NOTES
3010
tion rapidly dropped to a smaller constant value as the CFzO approached about 1% of the C3F7I. Presumably, the initial reaction is similar to that for CZFS radicals C3F7
f Oz
C3F70z
(11)
I n some manner, the C3F702radical must yield primarily CFzO. How this occurs is not clear at all. It is of interest to know whether the RO2 radical has a measurable lifetime. To that end, we did a number of experiments with 5 to 40 mm of HI added. Two series of experiments were done, one with 280 mm of CzFBIand 300 mm of 02,and the other with 100 mm of C3F71and 300 mm of 02. Hydrogen iodide had no effect at all on CF3 or CFClz o x i d a t i ~ n . ~However, ,~ with C2Fj and C3F7, very marked changes occurred in the oxidation. The results, the same for both series, showed no trend with H I pressure, thus indicating that the initially formed perfluoroalkyl radical was conipletely scavenged by 0 2 . The results can be summarized as follows. First, a red depo:it was formed. Second, a(CF20) was reduced at least 5- to 20-fold. Third, @(CF&FO) may have increased to 0.13 to 0.30 for CzF6radicals as based on the 9.05-p band of CF3CF0. The analysis is difficult because of the H I absorption in this region.
F Fourth, the characteristic C-C=O band at 5.31 p was the most intense band and was formed at the same rate in all experiments with HI. The CF3CFO can account for only 25 to 50% of the 5.31-12 band in the C3F71series. but perhaps all of it in the CZFSIseries. At least for the C3F71series, another product probably was formed There can be no doubt that H I interferes with the oxidation. Consequently, the ROz sec. radical must have a lifetime in excess of
Acknotdedgment. The authors wish to thank IIrs, Barbara Peer for assistance with the manuscript.
Heats of Transport of the Rare Gases
in a Rubber Membrane‘
by Riirion Y. Bearman and Richard J. Bearman Department of Chemistry, University of Kansas, Lawrence, Kansas (Receized February 21, 1966)
Revised values for the heats of transport, &*, of the rare gases He, Xe, Ar, Kr, and Xe in rubber are presented. I n the ease of helium, it is shown that, within The Journal of Phgsical Chemistry
experimental error, there is no pressure dependence of the heat of transport in the pressure range 25-65 cm. The apparent &* varies slightly with temperature difference across the membrane. Nevertheless, departures from linearity in the local phenomenological equations seem to be negligible even though the temperature gradients range up to 900”/in.
Revised Heats of Transport (Q*) In an earlier article, Bearman2 reported the heats of transport (or “transfer”), &*, of the rare gases in a rubber membrane. His values were obtained from thermoosmosis experiments where, at steady state
-(&*/R)(l/Tc - ~ / T H ) (1) Here, H and C refer to the hot and cold side, respectively, T is absolute temperature, p is pressure, and R is the gas constant. His measurements were subject to several errors of unknown magnitude arising chiefly from uncertainties in the pressure and temperature. With the use of strain gauge pressure transducers and several thermocouple probes, we have constructed an improved apparatus, fully described elsewhere,3 , 4 in which the errors have been greatly lowered. I n Table I, we present revised values for the heats of transport together with a comparison with the earlier results. The error estimates take into account the observed irreproducibility and also errors arising from temperature and pressure measurements. The irreproducibility is caused mostly by leakage, degassing, and adsorption in the system3 over the long course of the runs, which last days or sometimes weeks. A pure gum rubber membrane 0.0325 to 0.0350 cm in thickness was used for our measurements reported here. In (PH/Pc)-
=
Pressure and Temperature Difference Dependence of Q* Some additional measurements were made with helium. In Table 11, me show that, within the experimental error, the heat of transport at constant mean temperature and temperature difference is independent of mean gas pressure in the system in the range from 25 to 65 cm. From this, we conclude that the He-He interactions in the membrane play little role ( 1 ) This research was supported in its early stages by a grant from the National Science Foundation. We wish to make acknowledgment to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research in its later phases. (2) R. J. Bearman, J . Phys. Chem., 61, 708 (1957). (3) M. Y. Bearman, Dissertation, University of Kansas, 1965. Available from University Microfilms, Ann Arbor, Mich. (4) M. Y . Bearman and R. J. Bearman, J . A p p l . Polymer Sci., 10, 773 (1966).
NOTES
301 1
Table I Thia work
7
Pmean,
Besrman
tmean,
At,
Gas
cm
OC
OC
He Ne Ar Kr Xe
65-25 65-45 53 50 46-26
31 .O 31.4 30.7 30.5 30.5
7.9 7.3 7.7 8.2 8.7
,'Q cal/mole
P
I
-2540.-
-3000
1
"C
62.5 45 62 45 40
34.0 34.5 34.5 34.5 34.5
Q*!
At, OC
cal/mole
4 4 4 4 4
1130 900 - 60 - 170 320
-
where T is the arithmetic mean temperature. I n this case, THTCIn ( p ~ / p ~vs. ) , AT should be a parabola, which appears to be the shape of the curve in Figure 1. A parabolic least-squares fit of our data gives Q* = 1495 cal/mole and bQ*/dT = -31.4 cal/mole deg at the mean temperature of 31". The heat is clearly of the proper magnitude and the temperature coefficient is not unreasonable,6 so that it appears eq 2 adequately accounts for the experimental results. If eq 2 does correctly account for the temperature difference data, we may conclude that the usual local linear phenomenological equation for the flux of matter, Ji
(3)
\I
Figure 1.
in determining Q* at these pressures, and that the gas is effectively a t infinite dilution in the membrane. I n Figure 1, we plot, a t constant mean temperature, THTClog ( p ~ l p c ) us. , AT, the temperature difference across the membrane. We see that there is a perceptible departure from linearity in contradiction with eq 1 which predicts that the plot should be a straight line with slope proportional to Q*. However, eq 1 is not entirely general. It is valid only when Q* is independent of temperature and mole fraction of gas in the membrane. This can be seen, for example, from eq 13 of ref 2. If we assume that Q* varies linearly with temperature and that the gas is at infinite dilution in the membrane, then it is not difficult to show that in place of eq 1, we have
THTCIn ( p d p c ) , =
tmesn,
om
1375 f 39 1204 f 37 -58 f 11 -275 f 10 -589 f 18
1 -1
Pmean.
in the notation of ref 2, is valid, provided we use values of the phenomenological coefficients, L11 and LIU, appropriate to the state a t each point of the membrane. The nonlinearity of THTCIn ( p ~ l p c ) ,in AT is then caused solely by the variation of the transport coefficients across the membrane. Our experiments provide a fairly severe test of the linear phenomenological equation since the temperature gradients range up to 900°/jn. Evidently, the values for the heats of transport Table I1
O C
At, O C
cal/mole
Length of run, min
31.2 31.2 30.6 30.9 30.9 31.1 31.0
8.0 7.6 8.3 8.2 8.0 7.9 8.0
1385 1383 1442 1374 1365 1364 1378
4190 3255 2720 4190 3420 3465 3525
Pmean,
tmean,
Run
cm
27 40 1 3 30 32 31
64.8 54.5 51.8 51.6 34.9 34.9 25.2
Q*,
( 5 ) C. M. Crowe, Trans. Faraday SOC.,53, 692 (1957).
Volume YO, Number 9
September 1966
NOTES
3012
listed in Table I and calculated from eq 1 may be subject to systematic errors arising from the temperature dependence of &*. Thus, for precise work, our results must be accepted as effective values of &* valid at the quoted temperature difference and mean temperature.
The Methylene Blue-Ferrous Iron Reaction in a Two-Phase System‘
by D. Frapkowiak and E. Rabinowitch Department of Botany and Department of Physiology and Biophysics, University of Illinois, Urbana, Illinois (Received February 26, 1966)
The photosynthetic apparatus of living plants separates from each other the probably highly unstable, intermediate oxidation and reduction products of the primary photochemical process and thus permits their conversion to (relatively) stable final products, carbohydrates and oxygen. This is probably accomplished by conveying these intermediates into different phases in the lamellar structure.2 The failure to imitate in vitro the storage of light energy as chemical energy, achieved by plants in photosynthesis, may be due primarily to not providing such a separation mechanism. Nathai and Rabinowitch3 showed that an in vitro system can be constructed, in which the products of an oxidation-reduction reaction (that between thionine and ferrous ions), which runs in light against the gradient of chemical potential, are separated by distribution between water and ether in an emulsion. The light energy stored in this way can be liberated by permitting the two phases to mix again (e.g., by adding methanol). In continuing this work, Ghosh4 in this laboratory observed that separating is more effective if methylene blue is substituted for thionine; perhaps, more of the neutral species of the leuco dye is present in methylene blue than in thionine a t the pH values used. (This species alone is likely to be involved in the extraction of the leuco dye into ether.) The following experiments deal with the methylene blue-ferrous iron system. They provide some additional information concerning the effectiveness of the separation. The reaction vessel used was a cylindrical Pyrex-glass vessel containing 30 ml of aqueous solution and 15 ml of ether (or another solvent immiscible with water). The approximate initial concentrations of methylene blue and FeS04 were of the order of 10-5 and 5 x low3 The Journal of Physical Chemistry
M , respectively. The mixture was stirred by bubbling through a stream of purified argon. No buffer was used; the pH was 3.5-4. The light used for illumination was either white light from a 1000-w coiled filament incandescent lamp or the same light filtered through an interference filter (Balzer K-6) with maximum transmission of 650 mp (near the peak of the methylene blue absorption band at 664 mp). The experiments were made at room temperature maintained in a water bath. Merck reagent grade methylene blue was used without purification. Chromatography on aluminum oxide and the test of Bergmann and O’Konski5 indicated that the dye was pure enough for our purpose. We tried out several combinations of immiscible solvents, but the most efficient separation of the photoproducts we were able to obtain took place in the system water ethyl ether, already used in Rlathai’s work. The reaction is
+
light
NIB
+ %Fez+
dark
(S + L)
+ nFe3+
Here, MB is methylene blue, S, the semiquinone, and L, the leuco methylene blue; n is between 1 and 2, depending on relative amounts of S and L formed. From the work of Parkera and the earlier work of Rabinowitch,’ it appears that in the photostatior?ary state, partly reduced solutions of methylene blue contain only a small percentage of semiquinone, so that n is close to 2. The predominant ionic species (at the prevailing acid pH’s) are monovalent positive ions of MB and monovalent (or divalent) positive ions of L. The neutral form of L, which we can assume to be the only one soluble in ether, is present only in minute amounts. This probably accounts for the slowness with which the leuco dye is extracted into ether. Further experiments on the effect of pH on the rate of extraction should clarify this point. I n the stationary state, the extent of extraction de(1) This research was supported by research grants from the National Science Foundation (GB 1946 and GB 3305) and from the Atomic Energy Commission [AT(ll-1)-15021. (2) E. Rabinowitch, paper presented at the Biophysical Society Meeting, Washington, D. C., 1962, Abstract FC3. (3) K. G. hlathai and E. Rabinowitch, J . Phys. Chem., 66, 663 (1962). (4) A. K. Ghosh, unpublished. ( 5 ) K. Bergmann and C. T . O’Konski, J. Phys. Chem., 67, 2169 (1963). (6) C. A. Parker in “Photochemistry in the Liquid and Solid States,” L. J. Heidt, et al., Ed., John Wiley and Sons Inc., New York, N. Y., 1960, p 48. (7) E. Rabinowitch, J . Chem. Phys., 8 , 551 (1940); see also L. F. Epstein, F. Karush, and E. Rabinowitch, J . Opt. SOC.A m . , 31, 77 (1941).
