COMMUNICATIONS TO THE EDITOR
sured by surface tension and pinacyanol chloride color change, consistent with literature values for highly purified preparations.8 In Figure 2, second-order rate constants, determined spectrophotometrically at 228 M methyl omp, for hydrolysis of 5 X benzoate in aqueous solution in the presence of 0.01 M sodium lauryl sulfate at 25" are shown as a function of the concentration of several cations added as the chlorides. The pH was maintained near 4.7 with a 0.02 M acetate buffer. Each cation inhibits the detergent-catalyzed reaction, the inhibition being particularly striking at very low concentrations. The inhibitory capacity of the cations parallels their hydrophobic characteristics and their tendency to associate with sulfonate ion exchange resin^.^ The most reasonable interpretation of the marked salt effects observed for these reactions is given by the following model: (i) the site of such reactions in the micellar phase is in or near the Stern layer; (ii) the catalysis is principally due to the increased concentration of hydroxide ion or the hydrated proton in the Stern layer compared to those in the bulk phase; and (iii) competition exists between hydroxide ion and other anions present in solution and between the hydrated proton and other cations present in solution for available binding sites in the Stern layer. Thus, the salt effects are viewed as a type of competitive inhibition between solvent-derived ions and other ions for a restricted number of sites on the surface of the micelles.
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long wavelengths, but there is disagreement over the exact percentages of triplet present, particularly at short wavelengths. Ho, Unger, and Noyes12 using ketene-cis-butene-2 mixtures, estimated that less than 2% of the methylenes at 2800 A were triplet. In contrast, Kistiakowsky and CarrJ4 using ketene-transbutene-2 mixtures, found 15% triplet at the same wavelength. We report some results, using a different system, which support the findings of Kistiakowsky and Carr. We have photolyzed ketene in the presence of cyclopropane at 37" and at both 3130 and 2700 8. The products consist of carbon monoxide, ethylene, and C4 hydrocarbons. I n agreement with previous methane and ethane do not appear to be formed in significant amounts. Since there is evidence' that only singlet methylene inserts into CH bonds, the products, at high cyc1opropane:ketene ratios, must be formed by the reactions CHzCO
+ hv +CH2(S)or CH2(T) + CO CHz(S)
CH2(T)
+C A
+CiHli
+ CH&O +CzHi + CO
(1)
(2) (3)
where CH2(S) and CH2(T) denote singlet and triplet methylene, respectively. It follows that CH2(S) : CH,(T) = (carbon mon0xide:ethylene) - 2. Figure 1 shows the carbon monoxide: ethylene ratio as a function of cyc1opropane:ketene ratio. It will be seen that at both 3130 and 2700 8, the carbon monoxide :ethylene ratio becomes constant when the cycloAclcnozcledgwient. This research was supported by propane :ketene ratio exceeds 20 : 1. Further results, Grant AM-08232-03 from the National Institutes of excluded from Figure 1, indicate that this constancy is Health and the work of E. H. C. was supported by a maintained up to cyclopropane:ketene ratios of 80: 1. Career Development Award from the National InstiThe limiting values of the carbon monoxide :ethylene tutes of Health. ratio are 8.0 and 7.2 at 3130 and 2700 8, respectively. The corresponding proportions of triplet methylene at (8) M . Muira and T. Matsumoto, J. Sci. Hiroshima Uniz;. Ser. A . the two wavelengths are therefore 14 and IS%, respec21, 51 (1957). tively. These values are in excellent agreement with (9) J. Inczedy, "Analytical Application of Ion Exchangers," Pergamon Press Inc., New York, N. Y., 1966, p 27. the value of 15% found at both 3130 and 2800 -1by L. R. ROMSTED Kistiakowsky and Carr.4 DEPARTMENT OF CHEMISTRY INDIANA UNIVERSITY R. BRUCEDUNLAP Methane and ethane are by-products in the photolBLOOMINGTON, INDIANA47401 E. H. CORDES ysis of ketene-n-butane6 and ketene-butene-24 mixRECEIVED AUGUST11, 1967
The Photolysis of Ketenecyclopropane Mixtures
Sir: The relative amounts of singlet and triplet methylene formed in the photolysis of ketene at different wavelengths are of current There is general agreement that, the proportion of triplet is greatest at
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(1) J. U'. Simons and B. S. Rabinovitch, J . Phys. Chem., 68, 1322 (1964). (2) 5. Ho, I. Unger, and W. A. Noyes, Jr., J . A m . Chem. SOC., 87, 2297 (1965). (3) A. N . Strachan and D. E. Thornton, J . Phys. Chem., 70, 952 (1966). (4) R. W. Carr, Jr. and G . B. Kistiakowsky, ibid., 70, 118 (1966). (5) B. -4. De Graff and G . B. Kistiakowsky, {bid., 71, 1553 (1967). (6) H. M . Frey and G . B. Kistiakowsky, J. A m . Chem. Soc., 7 9 , 6373 (1957). (7) W7.von E. Doering and H. Prinzbach, Tetrahedron, 6, 24 (1959).
Volume 7i,Number 1.3 December 1967
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COMMUNICATIONS TO THE EDITOR
10
10
CYCLOPROPANE
30
40
5 0
I KETWE
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. A m . 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)
I
\
\ \
I 1
.
0
. J0
,20
.30
B
140
x2
Ordering in Liquids a n d 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.
- -
a,
(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.
