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Downloaded by UNIV OF SOUTH DAKOTA on September 6, 2015 | http://pubs.acs.org Publication Date: December 1, 1967 | doi: 10.1021/j100872a084
Figure 1. The variation of the carbon monoxide:ethylene ratio with cyclopropane: ketene ratio at 37".
tures. Their formation has been attributed to the abstraction by triplet methylene of hydrogen from the hydrocarbon, with the formation of methyl radicals. Their absence as by-products in the photolysis of ketenecyclopropane mixtures must indicate that the rate of hydrogen abstraction by triplet methylene from cyclopropane is considerably slower than from either n-butane or butene-2. This is to be expected if the reactivity of triplet methylene is similar to methyl, whose relative rates of attack on the total CH bonds of cyclopropane, n-butane, and butene-2 at 37" are calculated to be 1:228: 700 respectively.*-10 Further work is in progress to determine the CH2(S): CH2(T) ratio at longer wavelengths and to investigate its variation with temperature. Full details will be published later.
tion in concentration was at first attributed to experimental uncertainty. However, plots of AgCl,,,,, concentration us. the mole fraction of the organic component, 5 2 , (Figure 1) demonstrate a striking correlation, both among the different solvent mixtures we have investigated and with the results of previous experiments, some of which are detailed below.2 The structures of pure liquids and of binary liquidliquid mixtures have been studied by many investigators with the achievement of few definitive answers, as is stated in the excellent review by Franks and Ives.2 The initial effect of the addition of an alcohol to water always appears to be the enhancement of the ordering to produce a solvent even more highly structured than pure water itself.2 A hydrate of ethanol, EtOH0.06), has been r e p ~ r t e d ,as ~ has an 17H20 (z2 0.08 of constant ethanol-water composition of x2 temperature-invariant compressibility.2 Mobility studies of ions in ethanol-water* mixtures show maxima at z2 0.08 with a similar maximum noted for methanol-water6 at low x2. Plots of A G O us. z2for the dis-
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(8) J. R. McNesby and A. S. Gordon, J. Am. Chem. Soc., 79, 825 (1957). (9) J. R. McNesby and A. S. Gordon, ibid., 78, 3570 (1956). (10) A. F. Trotman-Dickenson and E. W. R. Steacie, J . Chem. Phys., 19, 169 (1951).
DEPARTMENT OF CHEMISTRY D. E. THORNTON LOUGHBOROUGH UNIVERSITY OF TECHNOLOGY A. N. STRACHAN LOUGHBOROUGH, LEICESTERSHIRE, ENQLAND
ACCEPTEDAND TRANSMITTED BY THEFARADAY SOCIETY (OCTOBER 4, 1967)
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Ordering in Liquids and Liquid-Liquid Mixtures Sir: We are studying the solubility of silver chloride in various water-organic solvent mixtures.' One of the species whose concentration we measure in these saturated solutions of silver chloride is associated silver chloride, AgCI,,,,. In mixtures of a given organic solvent with water, the concentration of AgCI.,,, does not vary in a regular manner as the per cent organic component is increased. The seemingly erratic variaThe Journal of Physical Chemistry
Figure 1. Concentration of associated silver chloride us. mole fraction of nonaqueous component in saturated water-organic mixtures: x2, mole fraction of nonaqueous component; A, water; ethanol-water; --e--, methanol-water; -C, dioxane-water; and -*-O---, acetonewater.
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(1) K. P. Anderson, E. A. Butler, D. R. Anderson, and E. M. Woolley, J . Phys. Chem., 71, 3566 (1967); unpublished research. (2) F. Franks and D. J. G. Ives, Quart. Reu. (London), 20, 1 (1966). (3) A. D.Potts and D. W. Davidmn, J . Phya. Chem., 69,996 (1965). (4) R. L. Kay and A. Fratiello, private communication.
COMMUNICATIONS TO THE EDITOR
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solution of argon in EtOH-H20 mixtures6 show minima at x2 0.03, followed by maxima at x2 0.13, 0.26. Extremes near and then go to zero at x 2 x2 0.1 and x 2 0.3 have also been observed7 in solubility studies of other substances (iodine, salicylic acid, dimethylglyoxime) in ethanol-water mixtures. Heats of mixing studies for p-dioxane-water mixtures* indicate the presence of a l : 6 complex at x2 0.14. While our results obviously justify no definite conclusions at this time, they do indicate that the concentration of AgCI,,,,, in saturated solutions may be a sensitive indicat,or of the extent of ordering present in solutions. We plan to investigate this possibility and to extend our studies t o include the temperature variable. Ordering within pure liquids as a function of temperature should be measurable by this technique.
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Downloaded by UNIV OF SOUTH DAKOTA on September 6, 2015 | http://pubs.acs.org Publication Date: December 1, 1967 | doi: 10.1021/j100872a084
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Figure 1. High-precision results for A+/A.\/~ of LiCl solutions a t 25’.
desirable to repeat the 25’ work in the neighborhood of the change, with maximum attention given to uniformity of measurement and the highest possible precision for (5) T. Shedlovsky in “The Structure of Electrolytic Solutions,” W. J. Hamer, Ed., John Wiley and Sons, Inc., New York, N . Y., 1959, each point. p 268. To an initial LiCl solution with concentration mea(6) A. Ben-Naim and S. Baer, Trans. Faraday Soc., 60, 1736 (1964). sured to O.Ol%, ten additions of stock were made giving (7) I. G. Mikhailov, Zh. Strukt. Khim., 2, 677 (1961). concentration increments of about 0.1 M. Each addi(8) J. R. Goates and R. J. Sullivan, J. Phys. Chem., 62, 188 (1958). tion was weighed to 1 part in 17,000and the density BRIGHAM YOUNG ~JNIVERSITY KEITHP. ANDERSON PROVO, UTAH 84601 ELIOTA. BUTLER measured to 0.2 ppm. The results for AO,/.\/C from three separate runs are EARLM. WOOLLEY shown in Figure 1, with end points taken from the emRECEIVED OCTOBER 16, 1967 pirical equation given in ref 1. The A’s represent changes in@, and d ifor successive experimental points with the ordinate at the center of each chord. The smooth curve is given by the above-mentioned equation Changes in Slope of the Apparent Molal which is shown on the figure. The parameters were obtained by least-squares optimization and fit the Volume Curves of Lithium Chloride Solutions‘ data with a standard deviation of 0.01. The standard deviation is consistent with the precision of measureSir: In a recent publication12evidence was presented ment given above and the parameters and values of @ for the existence of relatively abrupt changes in the slope of the a, (apparent molal volume) vs. d i (root are within the experimental error of the data in ref 1. The effect has been obtained consistently in each of molar concentration) curves of the alkali chlorides, seven independent experiments, under varied experiparticularly for LiCl solutions. mental procedures and different temperatures, and Since the changes were very small and the quantity of there can now be little question of its existence. While interest (change in slope) represented the second dethe physical significance of the effect is not yet proven, rivative of the measured function, a very high precision it is again suggested’ that it signifies a cooperative and closely spaced points were essential to a definite interaction among the cospheres3 of a moderate number conclusion. Although precise data were presented, of ions. the data nevertheless did not justify more than a tentative statement that an abrupt slope change ie., transition did exist. (1) Research sponsored by the U. S. Atomic Energy Commission under contract with Union Carbide Corp. With experience, improvements in technique and (2) F. Vaslow, J . Phys. Chem., 70,2286 (1966). apparatus were made and runs of LiCl at 5 and 35” (3) R. W. Gurney, “Ionic Processes in Solution,” Dover Publicashowed sufficient precision that reasonably coherent tions Inc.. New York, N. Y., 1954, p 4. Aav/A& curves could be drawn, although the curves CHEMISTRY DIVISION FREDVASLOW still did not conclusively show a distinctive slope OAKRIDQENATIONAL LABORATORY change. OAKRIDGE,TENNESSEE 37831 In view of the quality of the new curves, it was felt RECEIVED OCTOBER 16, 1967 Volume 71. Number 13 December 1967
