March, 1958
NOTES
left a t the Chemistry Department of the University of Wiscousin and some will be offered to the Smithsonian Institution in Washington for future observations. Perhaps other investigators will be' interested in repeating the experiments described here with new and improved catalysts which may bring the period required for detectable decomposition down to a reasonable time.
silver block in a furnace a t 452"; melting occurred within the range 449.4 to 449.7" over a period of 30 minutes. The furnace was then cooled to 447" and the supercooled liquid shaken occasionally until freezing commenced, after an hour; the sample temperature then rose to 449.5' and remai:ed constant for 20 minutes, after which it again fell to 447 . The thermocouples (Pt. vs. Pt-Rh) were calibrated by freezing standard samples of zinc (419.50') and aluminum (660.15"),obtained from the National Bureau of Standards, and copper-silver eutectic (779.2"), in graphite tubes under identical conditions to the above.
361
Discussion Most of the discrepancies indicated in Table I TELLURIUM can be explained. Many of the measurements BY ROBERT E. MACHOL A N D EDGAR F. WESTRUM, JR. were frankly inaccurate. Impurities may have Contribution from the Department of Chemistry, University of Michigan, played a part in some of the low values, but most Ann Arbor, Michzgan of these were due t o the phenomenon of superReceived September 66,1967 cooling.6 Many of the measurements were inThe melting point of tellurium is given in stand- cidental to thermal analysis designed to elucidate ard as 450". Critical examination the phase diagram of binary systems containing of the highly discordant values in the literature, tellurium, and the values given are often marked which are summarized in Table I, supports this "start of crystallization," which is the phenomenon value. However, recent publications by Weide14 of interest in marking off a liquidus curve. Finally, and Lark-Horovitz,6 who have worked with very in some instances where these criticisms are not pure material, give the melting point as 452 and applicable, and which deviate by one or two de445O, respectively. grees from the results given here, the authors do not indicate how their temperature scales were TABLE I derived, and it is well known that errors of several MELTINGPOINTOF TELLURIUM degrees can be made a t these temperatures unless Author Year M.p., OC. careful calibration procedures are observed. By Pictet 1879 525 these criteria, the only published reports worthy of Carnelley and Williams 1880 452,455 consideration are those of Matthey,' Pellini and Topler 1894 420 Via,* Jaeger and MenkeYgKraus and G1ass,lD Matthey 1901 450 Simek and Strehlik,*l Kracek12 and this paper. Fay and Gillson 1902 446 The first two agree within the limitations of their Monkemeyer 1905 428 accuracy. The errors in the measurements of Pellini and Vi0 1906 450 Jaeger and Menke have been discussed by DaChickashige 1907 438 miens.13 The deviation of Kraus and Glass remains PBlabon 1909 452 unexplained. The measurements by Simek and Bilta and Mecklenberg 1909 455 Strehlik were exceedingly careful, and their relaKobayashi 1910 437 tive temperatures must be considered accurate, so Jaeger and Menlce I912 452.5 that, for example, their conclusion that hydrogen Damiens 1922 453 and carbon dioxide lower the melting point 0.15 Umino 1926 446 and 0.20°, respectively, per atmosphere of presKraus and Glass 1929 451. I sure should be accepted; however, their calibration Simelc and Stehlik 1930 452.0 was obviously in error a t the sulfur point and, as Kracek 1941 449.8 f 0 . 2 Kracek points out, if this is taken into account Weidel 1954 452 their result is in agreement. The work of Kracek Epstein, et al. 1957 445 appears to be the most accurate of all. Due to This research 449.5 f 0 . 3 limitations in temperature measurement, the probable error of the present result is about 0.3", Experimental The triple-point temperature of tellurium was determined slightly larger than that of Kracek. directly by observing the halt in the heating and cooling Solid State Transition.-A solid state transicurves of pure tellurium in vacuo. The tellurium was semi- tion reported by urn in^'^ was sought with the conductor grade, 99.999 + % ' pure, from American Smelting and Refining Company. It was placed in a vitreous present apparatus by going through the temperasilica tube with a re-entrant well for a thermocouple, con- ture range from 300 to 450" in both directions a t nected to a vacuum of 10-8 mm., and boiled vigorously to rates well below one degree per minute. No transieliminate possible volatile contaminants; sensitive tests6 tion was found, though one a tenth as large as that have shown that tellurium and silica do not react a t these temperatures. The tube was then sealed and placed in a reported would certainly have been evident. Simek and Strehlik have also remarked on the ab(1) "Selected Values of Chemical Thermodynamic Properties."
THE TRIPLE-POINT TEMPERATURE OF
National Bureau of Standards Circular No. 500, Washington, 1952. (2) D. R. Stull and G. C . Sinke, "Thermodynamic Properties of the Elements," Washington, 1956. (3) 0. Kubaschewski, 2. MetaZEkunde, 41, 445 (1950). (4) J. Weidel. 2. Naturforach., BA, 697 (1954). ( 5 ) A. S. Epstein, H. Fritzsche and K. Lark-Horovitz, Phya. Rev., 101, 412 (1957). (6) R. E. Macho1 and E. F. Westrum. Jr., "The Vapor Pressure of Tellurium," t o be published.
(7) E. Matthey, Proc. Roy. Sac. (London), 68, 161 (1901). (8) G.Pellini and G. Vio, Uaea. chim. ital., 86 121.469 (1906). (9) F. M. Jaeger and J. B. Menke, 2. onorg. Chem., 75, 241 (1912). JOURNAL, 88,995 (1929). (10) C. A. Kraus and 1.W. Glass, THIS (11) A. Simek and B. Strehlfk, ColE. Czech. Chsm. Comm., I, 304
(1930). (12) F. C. Kracek, J . Am. Chem. rSoc., 68, 1989 (1941). (13) A. Damiens. Ann. Chim.. 191 10, 44 (1923). (14) 8. Umino, Kinzoku-no-Renkyu, 8 , 498 (1926).
NOTES
362
sence of this transition, as has Niwa16 in a careful series of measurements of the vapor pressure of soIid tellurium. Since only one experimenter has reported this transition, and that on the basis of weak evidence, it may be assumed that it does not exist. (15) K.Niwa, J . Fac. Sci. Hokkaido I m p . Univ., 111113, 75 (1940).
THE VAPOR PRESSURE O F VANADIUM OXYTRIFLUORIDE
Vol. 62
and collected in another cooled in Dry Ice. The system was then evacuated. This procedure was repeated several times until the vapor pressure at a given temperature showed no further change after resublimation. The vapor density of the sample used for the vapor pressure measurements was determined a t 97.4 A value of 124.6 g./G.M.V. was obtained. The formula weight is 123.95 g./mole. Chemical analysis of the sample indicated 40.6% vanadium and 46.0% fluorine. The theoretical values are 41.10% and 45.99%, respectively. The vapor pressure measurements were made on a sample of 10-15 g. The equilibrium vapor pressures were approached experimentally from both higher and lower temperatures.
.
1
BY LAVERNEE. TREVORROW
Results Chemical Engineering Division, Aroonne NationaE Laboratory, Lemont, The vanadium oxytrifluoride sample was exI11zn ois amined briefly by the method of thermal analysis to Received September #7# 1067 determine whether melting or solid transitions Very little information is available in the litera- occurred in the temperature range of 72 to 123". ture on the volatility of vanadium oxytrifluoride. The material showed no thermal halt when it was Ruff and Lickfett2 reported that the compound warmed through this temperature interval. melted at 300" and boiled a t 480". Haendlerat4 The results of the vapor pressure measurements stated that vanadium(V) oxide reacted with fluo- are summarized in Table I. rine at 475" to form volatile vanadium oxytrifluoVanadium oxytrifluoride was found to be much ride, VOF3. more volatile than was indicated by the data of In the present work, a sample of the pure com- Ruff.2 Interpolation of the results of the present pound was prepared and identified by chemical work gives a vapor pressure of 760 mm. at 110". analysis and by a vapor density determination. TABLE I The vapor pressure of solid vanadium oxytrifluoride was meahred at various temperatures from 72 to VAPORPRESSURE OF VANADIUM OXYTRIFLUORIDE Temp. ("C.) Pressure, mm. Temp. ("C.) Pressure, mm. 123". Experimental Materials.-Vanadium pentoxide of 99.5 to 99.7% purity was obtained from the Vanadium Corporation of America. High purity commercial fluorine was used. I n previous work6 this material was shown to be at least 99% fluorine by volume, and to contain less than 0.5% impurities. A paratus .-The preparation and vacuum manipulation of tce vanadium oxytrifluoride were performed in a nickel and Monel system. Monel diaphragm and Teflon-seated bellows valves were used. The system used for the purification of the compound and the vapor pressure measurements was assembled from components which were joined by welds or by flare connectors with Teflon gaskets. This system was contained in a thermostated air box, and it was e ui ped with a Booth-Cromer pressure transmitter and sif-galancing relay6 which permitted pressure measurement with a mercury manometer. Temperatures were measured to the nearest 0.1' with a copper-constantan thermocouple previously calibrated against a standard platinum resistance thermometer. The thermocouple was used with a Rubicon type B potentiometer for the vapor pressure measurements, and a Brown recording potentiometer was used to obtain thermal analysis curves. During the pressure measurement, the vanadium oxytrifluoride sample was contained immediately under the pressure transmitter in a S/d-inch nickel tube 6 inches in length. The thermocouple was inserted into a well in the bottom of the tube. Procedure.-The vanadium oxytrifluoride was prepared by the reaction of vanadium pentoxide with fluorine at about 475". The product was a pale yellow solid a t room temperature. In order to rid the product of oxygen, fluorine and hydrogen fluoride, the whole sample was sublimed from one Fluorothene (poly-chlorotrifluoroethylene) tube (1) Work performed under the auspices of the U.S. Atomic Energy Commission. (2) 0. Ruff and H. Lickfett, Ber., 44, 2539 (1911). (3) H. h l . Haendler, "The Reaction of Fluorine with Titanium, Zirconium, and the Oxides of Titanium(IV), Zirconium(1V) and Vanadium(V)," NYO-8123, 1953. ( 4 ) H. M. Haendler, S. F. Bartram, R. S. Becker, W. J. Bernard and 8. W. Bukata, J . A m . Chem. Soc., 16, 2177 (1954). (5) J. Fischer, J. Bingle and R. C. Vogel, ibid., 1 8 , 902 (1956). (6)S. Cromer, "The Electronio Pressure Transmitter and SelfBalancing Relay,'' SAM Laboratoriw, Columbia University, MDDC803. 1947.
72.1 72.1 72.1 80.8 84.0 84.1 89.3 89.5 96.3 96.3
122.7 124.1 124.7 173.3 200.4 201.9 251.9 251.6 365.0 365.2
109.3 109.3 111.3 111.4 111.4 116.7 116.7 122.8 122.8
749.7 752.0 791.6 795.1 795.7 1092 1093 1513 1519
KINETICS OF YIELD DISTRIBUTION I N BIMOLECULAR SIMULTANEOUS-CONSECUTIVE REACTIONS BYLOUISGOLD Massachusetts Institute of Technology, Cambridge, Massachuastls Received August 1% 1967
The distribution of products t o be expected in such synthetic systems where a reactant group R enters a bare benzene or monosubstituted nucleus M has been analyzed under the assumption that the sequence of simultaneous-consecutive reactions is essentially irreversible. Unlike the case of unimolecular or first-order reactions, the over-all rate of reaction of M cannot always be expressed as a sum of exponential terms as is usually supposed in biological tracer experiments.'S2 For M = benzene, a total of twenty reactions can occur to produce twelve distinct products which include one mono, three di, three tri, three tetra, one penta and one hexa substituted deriva(1) See, for example, W. E. Siri, "Isotopic Tracers and Nuclear Radiations," McGraw-Hill Book Co., Inc., N. Y . , 1949,Ch. 15,p. 388, et seq. (2) Recent treatment in M. Berman and R. Schoenfeld, J . A p p l . Phya., 17, 1361 (1956).
a i
