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L. A. QUARTERMAN, H. H. HYMAN AND J. J. K A T Z
chemical process. The necessity for this type of correction may be expected to be found for proc-
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esses occurring on high surface area active catalysts with porous structures.
A STUDY OF THE BROMINE-BROMINE TRIFLUORIDE AND BROMINE PENTAFLUORIDE SYSTEMS, PRIMARILY BY CONDUCTIVITY METHODS' BY LLOYDA. QUARTERMAN, HERBERT H. HYMAN AND JOSEPH J. KATZ Contributionfrom the Department of Chemistry, Argonne National Laboratory, Lemont, Illinois Received January 2, 1967
The electrical conductivity of solutions of BrF3 and Brz, and. BrF3 and BrFa have been measured. Poly-CchIomtrifluoroethylene) cells with bright platinum electrodes and Teflon insulators were employed. At 25', bromine added to pure bromine trifluoride reduces the specific conductivity from 8.02 x 10-8 ohm-' cm.-l to a minimum of 7.22 X a t 3.5 mole % and then increases it to 12.90 X 10-3 at 17.7 mole %, which represents the limit of the miscible region. Banks, Em6leus and Woolf first showed that a t higher temperatures, the conductivity of bromine trifluoride is lowered, indicating lower stability for ionic species. This effect is accentuated by increased bromine concentration. The visible absorption spectra of dilute solutions of Biz in BrFs show deviations from Beer's law in the region close to the absorption maximum (400-500 mp). I n bromine the molar conductivity of bromine trifluoride at 25" increases steadily from the lowest to the highest concentrat,ion a t which conductivity was measured 2.55 to 6.42 mole %. The rate of increase of conductivity with concentration increases sharply a t about 4.3 mole %. These data are interpreted in terms of the changing dielectric constant of the medium, a mobile e uilibrium involving bromine monofluoride in the Brz-BrFt s stem! and the nature of the ionic species present. On the o&er hand BrF3 and BrF6 are completely miscible and the con&ctivity versus concentration plot gives a smooth ciirve. Mixtures of HF and BrFs in general are more conducting than either pure reagent with the maximum conductivity near 70 mole % HF.
The interhalogen compounds of bromine and fluorine form an interesting family of compounds. Bromine monofluoride, bromine trifluoride and bromine pentafluoride have all been characterized as stable compounds! although the monofluoride has not been isolated as a pure compound because of partial disproportionation to bromine and bromine trifluoride. Bromine trifluoride, and to a somewhat lesser extent bromine pentafluoride, show remarkably interesting behavior as ionizing solvents. This phenomenon was first observed by Emdeus and co-workers,2 who studied the electrical properties of bromine trifluoride and pentafluoride systems. More recently Rogers and co-workers8 have undertaken a precision study of the electrical properties of the halogen fluorides. Fischer, Steunenberg and Vogel4 have discussed phase relationships in these systems. The present paper reports the results of an investigation of the bromine-bromine trifluoride and the brominetrifluoride-bromine pentafluoride systems by electrical conductivity methods, supplemented by spectrophotometric observations where appropriate. The object of the work has been to arrive a t a clearer picture of the nature of the ionic species present in these solutions. Experimental Materials.-Bromine trifluoride and bromine pentafluoride were obtained from the Harshaw Chemical Co. or from General Chemical. The commercial materials were purified by fractional distillation in a 40-inch nickel column l/S-inch ( 1 ) Based on work performed under the auspices of the United Statea Atomic Energy Commission. (2) A. A. Banks, H. J. Emel6us and A. A. Woolf, J . Chem. Soe., 2861 (1949). (3) (a) M. T. Rogers, J. L. Speirs and M. B. Panish, J . Am. Chem. SOC.,78, 3288 (1956); ( b ) M. T.Rogers, R. D. Pruett, H. Bradford Thompson and J. L. Speira, ibid., 7 8 , 44 (1956); (c) M. T. Rogers, J. G. Malik and J. L. Speirs, dbid., 78, 46 (1956); (d) M. T. Rogers. J. t. Speire, M. B. Panish and H. B. Thompson, ibid., 78, 036 (1956). (4) (a) J. Fischer, R. K. Steunenberg and R. C. Vogel, ibid., 76, 1497 (1954): (b) R. K. Steunonberg, R. C. Vogel and J. Fischer. I n d . Eng. Chem.. in press.
in diameter packed with 1/8-inch nickel helices and the distillate was stored in nickel vessels. Immediately prior to preparation of solutions used in the experiments the samples were further purified by batch distillation on the vacuum line described below. The purity of both bromine trifluoride and bromine pentafluoride was checked by conductivity measurements and observations of the absorption spectrum on samples which had been exhaustively fractionated. The samples of bromine trifluoride were indistinguishable from the best samples; however, the conductivity of bromine pentafluoride as usually employed, 1-2 x 10-7 ohm-' cm.-1, was slightly higher than that of the best material obtained, 9 X lo-* ohm-' cm.-l. Reagent grade bromine was used without further purification. Anhydrous Pennsalt hydrogen fluoride was distilled directly from a cylinder for the measurements reported below. Vacuum System.-A metal vacuum line was empIoyed for the manipulation of the halogen fluorides in final purification and solution preparation. This line is not a high vacuum system but rather one in which ordinary air and moisture are rigorously excluded during the manipulation. Packless valves of the bellows or diaphragm type and silver soldered connections are used to assemble the copper line, while molded poly-(chlorotrifluoroethylene) tubes with integrally molded flares make excellent removable traps. The highly soluble silver fluoride proved to be an annoying contaminant and metal Kjeldahl traps were introduced to reduce spray. This procedure and the use o€ heated lines to prevent condensation gave a distillation product free of detectable non-volatile impurities. Conductivity Equipment.-In the course of this. work a. variety of conductivity cells were investigated. Figures 1 and 2 show the most recent models for highly conducting and poorly conducting solutions, respectively. In each design the body of the cell is poly-(chlorotrifluoroethylene), t h e electrodes bright platinum, and the leads pass through Teflon) which is compressed between metal plates to effect a vacuum and pressure tight seal. All measurements were made in a closed system. Temperatures at the electrodes were measured with t h e aid of a 10% platinum rhodium thermocouple wire welded to. one of the platinum electrode leads, which served as a thermocouple. When measurements were being taken the conductivity cells were placed inside a hollow brass jacket through which thermostated water was circulated. A fluorocarbon oil between the brass jacket and the conductivity cell. proper, served to improve thermal contact. Since equilibrium between the solution under investigation and the circulating thermostated water is established more slowly in
July, 1957
THEBROMINE-BROMINE TRIFLUORIDE SYSTEM
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,-PLnTINUM - 10% RHODIUM this system than in the caoventional conductivity cell imPLATINUM ELECTRODEI,/' Ill mersed in the thermostat, omission of the thermocouple actually in the conductivity cell entails some risk of inade,quate temperature measurement. Conductance measurements were made with an Industrial -TAPERED TEFLON P l U 6 Instrument, R C 16, a.c. conductivity bridge with an ex7 0 ( 0,) ternal capacitor in the balancing circuit. Measurements were made at 60 and 1000 cycles to permit corrections for 114" HdKE NICKEL DIAPHRAGM VALVE polarization. Such corrections were not usually significant. 'The precision of the conductivity measuiements is =kl.O% FLUOROTHENE and the temperature measurements 320.2 S I N T E R E D D I S C __ Spectrophotometric Equipment.-Poly-(chlorotrifluoroethylene) is available in moderately clear sheets from which may be cut windows quite suitable for spectrophotometric (cells. The fabrication of nickel cells with such windows has lbeen discussed elsewhere.' A variety of improved cells have been built since then. 'The most useful one for the present program was a Teflon gasketed variable spacer cell which could be adjusted to optical path lengths of less than 0.01 cm. (Fig. 3). For the present program Kel-F windows and nickel bodies were em,ployed. For some purposes sapphire windows may be used .and the cells gold plated. PLATINUM ELECTRODE A Beckman DK-1 automatic recording spectrophotomceter was used, and Corning A5543 Lantern Blue filter FORCING PLATE to reduce the stray light problem, which can be serious in the case of strong absorbers such as bromine-bromine trifluoride solutions. The variable light path cells furnished PLATINUM LEAD a check on the error due to stray light which does not appear to be significant for the measurements reported below. The absolute values of extinction coefficients may be in error by as much as 10%. Spectral scans were made over the wave length region 350Fig. l.-Br2-BrF3 conductivity cell. '700 mp using the tungsten lamp and blue sensitive photo-multiplier. Thermocouple f l Electrods Leads Preparation and Stability of Solution -The preparation
