H. LAWRENCE CLEVER
1082
Vol. 61
vents and the 9, 10, 12 and 14 carbon solvents. The parameters calculated in this manner reproduce the solubilities in the 6, 7 and 8 carbon solvents better than for the higher molecular weight solvents.
"42 3
24
X 38
rn ~~
n
20 5 16
30
- 12
ARGON
28
-
24
-
I
I
I
I
NEON
I I
I
0 0
I
TABLE IV COMPARISON OF CALCULATED A N D EXPERIMENTAL SOLUBILITIES AT 25O, HILDEBRAND EQUATION
I
Splu-
I.
-
Gas
bility parameter,
Helium Neon Argon Krypton
Molar vol.,
82
VZ
6.3 4.41 5.43 5.54
75 50 40 32.5
so$:$yt
Moan % error of calcd. mole fraction solubility 9,10. 6 7 8 1214 All 13 ca;bbn carbon solsolsol104 vents vents vents
x 2.51 5.13 17.2 38.1
Xi
14 10
5 5
10 9 3 3
21 12 10 9
D. Some Empirical Relations.-Hildebrand20 recently has pointed out an empirical linear relation between the logarithm of the molar gas 440 460 480 solubility and the solvent solubility parameter. A Bondi empty vol., cm.a/l. Fig. 4.-Rare gas molar solubility vs. Bondi empt similar plot (Fig. 3) for the rare gas solubilities volume of solvent. The straight lines are drawn wit[ shows a t least two linear relationships. The octane respect to the seven n-chain hydrocarbon solvents, 0 cyclo- isomers, benzene and cyclohexane fall on one line hexane. while the normal chain hydrocarbon solvents give For gases above their critical conditions it is another line. Of the twelve solvents Hildebrand customary to evaluate .a2 and V z from the experi- uses ten are 6, 7 or 8 carbon solvents which suggest mental solubility in selected solvents for neon, argon a similarity in solvent size that may mask some enand krypton. This has been done using the ex- tropy effect which may be present in a larger range perimental solubility in the two solvents differing of molecular size. most in the solubility parameter (2,2,4-trimethylBondiZ1gives data from which one can calculate pentane 61 = 6.85 and benzene 61 = 9.15) along with the empty volume of a paraffin hydrocarbon, which values of X i at 25" from log Poagainst 1/T plots19 he defines as the macroscopic volume minus the van extrapolated through the critical pressure. For der Waals volume of the liquid. There appears to helium X i cannot be evaluated from log Po be a direct linear relation between the molar rare against 1/T plots so the cyclohexane (a1 = 8.20) gas solubility and the empty volume of the hydro, and X i evaluated carbon (Fig. 4) which suggest the gas fits into acsolubility was included and V p 6z as unknowns. tual spaces present in the solvent. Results are in Table I V along with the mean per Molar solubility plotted against solvent density cent. error in the calculated mole fraction solu- approximates a linear relation but correlation is not bility for all 13 solvents, the 6, 7 and 8 carbon sol- quite as good as with the empty volume. (19) J. H. Hildebrand and R. L. Scott, "The Solubility of Non-eleotrolytes," Reinhold Publ. Corp., New York, N. Y., 1950, Chap. 15.
(20) J. H. Hildebrand, THIS JOURNAL, 68, 871 (1954). (21) A. Bondi, ibid., 68, 929 (1954).
THE SOLUBILITY OF ARGON AND KRYPTON I N p-XYLENE AND p-XYLENE-p-DIHALOBENZENE MIXTURES AT 30°1 BYH. LAWRENCE CLEVER^ Contribution from the Department of Chemistry, Duke University, Durham, N . C. Received November Id, 136%
The solubility of both argon and krypton a t 30" and one atmosphere total pressure in p-xylene decreases linearly a6 the mole fraction of the p-dihalobenzene increases in the mixed solvents. Some relationship between the solubilities and the surface tension of the solvents are discussed.
This study was undertaken to provide information to help elucidate the forces that contribute t o (1) Presented before the Division of Physical and Inorganic Chemistry, 127th National Meeting of the American Chemical Society, Cincinnati, Ohio, April, 1955. (2) Department of Chemistry, Emory University, Emory University Georgia.
solubility. The effect of progreqsively increasing polarizable groups in a solvent without a macro dipole moment was inve3tigated by determining the solubility of argon and krypton a t 30" in p-xylene and fixtures of p ~ x y ~ e n e - l o ~ ~ ~ c ~ ~ op-r o ~ e n z ~ ~ e , xylene-P-dibromobenzene and p-xylene-P-diiodobenzene.
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SOLUBILITY OF ARGON AND KRYPTON IN P-XYLENE
August, 1957
TABLE I MIXEDSOLVENT PROPERTIES AND ARGON AND KRYPTON SOLUBILITIES, 30"
Solvent
p-Xylene p-Xylene p-Dichlorobenzene p-Xylene p-Dibromobenzene p-Xylene p-Diiodobenzene
p-Dihalobenzene, mole fraction
Density,
0 0.170 0.310 0.455 0.130 0.255 0.078
0.852 0.920 0.978 1.040 0.992 1.128 0.987
g./ml.
VOl. of one mole of solvent, ml.
Surface tension dyne/cm.
Solvent solubility parameter, 61 oalcd.
124.6 122.9 121.5 120.0 124.0 123.4 125.2
27.15 27.50 28.50 29.50 27.95 30.55 27.75
8.50 8.55 8.70 8.85 8.60 8.95 8.55
Experimental The solubility apparatus, procedures and gases have been described before.3 p-Xylene, Eastman Kodak white label, was fractionally crystallized twice, discarding over one-third the material each time, dried over sodium and distilled. The fraction distilling between 138.0 and 138.2' was used. p-Dichlorobenzene, p-dibromobenzene and p-diiodobenzene, all Eastman Kodak white label material, were each recrystallized twice from boiling methyl alcohol and thoroughly dried in air. The m.p.'s taken on a hot stage, m.p. apparatus were p-dichlorobenzene 53 .O ', p-dibromobenzene 87.8' and p-diiodobenzene 128.9" which agree satisfactorily with recorded melting points.4 The density of the mixtures was determined by direct, weighing of 250 ml. of the mixed solvent thermostated a t 30' in a 250-ml. volumetric flask that had been previously calibrated with water. Surface tensions of the mixed solvents were determined by the maximum bubble pressure method.6
Results and Discussion Mixed solvent composition, density, molar volume, surface tension, solubility parameter and solubilities (corrected to 1 atm. by Henry's law) in units of both Ostwald coefficient and mole fraction, are given in Table I. The mole fraction gas solubility decreases linearly with increasing mole fraction of the p-dihalobenzene in the mixed solvent. The slopes in the mixed solvent containing p-dichlorobenzene are -0.00050 and -0.0018, p-dibromobenzene -0.00097 and -0.0027 and p-diiodobenzene -0.00155 and -0.0093 for argon and krypton solubilities, respectively. I n Fig. 1 is plotted the logarithm of the Ostwald coefficient against the mixed solvent surface tension. The straight line drawn through the p-xylene point is drawn t o have the same slope found previously for thirteen hydrocarbon solvents3 and represents the present data better than might be expected for mixed solvents. Gjaldbaeks finds the linear relation between the logarithm of the Ostwald coefficient and solvent surface tension first observed by Uhlig' does not hold for water to which surface active agents have been added. However, in the present case it may be that p-xylene and the p-dihalobenzenes are sufficiently alike so that the composition of the surface layer approximates that of the bulk of the mixture. (3) H. L. Clever, R. Battino, J. H. Saylor and P. R.1. Gross, Tms JOURNAL, 61, 1078 (1957). (4) "Beilstein," Band V. (6) Surface tensions measured at Emory University on apparatus of the late 0. R. Quayle, see Chem. Reus., I S , 439 (1953). (6) J. Chr. Gjaldbaek, Acta Chim. Scand., '7, 537 (1953). (7) H.H. Uhlig, THISJOURNAL, 41, 1215 (1937).
A
Ostwald
0.250 0.236 0.224 0.212 0.225 0.204 0.225
Solubility Mole fraction X 10' A Kr
Kr
0.762 0.724 0.628 0,647 0.686 0.631 0,695
1.25 1.17 1.09 1.02 1.12 1.01 1.13
3.81 3.56 3.32 3.10 3.41 3.13 3.48
Hildebrand and Scott*show the solubility parameter of a pure non-polar solvent can be calculated from its surface tension, u, and molar volume, V ,by the relation 61 = 4.1
(&)
0.43
The solubility parameter of the mixed solvent (Table I) has been approximated from this equation. The calculated solvent solubility parameter, values of 62 and V 2 evaluated from the experimental gas solubilities in benzene and isooctanea using a value of the ideal solubility obtained by extrapolating log Po against 1/T beyond the critical 0.13 0.17
4
2
0.21
I 0.62
0.66 0.70
28 29 30 Solvent surface tension, dynes/cm. Fig. 1.-Logarithm of the Ostwald coefficient of solubility vs. the mixed solvent surface tension: 0 , p-xylene; a, pdichlorobenzene-p-xylene; 0 , p-dibromobenzene-p-xylene; 0 , p-diiodobenzene-p-xylene. Lines drawn through pxylene point with same slope previously observed for 13 hydrocarbon solvents. 27
point reproduce the experimental mole fraction solubilities with an average error of 21% for argon and 20% for krypton when substituted in the Hildebrand and Gjaldbaekg equation -log X z = -log X2+ log VZ + 0.434 (1 -
): +
T71
Acknowledgment.-The author is indebted to Professors P. M. Gross and J. H. Saylor for helpful discussions. (8) J. H. Hildebrand and R. L. Scott, "Solubility of Nonelectrolytes." 3rd ed., Reinhold Publ. Corp., New York, N. Y., 1950,Chap. 21. (9) J. Chr. Gjaldbaek and J. H. Hildebrand, J . Am. Chsm. Soc., '71, 3147 (1949).
