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NOTES
Vol. 63
A STRUCTURE PROPOSAL FOR Na.1ZreF31
In the course of this study, an accurate cell size for this compound was obtained. To refine the accuracy of the cell size measurement, two Chemistry Division. Oak Ridge National Laboratory,' Debye-Scherrer patterns were taken, using Cr-K, Oak Ridpe, Tennessee radiation. The samples were prepared by grinding Received June 18, 1960 several of the above mentioned single crystals. A structure for one of the binary phase compounds These patterns were measured with a steel scale occurring in the NaF-ZrF4 system2 is proposed. and vernier and corrections were made for film Powder diffractions data of samples crystallized shrinkage and sample absorption. All clearly from melts of the composition 50 mole % NaF-50 resolved and unambiguously indexed reflections in mole % ZrF4 have indicated that these crystals are the range 18" < 28 < 142' were used to obtain a isomorphous with crystals of NaUFs. The latter least squares fit of the cell size to the data by a were found by Zachariasen and reported by Kate method described elsewhere.6 The refined hexagand Rabinowitch4 to be rhombohedral with space onal cell size was found to be group R3-(C23i) and 6 molecules per unit cell. a = 13.802 0.002 R. The metal ions are in the sixfold general positions c = 9.420 f 0.001 A. (f): ( X Y Z ) ; (ZXY);( Y Z X ) with the parameters The corresponding rhombohedral unit cell is X Y z a = 8.565 R., a = 107'21' BY P. A. AGRON AND R. D. ELLISON
*
U Na
3/13 6/13
1/13 2/13
9/13 5/13
Density measurements made on the single solid phase produced from large melts of slightly different compositions, namely, 52 mole % NaF48 mole % ZrR and 53 mole % NaF-47 mole % ZrF4, indicate the existence of a stoichiometry different from NaZrFS. The densities observed are 52 mole % NaF: 4.14 =k 0.03 g./cc. 53 mole % NaF: 4.11 f 0.01 gJcc.6 while the calculated density for NaZrFb is 4.01 g./cc. The unit cell volumes of the solids crystallized from melts of compositions in the region 50 mole yo NaF to 53.8 mole yo NaF differ by less than 0.5%. In order to satisfy the requirements of a greater density with a greater amount of the lighter component in a substantially constant volume, it is necessary to assume the addition of an NaF molecule to the unit cell, rather than the substitution of a lighter sodium for a zirconium ion with the accompanying fluorine vacancies even further reducing the density. It is significant that the additional Na+ cation could fit into the vacant special position, (000), without changing the space group. This would yield a unit cell of the stoichiometric composition Na&eFal (7NaF.GZrF4) with a calculated density of 4.16 g./cc., in reasonable agreement with the above measured values. Single crystals obtained from melts of the 53 mole % NaF composition have become available. Diffraction patterns obtained by using film techniques on the Buerger precession and the Weissenberg cameras have confirmed that the space group R3 is still possible for this composition. It is hoped that further measurements of the diffracted intensities using counting techniques will yield the fluorine positions, as well as confirm the suggested position (000) for the added Na+. (1) Work performed for the U. 9. Atomic Energy Commission at the Oak Ridge National Laboratory, operated by the Union Carbide Corporation, Oak Ridge, Tennessee. (2) C. J. Barton, W. R. Grimes, H. Insley, R. E. Moore and R. E. Thoma, Tam JOURNAL, 62, 665 (1958). (3) P. A. Agron and M. A. Bredig, ORNL-1729,47, 1954. (4) J. J. Kats and E. Rabinowitch, "The Chemistry of Uranium," McGraw-Hill Book Co., Inc., New York, N. Y.. 1951, p. 378. (5) 9. I. Cohen, Oak Ridge National L&boratory, personal communication.
(6) W. R. Busing and H. A. Levy, Acta Cryst., 11, 798
(1958).
THE TIN(I1) REDUCTION OF METHYL ORANGE' BY F. R. DUKEAND N. C. PETERSON
-
Institute for Atomic Research and Department of Chemistry, Iowa Stale Unzveraaty. Ames, Iowa Received June 88, 1068
The possibility that one particular Sn(I1) chloride complex might have high reactivity relative to others led to this kinetic study of the reduction of an azo compound to the amine 8C1
+ 4H + Ar-N=N-Ar +
+ 2Sn(11) +
2ArNHg
+ 2SnCla
The rates of reduction of a number of such compounds were measured by Goldschmidt and Braanaas,2 who reported a variable order in chloride ion, first order in azo compound and first order in Sn(I1). The recent equilibrium data for the Sn(11) chloride complexes3allow a more precise interpretation of the mechanism of the reaction relative to the role played by the chloride. The reduction of methyl orange was found to proceed at a convenient rate and, thus, was selected for study. Experimental Sn(I1) perchlorate was prepared by dissolving A.C .S. reagent grade Sn(I1) chloride in 2 N HCIOl and passing the solution through a column of Dowex 50 exchange resin in the acid form, followed by an elution with 2.0 m perchloric acid. Chloride ion was shown to be absent from the solution. Commercial methyl orange was recrystallized twice from water and dried in a desiccator over anhydrous calcium sulfate. Perchloric and hydrochloric acid solutions were prepared by diluting the concentrated reagents to 2.00 M with water distilled from alkaline permanganate. A model 6A Coleman Junior Spectrophotometer was used to follow absorbancy for all rate measurements, with Pyrex 1 om. cells. (1) Contribution No. 768. Work was performed in the Ames Laboratory of the U. 9. Atomic Energy Commission and Department of Chemistry at Iowa State University. (2) H. Goldachmidt and A. Braanaas, 2. physik. Chem., 96, 180 (1920). (3) C. E. Vanderzee and D. E. Rhodea, J . A m . Chem. Soc., 1 4 , 3552 (1952),
*
I
I
NOTES
Dec., 1959
Results and Discussion The reaction between Sn(I1) and methyl orange was found not to proceed in the absence of chloride. I n the presence of chloride at all concentrations, the reaction was found to be first order in Sn(I1) and first order in methyl orange. The chloride effect was studied by using very low methyl orange concentrations and relatively high Sn(I1) and chloride ion concentrations. Under these conditions, the reaction is pseudofirst order in methyl orange. Since Sn(I1) forms the complexes SnClf, SnC12 and SnC13- in appreciable concentrations under the conditions of these experiments, a general rate equation would be
2077
slope would be observed, the slope increasing as C1- increases; however, a straight line, with slope = 3 resulted. Thus we reach the conclusion that the appropriate rate equation is
Thus, it appears that SnC13- reacts much more rapidly than any other tin species. It is not unlikely that the tin is tetracoordinated in the activated complex, the fourth position being occupied by the methyl orange. SILICA-ALUMINA-CATALY ZED OXIDATION OF ANTHRACENE BY OXYGEN BYRICHARD M. ROBERTS, CYRIL BARTER AND HENRY STONE
where M is the methyl orange concentration. If Shell Development Company, Emeryville, California the stepwise formation constants for the Sn(I1) Received June 66, 1969 complexes are K I , K 2 and Ka for the formation of We have found that silica-alumina catalyzes the complexes containing 1, 2 and 3 chlorides, respectively, and Sn(I1) = [Sn++] [SnCl+] [Sn- oxidation of anthracene by molecular oxygen at room temperature. Cl21 [SnC13-], then Before describing this reaction, it is necessary to --dM = give an account of the behavior of anthracene and dt silica-alumina in the absence of oxygen. Silicaalumina, anthracene and n-heptane (solvent) were separately outgassed and were mixed under strictly anaerobic and anhydrous conditions, emSince Sn(I1) and C1- are large compared with M , ploying all-glass apparatus, break-seals and high k’ = ASn(II), where k’ is. the slope of the log M vs. vacuum technique. The silica-alumina had been time and A is the bracketed term in the above evacuated a t 500°,the anthracene at room temperaequation. If P is the denominator of the brack- ture and the anhydrous n-heptane by repeated eted term, then we define a parameter F(Cl-) freezing, evacuation and thawing. When the = Ic’P/Sn(II) where F(C1-) is the numerator of three components were mixed under the above the bracketed term, such that F(C1-)/P = A . conditions, the silica-alumina turned green. (AnThe term P was evaluated from the literature thracene solutions do not absorb visible light.) values for K1,Kz and Ka.2 It was first assumed The green color is characteristic of anthracene that C1- = T,, where Tc is the total chloride. adsorbed on acidic solids under anaerobic and Since Tc = C1SnCl+ 2SnCl2 3SnCla-, a anhydrous conditions; anthracene adsorbed on series of approximations allowed calculation of C1-, pure silica gel, an extremely weak acid, is colorthe uncomplexed chloride. This was used to make less. The green color of anthracene adsorbed on a final calculation of P. The data and calculated silica-alumina may be due to a carbonium ion values of [Cl-1, P and F(Cl-) are given in Table formed by transfer of a proton from the silica-aluI. mina to the anthracene molecule, probably on the 9-carbon atom.’ TABLE I The adsorption of anthracene on silica-alumina METHYL ORANGE REDUCTION RATES‘ under the above conditions, producing the green color on the solid, is reversible, When a little outgassed n-butylamine was added through a 1 0.190 0.00217 0.187 5 . 2 1 11.5 27.6 break-seal to the anaerobic mixture of silica2 .472 .00217 .468 21..3 83.5 820 alumina, anthracene and n-heptane, the green 3 .0950 .00217 ,0930 2.56 5.69 6.71 color disappeared and the silica-alumina became .181 5.01 27.0 4 ,187 .00429 31.5 5 .OB8 .0093Q .0169 1.21 0.371 0.0478 perfectly white. The n-butylamine is evidently more basic than anthracene and displaces the 6 .0574 ,00939 .0522 1.74 3.76 0.697 latter from the silica-alumina surface. It may be 7 .0960 .00939 ,0881 2.43 12.45 3.22
+
+
+
+
+
+
8 9 10
.1356 ,00939 .1255 3.34 28.3 10.2 .1732 .00939 .1620 4.38 49.3 23.1 .2026 .00469 .1965 5.54 40.4 47.4 a To and TBare total concentrations in Cl- and in Sn(II), respectively, [Cl-1 is uncomplexed chloride; P , IC‘ and F(Cl-) are defined in the text.
A plot of log F(Cl-) vs. log [Cl-] was prepared. It might be expected that at low [Cl-1, a small
(1) G. Dallinga, E. L. Mackor and A. A. Verrijn Stuart, MoZecuEar Phys., 1, 133 (1958). We have examined the absorption spectrum of anthracene adsorbed on silica-alumina from decahydronaphthalene solution under anaerobic and anhydrous conditions, with a Cary spectrophotometer. Decahydronaphthalene was employed as solvent to reduce the scattering of light. Absorption bands not present in the spectrum of anthracene in solution were noted at 4200 and 7500 A. with two possible very weak bands at 5850 and 6400 A. A publication on the absorption apectra of adsorbed molecules, including anthracene, is planned by one of us (C.B.).
