NOTES
3349 glasses2 and for studies of rheological phenomena3 in such glasses, more data are needed on the viscosity of the media. In an earlier paper4 we have reported the viscosities of eight organic glasses as a function of temperature. Similar data are given below for additional glasses of varied molecular structure and polarity.
1.40
1.00
4 0.60
0.20
0.00
0
0.25
0.50 0.76 Mole ratio of the acid.
1.00
Figure 3. Dielectric titration of triethylamine-monochloracetic acid in benzene. The total solute concentration is 0.470 M .
Yergerz for the A2B complex (Figure 2) (and using the bond moments shown), a dipole moment of 2.2 D is calculated for the hydrogen-bonded form of the complex. The group moment of the OH---K group must be increased tal 5.9 D to reproduce the measured moment of the complex. If the OH bond distance in the complex is 1.02 A , 8 the OH dipole carries a charge of 5 X 10-10 esu ( i e . , in excess of the electronic charge). This shows that the OH---N group acquires an ionpair character, and the complex exists in predominantly an ionic form.
Triethylamine-Monochloracetic Acid Complex The experimental results for total solute concentrations of 0.470 and 0.188 M are shown in Figure 3. These show a cllear evidence for complex formation, but the maximum occurs a t molar ratios intermediate between those required for a 1:l and a 1:2 complex. The system probably exists in an equilibrium
2A
+B
Z A B
+A=
AzB
Dipole moments derived from permittivity measurements on this system have limited significance unless the equilibrium is defined. The concentration dependence of th.e permittivity of a 1 : l molar ratio of solutes yields a m effective dipole moment of 6.4 D, in agreement with the values previously mentioned. An effective dipole moment of 7.5 D is calculated for the 1 :2 molar ratio.
Experimental Section Method. Viscosities were determined from the rate of extrusion of a plug of the organic glass from the end of a glass tube to which high pressures of He gas were applied. The temperature was controlled by the rate of flow of gaseous nitrogen which passed over the sample after generation from a liquid nitrogen bath. Full details of the method have been described previously. Except where noted, a glass viscometer tube of 0.90cm radius was used. Viscosities were determined at approximately 1“K intervals covering the range of about lo6 to 1Olo P. Materials. All compounds were used as received. 3-Ethylpentane (3EP), 4-methylheptane (4MHp),ethylcyclohexane (ECHx), methylcyclohexane (MCHx), 2,3dimethylpentane (DhlP), and 3-methyloctane (3MO) were from the Aldrich Chemical Co. ; 3-methylhexane (3h”Hx) was from J. T. Baker Chemical Co.; perfluoro1,2- and perfluoro-l,4-dimethylcyclohexane(PFCHx) isomer mixture and trans-l,2-dimethylcyclohexanewere from Halogen Chemicals, Inc. ; anhydrous methanol and ethanol were from Merck Chemical Co.; 3methylpentane (33IP) was from the Phillips Petroleum Co. ; and totally deuterated 3-methylpentane (3MPd14) was from Merck Sharp and Dohme. Anhydrous CHBOHand CzHsOH crystallize when cooled to 77°K. Therefore, 4% H20 by volume was added to each of these compounds to produce glass-forming mixtures. Results Data for 11 organic glasses are plotted in Figure 1. Figure 2 gives data for mixtures of MCHx and 3MP. Figure 3 compares results for perdeuterated 3-methylpentane with results for the normal protiated compound measured under the same conditions. For convenience in comparing different compounds and in extrapolating to temperatures beyond the range
(8) M. Davies and L. Sobczyk, J . Chem. SOC., 3000 (1962).
Viscosities of Some Organic Glasses Used as Trapping Matrices.
11’
by A. Campbell Ling and John E. Willard Department of Chemistry, University of Wisconsin, Madison, Wisconsin 63706 (Received M a y 6 , 1068)
For studies of the trapping and decay of electrons, ions, and free mdicals produced by radiation in organic
(1) Tlis work has been supported in part by U. S. Atomic Energy Commission Contract AT(l1-1)-1715 and by the W. F. W a s Trust of the University of Wisconsin. (2) For examples and references, see: (a) W. H. Hamill, “Ionic Processes in ?-Irradiated Organic Solids at - 196’,” a chapter in “Radical Ions,” E. T. Kaiser and L. Kevan, Ed., John Wiley and Sons, Ino., New York, N. Y., 1968; (b) J. E. Willard, “Radiation Chemistry of Organic Solids,” a chapter in “Fundamentals of Radiation Chemistry,” P. Ausloos, Ed., John Wiley and Sons, Inc., New York, N. Y., in press; (c) B. Wiseall and J. E. Willard, J . Chem. Phys., 46, 4387 (1967); (d) J. Lin, K. Tsuji, and F. Williams, J. Amer. Chem. Soc., 90, 2766 (1968). (3) (a) D. J. Plazek and J. H. Magill, J . Chem. Phys., 45, 3038 (1966); (b) J. H. Magill, ibid., 47, 2802 (1967); (0) J. H. Magill and D. J. Plazek, ibid., 46, 3757 (1967); (d) G. A. von Salis, H. Labhart, J . Phys. Chem., 72, 752 (1968) ; (e) for further references see ref 4. (4) A. C. Ling and J. E. Willard, J . Phys. Chem., 72, 1918 (1968).
Volume 78s Number 9 September 1968
NOTES
3350 Table I: Viscosity Parameters for Organic Glasses
Figure 1. Viscosities of some organic glasses as a function of temperature: (1)perfluorodimethylcyclohexane, (2) isoamyl alcohol, (3) n-amyl alcohol, (4) 3-methyloctane, (5) methanol 4 vol 7, water, (6) ethanol 4 vol 7, water, (7) ethylcyclohexane, (8) 4-methylheptane, (9) 3-ethylpentane, (10) 3-methylhexane, (11) 2,3-dimethylpentane.
+
+
T, 95.2
90.9
I
10.5
OK
85.5
I
83.3
80.0
!
3-Methylpentane" 2-Methylpentane' 2-Methylpentene-lo 3-Ethylpentane 2,3-Dimethylpentane 3-Methylhexane 4-Met hylhep tane 3-Met hylo ctane Methylcyclohexaneb E t hylcyclohexane Perfluorodimethylcyclohexane Methanol 4% water Ethanol 47, water 2-Methyltetrahydrofuran' n-Propyl alcohol" n-Amyl alcohol Isoamyl alcohol Isopropyl benzenea n-Butylbenzene" Di-n-butyl phthalate'
+
+
' Reference 4. tures.
Viaoosity at 77.6OK (extrapolated), P
A, OK-' X 10-1
-B
eV
3.46 3.48 3.96 3.64 3.67 4.15 4.89 5.75 4.16 3.97 6.99
32.2 31.5 34.3 28.68 30.91 35.06 37.82 43.05 35.57 28.64 42.94
0.69 0.69 0.72 0.72 0.73 0.82 0.97 1.14 0.83 0.78 1.39
2.2 2.4 3.8 2.4 3.6 3.2 2.0 1.2 1.2 4.4 2.4
4.22 2.95 4.93
29.60 18.78 43.1
0.84 0.59 0.98
1.1 x 1026 2 . 1 X 1019 3.7 X 1020
2.70 5.09 4.79 7.01 6.31 7.51
16.35 31.38 28.63 43.33 37.98 32.08
0.54 1.01 0.95 1.39 1.25 1.49
3.0 2.1 1.6 1.7 3.5 8.7
E,
X 10l2 X 10la x 1018 X 10l8
x
1018 X 10l8 X 10% X 1031 x 1018 X 1O2a X 10'7
X X X X X X
10'8 1034
loa3 1047
1043
By extrapolation from MCHx-3MP mix-
llD
11.5 12.0 125 T-I x 103 Figure 2. Viscosities of mixtures of methylcyclohexane with 3-methylpentane in the glassy phase as a function of temperature, mole fraction of methylcyclohexane: A, 0.95 mf; B, 0.67 mf; C, 0.50 mf; D, 0.33 mf; E, 0.29 mf; F, 0.17 mf; G, pure 3MP.4
Figure 3. Viscosity of perdeuterated 3-methylpentane glass compared with nondeuterated samples: 0 , 3-methylpentanedl4, determined with a 1-g sample; 0, 3-methylpentane-h~, determined with a 1-g sample. Dashed line shows viscosity-temperature dependence determined over more extended range with 5-g samples of 3-methylpentane-hl4.
of the current measurements, columns 2 and 3 of Table I give the values of A and B from the equation log q = AT-' B , as obtained from a least-squares fit of the data. Column 5 gives the viscosities a t 77°K calculated using this equation. The extrapolation to 77°K has been made for the purpose of obtaining an approximate indication of relative viscosities a t a single tem-
+
The Journal of Physical Chemistry
perature and some indication of their absolute magnitudes a t the temperature most frequently used in matrix trapping studies. The values may devjate considerably from the true values, since the extrapolation from the experimental data crosses the glass transition temperature. Column 4 of Table I gives the Arrhenius E factors. As noted earlier,4it has not been possible to measure the viscosity of methylcyclohexane glass by the extrusion method because of the tendency for the glass to crack and to crystallize. However, a stable glass is formed from solutions containing 0.98 mol fraction or less of MCHx in 3MP. Extrapolation of the data of Figure 2 for each concentration to 773°K gives the following values: 0.95 mf, 4 X 10'' P; 0.66 mf, 3 X 10l6 P; 0.50 mf, 2 X 1014 P; 0.33 mf, 4 X 10la P; 0.28 mf, 2 X 10laP; 0.17 rnf, 3 X 10l2P. Extrapolation of these estimatedvalues t o an MCHx mol fraction of unity gives a value of 1.2 x 1018 P as the viscosity of of pure MCHx glass a t 77.5"K. The value for pure 3MCHx at 77.5"K was previously4 bracketed as falling between 10l6and 1021P. Plots of viscosity against composition of the 3MPMCHx mixture appear to have a slight curvature in the direction of more rapidly increasing viscosity as the concentration of MCHx increases, in contrast to 3RIIPisopentane mixtures. Because deuteration has been observed to cause cer-
3351
COMMUNICATIONS TO THE EDITOR tain striking effects on the decay rates of radicals in glassy matrices, the viscosity of perdeuterated 3MP was determined. Four measurements on a 1-g sample in a 0.55 cm in dialmeter viscometer tube were compared with results on an identical sample of the nondeuterated compound (Figure 3). The dotted line in Figure 3 is from measuremients4 with the more accurate 0.9-cm tube. The results indicate that there is no major difference between the viscosities of 3 M p - h ~and 3MPd14 glasses. The viscosity of trans-l,3-dimethylcyclohexaneglass a t 112°K is 8.3 :X lo7P.
terminations of the viscosities of MCHx in the region 135-205°K and of 3MP in the region 95-120°K, using a commercial rotating cylinder viscometer. The former values are above the glass softening temperature, and the latter span it, so that comparison with extrapolated values of the present work is not meaningful. It appears, however, that their value for pure 3MP a t 95°K (lo5 P) is about one order of magnitude higher than that found in our earlier work4at this temperature, although our investigations4 of other highly viscous glasses have agreed well with earlier results extending from lower vi~cosities.~
Related Measurements von Salis and Labharts have recently reported de-
(6) G. A. von Salis and H. Labhart, J . Phys. Chem., 72, 762 (1968).
C O M M U N I C A T I O N S TO T H E E D I T O R
Intramolecular Elimination Reactions in the Photolysis of Fluoroaldehydes
Sir: Recently, perfluoroalkyl radicals have been generated by the photolysis of various fluoroaldehydes,' and data have been obtained for the abstraction of the aldehydic hydrogen atom by the radical Rf
+ HCORr
RfH
+ CORf
The aldehyde has also been used2 as a radical source to investigate the removal of hydrogen from various substrate molecules, i.e.
Ftf + R H A- RtH
+R
This technique is satisfactory if there is no other source of R f H in the reaction system. I n a study of the photolysis of CF&OCFs-HCOCzFs mixtures it beca,me apparent that although the fluoroform formation could be adequately accounted for by the reactions CF3
+ HCOCzFs A CF3H + COCzFs 2CF3 -% CzFa
the pentafluoroethane formation was not similarly expressed by the reactions CzFs
+ ECCOCZF~--% CzFsH + COCZFS 6
2CzFs +C4Fio Our evidence for this conclusion was that although a plot of the ratio R c F ~ H / R ' /us. ~ c aldehyde ~F~ concentra-
tion gave, within experimental error, zero intercept, a ~ ~ ~ l o a markcorresponding plot for R C 2 F b ~ / R 1 / a yielded edly positive intercept. Analysis of the data published for the HCOC2Fh system yielded essentially the same conclusion. When cyclopropanecarboxaldehyde is p h ~ t o l y z e d , ~ ~ ~ its decomposition has been shown to involve production of free radicals and also the formation of propylene by an intramolecular elimination reaction (8), HCOa
A 8
HCO 3. CO
+
a
CHFCH-CH~
It seemed likely that such an intramolecular elimination reaction was also contributing to pentafluoroethane formation when the fluoroaldehyde was photolyzed; Le., the primary processes were
+ CZF5 -% CO + CzFsH
HCOCZFS
HCO
We have photolyzed under similar conditions the aldehyde alone and also aldehyde-nitric oxide mixtures. In the latter cases perfluorobutane formation was completely inhibited although extensive pentafluoroethane formation occurred, the yield decreasing by only -75% (1) G. 0.Pritchard, G. H. Miller, and J. K. Foote, Can. J . Chem., 40, 1830 (1962). (2) G.0. Pritohard and J. K. Foote, J . Phys. Chem., 68, 1016 (1964). (3) G. Greig and J. C. J. Thynne, Trans. Faraday Soc., 63, 1369 (1967). (4) J. J. I. Overwater, H. J. Herman, and H. Cerfontain, Rec. Trav. Chim., 83, 637 (1964).
Volume 78, Number 9 September 1968
