COMMUNICATIONS TO THE EDITOR
Mar. 5, 1954
1455
for which the Nernst equation a t 2.5’ is E = EO + 0.0296 log ( 0 3 ) / ( H ~ 0 2 -0.0592 ) $” ( 2 ) Supposing that the absolute rate theory as recently applied to polarographic phenomena4 is applicable here, i t can be shown that these equations apply a t the crossing point, however irreversible the waves may be. In fact, Equation (2) was found to hold very well DEPARTMEST O F CHEMISTRY both with regard to the pH and the 02-H202 ratio SORTHTVESTERN USIVERSITY FREDBASOLO {corrected for the acid dissociation of Hz02) over EVANSTOS, ILLIXOIS FRASKP. DWYER the entire range investigated. The value Eo = RECEIVED JANUARY 13, 1954 +O.i’O v. i 0.01 v. was found for the standard potential of the half-cell of Equation (l),in good THE OXYGEN-HYDROGEN PEROXIDE COUPLE AT agreement with Latimer’s calculated value +0.682 THE DROPPING MERCURY ELECTRODE v.5 Sir : These experimental results are also in good The first oxygen wave of the dropping mercury accord with the observations of Berl,6 who found electrode (D.M.E.) arises from the two electron that the 02-H202 couple was reversible a t graphite reduction of oxygen t o hydrogen peroxide. Al- and activated carbon electrodes in solutions of PH though this wave has universally been considered between 13 and 1.5, with an Eoof +0.684 v. highly irreversible, it was recently reported2 that In the range of pH studied the Oz-HzOz couple in unbuffered basic solutions hydrogen peroxide a t the D.M.E. evidently is of the transition (semiyields an anodic wave a t the same potential. reversible) type.’ The situation is complicated From this and other observations the investiga- by the probable presence of two steps8 which may tors concluded that the oxygen-hydrogen peroxide differ in degree of reversibility and dependence on reaction is completely reversible, but involves only pH. Analysis of the irreversible nature of the one electron. waves is continuing with the hope of elucidating These conclusions are not consonant with the the mechanism and kinetics of oxygen reduction. fact that HzOZ (or HOz-) and 0 2 must be the The combined results will be presented in a future diffusing species, and hence two electrons be in- publication. volved in the over-all electrode process; and they (4) Tanford and Wawzonek, “Annual Reviews of Physical Chemisconflict with the insensitivity of the oxygen half- try,” 3, 247 (1952). ( 5 ) W. M. Latimer, “Oxidation Potentials,” 2nd edition, Prenticewave potential (Ell2)to changes in PH, as reported Inc., New York, N. Y., p. 43. by Kolthoff and itliller.a In view of the funda- Hall, (6) W. G. Bed, J . Elecrvochcm. SOC.,83, 253 (1943). mental importance of the oxygen wave in polarog(7) P. Delahay, THISJOURNAL, 75, 1430 (1953); >I. Smutek, Coll. raphy, i t was considered important to resolve this Czech. Chem. Comm., 18, 171 (1953). (8) One of these may he the reversible one-electron step postulated problem, and a preliminary report is provided in by Hacobian, see ref. 2. this Communication. CHEMICAL LABORATORY Polarograms of oxygen, hydrogen peroxide and MALLINCKRODT UNIVERSITY DAVID M. H. KERN their mixtures were run in buffered solutions, pH HARVARD CAMBRIDGE 38, MASS. range 7.5-13, of ionic strength 0.15. In all these RECEIVED JANUARY 27, 19A4 solutions, anodic and cathodic waves were observed, which in the less basic media exhibited the usual criteria of irreversibility-drawn-out shapes, 9a-FLUOR0 DERIVATIVES OF CORTISONE AND HYDROCORTISONE non-linear “log plots,” and in the case of the oxygen wave an El/, which hardly varied with PH. In Sir : I n a recent communication’ we have described mixtures of hydrogen peroxide and oxygen the two waves joined without inflection; however, the E l / , a new group of derivatives of cortisone and hydroshifted as the composition of the mixture was cortisone, in which the %-hydrogen atom is revaried. This irreversible nature diminished as placed by halogen. The main interest in this sethe alkalinity increased, until a t pH 12 both anodic ries of compounds derived from the fact that they and cathodic waves gave identical EI/,’s, and the possessed marked glucocorticoid activity, which in log plot of both had the theoretical slope for a the case of the chloro derivatives exceeded by a factor of 4 that of the parent hormones. The findtwo-electron reaction. At the point a t which the electrolysis current ing that the activity was inversely proportional to in a Hz02-02 mixture crosses the residual current, the size of the halogen atom prompted the preparathe D.M.E. is functioning as a potentiometric tion of the last remaining members of this group, null point detector. The “crossing point” poten- the Sa-fluoro derivatives, the description of which is tial will depend upon the bulk concentration as the purpose of this communication. 9a-Fluorohydrocortisone acetate (I), m.p. 233predicted by the Nernst equation, provided that we are dealing with the over-all reaction 23402; [ c Y ] ~$123’ ~ D ( 6 , 0.64 in CHCI,); ,;:A: 238 m p ( E = 16,800); A”,?’ 2.94 p , 3.03 p (OH), 5.75 0 2 2H+ + 2e- _r H202 (1) p , 5.82 p (acetylated side chain), 6.07 p , 6.11 p (1) Kolthoff and Lingane, “Polarography,” 2nd edition, Vol. 11, perimental support to the postulate of orbital stab i l i ~ a t i o n . ~The susceptibility of the mono compound, 1.8 B.M., corresponds to one unpaired electron. This is not consistent with the theoretical values expected from the simple formula [FedipyClz] and may suggest a certain amount of metalmetal interaction. Detailed studies on these and similar compounds will be published later.
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Interscience Publishers, Inc., New York, N.Y., p. 652. (2) S. Hacobian. Ausfralian Journal of Chemistry, 6 , 211 (1863). (3) I. M. Kolthoff and C. 5. Miller, THISJOURNAL, 68, 1018 (1941).
(1) J. Fried and E.F. Saho, THISJOURNAL, 76, 2273 (1963). (2) Occasionally samples began t o melt at 205-208’, reiolidiEed and eventually melted at 228-228O, probably due to polymorphiam.
