Dec., 1960
ABSORPTION SPECTRA OF URANIUM(III) AND (IV)
IN
DCLO~ SOLUTION
1933
as observed. A t higher values, the term D 2would not be constant and hence a curvature should appear as observed. Approximate values of A and B may be obtained by plotting kr/D2 vs. H + ion concentration and drawing the best line, Fig. 6. I n this manner the following were found: a t 79.9", A 0.32, B 1.0: a t 85O, A 0.31, B 1.6; a t 90°, A 0.30, B 2.5. Since A and B are functions of the rate constant lcl and kl', respectively, they might be expected to vary with temperature. If the Arrhenius equation holds (assuming that the equilibrium constants involved do not change over the range SO-SO") a plot of log A or log B vs. reciprocal temperature and a plot of k, vs. hydrogen ion concentration, should be linear. But the values of A given above Fig. 5, a t constant reaction temperature and iodide are the same within experimental error, so it appears concentration of 5.7 mg./100 ml., affords a linear that the energy of activation of the step involving relationship a t pH values of 0.2 to 1.0; a t values k l , equation 9, is close to zero, as expected for a over 1.0, the linear relationship breaks down. reaction involving oppositely charged ions. The In equation 22, a t low pH values, the term ([H+]/ plot of log B gives an activation energy of 22 kcal./ [H+] K ) 2 designated henceforth as D2,is ap- mole for the step involving kl', equation 10. This proximately constant,21and therefore, k, = A B value compares favorably with activation energies [H+],and a linear relationship should be obtained reported for reactions between ions and neutral molecules in solution.22
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on August 27, 2015 | http://pubs.acs.org Publication Date: December 1, 1960 | doi: 10.1021/j100841a031
sulfinyl sulfone to sulfenic acid was favored in the present mechanism. The mechanism above distinguishes between the possible forms of thiolsulfonate. The anhydride structure was assumed as incapable of existence under the experimental conditions.20 Also, in acidic media, the form RS-OH would be expected to predominate in equation 11. This would favor the formation of the unsymmetrical thiolsulfonate structure, 11. Application of Equation 2 1 to the Experimental Data.-In the general equation 21
+
+
(20) K. Fries and G. Schurman. Ber.. 47. 1195 (1914). (21) The ionization constant K of p-toluenesulfinic acid was taken as 0.02 (R. R. Coats and D. T. Gibson, J . Chem. Soc., 442 (1940)).
(22) A. A, Frost and R. G. Pearson, "Kinetics and Mechanism.'' John Wiley and Son, Inc., New York, N. Y., 1953, p. 136.
ABSORPTIOS SPECTRA OF URANIUM(II1) AND URANIUM(1V) I N De104 SOLUTION' BY DONALD COHENAND W. T. CARNALL Argonne National Laboratory, Argonne, Illinois Received July 6, 1960
The absorption spectra of U(II1) and U(1V) in DClOd has been observed from 0.2 to 2.6 p . Solutions of a pure valence stmatewere prepared and maintained by electrolytic reduction in a combination electrolysis-absorption cell. Several new bands have been discovered in the ultraviolet atld near infrared regions, and their positions as well as those of the other bands in the spectra are compared with the energy levels calculated from theory.
The theoretical treatment by Jorgensen2
