2417
C O M M U N I C A T I O N S TO THE EDITOR
The Thermodynamics of the System Pentafluorobenzene-Benzene
Sir: Much interest has recently been shown in the thermodynamic properties of binary systems of the type aromatic fluorocarbon-aromatic hydrocarbon. Hexafluorobenzene has been shown to form solid equimolar coniplexes with most aromatic hydrocarbons, and this is believed to be clue to charge-transfer interaction with the fluorocarbon acting as the electron acceptor. From the experimental excess volumes of mixing,a it appears that the extent of complexing increases as the electron-donating power of the hydrocarbon is increased. The heats of mixing of the two systems hexafluorobenzene-benzene and pentafluorobenzene-benzene have been measured recently by Fenby, blclure, and Scott,' who show that a reasonable interpretation of the results is that the specific interactions are much weaker in the system containing pentafluorobenzene. Our results presented here confirm that, in the solid state, this interpretation is correct. The experimental phase diagram for the system pentafluorobenzene-benzene is shown in Figure 1 and was obtained using an apparatus previously describedV2 The system is seen to form two weak compounds s2
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~~
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(1) C.R.Patrick and G . S. Prosser, hiature, 187,1021 (1960). (2) W. A. Duncan and F. L. Swinton, Trans. Faraday Soc., 62, 1082 (1966). (3) W. A. Duncan, J. P. Sheridan, and F. L. Swinton, ibid., 62, 1090 (1966). (4) D.V. Fenby, I. A. McLure, and R. L. Scott, J . Phys. Chem., 70,602 (1966).
DEPARTMENT OF PUREAND APPLIED CHEMISTRY UNIVERSITY OF STRATHCLYDE GLASGOW C.l., SCOTLAND
WILLIAM A. DUNCAN FINDLAY L. SWINTON
RECEIVED APRIL18, 1966
Isomeric Transition Induced Reactions of Iodine-130 in Cyclohexane Sir: Discovery of the I3OIrn (I.T.) nuclear reaction (TI,*9.2 min)' has made it possible to compare isomeric transition induced reactions with reactions effected by other nuclear transformations in the iodine system. Several processes were reported to produce the same effects in several liquid alkyl halide^.^^^ I n the cyclohexane-iodine system, where iodine is not contained in the target molecule, the (n, 2n) reaction was reported to cause higher organic yields than the (n, y) reaction due to its higher recoil energy.4 Since isomeric transition activated I3OI would be expected to have less kinetic energy than (n, ?)-activated lZsI,an isotope effect might be expected. None was found in the nhexane-iodine system' within f5%. Using the freeze-thaw technique developed in the study of *2Brm(I.T.) s2Br reaction^,^ we obtained the
10
0
-20
9 h-
-40
-60
with incongruent melting points, the mole ratios of fluorocarbon to hydrocarbon being 1 : l and 3:2. The occurrence of an intermolecular complex of a molar ratio 3:2 appears to be unique among binary systems of organic substances. Our results do not agree with those of Patrick and Prosser,' who found no evidence for compound formation in this system. I n contrast, hexafluorobenzene-benzene forms a strong 1 :1 complex melting some 20" higher than the melting point of either pure component.
t 0
Figure 1. T h e phase diagram of the system pen tafluorobeneene-benzene.
1.0
(1) D.D.Wilkey and J. E. Willard, J . Chem. Phys., 44,970 (1966). (2) R.H.Schuler, ibid., 22,2026 (1954). (3) G.Levey and J. E. Willard, J . Am. Chem. Soc., 74,6161 (1952). (4) R. H. Schuler and C . E. McCauley, J . Chem. Phys., 25, 1080 (1956). (5) J. A. Merrigan, W. K. Ellgren, and E. P. Rack, ibid., 44, 174 (1966).
Volume 70,Number 7 Julg 1966
