R. Massaudi and A.
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D. King, Jr.
o ~ of Alcu ~ ompressed ~ ~ Gases. ~ A Comparison ~ ~ of Vapor-Phase lnteractioas of Alcohols and Homomorphic Compounds with Various Gases. gi 1. 1 -Butanol, Diethyl Ether, and n-Pentane in Compressed Nitrogen, n, Methane, Ethane, and Carbon Dioxide at 25"' W. Massoudi and A. D. King, Jr.* Department of Chemistry, University of Georgia, Athens, Georgia 30602 (Received February 12, 1973)
The vapor concentrations of 1-butanol, diethyl ether, and n-pentane have been determined as a function of pressure in a series of compressed gases, including carbon dioxide. Second cross virial coefficients representing deviations from ideality caused by bimolecular interactions of these three compounds with the individual gases have been evaluated from the data. With the exception of COz, the cross virial coefficients of each of the three homomorphic molecules with a given gas are found to be the same within experimental error. In the case of CQz, it is found that the cross virial coefficients of 1-butanol and diethyl ether with COz are similar in magnitude but considerably larger than that resulting from pentane-C0z interactions. This anomaly is interpreted as indicating that the alcohol and ether undergo a reversible association with C02 in the gas phase.
Introduction
ity resulting from bimolecular interactions between molecules of the liquid component and those of the gas have In a series of papers reporting vapor compositions a t elbeen evaluated from the vapor composition-pressure data, evated pressures for various compressed gases in equilibrias outlined in the previous paper, and are listed in Table um with liquid water,2 methanol,3 and ethan01,~considerI. Values for molar volumes and vapor pressures of the able evidence has accumulated indicating that weak compure liquids used in these calculations were taken from ref plexation occurs between gaseous COz and vapors of these 7-9. The pure component virial coefficients required were oxygen containing liquids. Various arguments based on obtained from ref 10. ~ measurecomparisons involving NzO and C O Z , solubility ments of chloroform in dense gases,4 as well as t h e ~ r y ~ , ~ The only additional information required for these calculations is a knowledge of the liquid-phase composition all suggest that the stabilization leading to the formation as a function of pressure. This was estimated by using of these complexes does not arise from electrostatic forces Henry's law expressed in terms of fugacity. The Henry's but rat,ber involves either hydrogen bonding or the direct law constants used in these calculations are listed in interaction of the oxygen atom of the vapor molecules Table II.11-16 It is seen that in many cases experimental with COz, either through a simple donor-acceptor mechagas solubility data were not available from the literature. nism or possibly an esterification reaction leading to carFortunately, for systems where chemical interactions are bonic acid or its monoalkyl esters. This paper reports an unimportant, reliable estimates of gas solubility can be extension of the above studies in which gas-phase solubiliobtained using a method developed by Shair and Prausty measurements are used to compare the vapor-phase benitz.17 Correlations given by these authors suggest that havior of three homomorphs, l-butanol, diethyl ether, and Henry's law constants can be estimated to an accuracy of n-pentane in dilute gaseous solutions involving various better than 10% for the systems of interest here. Since the unreactive gases as well as carbon dioxide. values calculated for BIZ(T ) are relatively insensitive to gas solubility a t the pressures of these experiments, incluExperimental Section sion of an assumed error of 10% for K H leads to a total The experimental apparatus and techniques used in error of only *30 cc/mol for diethyl ether and pentane this work are the same as those outlined in a previous pawith C2H6, and f12, &8, and k7 cc/mol for pentane with per.5 The n-pentane, diethyl ether, and l-butanol used in CH4, Ar, and Nz, respectively. The solubilities of CO, in these experiments were reagent grade or the equivalent. n-pentane and diethyl ether were d e t e r n h e d in this laboratory by a very simple technique in which known amounts of these solvents are first saturated with COZ Results a n d Discussion then allow to react with standardized aqueous solutions of sodium hydroxide. After the extraction of COz is comIn this study, vapor compositions have been determined plete, the remaining sodium hydroxide is titrated with as a function of total pressure for two phase systems instrong acid to the bicarbonate end point. The number of volving three homomorphic liquids, n-pentane, diethyl equivalents of acid necessary to effect this is subtracted ether, and 1-butanol with a series of gases including COz, from that required to neutralize an equal volume of the all a t 25". The vapor composition data determined in pure sodium hydroxide solution, the difference being these experiments will not be listed here for the sake of equal to the number of moles of COz extracted from the brevity but can be obtained from this journal.6 Second known volume of organic solvent. The results obtained cross virial coefficients representing deviations from idealThe Journal of Physical Chemistry, Pol. 77, No. 76, 1973
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Comparison of Vapor-Phase Interactions of Alcohols and Homomorphic Compounds using this method were checked against literature values for several GO2-solvent systems and the agreement was excellent. An inspection of the data in Table I shows that the values obtained here for systems involving n-pentane generally agree, within experimental error, with values obtained from high-pressure gas-liquid chromatography. They are, however, consistently outside the estimates of error and smaller in magnitude than those derived from PVT measurements. A detailed review of our experimental procedure and methods of calculation show no source of error in this work which could lead to such a discrepanCY.
Secondly, it is seen that the second cros,s viriai coefficients of the three homomorphs with nonreactive gases are the same within experimental error. This is, of course, not unexpected since there is no reason to expect purely physical interactions to differ significantly among these systems. As pointed out previously,4 this close similarity suggests that any decrease in dispersion forces among the oxygen-containing systems (relative to n-pentane) arising from the fact that an oxygen atom is less polarizable than a methylene group is either insignificant or is cancelled out by the additional dipole-induced dipole attraction. In contrast with this, it is seen that with carbon dioxide, the cross virial coefficients of the alcohol and ether are considerably more negative than the value for pentane with C 0 2 . If the cross virial coefficient for pentane with C 0 2 is taken as representative of the deviations from ideality caused by physical forces in these systems, then one concludes that the excessively large values for the oxygen-containing homomorphs with C 0 2 reflect contributions arising from chemical interactions. While it can be argued that dipole-quadrupole and dipole-induced dipole forces provide additional modes of attraction which are absent in the CO2-n-pentane system, estimates based on derivations by Poplel8 and Kielichlg show that such interactions would be expected to contribute approximately -10 cm3//mol to the second cross virial coefficients of these systems. This is far less than the observed discrepancies which are the order of 100-200 cm3/mol. If it is assumed that the differences between the virial coefficients of the alcohol and ether with C02 and that for n-pentane with COa result from a n increase in vapor concentration caused by bimolecular complex formation of the oxygen-containing homomorphs with C 0 2 , then one can arrive a t values for the. equilibrium constant for dissociation of the complex, K p , from the simple relationship4
Here all symbols have their usual meaning and the subscripts are self-explanatory. On substituting the values in the last row of Table I in eq 1, one obtains values of K, = 87 f 23 and 56 f 12 atm for the complexes of 1-butanol and diethyl ether with C 0 2 a t 25". The value for 1-butanol is essentially the same as K , = 91 atm found for the lower alcohols, methanol and ethanol, with C 0 2 a t this temperature. The inability of an ether to form a hydrogen bond or a n ester with a n acid anhydride like C 0 2 suggests strongly that the complex formed between diethyl ether and CO2 is of a charge transfer type, presumedly involving donation of lone pair electrons localized on the ether oxygen atom to a n antibonding orbital of C 0 2 . While it can not be proven in the absence of direct spectroscopic observa-
Second Cross Virial Coefficients for 1-Butanol, Diethyl Ether, and n-Pentane with Variaus Gasesa
TABLE I:
690
Gas
Nz Ar
1-Butanol
-72 f lob -90 f 1 1 12
(25')
Diethyl ether
-67 f 9 -89 f 6 -161 f 3
CH4
-160 f
CzHtj
-375 f 35
-388 f 30
COz
-414 f 14
-491 f 23
n-Pentane
-77 f 7 (-103 f 6 ' ) -97 f 8 (-,98f 6,' -125 f 2 3 9 -170f 12(-207f42,e -218,f-222 f 13q -386 f 30 (-414 f 171,e-448f 16g) -273 f 23
a Literature values for n-pentane shown in parentheses. Error expressed as average deviation from mean. C A . J. B. Cruickshank. M. L. Windsor, and C. L. Young, Proc. Roy. Soc., Ser. A, 295, 271 (1966); glc method. E. M. Dantzler, C. M. Knobler. and M. L. Windsor, J. Chrcmatogr., 32, 433 (1968); PVT method. e R . L. Pecsok and M. ,L. Windsor, Anal. Chem., 40, 1238 (1968); glc method. fSh. D, Zaalishvili, Zh. Fiz. Khim., 30, 1891 (1956); PVT method. gE. M. Dantzler, C. M. Knobler, and M. L. Windsor, d . Phys. Chem., 72, 676 (1968); PVTmethod.
TABLE II: Henry's Law Constants for 1-Butanol, Diethyl Ether, and n-Pentane with Various Gases at 25' Liquid
Gas
K I i , atm
21 10 1080 524 91.7 134 799 390 221 29.6 29.6 665 357 197 28.5 64.7
Ref 11
11 11 11 12 13 14 13 15 16
15 15 15 15 16
tions, it is not unreasonable to assume that the chemical bonding responsible for the alcohol-CO2 complexes is of a similar nature. The observed trend in the dissociation constants with the ether having a similar but somewhat smaller value than the alcohol is in keeping with such an assumption. Acknowledgment. The authors are grateful for support provided by the National Science Foundation (NSF Grant NO. GP-29324). Supplementary Material Available. A listing of the experimentally determined vapor mole fraction data will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper only or microfiche (105 x 148 mm, 20 x reduction, negatives) containing all the supplementary material for the paper in this issue may be obtained from the Journals Department, American Chemical Society, 1155 16th St., N.W., Washington, D. C. 20036. Remit check or money order for-$3.00 for photocopy or $2.00 for microfiche, referring to code number JPC-732016. The Journal of Physical Chemistry, Vol. 77, NO. 76, 7973
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References and Notes (1) This work was supported in part by the National Science Foundation (NSF Grant No. GP-29324). (2) C. R. Coan and A. D. King, Jr.. J. Amer. Chem. SOC., 93, 1857 (1971) (3) B. Hernmaplardh and A. D. King, Jr., J. Phys. Chem. 76, 2170 (1972). (4) S. K. Gupta, R. D. Lesslie, and A. D. King, Jr., J. Phys. Chem., 77, 2011 (1973). (5) C. R. Coan and A. D. King, Jr., J. Chromafogr., 44, 429 (1969). (6) See paragraph at end of paper regarding supplementary material. (7) R. R. Dreisbach, Advan. Chem. Ser., No. 22 (1959). (8) E. D. Washburn, Ed., "International Critical Tables," Voi. 3, McGraw-Hili, New York, N. Y., 1928. (9) T. E. Jordan, "Vapor Pressures of Organic Compounds," Interscience, New York, N. Y., 1954.
The Journal of PhysicalChemistry, Voi. 77, No. 76, 7973
R. Massoudi and A.
D.King, Jr.
(10) J. H. Dymond and E. B. Smith, "The Virial Coefficients of Gases," Oxford University Press, London, 1969. (11) F. L. Boyer and L. J. Bircher, J. Phys. Chem., 64, 1330 (1960). (12) R. Mayerand M. Hoffman,J. Prackt. Chem., 11,327 (1960). (13) J. Horiuti, Sci. Pap. Inst. Phys. Chem. Res., Tokyo, 17, no. 311, 125 (1931). Cited in J. H. Hiidebrand and R. L. Scott, "The Solubility of Nonelectrolytes," Reinhold, New York, N. Y., 1950; reprinted by Dover Publications, New York, N. Y.. 1984, p 243. (14) W. F. Linke, Seideil. Ed., "Solubilities of Inorganic and Metal-Organic Compounds," 3rd ed, Van Nostrand, Princeton, N. J., 1958. (15) Calculated using method of ref 17. (16) Measured in this laboratory. (17) J. H. Hildebrand, J. M. Prausnitz, and R. L. Scott, "Regular and Related Solutions," Van Nostrand-Reinhold, New York, N. Y., 1970, p 125. (18) J. A. Pople, Proc. Roy. SOC., Ser. A, 221, 508 (1954). (19) S. Kielich,Acta Phys. Pol., 20, 433 (1961).
