NOTES
2268
Vol. 65
much higher melting points than do the others, the occurrence of an increase in heat capacity over this larger temperature interval is not unexpected. However, the reason for the much larger change for CdClz than for CdBrz is not clear in view of the similar nature of these salts.
PARTIAL MOLAL VOLUMES IN LIQUTDLIQUID MIXTURES BY RYOICHIFUJISHIRO, Kbz6 SHINODA AND J. H. HILDEBRAND
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Department
OJ
Fig. 1.-Partial
Chemistry, Unirersity of CaliJornia, Berkeley 4 , CaE. Receiiied J u n e 19, 1061
The work here report,ed is part of a study of the role of expansion in the theory of solution. The magnitude of this factor first became strikingly evident by the observation of Glew' that the partial molal volume, Vz, of iodine in f-heptane at 25' and at virtually infinite dilution (mole fraction 1.8 X is 100 cc., a 70% expansion over its (extrapolated) liquid molal volume, 59 cc. Its partial molal volumes in a number of other solvents were measured by Shinoda and Hildebrand. Smith, Walkley and Hildebrand3 obtained figures for the partial molal volumes of bromine and stannic iodide at high dilution in the same series of solvents. Jolley and Hildebrand4 published values of the partial molal volumes of gases. Walkley and Hildebrand6found that VZ for Hz in benzene and in toluene exceeds that of Dzby 10%. The paper by Smith, Walkley and Hildebrand compared the partial molal volumes of one solute in a series of solvents; this research compares a series of solutes in the same solvent. The method used was t.he simple, rapid, accurate one described in ref. 2. A long, thin glass capsule containing a small, weighed amount of a solute is drop ed into a large bulb filled with a solvent through its capilkry stem. The capsule is broken and the solute dissolved by means of a large glass ball within the bulb. The partial molal volume is calculated from the rise of the liquid in the capillary stem. The amounts of the solvent and solute are such that the values of ?n are virtually those for infinite dilution (mole fraction M 10-3). The materials used were purified by methods previously described.2
The values of V2 thus obtained are given in Table I, together with t'he molal volumes, Vzo, and the solubility parameters of the pure components, 6. The values of Vz are the means of two or more determinations agreeing well within 1%. Figure 1 is a plot of [(Vz - V Z O ) / V ~ ~ ] 'us. / ~ solubility parameters in the two solvents, CC14 and CSz. This method of plotting is suggested by the equation 02
- vP
=
nfllRT In
y2
(1)
where is the compressibility of t,he solvent when the solute is very dilute, as in these experiments; yz is the activity coefficient of the solute, and n is (1) D. N. Glew and J. H. Hildebrand, J. Phys. Chem., 60, 618 (1956). (2) I(. Shinoda and J. H. Hildebrand, ibid.,62, 272 (1958). (3) E. B. Smith. J. Walkley and J. H. Hildebrand, ibid., 63, 703 (19591. (4) J. E. Jolley m d J. H. Hildebrand. J . A m . Phern. Soc., 80, 1050 ( 1 958). ( 5 ) J. IVdkIey and J . If. IIildebrand, ibid., 81, 4139 (1959).
excess volumes at high dilution and solubility psrameters.
the ratio (bEl/bV1)p,~to AE~"/VL E is energy in cal./mole, AE" is energy of vaporization. Equation l, without the factor, n, was given by Hildebrand and Scott.6 Inclusion of the factor, n, is explained in a more detailed derivation to be given in a book now in press.7 Upon combining equation 1 with the simple equation for regular solutions R T In
y2 =
v20912(6n -~ 3 ~ ) ~
(2)
where cpl is the volume fraction of the solvent, here -1, we obtain (3)
We see from Fig. 1 that the left-hand member is closely proportional t'o f (62 - 61) except in the cases Of n-C7H1tj1 i-CsHu, C6H6 and 1,2,3-CeH~(CH,):, the points for which are designated by crosses. The slopes of the lines are almost exactly 4 5 O , hence the proportionality constant is close to 0.1. The wide range of expansion covered by this regularity, up t o 9%, is especially noteworthy. TABLE I PARTIALMOLALVOLUMES OF SOLUTES, V2, AT 25" A N D HIGH DILUTION -vZ
Solute
6
C7F16 c-C~FUCF~ i-CsHn c-CdClnFs n-C~Hls CClzF.CClF2 c-CsHiz
5.85 6.0 6.85 7.1 7.45 7.5 8.2 8.6 8.8 9.15 9.5 10.0 10.5 11.5
cc1,
s-CsHs(CHt)r CsH6 CsHsC1
csn CHBr3 Brz
V1'
225.5 195.8 166.1 142.5 147.5 119.8 108.8 97.1 139.6 89.3 102.1 60.7 87.8 51.5
cs2
... .., 172.2 155.5 154.4 127.7 112.1 99.2 144.5 91.6
... ... 88.1 52.6
In----CCl4
246.5 211.6 167.5 146.6 149.1 120.9
n-CIHl6
... ...
254.6 218.3 167.4 153.6 ... 124.5 ... 98.2
,
...
. .
... .. .
91.0 105.5 62.0 63.4 90.9 92.1 54.75 . . .
This empirical constant does not agree very 'Iz. The compressibilities well with values of (np) of CC14 and CS2 are 1.11 X and 0.93 X atm.-',, respectively, and the n-values are, respectively,8 1.07 and 0.89. The figures for p are (6) J. H. Hildebrand and R. L. Soott, "Solubility of Nonelectrolytes," Reinhoid Publ. Corp., New York, N. Y., 1950, p. 141. (7) J. H. Hildebrand and R. L. Scott, "Regular Solutions," Prentice-Hall, New York, N. Y.,1962, i n press. (8) Ref. 6, p. 97.
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Dec., 1961
NOTES
2269
in atm.-l; to convert them to the units used for pyrolysis of methylenecyclobutane was of inter6, cal. cc.-', we introduce the factor 41.3 and obtain est since this molecule represents a structure interfor the theoretical values of (np)'" 0.070 and 0.058, mediate between the alkylcyclobutanes on the one respectively, for the two solvents, considerably less hand and cyclobutanone and other carbonyl-group than the experimental value, 0.1. containing cyclobutanes on the other. The points for i-CSH18 are found far to the left of Experimental the lines in both solvents. Its solubility paramMaterials.-The methylenecyclobutane was obtained eter would have to be 7.7 instead of 6.85, as de- from Reaction Products, Inc. After fractionation in this rived from its energy of vaporization, in order to Laboratory through an 85-cm. Lecky-Ewe11 column (b.p. agree with the other solutes. Its solubility re- 41.0 f 0.5" a t 760 mm.) this sample was used directly for preliminary experiments. Since the sample subsequently lations with such diverse substances as C7F169 the was found to contain a trace of 2-methyl-1-butene and about and IZlo yield the values 7.9 and 7.95 for its solu- 7% of spiropentane, it was purified further by vapor fractobility parameter, in good agreement with the value metry before use in the kinetic experiments. No evidence of 7.7 above. The much smaller discrepancies for impurities was found by either infrared spectrometry or gas after this treatment. n-C7Hls correspond similarly to an adjusted chromatography The allene used in this work was prepared by Dr. M. solubility parameter. Szwarc of the New York State College of Forestry and was The point for cyclohexane in CSa falls upon the fractionated in this Laboratory in a Podbielniak column. line. This substance, although a hydrocarbon, The middle fraction (b.p. -35") was used after repeated dea t - 160". is compact. In its solvent power for iodine it is gassing Ethylene from the Phillips Petroleum Company (research likewise quite normal. Evidently the behavior grade, 99.9% min. purity) was subjected to trap-to-trap of i-CSH18 is to be referred primarily to loose distillation and degassed at - 196". Apparatus.-The early experiments were performed in a structure. 500-ml. Pyrex reaction vessel with a conventional furnace We have added in Fig. 1 a point for benzene in and temperature control system. The effect of increased carbon tetrachloride obtained from measurements surface area was tested by use of a vessel packed with thinby Scatchard, Wood and Mochel.ll Plotting walled Pyrex capillary tubing so as to have a surface-totheir values of Avm/vOus. sz(CeH6),the slope at volume ratio 34 times that of the unpacked vessel. The kinetic experiments were carried out in a cylindrical a = 0 gives 02 - VZ" = 1.45 X 10-4whence (02- final 3 2 0 4 . vessel contained in an electrically heated furnace VzO/V20 = 0.012. mounted with the axis of the cylinder in a vertical position. The points for benzene and mesitylene also de- Platinum, platinum-l3% rhodium thermocouples attached part from the general relation depicted in Fig. l. to a Leeds and Northrup type K-2 potent,iometer were used the temperature measurements. The pressure in the The molecules of these solvents have ?r-electrons, for reaction vessel was measured with a 3-mm. bore capillary whereas those that agree with the relation all have mercury manometer for the high pressures (45-65 mm.), and non-bonding electrons. WalkIey, GIew and Hilde- with a 20-mm. bore mercury manometer read with a cathebrand12 showed that these two classes of solvents tometer for pressures below 12 mm. Infrared absorption measurements were made on a Perkinfall into different groups with respect to their Elmer Model 21 double beam infrared spectrometer equipped effect upon the wave length of the visible peak of with a one meter path length gas cell. Chromato raphic iodine. analyses were performed on a Perkin-Elmer M o d 8 154B The values of 92 for various solutes in n-heptane Vapor Fractometer, separations being effected by tetraisoon firebrick or diisodecyl phthalate on Celite. as solvent, given in Table I, yield points that are butylene Synthetic mixtures of reaction products served as standards somewhat scattered when plotted as in Fig. 1, for quantitative determinations. as might be expected. Results The study confirms (a) the intimate relation bePreliminary Experiments.eMethylenecyclobutween excess volumes and solubility and (b) the role that differences in the type of molecular electronic tane was found to decompose in the gas phase near 450". The principal products first were identified structure may play in solubility relations. We gratefully acknowledge support of this as ethylene and allene by infrared absorption work by the Atomic Energy Commission and by measurements. Subsequently the combined products from the decomposition at 460" of two 11-mm. the National Science Foundation. samples were separated into a fraction volatile at (9) J. Hildehrand, B. B. Fisher and H. A. Benesi, J . A m . Chem. Soc.. -139" and one volatile at -78". Mass spectro72,434s (1950). (10) G.R. Negishi, L. H. Donnally and J. H. Hildebrand, i W . , 65, metric analysis5 confirmed ethylene and allene as 4793 (1933). the chief constituents of the two respective frac(11) G. Scatchard, S. F. Wood and J. M. Mochel. ibid 62, 712 tions. (1940). Since for 45 to 65 mm. of methylenecyclobutane (12) J. Waikley, D. N. Glew and J. H. Hildebrand, J . Chem. Phys., 88,621 (1960).
(1) This work was supported by a grant from the National Science Foundation. (2) Participants in the NSF Summer Research Program for Science Teachers during 1959 and 1960, respectively. T H E THERMAL DECOMPOSITION OF (3) (a) Department of Chemistry, St. Michael's College, Winooski, METHYLENECYCLOBUTANE Vermont; (b) Postdoctoral fellow during the summer of 1960 under a research grant from the Shell Companies Foundation, Inc. BY R. L. B R A N D A UB. R , SHORT$ ~ AND S. M. E. KELLNER~ ( 4 ) Performed by Eugene Johnson and M. N. Das in this Lahoratory. The work of E. J. was part of a senior research problem for Deportment of Chemistry of the University of Rochester, Rochester, N . Y . the B.S. degree and was mentioned in footnote 24 of W. B. Guenther Rereined June 86,1981 and W. D. Walters, J . A m . Chem. Soc., 81, 1314 (1959). M. N. D. working a8 a postdoctoral fellow under a research grant from the In coilsidering the influence of the side chain con- was Celanese Corporation of America. stituent on the rate and mechanism of decomposi( 5 ) Performed by Consolidated Engineering Corporation, Pasation of subst,itut,ed cyclobutanes, a study of the dena, California.
