NOTES
Dec., 1959 ported conclusive paramagnetic resonance evidence for the existence of long-chain biradical poly.S+S)-S.
.. .. ..
:&2+(s),-2-s~:..
.. .. *.
..
.. ..
&-(S)-S@
*.
I I1 I11 mers in liquid sulfur. I n the present paper, we report our findings. Results and Discussion A determination on a carbon disulfide-insoluble sample of “supersublimation” sulfur showed a resonance signal a t g = 2.0044,which is close to the g value of 2.0023 for a free electron.ll This result constitutes definite evidence in favor of structure I. It should be noted that the line (Fig. 1) is asym-
kg2;?-1 n
W
Fig. 1.-Electron paramagnetic resonance absorption line for carbon disulfide-insoluble supersublimation sulfur.
metric and thus unlikemost organic free radical lines. This asymmetry is indicative of anisotropy in gl and gll which is a result of an appreciable amount of spin-orbit coupling, the unpaired electron being localized on the sulfur in a p orbit. In comparison, the average g value found by Gardner and Fraenkell0 for liquid sulfur was 2.024,a value which is shifted ever further from the g value for a free electron. The general interpretation has been madelo that shifts in g-values for molecules in nondegenerate orbital ground states increase with the magnitude of the spin-orbit coupling and decrease with the separation between ground and excited states. The absolute concentration of unpaired electrons was estimated to be about 1 X mole/l. which can be compared with the value 1.1 X 10+ found by Gardner and Fraenkel’O for liquid sulfur a t 300”. The number average chain length ( p ) of the sulfur helix polymers was calculated to be 1 X lo7 using the relation:1° p = (1000/32)(p/Cc), where p the density was taken as 1.95 g./m1.12; the concentration of helix fragments (C,) taken as 5 X 10-6 mole/ l.,la assuming two independent electrons per helix fragment. The corresponding values obtained by Gardner and Fraenkel‘O for liquid sulfur were (5.0 2.5) X lo4 a t 300” and a maximum value of (1.5 f 0.7) X lo6 at 171”. Thus, the value obtained in the present work appears to be in the right order of magnitude. Based on the information that the sulfur particles are spheres with an average diameter of 2 to 4 p,la an estimate of the average number of helix chains per sulfur particle (aa) can be calculated = NDPC,/2, where N = from the relation: Avogadro’s number, D = density, V = volume of
*
(11) J. E. Werta, Chem. Reus., 66, 829 (1954). (12) The Stauffer Product Report No. 819 A lists this value for Crystex. (13) Stauffer Product Report No. 819 A.
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the sulfur sphere, and Cg = absolute concentration of electrons in mole/g. The calculated value is (2 to 4) X 104 helix chains per sulfur particle, assuming two odd electrons per helix chain. Since X-ray diffraction patterns reveal a regular crystalline structure for this form of sulfur,6s6it is reasonable to postulate that the helix chains are oriented with their central axes parallel. This arrangement would of necessity locate the odd electron ends of the helix chains a t opposite ends of the spherical particle and would result in the localization of the unpaired electrons which would explain the anisotropy suggested by the asymmetry in the absorption line noted above. Experimental The measurements were made on a Varian Associates Model V-4500 E-P-R Spectrometer. The g-value of the sample was calibrated by placing a small amount of 1,l-diphenyl-2-picrylhydrazyl in the sulfur sample. This mixture showed a slight shift from the known” g-value of 2.0036 for l,l-diphenyl-2-picrylhydrazyl. The concentration of unpaired electrons was estimated by comparing the first moment of the line from a 500-mg. sample of sulfur with that from a 5 X 10-* M solution of vanadyl sulfate (containing the VO++ ion), using one line of the 8-line spectrum of the latter. The concentration of unpaired electrons determined in this manner was 5 X 10-9 m?le/g. A sample of “supersublimation” sulfur14 weighing 9 -82 g. was extracted with 200 ml. of redistilled ACS grade carbon disulfide by means of a Soxhlet extractor. After three extractions (totaling 47 hours), the amount of insoluble material remaining after drving to constant weight in VUCUO at room temperature was 8b.3%.ls
Acknowledgment.--Helpful discussions with Professor Charles E. Reeder of Baylor University are gratefully acknowledged. (14) Specifications and properties of this form of sulfur (“Crystex”) are described in several Stauffer technical data sheets, product reports and a brochure entitled, “Stauffer Sulfure.” The authors thank the Stauffer Co, for a n experimental sample. (15) This does not necessarily represent extraction to constant weight since there was still a small percentage of material extracted during the third extraction. However, since according to the Stauffer Technical Data Sheet No. 717 Y,“Crystex” undergoes slow reversion t o soluble sulfur (the rate increasing with increase in temperature), i t is possible that this is the reason for the inability to attain a constant weight by repeated extraction.
COMPLEX FORMATION CONSTANTS OF LEAD AND CADMIUM IONS WITH CHLORIDE I N FUSED LITHIUM PERCHLORATE’ BY FREDERICK R. DUKEAND WALTERW. LAWRENCE Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, I o w a Received J u l y 99,1969
Complex formation constants involving lead and cadmium ions with chloride ion have been determined in a fused KN03-NaN03 eutectic.2 It is of interest to compare the complex formation constants in a nitrate solvent with those in a perchlorate. Lithium perchlorate is the only stable fused perchlorate and it has been shown to dissolve insignificant amounts of water a t low h ~ m i d i t y . ~ Therefore the constants were determined in fused (1) Contribution No. 780. Work was performed in the Ames Laboratory of the U. S. Atomic Energy Commission. (2) F. R. Duke and M. L. Iverson, THIBJOURNAL, 62,417(1958). (3) F. R. Duke and A. Doan, Iowa $tale Colleoe J . Sci., 89, 451 (1958)-
2088
COMMUNICATION TO THE EDITOR
LiClOa. The experiments paralleled exactly those reported in fused nitrates.2 Results and Discussion The data are shown in Table I. The constants calculated from the data are listed in Table 11.
TABLEI1 STABILITY CONSTANTS FOR METALHALIDE COMPLEX IONS IN MOLTEN LITHIUM PHRCHLORATE (Concentration unit, molality)
Complex TABLE I OF METAL CHROMATE IN LITHIUM PERCHLORATE SOLUBILITY PbCI+ CONTAINING SODIUM CHLORIDE@ PbClz Sodium -Solubility (mg./g. ~01v.)PbC13chloride, PbCrOa PbCrOi CdCrOt CdC1+ m 275a 300' 250-275
0.0 .02 .033 .05 .08 .125 .206 ,325 .413 .5
0.09 .ll .13 .16 .21 .30 .51 .85 1.10 1.35
0.10 .14 .17 .21 .30 .44 .73 1.20 1.60 2.00 3.25
.75 a
K , = 9 . 6 X 10-n(M/1000
2.3 3.1 5.6 7.1
g.)2.
Vol. 63
LiCloi
30f 5 9& 5 5f 5 40 & 1 5
Stability constanLiClOi
K-NaNOa
275O
8f 2 3 A1.5 1 f1 22 A 4
300'
50 f 8 10 f 5 4 . 5 1 5 40 f 1 5
K-NaNOz
6&2 3f1.5 If1 24f4
The high solubility of CdCrOc limits the range of chloride over which the solubility may be conveniently studied and results in lower precision for the value of the constant. It was observed, however, that, within experimental error, there was no temperature effect. The higher constants than those found in nitrate solvent are a reflection of the lower polarizability of the perchlorate ion. It is interesting that the temperature effect in perchlorate is in the opposite direction, the constant formation being endothermic.
i
I)
COMMUNICATION TO THE EDITOR PHOTOLYSIS OF GAMMA-RAY PRODUCED FREE RADICALS I N ETHANOL AT LOW TEMPERATURES' sir: Great interest recently has been evinced in the nature of the various species produced in organic solids irradiated at low temperatures.2 The absorption and Electron Paramagnetic Resonance spectra, as well as the effects of bleaching with visible and ultraviolet light, have been studied.3 The chemical consequences of bleaching the unstable intermediates in terms of the nature of the stable species produced after the sample is melted have not been studied. Such studies should provide valuable data as to the nature of these transient species. Preliminary to a general investigation of this phenomenon the consequences of both types of bleaching on y-irradiated ethanol glasses have been studied. Degassed ethanol which was both anhydrous and benzene-free was sealed in thin Pyrex ampoules (5% transmission at 275 mp) and irradiated with cobalt-60 y-rays a t liquid air temperature. The samples were warmed up in the dark or bleached a t liquid nitrogen temperature with either visible or ultraviolet light4before warming. Analysis of the gaseous products was made by (1) Based on work supported in part by USAEC contract AT(40-1)2001. (2) (a) M. C. R. Symonrr and M . Townsend, J . Chem. Phvs., 26, 1299 (1956); (b) B. Smaller and M. 6. Matheson, ibid., '28, 1169 (1958); (c) C. F. Luck and W. Gordy, J . Am. Ckem. Boc., 78, 3240 (1956). (3) (a) R. S. Alger, T. H. Anderson and L. A . Webb, J . Chem. Phge.. 80, 695 (1959); (b) H. Zeidea and R , Livingston, ibid., 30, 40 (1959). (4) An AH-O mercury arc with quartz envelope and a water filtor was used.
a modification of the Saunders-Taylor6 method combined with vapor-phase chromatography for the less volatile fraction. Dosages are based on the Fricke Dosimeter, using G(Fe+a) of 15.6. A summary of experimental results is to be found in Table I. TABLE I YIELDS OF GASEOUSDECONPOSITION PRODUCTS FROM IZTHANOL IRRADIATED AT 83°K. Apparenta U-values (100 ev. yields) Conditions of irradiationb U(Hd U(CH4) U(C0) U(CnHs) G'(CzH4) 1 1 X IOleev./g.,nobleach 4.71 0 . 2 8 0.01 0 . 2 9 0 . 3 2 5.87 0.46 0.30 0.28 0.33 2 1 X 10l9ev./g,vab.light 3 1 X 10~~ev./g.A-H6AroC 25.20 7 . 8 3 4 . 2 0 4 . 6 2 0 . 3 8 4 0 . 5 X 10'@ev./g.A-H6ArcC 33.98 12.14 8 . 8 5 7 . 1 6 1 . 4 5 5 0 . 2 5 X lOlgev./g.A-H6Arc 33.15 11.10 7.32 7.52 3.53 a Calculated on the assuniption that sole source of energy for decomposition is gamma radiation. Dose rate = 2 X lO17ev./g./min. A residual pink color observed.
A striking increase in the amount of gaseous decomposition products is observed when ultraviolet light is used. This agent by itself produces no significant decomposition. The yield-determining factor seems to be the extent to which the paramagnetic species are decomposed by the ultraviolet light (experiments 3, 4, 5 ) . It is conjectured that these increased yields are due to the photolysis of the ethanol free radical which under ordinary conditions would either dimerize or recombine with hydrogen atom. Support for this postulate is to be found in the work of V. V. Voevodskya who reports that under ultraviolet illumination the ethanol quintet is replaced (5) K. W. Saunders and H. A. Taylor, J . Chsm. Phyr., 9, 616 (1941). (6) V. V. Voevodsky, Abstracts, 4th International Symposium on Free Radical stabilization, Washington, D. C., 1959.
C
