy and precision in the temperature measurements were better than ±.1 K and ±.1 K, respectively. All the samples were prepared by mass weighted on a balance with a precision of ±5 1 5 g. Attention was paid to the changes in composition of the samples during weighing and partial degassing. To diminish this effect, the samples were weighed, degassed, and stored in vessels designed and recommended by Takenaka et al. [5]. All molar quantities were based on the relative Atomic Mass Table issued by IUPAC in 1986 [6]. 3 Results and Discussion 3.1 Apparent Molar Volume The apparent molar volume of solute, φ V, is defined as [7 1] φ V =(V n A V * A )/n (1) where V denotes the volume of solution, n A and n are the molar amounts of solvent and solute, respectively, and V * A is the molar volume of pure solvent. Eq.(1) can be rearranged to Eq.(2) when the solute concentration is mole fraction x : φ M Β M Α(1 xβ) 1 1 V = + (2) Β ρ xβ ρ ρα where ρ and ρ A denote the densities of solution and solvent respectively, M and M A are respectively the molecular weight, x is the molar fraction of solute. Herein, the molecular weight is the average molecular weight of pseudo-pure component. In fourteen ternary-pseudo-binary mixtures of x[(1-y)c 6 H 5 CH= CH 2 +ych 3 COOC 2 H 5 (or C 6 H 6 )](1)+(1-x)[(1-y)NMP+ ych 3 COOC 2 H 5 (or C 6 H 6 )](2), the compositions are y=.1593,.2648,.3587,.533,.628,.7539, and.8538 for the mixtures containing CH 3 COOC 2 H 5, and y=.1525,.253,.3892,.518,.6493,.7534 and.8549 for the mixtures containing C 6 H 6. In the case of either pseudo-pure component can be considered as solute of the ternary-pseudo-binary mixtures, the apparent molar volumes of each pseudo-pure component were calculated by means of Eq.(2) and the results are listed in Tables 2 and 3. The apparent molar volumes and molar fractions of each pseudo-pure component in the ternary-pseudo-binary mixtures were fitted by the least-squares method for all points to Eq.(3) [11 13], and are shown in Figs.1 and 2.

3 No.2 HOU Hai-yun et al. 311 Table 2 Molar fractions, densities, apparent molar volumes of pseudo-pure components 1 and 2 in ternary-pseudobinary solutions x[(1-y)c 6 H 5 CH=CH 2 +ych 3 COOC 2 H 5 ](1)+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 ](2) y x ρ/(g cm 3 ) /(cm 3 /( cm 3 y x ρ/(g cm 3 ) /(cm 3 /( cm To be continued on the next page.

4 312 CHEM. RES. CHINESE UNIVERSITIES Vol.26 y X ρ/(g cm 3 ) Table 3 Molar fractions, densities, apparent molar volumes of pseudo-pure components 1 and 2 in ternary-pseudobinary solutions x[(1-y)c 6 H 5 CH=CH 2 +yc 6 H 6 ](1)+x[(1-y)C 6 H 5 CH=CH 2 +yc 6 H 6 ](2) y x ρ/(g cm 3 ) /(cm 3 /( cm 3 y x ρ/(g cm 3 ) /(cm 3 /( cm To be continued on the next page. /(cm 3 /( cm 3 y x ρ/(g cm 3 ) /(cm 3 /( cm

5 No.2 HOU Hai-yun et al. 313 y x ρ/(g cm 3 ) /(cm 3 /(cm 3 y x ρ/(g cm 3 ) /(cm 3 /( cm Fig.1 Plots of apparent molar volume against molar fraction for ternary-pseudo-binary mixtures x[(1-y)c 6 H 5 CH=CH 2 + ych 3 COOC 2 H 5 ](1)+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 ](2) at K and atmospheric pressure (A) -x 1 ; () -x 2. y:.8538;.7539;.628;.533;.3587;.2648; Fig.2 Plots of apparent molar volume against molar fraction for ternary-pseudo-binary mixtures x[(1-y)c 6 H 5 CH=CH 2 + yc 6 H 6 ](1)+(1-x)[(1-y)NMP+yC 6 H 6 ](2) at K and atmospheric pressure (A) -x 1 ; () -x 2. y:.8538;.7539;.628;.533;.3587;.2648; In each figure, the solid lines represent the values calculated from the smoothing Eq.(3), the points represent the experimental values from Eq.(2). φ φ 2 3 V = V + x + x + x + (3) In each case, the optimum value of coefficient is ascertained from an examination of the variation of the standard deviation σ:

6 314 CHEM. RES. CHINESE UNIVERSITIES Vol.26 φ φ 2 ( V V ) 1 / 2 n σ =, exp., i, cal., i ( n j) (4) i= 1 where, φ V, exp. is from Eq.(2), φ V, cal. from Eq.(3); n, j are the numbers of experimental data and parameters, respectively. The fit results of Eq.(3) for each quasi-pure component are listed in Table 4, where the correlation coefficients φ V, 1, 2, 3 and the corresponding standard deviation σ can be obtained. These coefficients are all constants at a definite y va- lue and temperature K, in which the constant φ V represents the apparent molar volume of a pseudo-pure solute at infinite dilution that equals the limiting partial molar volume of the solute, which can provide some information on solvent-solute interactions and solvation of solute. 1, 2, 3 are empirical parameters that depend on solvent, solute, temperature and the amount of the third component. Table 4 Least-squares parameters φ V, 1, 2, 3 and standard deviations σ of Eq.(3) for pseudo-pure components 1 and 2 at K and atmospheric pressure * Component y φ V /(cm 3 1 /(cm 3 I 2 /(cm 3 3 /(cm 3 σ/(cm 3 Component y φ V /(cm 3 1 /(cm 3 II 2 /(cm 3 3 /(cm 3 σ/(cm * I: x[(1-y)c 6 H 5 CH=CH 2 +ych 3 COOC 2 H 5 ](1)+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 ](2); II: x[(1-y)c 6 H 5 CH=CH 2 +yc 6 H 6 ](1)+(1-x)[(1-y)NMP+ yc 6 H 6 ](2). 3.2 Limiting Partial Molar Volume, Molar Volume, Solvation Coefficient and Interactions of Solute-solvent The apparent molar volume of a solute at infinite dilution is equal to the limiting partial molar volume of the solute [8,14], and that in an infinite concentrated solution is equal to the molar volume. Therefore, Table 5 Eq.(5) can be obtained from Eq.(3) by setting x =: φ V = V (5) Similarly, substituting x =1 into Eq.(3) leads to: φ V = V L (6) So, the limiting partial molar volumes and molar volumes can be evaluated from Eqs.(5) and(6), the results are listed in Table 5. Molar volumes, limiting partial molar volumes and solvation coefficients of pseudo-pure components 1 and 2 at infinite dilution, K and atmospheric pressure V * 1 /(cm 3 V * 2 /(cm 3 1 /(cm 3 2 /(cm 3 δ Composition y 1 /(cm 3 δ 2 /(cm 3 mol γ ) γ a b a b c d c d 2 I II a. from eq.(6); b. from eq.(9); c. from eq.(5); d. from eqs.(7) and (8). I: x[(1-y)c 6 H 5 CH=CH 2 +ych 3 COOC 2 H 5 ](1)+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 ](2); II: x[(1-y)c 6 H 5 CH=CH 2 +yc 6 H 6 ](1)+(1-x)[(1-y)NMP+ yc 6 H 6 ](2).

7 No.2 HOU Hai-yun et al. 315 On the other hand, it is also known that the limiting partial molar volume could be derived from Eqs.(7) and(8), though which does not always provide the best representation of the limiting partial molar volume at infinite dilution. There, the subscripts 1 and 2 denote the pseudo-pure components(styrene+ ethyl acetate, or benzene) and (NMP+ ethyl acetate, or benzene). 1 2 V, V denote the molar volumes of pseudo-pure components 1 and 2, respectively, which can be calculated from the density data via Eq.(9). A i denotes the Redlich-Kister equation coefficients, which have been all shown in our previous work [2]. The derived results are listed in Table 5. V j 1 A i i= j * i 2 = V2 + A i 1) i= * V 1 = V + (7) ( (8) Moreover, the values of molar volumes can also be calculated via Eq.(9) from density data listed in Tables 2 and 3. V = M / ρ (9) The results in Table 5 show that the values of the limiting partial molar volumes evaluated via Eqs.(5), (7) and (8) are consistent with each other and almost within.3 cm 3 /mol, the molar volumes evaluated via Eqs.(6) and (9) are also consistent with each other and almost within.2 cm 3 /mol for each pseudo-pure component. All those demonstrate that the apparent molar volumes and the mole fractions of each pseudo-pure component in the investigated ternarypseudo-binary mixtures can be correlated well by the four parameters cubic polynomial Eq. (3) over the entire concentration range, where the limiting partial molar volumes and the molar volumes of either pseudo-pure component in the either ternary-pseudobinary mixture can be derived successfully. It is well known that at infinite dilution, only solute-solvent, solvent-solvent interactions can exist, and solute-solute interactions can be negligible. Therefore, the variable V can provide some evidence about the effect of the solvent on the structure of the solute. The variable V may be assumed to result from the sum of two contributions: the intrinsic volume of the non-solvated solute molecules and a term which takes into account the volume changes of solute caused by the solvent molecules during the solvation process [7,15]. In order to estimate the strength of solute-solvent interaction at dilution, the influence of the third component on the interaction, and the solvation degree of solute from the macroscopical thermodynamics viewpoint, the solvation coefficient γ, at a definite y value and temperature, is defined as Eq.(1), V V NsM / ρ Ns γ = = = (1) V NAM / ρ NA where the numerator, the variable( V V ) presents the changed volume of pseudo-pure solute in solution via the solvation process; N A and N s are, respectively, the Avogadro constant and the pseudo-pure solute molecules number corresponding to the changed solute volume during the solvation process; M, ρ are, respectively, the molecular weight and density of pseudo-pure solute. At a definite y value, for a definite pseudo-pure solute, the larger the changed volume of solute during the solvation process, the bigger the value of the numerator of Eq.(1), the more the molecules of pseudo-pure solute interacted with the pseudo-pure solvent molecules during the solvation process, and the stronger the solvation process of the solute. In other words, the values of the variable[( V V ), numerator in Eq.(1)], can be used to compare the interactions between the solute molecule and the solvent one as well as the solvation degrees of the solute interacted with different solvents at a definite y value and temperature. However, on the other hand, the variable, ( V V ), shows its weakness to present the solvation degree when the amount of the third component and temperature changes are considered, for the variable N s may be influenced by the amount of the third component and the temperature as well as variable ρ. The equivalent of the macroscopical thermodynamic variable ( V V ) can simply be considered as (N s M /ρ ). It is difficult to distinguish the contributions of the solvated molecules from the thermal agitation s to the macroscopical thermodynamic variable. So, the variable V * is introduced as the denominator of Eq.(1), which deducts the influences of the amounts of the third component and the thermal agitation on ρ, namely, which deducts the influences of the amounts of the third component and the thermal agitation on the volumes of non-solvated pseudo-pure solute molecules and solvated pseudo-pure solute mo-

8 316 CHEM. RES. CHINESE UNIVERSITIES Vol.26 lecules. Then, only the number of the solvated solute molecules, N s, the inner essential variable is reserved to couple with the Avogadro constant to present the solvation degree at any amounts of the third component and temperature. Thirdly, how the solvation degrees of different solutes expressed for a definite solvent? Obviously, the variable, ( V V ) shows its insufficiency, too. ecause both the number of the solvated solute molecules N s and the molecular weight of solute M can influence the value of the variable at a definite amount of the third component and temperature. When the variable V * is introduced as the denominator in Eq.(1), the influence from molecular weight of solute M is deducted, too. Now a conclusion can be tentatively drawn out that the solvation coefficient γ in Eq.(1) is a universal coefficient to describe the solute-solvent molecule interactions and the solvation degrees of solutes whether the amount of the third component, the temperature or the different solute-solvent pairs are considered. Contrast to the total interactions of solutesolute molecules, for γ>, the total interactions of solute-solvent molecules are attractive, for γ=, the total interactions of solute-solvent molecules are equal to that of solute-solute ones, for γ<, the total interactions of solvent-solvent molecules are repulsive. From the view mentioned above, the solvation coefficients of each pseudo-pure component in these ternary-pseudo-binary mixtures at each amount of the third component, ethyl acetate or benzene, at temperature K, are obtained and listed in Table 5. The results show that the values of γ decrease steadily and slightly with the amount of the third component increasing for each pseudo-pure component, which demonstrates that less and less pseudo-pure solute molecules are solvated, the relative attractive interactions of solute-solvent molecules are weakened more and more with the amount of the third component increasing in the two ternary-pseudo-binary mixtures, whether either of pseudo-pure components 1 and 2 is solute, which is consistent with the result from excess volumes [2]. The amount of the third component controls the interactions of pseudo-pure components 1 and 2 and the solvation coefficients of each pseudo-pure component. The solvation coefficient of pseudo-pure component 1 decreases from to , and that of pseudo-pure component 2 decreases from to with y value increasing from.1593 to.8538 for the mixtures containing CH 3 COOC 2 H 5. For the mixtures containing C 6 H 6, with y value increasing from.1525 to.8549, the solvation coefficient of pseudo-pure component 1 decreases from to , and that of pseudo-pure component 2 decreases from to As we know, the molecules of styrene and NMP are polar. There is a strong interaction between styrene and NMP when they are mixed, the volume contracts, which has been proved from the study of excess volumes of mixtures [1,2]. In view of the solvation coefficient, the addition of the third component, CH 3 COOC 2 H 5 or C 6 H 6, which is a weak polar or a non-polar molecule, can destroy the strong attractive interactions between styrene molecules and NMP ones of the binary mixture, leading to the decrease of the solvation coefficient. However, the ability of CH 3 COOC 2 H 5 is stronger than that of C 6 H 6, so the solvation coefficients of quasi-pure components 1 and 2, containing CH 3 COOC 2 H 5, are both smaller than those containing C 6 H 6 at a certain y value, which is shown in Fig.3. The reasonable explanations are that benzene is a cyclic molecule, and it can more efficiently stack with styrene and NMP, both also cyclic molecules, than with ethyl acetate, a linear molecule. Simultaneously, though C 6 H 6 is non-polar molecule, the π-electrons of benzene ring form π 6 6 chemical bound. Styrene and NMP molecules are both polar ones with π-electrons, which lead the non-polar C 6 H 6 into an induced-dipolar state easily. The different molecules, styrene, NMP and C 6 H 6 can interact on each other through π π interactions. The Fig.3 Solvation coefficients of pseudo-pure components at different y values in two ternarypseudo-binary mixtures at K and atmospheric pressure x[(1-y)c 6 H 5 CH=CH 2 +ych 3 COOC 2 H 5 ](1)+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 ](2): pseudo-pure component 1; pseudo-pure component 2; x[(1-y)c 6 H 5 CH=CH 2 +yc 6 H 6 ](1)+(1-x)[(1-y)NMP+yC 6 H 6 ](2): pseudopure component 1; pseudo-pure component 2.

9 No.2 HOU Hai-yun et al. 317 π-electrons of benzene ring lower the shelter effect of benzene between styrene and NMP molecules in contrast to ethyl acetate as shelter molecules. The last, the component with smaller structure size has the bigger solvation coefficient for a pair of pseudo-pure components in a solution, which can explain the fact that the solvation coefficient of pseudo-pure component 1 is smaller than that of pseudo-pure component 2 at the same y value whether the third component is CH 3 COOC 2 H 5 or C 6 H 6. 4 Conclusions This paper not only provides a set of fundamental thermodynamics data of ternary-pseudo-binary mixtures of x[(1-y)c 6 H 5 CH=CH 2 +ych 3 COOC 2 H 5 (or C 6 H 6 )](1)+(1-x)[(1-y)NMP+yCH 3 COOC 2 H 5 (or C 6 H 6 )] (2) at K and atmospheric pressure, but also provides a universal method to describe quantitatively the interactions of solute-solvent molecules and the solvation degree of pseudo-pure solute in the ternary-pseudo-binary mixture from the macroscopic thermodynamic viewpoint, this method is suitable for the investigated mixtures, and assesses the influences of the third component, ethyl acetate or benzene, on the molecular interactions between styrene and NMP further. Three conclusions are thus drawn as follows. First, the apparent molar volumes have been calculated from the density data. The apparent molar volumes and the molar fractions over the entire concentration range can be correlated well by a four parameters cubic polynomial equation, the parameters of the equation for each investigated quasi-pure component are obtained by the least-square fitting method. The limiting partial molar volumes at infinite dilution obtained by two different methods are consistent with each other and almost within.3 cm 3 /mol, the molar volumes are also consistent with each other and almost within.2 cm 3 /mol for each pseudo-pure component, which demonstrates that the four parameters cubic polynomial equation can successfully correlate the apparent molar volumes and the molar fractions over the full molar fraction range. Second, the limiting partial molar volume and the molar volume are used to define a new universal coefficient termed as solvation coefficient to express quantitatively the solvation degrees of pseudo-pure solutes and discuss the specific interactions of solute-solvent molecules in the presence of the third component, ethyl acetate or benzene in the ternary-pseudo-binary mixtures of x[(1-y)c 6 H 5 CH= CH 2 +ych 3 COOC 2 H 5 (or C 6 H 6 )](1)+(1-x)[(1-y)NMP+ ych 3 COOC 2 H 5 (or C 6 H 6 )](2). Third, it is reasonable to presume that the solvation coefficient can be considered as a macroscopical thermodynamics variable to scale the interactions of solute-solvent molecules and the quantitative solvation degrees of solutes in ternary-pseudo-binary or binary mixtures. References [1] Liu X. H., Su Z. X., Wang H. J., et al., J. Chem. Thermodyn., 1996, 28(3), 277 [2] Peng S. J., Hou H. Y., Zhou C. S., et al., J. Solution Chem., 27, 36(8), 981 [3] Riddick J. A., unger W.., Organic Solvents, 4th Ed. Techniques of Chemistry, Vol. II, Wiley, New York, 1986 [4] Weast R. C., Handbook of Chemistry and Physics, 58th Ed. CRC Press Inc., Florida, 1978 [5] Takenaka M., Tanaka R., Murakami S., J. Chem. Thermodyn., 198, 12(9), 849 [6] IUPAC Commission on Atomic Weights and Isotopic Abundances 1985, Pure Appl. Chem., 1986, 58, 1677 [7] Tasic D. R., Klofutar C., Monatshefte Für Chemie, 1998, 129(12), 1245 [8] Harned H. S., Owen.., The Physical Chemistry of Electrolyte Solutions., Reinhold, New York, 1954 [9] landamer M. J., Chem. Soc. Rev., 1998, 27, 73 [1] Wawer J., Krakowiak J., Placzek A., et al., J. Mol. Liq., 28, 143(2/3), 95 [11] Liu D. X., Li H. R., Deng D. S., et al., Chin. J. Chem. Eng., 22, 1(4), 454 [12] Hou H. Y., Peng S. J., Wang X. X., et al., Chem. J. Chinese Universities, 29, 3(3), 563 [13] Hou H. Y., Wang X. X., Peng S. J., et al., Chem. J. Chinese Universities, 29, 3(7), 1386 [14] Tasic D. R., Klofutar C., Monatshefte Für Chemie, 23, 134(9), 1185 [15] Wurzburger S., Sartorio R., Guarino G., et al., J. Chem. Soc. Faraday Trans. I, 1988, 84, 2279