NOTES
radical^^^-^^ followed by recombination to give apparent insertion products. The variations in selectivity found for nonscavenged systems with different photolysis energies and methylene radical sources are best explained by variations in the proportion of tripletstate methylene produced by these conditions. It is well known that singlet state methylene radicals from the photolysis of diazomethane carry considerably more energy into an insertion or C=C addition reaction product than do those from ketene photolysis, and in both cases some fraction of any excess photon energy is also contained in the methylene r a d i ~ a l s . ' ~ JIn ~ view of the invariance in the selectivity between tertiary, secondar,y,and primary C-H bonds under varying conditions that are known to give methylene radicals of different energies, one might deduce that the 'excess energy carried into an insertion product by a methylene radical from ketene or diazomethane photolysis is not contained in the methylene radical's translational degrees of freedom but is all in its vibrational and possibly rotational degrees of freedom which do not contribute significantly to its insertion rate. This assumes, of course, that the invariance in selectivity implies invariance in rate, which would be the case if the selectivity is solely due to activation energy differences. Studies at different temperatures should provide some information on this point. It is quite possible that the initially formed singlet methylene radicals undergo a sufficient number of collisions prior to reaction in order to remove all of the excess translational energy but not a sufficient number to remove all of the excess vibrational energy. The possibility that the selectivity is primarily due to frequency factor differences which would not be altered by varying amounts of excess translational energy in the singlet methylene radicals cannot be ruled out.
751
CaH&NBr, we have determined the solubility of benzene in concentrated aqueous solutions of the tetraalkylammonium salts mentioned above. Experimental Section Eastman (CH&NBr, (CzHJdNBr, (n-CsH&NBr, and (n-C4H9)4NBr were used. Solutions of known molality were prepared by weight and were agitated for 24 hr with excess benzene a t 25". Samples (1 ml) of the saturated solutions were diluted to 50 ml ((CH3)4NBr), 100 ml, or 250 ml (some of the ( T Z - C ~ H ~ )solutions) ~NB~ with 22% ethyl alcohol solution. The benzene concentration in the diluted solutions was determined from the absorbance a t 254 and 248 mp, using a Perkin-Elmer Model-4000A spectrometer. Solutions of the salts, diluted in the same way with 22% ethyl alcohol, were used in the reference cell. From these data, the molality of the benzene in the original solution was calculated on the assumption that the molar volume of benzene in the solutions is the same as that of pure b e n ~ e n e . ~The density data of Wen and Saito5were used in the calculations. Results and Discussion The results are given in Figures 1 and 2. The solubility of benzene in (CH&NBr solutions increases linearly with salt molality through the range of concentration studied (1 m to near saturation). With the other three salts, there are relatively sharp changes in the slope of the solubility curves. The change occurs a t around 5 m in (CzHJ4NBr solution, a t 2-3 m in
Solubility of :Benzenein Concentrated Aqueous Solutions of Tetraalkylammonium Bromides 4
by Henry E. Wirth and Antonio LoSurdo Department of Chemistry, Syacuse University, 18210 (Received October 86, 1967)
Syacuse, New York
6
e
10
m,,,, Figure 1. Solubility of benzene (mole/1000 g of water) in solutions of tetramethylammonium bromide and tetraethylammonium bromide.
Desnoyers, I'elletier, and Jolicoeur' have determined (1) J. E. Desnoyers, G. E. Pelletier, and C. Jolicoeur, Can. J . Chem., the solubility of benzene in aqueous solutions of (CH& 43, 3232 (1965). NBr, (C2HJ4NBr, (n-CaH7)4NBr,and ( T Z - C ~ H ~ )in ~ N B (2) ~ N. C. Den0 and C. H. Spink, J. Phys. Chem., 67, 1347 (1963). the concentration range 0.1-1.4 M . The salting-in (3) H. E.Wirth, ibid., 71, 2922 (1967). constants obtained were in excellent agreement with (4) T v s assumption was checked by direct determination of the densities of several solutions of (wCaH7)rNBr and (wC4Ho)pNBr those cited by :Den0 and Spink2 for the first three salts. saturated with benzene. The maximum difference between calcuIn view of the ~iuggestion~ that micelle formation is poslated and observed densities was 3 ppm. sible in concentrated solutions of (C&I6)4NBr and (n(5) W.Y.Wen and S. Saito, J. Phus. Chem., 68, 2639 (1964). Volume 71, Number 8 February 1968
752
NOTES
12
10
-
bromide (2.1&2.36), tetradecylpyridiniumammonium bromide (2.14-2.45), and tetradecyltripropylammonium bromide (2.18-2.69). In these solutions, the evidence for micelle formation is convincing. The results presented here strongly suggest that the structure of concentrated solutions of (C2H6)4NBr, (n-CsH,)dNBr, and (n-C4H&NBr is different from that of dilute solutions and from that of normal electrolytes. Whether this structure difference can be best described as due to micelles, changes in the structure of water in the presence of the large tetraalkylammonium ions,' or the presence in solution of clathrate hydrates6 is an open question.
0 -
4-
0
2
8
4
8
IO
mrott
Acknowledgment. This work was supported by the office of Saline Water, Grant No. 14-01-0001-623. (6) R. L. Venable and R. V. Nauman,
J. Phys. Chem.,
Figure 2. Solubility of benzene (moles/1000 g of water) in aqueous solutions of tetrapropylammoniumbromide and tetrabutylammonium bromide.
(1964).
(n-CaH&NBr solution, and at 1 m in (n-C4H&NBr solution. It had previously been assumeds that micelle formation was possible above 4 m in (C2HJ4NBr solutions and above 1.4rn in (n-GH7)dNBr solutions. The same general behavior was observed when other methods of representing the results were used. Plots of
On the Temperature Dependence of
molarity of the solution saturated with benzene)all show changes in slope at approximately the same point. In Table I, the moles of benzene per mole of electrolyte is given for the maximum concentrations studied and compared with the value at zero salt concentration calculated from the salting-in coefficients of Desnoyers, et a1.I Table I: Moles of Benzene Associated with 1 Mole of Salt
68, 3498
the Viscosity of Organic Glasses
by G. A. von Salis and H. Labhart Physikalisch-chemisches Institut der Universitat Zwich, zarich. Switzerland
As far as we are aware, only relatively few data are available concerning the temperature dependence of the viscosity of organic glassesl-ll and almost nothing seems to be known about their flow properties. Since glass-forming solvents are often used in studies on the deactivation of optically excited molecules, in measurements of fluorescence and phosphorescence polarization, and in photochemistry, we considered the determination of the temperature dependence of the viscosity of some solvent media to be useful. With our apparatus, a commercial viscometer,
Salt
(CHdrNBr
0 5
(CJXW"r
0 10
(~-c*H,) , N B ~
0 10 0 10
(n-CdHg)tNBr
0.0080 0,009 0.013 0.11 0.021 0.60
0.028 2.6
The observed value of 2.6 mol of benzene/mol of (n-C4He)4NBr in 10 m solution is comparable to the values found by Venable and Naumana for the number of benzene molecules per detergent monomer in dilute aqueous solutions of tetradecyltrimethylammonium The Journal of Physieal Chemktry
(1) M. R. Carpenter, D. B. Davies, and A. J. Matheson, J. Chem. Phys., 46, 2451 (1967). (2) D. J. Denney, ibid., 30, 169 (1969). (3) D. J. Denney, H. gutter, R. Wood, and A. Jones, ibid., 45, 402 (1966). (4) H.Greenspan and E. Fischer, J . Phys. Chem., 69, 2466 (1966). (6) R. H.Greet and D. Turnbull, J. Chem. Phya., 46, 1243 (1967). (6) G.S. Parks, L. E. Barton, M. E. Spaght, and F. W. Richardson, Physics, 5 , 193 (1934). (7) R. Passerini and J. G. Ross, J. Sci. Instr., 30, 274 (1953). (8) K.J. Rosengren, Acta Chem. S c a d . , 16, 1421 (1962). (9) F. J. Smith, J. K. Smith, and S. P. MoGlynn, Rev. Sci. Instr., 33, 1367 (1962). (10) G.Tamman and W. Hesse, Z . Anorg. Allgem. Chem., 156, 245 (1926). (11) M.L. Williams, R. F. Landel, and J. D. Ferry, J. Am. Chem. Soc., 7 7 , 3701 (1955).
