NOTES new run, the cell and connecting tubing were washed thoroughly, dried, reassembled, and evacuated overmm. night at a pressure of less than Dark runs were made which were identical in other respects with the photochemical runs. The amount of so3 derived from these experiments was considerably smaller than that formed photochemically and was very reproducible. For a dark run of given duration the amount of SO3 formed thermally was the same for pure SOZ, SO2-MeZCO, and SOz-Ac2 mixtures within the experiment,al error. Correction for SO3 formed thermally has been made in the data for the photochemical runs shown in Figure 1. Actinometry was carried out using the potassium ferrioxalate system.la Correction was made in the quantum yield calculations for the 3650-60 and 3341-A light present in the photolysis beam which was absorbed by the actinometer solutions but not by the SOz. The light intensity absorbed by sulfur dioxide was essentially constant throughout the series of runs: 2.9 X quanta/sec (3126-2537 A). Acknowledgment. The authors acknowledge gratefully the support of this work through a research grant from the National Air Pollution Control Administration, U. S. Department of Health, Education, and Welfare, Public Health Service, Arlington, Va. We are indebted to Professor Paul Urone (University of Colorado) for helpful suggestions which formed the basis for the development of the analytical system employed, and Dr. James W. Gall, who performed the SOz-acetone mixture analyses. (13) C. G. Hatchard and C. A. Parker, Proc. Roy. SOC.,A235, 518 (1956).
Anion Exchange of Metal Complexes.
X1X.l Volumetric Studies of the Exchanger in Mixed Solvents by Y. Marcus, Depurtment of Inorganic and Analytical Chemistry, The Hebrew University, Jerusalem, Israel
J. Naveh, and Mayo Nissim Israel Atomic Energy Commission, Nuclear Research Center-Negev, Israel (Received June $0,1060)
In a recent paper2 we reported the selective swelling of a divinylbenzene polystyrene-methylene-trimethylammonium salt copolymer (Dowex-1) in several aqueous organic solvent mixtures. This information is essential for an understanding of the factors affecting the sorption of metal complexes on the exchanger, which
4415 is of great practical importance. The applicability of anion exchange of metal complexes in mixed solvents depends, among other factors, on the rate of particle diffusion and on the dimensional stability of the column of resin, and these quantities depend, in turn, on the specific volume of the exchanger and on the solvent composition. It is further expected that some useful information concerning the interaction of the water and organic solvent with resin functional groups can be obtained from a study of the partial molar volumes of these components as a function of composition. These, again, are obtainable from the specific volumes. A study has therefore been undertaken of the density of the swollen resin, in equilibrium with a mixed solvent of known composition. The densities of 4 and 8% cross-linked resins in chloride form were measured in water and in aqueous methanol, ethanol, n-propyl alcohol, acetone, and formamide, a t 22’. Experimental Section Densities were measured in 25-ml picnometers at 22 f l o , the displaced liquid being the equilibrium solution itself, the density of which was separately measured. I n this way there is no fear from changes in the composition when the density of the swollen resin is measured. The effect of the temperature variations on the densities were within the reported experimental precision. The characterization of the resin and other materials, the procedure for drying the resin, and other operations have been reported.2 Calculations The specific volume, that is the volume per gram of dry chloride form of resin of a,resin sample swollen in a mixed solvent, is given by
P=
PR
+ nsPs’ + nwPw’
(1) where PR is the specific volume of the resin skeleton with its functional groups, assumed invariant with solvent composition, ng and nw are the specific numbers of moles of solvent (S) and water (W), and Vs‘ and Vw’ are the partial molar volumes, respectively. The specific swollen volume is obtained experimentally as
T‘
=
(1.000
+ nsMs + nwMw)/d
(2)
where M s and MW are the molecular weights and cl the measured density of the swollen resin. The molar volume of the solvent in the resin is now obtained from while a reference molar volume is calculated as
(1) Previous paper in series: Y. Marcus and E. Eyal, J . Znorg. Nucl. Chem., submitted, 1969. (2) Y. Marcus and J. Naveh, J . Phys. Chem., 73,591 (1969).
Volume 75, Number 12 December 1069
NOTES
4416 Table I : Densities, Molar Volumes, and Molar Cont.raction of Aqueous Ethanol in Dowex-1 X-4 Chloride Its za
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -1.0
+
2s
d, m d m l
nw# mmol/g
0.135 0.190 0.205 0.230 0.260 0.305 0.350 0.485 0.675 0.870
950 933 929 921 914 901 888 860 827 799
55.5 52.8 48.0 42.8 37.3 32.1 26.5 22.9 20.1 18.0
naMs
+ nwMw,
mg/g
1175 1125 1070 990 895 810 727 680 717 875
-
2, mg/ml
V’ ml/mol
1052 1046 1044 1043 1042 1042 1040 1033 1008 963
21.0 21.4 22.6 23.5 24.6 26.1 28.7 31.7 40.0 58.0
-AT’,ml/mol 1.26 1.36 1.42 1.56 1.64 1.93 2.07 2.75 2.93 2.61
~~
Table 11: Molar Contractions of Solvents in Chloride-Form Anion Exchangers Swollen by the Neat Solvents (in ml/mol) Water X-4b X-8b
2.60” 2.42“
VOC
0.59 0.89 18.0
“ Perchlorate form.
Nominal cross-linking.
Methanol
Ethanol
n-Propyl alcohol
Acetone
Formamide
2.3 3 2 40.3
2.0 3.3 58.2
2.7 75.0
5.3 6.5 73.5
0.3 0.5 39.8
’ Molar volume of the pure solvent.
where d is the density of a mixed solvent having a mole fraction 2s of solvent, 2 being the equilibrium mole fraction in the resin. The molar solvent contraction in the resin is now defined as
and it measures the change of volume the solvent of composition zS undergoes when it enters the resin. If the contraction (AP’ being negative) is thought to be due to electrostriction, then the partial molal electrostriction of the water in the resin is obtained from
AP,’
=
AV’ - Zs(dAV’/dZs)
(6)
Results The values of OR required for the calculation (eq 3) were obtained by dodecane displacement2 and are 898 pl/g for 4% cross-linked resin and 907 pl/g for 8% cross-linked resin. Table I shows the quantities obtained experimentally (z, d, and d ) and by calculation (17’ and AO‘) for one of the systems studied. The experimental accuracy attained can be estimated from these data. All the data obtained are shown in Figure 1 as plots of AP’ against z ~ .Unfortunately, the region above 2s = 0.9 could not be measured, since the resin could not be dried completely in all cases. Since the curves are rather steep a t high mole fractions of the solvent, the initial partial molar electrostriction of the solvent, lim AOS’ ($8 -+ l), could not be calculated exactly. It could, however, be estimated to within 0.2 ml/mol by extrapolation of the curves to 2 s = 1, and is The Journal of Physical Chemistry
shown in Table I1 for the various solvents a t the two cross-linkings studied.
Discussion The use of picnometry in resin density measurements is well e s t a b l i ~ h e dalthough ,~~~ other methods such as sedimentatioq6buoyancy or microscopy’ are also applicable. The former method was adequate for our purposes, and because of the good but still limited reproducibility of the resin samples, a precision in the densities higher than kl mg/ml was not warranted. Hydrocarbons are standard displacement fluids for water-swollen resinsav4 and have also been used for dry resin^.^,^ We have observed a small amount of swelling (-201,) with dodecane for the dry resin, which was neglected. The results in Table I and in Figure 1 show that the solvent in the resin contracts as compared to a solvent of similar composition outside the resin. The molar contraction increases as the concentration of the organic component increases. Since, however, the average molar volume of the solvent, V’, increases also, the relative contraction AV’/V’ does not change very much in the water-rich region (at least for methanol, ethanol, and formamide). Indeed, the relative con(3) H. P. Gregor, K. M. Held, and J. Bellin, Anal. Chem., 23, 620
(1951). (4) K. W. Pepper, D. Reichenberg, and D. K. Hale, J. Chem. Soc.,
3129 (1952). (5) M. G. Suryaraman, Ph.D. Thesis, University of Colorado, 1962; M. G. Suryaraman and H. F. Walton, Science, 131,829 (1960). (6) D. H. Freeman, private communication, 1962; G. Dickel, private communication, 1969. (7) D. H. Freeman and G. Scatchard, J. Phys. Chern., 69, 70 (1965).
4417
NOTES
concentration of water decreases in the resin, the partial molar electrostriction of water A Vw', estimated by the intercept method, becomes very large. This points to a strong preferential hydration of the ions in the resin. That means that even if the total sorption of solvent in the resin may not show a great preference to water a t low water concentrations,2 whatever water is present is in the vicinity of the ions and is influenced by their electric field. The higher the positive slope of the right-hand part of the curves in Figure 1, the stronger is the effect. It is puzzling that acetone should show such a large contraction. Its carbonyl group must interact strongly with the resin, permitting it a much denser packing than in the neat liquid or in aqueous solutions, but there is no apparent reason for this. The consequence of this, however, is that exchange in acetone-swollen resins becomes very slow, which is a disadvantage when the enhanced selectivity of the resin for anions in acetone' is to be utilized.
FA
0
c
MeOH
-.L -41 EtOH
0
PrOH
mole
Me,CO
-6
-8 0
0.6
0 3
2s
-
09
I
I
03
06
c
2s
Figure 1. The molar contraction of solvents swelling X-4 (left hand side) and X-8 (right hand side) chloride form Dowex-1, as a function of solvent composition inside the resin. FA, formamide; MeOH, methanol; EtOH, ethanol; PrOH, n-propyl alcohol; Me2C0, acetone.
(8) K. W. Pepper and D. Reichenberg, Z. BZektrochenz., 57, 183 (1953). (9) H. P.Gregor, B. R. Sundheim, K. M. Held, and M. H. Waxman, J . Coll. SCi., 7,511 (1952);H. P.Gregor, F. Gutoff, and J. I. Bergman, ibid., 6,245 (1951). (10) G.E.Boyd and B. A. Soldano, 2. Elektrochem., 57, 162 (1953). (11) E.Hogfeldt, Acta Chem. Scand., 12, 182 (1958).
Electron Spin Resonance Study of Ultraviolet-Irradiated Di- t-butyl Peroxide
traction decreases for all solvents when the concentration of water diminishes below ca. 40%. The limiting molar contraction (Table 11) is highest for acetone both absolutely and relatively, the relative contraction decreasing in the order (for X-8 resin) acetone > methanol > ethanol > water > propanol > formamide. The contraction of water in a swollen cation exchange resin has been ascribed to e l e c t r o ~ t r i c t i o n . ~ ~ A ~-'~ molar contraction of water as high as 1.15 ml/mol has been noted for the H + or Mg2+forms of a polystyrenesulfonate resin as an average a t relative humidities of above 45%. The first molecule of water sorbed per functional group in a cation exchanger suffers even more electrostriction than that,8 but as swelling proceeds, and as soon as there is some free water in the system, the partial molar volume of water becomes again equal to its molar volume in the pure state. I n the present case of mixed aqueous-organic solvents in anion exchangers, electrostriction is again larger for the less highly swollen form of the resin, ie., perchlorate compared with chloride (data for water in Table II), and .X-8 resin compared with X-4 (for cation exchangers the cross-linking effect is smalls). As the
in the Frozen State'
by P. Svejda and D. H. Volman Department of Chemistry, University of California, Davis, California 96616 (Received Julv 8, 1969)
Recently, Krusic and Kochi2 have shown that the photolysis of liquid solutions of di-t-butyl peroxide in alkyl hydrocarbons yields esr spectra of the hydrocarbon radicals produced via hydrogen atom abstraction, presumably by the t-butoxy radical formed in the primary process. Independently, Adams3 reported the ear spectra of a-hydroxy alkyl radicals formed in the photolysis of liquid solutions of di-t-butyl peroxide in alcohols or alcohols and isooctane. I n the photolysis of solid solutions of the peroxide in 3-methylpentane, Shida4 observed the spectrum of methyl radicals, at(1) This investigation was supported by a grant from the National Science Foundation. (2) (a) P. J. Krusic and J. K. Kochi, J . Amer. Chem. Soc., 90,7156 (1968);(b) J. K. Kochi and P. J. Krusic, ibid.,90, 1757 (1968). (3) J. Q. Adams, ibid., 90, 5363 (1968). (4) T . Shida, J. Phys. Chem., 72, 723 (1968). Volume 75,Number 12 December 1969
