NOTES
4560
and Jz4= 5.8 Hz for p-fluorotoluene.6” The 19F31P couplings (J14) are of the same order of magnitude as the corresponding coupling constants in a variety of pentafluorophenylphosphorus derivatives.l 2 Acknowledgment. We wish to thank Mr. D. E. Wisnosky for his invaluable technical assistance in modifying the HA-100 spectrometer. This work was performed using, in part, instrumentation provided by a grant (FR 00292) from the National Institutes of Health. ~
~~
~
~~
(12) M. G. Barlow, M. Green, R. N. Haszeldine, and H. G. Higson, J . Chem. Soc., Sect. B , 1025 (1966); M. G. Hogben, R. S. Gay, and W. A . G. Graham, J . A m . Chem. SOC.,88, 3457 (1966).
Radiation Decomposition of Solid Chlorates by C. E. Burchill, P. F. Patrick, and K. J. McCallum Departmen lof Chemistry and Chemical Engineering, University of Saskatchewan, Saskatoon, Saskatchewan (Received June 19, 1987)
The decomposition of solid chlorates by ionizing radiation has been reported by several authors. 1-6 These studies, however, have not resulted in complete agreement regarding the identity of the decomposition products or their yields. I n the present work, irradiation of crystalline sodium, potassium, and barium chlorates by Cow y rays followed by solution in water was found t o lead t o the formation of oxygen, chlorine dioxide, and perchlorate, chlorite,, hwochlorite, and chloride ions. ” *
Experimental Section The purified salts were irradiated in Pyrex test tubes a t room temperature in a Gammacell 220 unit manufactured by Atomic Energy of Canada Ltd. Dosimetry measurements were made with the Fricke dosimeter, using a G value of 15.5 for the production of ferric ion. Dose rates in the solid sample were corrected on the basis of Compton absorption in sodium and potassium chlorates, with an additional small contribution from photoelectric absorption in barium chlorate. The yield of oxygen on solution of the irradiated crystals was determined chromatographically on Linde Riolecular Sieve Type 5A using either helium or argon as the carrier gas. A correction for the small amount of oxygen which remained dissolved in the solution was made by polarographic measurement. When argon was used as the carrier gas, it was possible to detect and measure the production of a small amount of hydrogen. The Journal of Physical Chemistry
I n some experiments, volumetric estimations of gas yields were made, giving results in agreement with those obtained chromatographically. The aqueous solution obtained when the irradiated salt was dissolved was analyzed for products containing chlorine in all of the oxidation states stable in solution. Perchlorate ion produced in the solution was determined by measuring the optical density of the methylene blue complex at 665 mp.’ The yield of chloride ion was measured mercurimetrically in neutral solution, using sodium nitroprusside indicator.8 The yields of chlorine dioxide, hypochlorite, and chlorite were determined using a modification of the procedure due to White.g The total number of oxidizing equivalents of these products was determined iodimetrically in acetic acid solutions. Chlorine dioxide was estimated from the decrease in the number of oxidation equivalents following disproportionation of this species in basic solution to chlorate and chlorite. In another aliquot the arsenious oxide methodlo was used to determine hypochlorite after the interfering chlorine dioxide was removed by treatment with base. Finally, the amount of chlorite present was calculated by difference. Results and Discussion The G values for the yields of products, measured at a dose rate of 7 X 10l6ev/g min, are given in Table I. The deviations quoted in this table represent the standard deviations of individual points on the dose-yield curves. The yields of products were found to increase linearly with increasing dose over the range examined (up t o loz1ev/g). The G values were found to be independent of dose rate over the range 1.4 X 10’6 to 7 X 1016ev/gmin. The general features of the product yields of the three chlorates are very similar, suggesting that the same general mechanism is operative. The decomposition scheme proposed by Heal4is consistent with the (1) G. Hennig, R. Lees, and M.S. Matheson, J . Chem. Phys., 21, 664 (1953). (2) L. J. Sharman and K. J. McCallum, ibid., 23, 597 (1955). (3) T . P. V. Bakerkin, Dokl. Akad. S a u k SSSR, Otd. Khim. Sauk, 167 (1957). (4) H. G. Heal, Can. J . Chem., 37, 979 (1959). (5) C. J. Hochanadel, J . Phys. Chem., 67, 2229 (1963). (6) P. F. Patrick and K. J. McCallum, Sature, 194, 776 (1962). (7) D. F. Boltz and W. J. Holland in “Colorimetric Determination of Nonmetals,” D. F. Boltz, Ed., Interscience Publishers, Inc., New York, N. Y.,1958, p 176. (8) 1. M. Kolthoff and V. A. Stenger, “Volumetric Analysis,” Vol. 11, 2nd revised ed, Interscience Publishers, Inc., New Tork, N. Y., 1947, p 331. (9) J. F. White, A m . Dyestuff Reptr., 31, 484 (1942). (10) I. M. Kolthoff, “Textbook of Quantitative Inorganic Analysis,” 3rd ed, The Macmillan Co., New Tork, N. T.,1952, p 597.
NOTES
4561
Table I : G Values for the Radiation Decomposition of Chlorates
c102-
c10cion
C1c1040 2
HP
Ba(ClOa)?
KClOa
NaClOa
2.05 f 0 . 0 6 0.26i0.06 0.2.5 i 0 . 0 9 l.'i2+O0.O7 0.60i0.11 3.90i0.04 0.1110.02
2.07 f 0 . 0 7 0.27 f 0 . 0 4 0 . 2 1 i 0.04 1.64f0.09 1.13 i 0 . 0 6 2.76i0.16 0.O6=tO0.03
1.32 f 0.03 0.18 i0.03 0 . 1 3 i 0.03 0.91 f 0.03 0.22 i0.04 2.36 f 0 . 2 5 0.05 f 0.01
observations. This suggests that the absorption of energy by the chlorate ions leads to the formation of chlorite, hypochlorite, and chloride. Chlorine dioxide could be formed from the loss of an oxygen atom and an electron. The loss of an electron would lead to chlorine trioxide which could then dimerize to form dichlorine hexoxide. Hydrolysis of this species could account for the observed perchlorate formation. The oxygen gas could arise from the recombination of oxygen atoms, while the small yield of hydrogen could be explained by the interaction of trapped electrons with the solvent. Absorption spectra of irradiated single crystals of sodium and potassium chlorates obtained in the region 2000-5000 A showed results similar to those obtained by Heal4 for potassium chlorate crystals irradiated by Xrays. His interpretation of the spectra indicated the presence of chlorite, hypochlorite, chlorine dioxide, and dichlorine hexoxide in the solid. The G values for products formed from potassium chlorate by Co60 y rays are consistent with those reported by Hea1.l The G value of 2-3 for oxygen production by pile irradiation' agrees with that reported in the present work. However, the reported G value of 1.2 for the production of chlorite ion by Co60irradiation3 is significantly lower than our present value. The method of HochanadeP gave a G value of 1.50 for chloride ion formation in irradiated sodium chlorate, rather than the value of 0.9 reported here. However, in acid solution the oxgchlorine species present may interfere in the method he used for the chloride determination. Other workers have made detailed studies of the with radiolysis of perchlorate^^^-'^ and similar results regarding the identity of the decomposition products. The presence of Br02 in irradiated bromates was inferred, while low yields of hydrogen gas were observed only for large absorbed doses. Also, similar decomposition mechanisms for perchlorates and bromates have heen proposed, involving excitation, ionization, and the losfi of oxygen from the anion.
The concept of "free space" within the crystal has been correlated with the over-all probability of dec o m p ~ s i t i o n . ~ J ~ Extending this interpretation to the chlorate system, relative sensitivities to radiation decomposition have been calculated. The chlorates, ranked in theoretical order of increasing sensitivity, are ~ a C 1 0 3Ba(C103)2, , and KC1O3. I n actual fact, potassium chlorate undergoes more decomposition than sodium chlorate, but the over-all decomposition of barium chlorate is slightly higher than that of the potassium salt. Cunningham and Heallg found that the variation of decomposition with free space for alkaline earth nitrates was similar to that for alkali metal nitrates but lay on a different curve; presumably, comparisons between the two types would not be valid. The C1-: C102-: C10-: CIOz ratios are nearly the same (within experimental error) for all three of the chlorates studied. This suggests the relative probabilities for the different modes of decomposition may be independent of the nature of the cation. Only the overall probability of decomposition by this mechanism seems to be affected. The C1-:C104- ratio in KClO3 is higher than that of the other two salts, indicating the mechanism of perchlorate formation may be different in this compound. Information on the reactions of the species present in the irradiated solid can be obtained from the effects of thermal annealing. The results of this treatment will be reported in a later paper. (11) L. A. Prince and E. R. Johnson, J. Phys. Chem., 69,359 (1965). (12) L. A. Prince and E. R. Johnson, ibid., 69, 377 (1965). (13) H. G. Heal, Can. J . Chem., 3 7 , 979 (1959). (14) G. E.Boyd, E. W. Graham, and Q. V. Larson, J . Phys. Chem., 66,300 (1962). (15) G.E.Boyd and T. G. Ward, Jr., ibid., 68, 3809 (1964). (16) G.E.Boyd and Q. V. Larson, ibid., 68,2627 (1964). (17) G. E. Boyd and Q. V. Larson, ibid., 69, 1413 (1965). (18) J. W. Chase and G. E. Boyd, ibid., 7 0 , 1031 (1966). (19) J. Cunningham and H. G. Heal, Trans. Faraday SOC.,54, 1355 (1958).
Solubility of Iodine in Dimethyl Sulfoxide by Toshiro Soda and Joel H . Hildebrand Department of Chemistry, UnQersdy of California, Berkeley, California 94780 (Received August 89, 1967)
Figures for the solubility of iodine in dimethyl sulfoxide (DMSO) between 27 and 38" were pubVolume 71, Number 19 December 1067
