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
where M is the methyl orange concentration. If the stepwise formation constants for the Sn(I1) complexes are K I , K 2 and Ka for the formation of complexes containing 1, 2 and 3 chlorides, respec[SnCl+] [Sntively, and Sn(I1) = [Sn++] [SnC13-], then Cl21 --dM =
+
+
+
dt
Since Sn(I1) and C1- are large compared with M , k’ = ASn(II), where k’ is. the slope of the log M vs. time and A is the bracketed term in the above equation. If P is the denominator of the bracketed term, then we define a parameter F(Cl-) = Ic’P/Sn(II) where F(C1-) is the numerator of the bracketed term, such that F(C1-)/P = A . The term P was evaluated from the literature values for K1,Kz and Ka.2 It was first assumed that C1- = T,, where Tc is the total chloride. Since Tc = C1SnCl+ 2SnCl2 3SnCla-, a series of approximations allowed calculation of C1-, the uncomplexed chloride. This was used to make a final calculation of P. The data and calculated values of [Cl-1, P and F(Cl-) are given in Table
+
+
+
I.
TABLE I METHYL ORANGE REDUCTION RATES‘ 1 0.190 0.00217 0.187 5 . 2 1 11.5 27.6 .468 21..3 83.5 2 .472 .00217 820 3 .0950 .00217 ,0930 2.56 5.69 6.71 .181 5.01 27.0 4 ,187 .00429 31.5 5 .OB8 .0093Q .0169 1.21 0.371 0.0478 6 .0574 ,00939 .0522 1.74 3.76 0.697 7 .0960 .00939 ,0881 2 . 4 3 12.45 3.22 8 .1356 ,00939 .1255 3.34 28.3 10.2 9 .1732 .00939 .1620 4 . 3 8 49.3 23.1 10 .2026 .00469 .1965 5 . 5 4 4 0 . 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
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 Shell Development Company, Emeryville, California Received June 66, 1969
We have found that silica-alumina catalyzes the oxidation of anthracene by molecular oxygen at room temperature. Before describing this reaction, it is necessary to give an account of the behavior of anthracene and 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, employing all-glass apparatus, break-seals and high vacuum technique. The silica-alumina had been evacuated a t 500°,the anthracene at room temperature and the anhydrous n-heptane by repeated freezing, evacuation and thawing. When the three components were mixed under the above conditions, the silica-alumina turned green. (Anthracene solutions do not absorb visible light.) The green color is characteristic of anthracene adsorbed on acidic solids under anaerobic and anhydrous conditions; anthracene adsorbed on pure silica gel, an extremely weak acid, is colorless. The green color of anthracene adsorbed on silica-alumina may be due to a carbonium ion formed by transfer of a proton from the silica-alumina to the anthracene molecule, probably on the 9-carbon atom.’ The adsorption of anthracene on silica-alumina under the above conditions, producing the green color on the solid, is reversible, When a little outgassed n-butylamine was added through a break-seal to the anaerobic mixture of silicaalumina, anthracene and n-heptane, the green color disappeared and the silica-alumina became perfectly white. The n-butylamine is evidently more basic than anthracene and displaces the latter from the silica-alumina surface. It may be (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.).
NOTES remarked that water also displaces anthracene from silica-alumina. Now when oxygen was admitted at room temperature to the anaerobic system containing green silica-alumina, the color of the solid rapidly changed from green to very dark brown. On addition of n-butylamine to this mixture, the solid did not revert to its original white appearance, but remained brown, suggesting that in this case the adsorbed material may hsve been more basic than the amine. Aiithracene adsorbed on pure silica gel is not oxidized by oxygen under the present conditions. A quantitative oxidation experiment was made in a static system consisting of a glass reaction vessel connected through a Kovar seal to a metal packless valve, and then to an allmetal pressure gage through a stainless steel line. Silicaalumina (1.03 g.) was evacuated a t 550’ for 1.5 hr.; 10 mi. of n-heptane and 20 mg. of anthracene were separately thoroughly outgassed; the three components then were mixed by break-seal technique. Oxygen was admitted to the reaction vessel at room temperature at a pressure of 540 mm. and the vessel was shaken. A gradual decrease in pressure was observed, the green silica-alumina began to darken and in three minutes was almost black. After one hour there was no further decrease in pressure. The remaining oxygen was removed and measured, and the solution was analyzed for anthracene by ultraviolet spectroscopy before and after treatment of the silica-alumina with n-butylamine. There was 78% conversion of anthracene, and 1.6 moles of 0 2 was consumed per mole of anthracene converted. The absorption spectrum of the brown silica-alumina was not obtained. However, at the conclusion of an experiment similar to that described above, the brown catalyst was eluted with methanol (all the adsorbed material was not removed by this treatment), givin! a red solution with ari absorption maximum a t 5550 A. This solution turned yellow on standing in air for a few hours. I t should be emphasized that anthracene in n-heptane solution is completely unreactive with oxygen a t room temperature in the absence of a catalyst. Eastman Kodak Company “blue-violet fluorescent” anthracene was employed in the above experiments. The a-heptane was treated with an excess of NOz-N?Od to remove traces of olefins and then was chromatographed on silica gel. The silica-alumina was American Cyanamid Company ‘4erocat cracking catalyst, with the following properties: 22.1 % AlzOa,0.92% SO4,0.032% Fe, O.OOS%.Na and B.E.T. surface area of 526 m.Z/g. Before use, this catalyst was heated in air for five hours and was perfectly white after this treatment.
Vol. 63
that oxidation to a free radical positive ion was responsible for the alteration in spectrum in the case of perylenee6 Matsumoto and Funakubo observed a small amount of oxidation of anthracene to anthraquinone during chromatography of a benzene solution of anthracene on activated This observation may be an example of the reaction reported here, although alumina is considered a very weak solid acid. The present experiments raise a warning that oxidation may interfere with the chromatographic separation of aromatic hydrocarbons. By the same token studies of hydrocarboii catalysis by acidic solids may involve errors due to an attenua,tion of catalytic activity by products of oxidation or other basic molecules such as water. The latter may be especially true when catalysts are “regenerated” by contact with air immediately before use . The experimental assistance of R. M. ROSSis gratefully acknowledged. (5) G. Dallinga, E. L. Mackor and A . A . Verrijn Stuart, MoEecular PhuS., 1, 125, 137 (1958). (6) Y . Matsumoto and E. Funakubo, J . Chem. Sor. Japan, Pule Cliem. Sect., 731 (1951); Y . Matsumoto, ibid., 733 (1951).
A GLASS CONDUCTANCE CELL FOR T H E MEASUREMENT OF DIFFUSION COEFFICIENTS BY HERBERT S. HARNED AND MILTONBLANDER Conlribulion N o . 1666 f r o m the Department of Chemistry of Yale Universzty, New Haven, Conn. Received June 86,1969
The determination of diffusion coefficients of electrolytes by the conductance method has been carried out in Lucite cells of types described by Harned and Nuttall.1 To avoid the disadvantages of the use of Lucite and of grease in the region of the electrodes, the glass cell, the cross section of which is shown in Fig. 1, was constructed. The cell is of soft glass tubing of 8 mm. internal diameter. The electrodes a t positions C are platinum tubes about 2
The reaction reported above appears a t first cm. in length and 3 mm. in diameter. The ends of these sight to be anomalous because there seems to be tubes were closed and made flat by spinning. They are at positions C a t a distance from the top and bottom agreement that hydrocarbon reactions catalyzed by sealed of the cell of one sixth its depth. The top of the tube was silica-alumina involve ionic or polar intermediates,2 flanged at B. A glass plate A ground to this flange serves while hydrocarbon autoxidations are generally when clamped to seal off the top of the cell. The bottom believed to proceed by homolytic mechanisms. of the cell is attached to a special stopcock E with a hole half way through it. This hole or cup D in the stopAs far as is known, hydrocarbon oxidations cat- only cock can be turned to any position and serves to introduce alyzed by the solid acid, silica-alumina, have not salt solution into the cell. The cell, with lead wires from been reported. the conductance bridge attached to electrodes, is mounted on a brass block in a Lucite box which is covered and subWe find two reports in the literature which appear in a water-bath. A cork was sealed to the stopcock to demonstrate acid-catalyzed oxidation of hydro- merged handle and Nylon cord was attached to the cork so that the carbons. Friedel and Crafts found that phenol stopcock could be turned from outside the Lucite box. wa,s formed when air was bubbled through a reThe sequence of manipulation of the glass cell is similar fluxing mixture of benzene and aluminum ~ h l o r i d e . ~to that previously used with the cells made of Lucite. After were platinized, the cell was repeatedly washed Dallinga, Mackor and Verrijn Stuart reported that the electrodes distilled water until the resistance between any pair the spectra of solutions of perylene, pyrene and with of electrodes after standing overnight was over 500,000 ohms. naphthacene in hydrogen fluoride were greatly The cell in the upright position was filled with fresh distilled altered by the presence of oxygen and suggested water. The flange was greased lightly. A mound of water (2) H. H. Voge in “Catalysis,” Val. VI, P. H. Emmett, Editor, Reinhold Publ. Corp., New Pork, N. Y., 1958, pp. 407-493. (3) G. A. Russell, J . Chem. Ed., 36, 111 (1959). (4) C . Friedel and J. M. Crafts, Compf. r e n d . , 8 6 , 885 (1878). The conveision of benzene and tho yield of phenol were not repolted.
above the surface of the flange was built up so that by sliding the glass plate along the ground surface of the flange, the liquid could be sheared off completely. Care was exer(1) 15. S. Harned and R. L. Nrittall, J . A m . Chem. Soc., 69, 730 (1947).
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