Chemical Analysis of Bromine Trifluoride

Journal of NUCLEAR SCIENCE and TECHNOLOGY, 3 [l], p. 10~13 (January 1966).

Tsutomu SAKURAI*, Yasuko KOBAYASHI* and Matae IWASAKI*

Received August 6, 1965

The chemical analysis of bromine trifluoride (BrF3) was studied with the view to establishing a method for determining the purity of this substance, as attained by vacuum distillation. The sample bromine trifluoride was hydrolyzed in NaOH solution. The fluorine in the bromine trifluoride was converted to fluoride (F-) by the hydrolysis, and could thus be determined by thorium nitrate titrationn(1). The bromine in the bromine trifluoride was converted to bromide (Br-), hypobromite (BrO-) and bromate (BrO-3), and was determined by the Mohr method, after reducing the BrO- and BrO-3 to Br- with hydrazine hydrate (H2NNH2,H2O). A value of 2.97+-0.03 wes obtained as ratio of fluorine to bromine for purified bromine trifluoride, and 2.84 for unpurified bromine trifluoride. Prior to analyzing the sample bromine trifluoride the conditions for reducing BrO-3 to Br- by hydrazine hydrate were studied, using KBrO3 solution as sample. It was found that the alkalinity of the sample solution and the reduction temperature had considerable influence on the reduction.

ing, while purified bromine trifluoride was I. INTRODUCTION retained in the vessel. During this operation, the U-tube shown Bromine trifluoride(BrF3), used as a in Fig. 1 was cooled in a cold trap with fluorinating reagent, is so reactive that it trichloroethylene-dry ice mixture at regular decomposes gradually during storage, giving intervals, to check whether or not the im- such products as hydrogen fluoride and purities were still vaporizing. The vacuum bromine. Prior to its use therefore, bromine distillation was continued until no impurities trifluoride must be purified by some method became trapped in the U-tube. such as vacuum distillation. The efficacy of this vacuum distillation must then be verified, and for this purpose, an attempt was made in the present study to determine by chemical analysis the ratio of fluorine to bromine in the bromine trifluoride. Fig. 1 Apparatus for Purification of II. EXPERIMENTAL Bromine Trifluoride 2. Analytical Procedure 1. Preparation of Bromine Trifluoride Sample Commercial grade bromine trifluoride was (1) Hydrolysis of bromine trifluoride The sample bromine trifluoride was hy- used. It was purified by vacuum distillation drolyzed by a method similar to that of the using the apparatus shown in Fig.1, which was constructed throughout of Kel-F. Hydrogen hydrolysis of mixtures of uranium hexafluo- fluoride(HF) and bromine(Br2), constituting ride and bromine pentafluoride reported by Ivins(2). the principal impurities in bromine trifluoride, About 0.5~1g of the sample material was have, at room temperature, vapor pressures considerably higher than pure bromine put in a Kel-F tube 4 mm in internal diameter trifluoride (that of HF being 760mmHg at 20dc, and 60 mm long, which had been closed at that of Br2 180mmHg, and that of BrF3 only 5.6 one end by welding; the sample was then mmHg). Therefore, these impurities vaporized frozen by immersing in trichloroethylene-drv first when the vessel containing crude * Japan Atomic Energy Research Institute, Tokai- bromine trifluoride was evacuated by pump- mura, Ibaraki-ken.

10 Vol. 3, No. 1 (Jan. 1966) 11 ice; and weighed together with tube. The was not previously reported among the pro- tube with sample was placed in a 2l poly- ducts for the case of reaction between bromine ethylene bottle containing 200ml of 2.5% trifluoride and watery(4). The yields differed sodium hydroxide solution; a lid was screwed from run to run despite the use of the same on the bottle. (Fig. 2) The bottle was shaken; material (Table 1), but it was found that on the bromine trifluoride then decomposed ex- Table 1 Ratio of Br- , BrO- and BrO-3 Produced plosively, changing the color of the solution by Hydrolysis of BrF3, to the Total to yellow. If a small amount of hydrazine Amount of Bromine Determined hydrate (H2NNH2,H2O) was previously added to the 2.5% solution of sodium hydroxide, the solution did not color because hypobromite (BrO-) ion was not produced.

the whole about 20~30% of the bromine in the bromine trifluoride changed to bromide ion, 50~40% to hypobromite ion and the remaining 30% to bromate ion. In the present analysis, bromite(BrO-2) ion was not counted as product, since it was not stable enough to be detected, and changed to bromide, hypobromite and bromate ions in alkaline solution(5)(6). Fig. 2 Bottle Assembly for Hydrolysis 2. Reduction by Hydrazine Hydrate (2)Determination of fluorine in In the determination of bromine, total the sample material bromide(Br-) ion, was determined by the The determination of fluorine in the above Mohr method; using hydrazine hydrate as sample solution was done by thorium nitrate reducing agent. titration, using Alizarine Red S as indicator. Prior to the analysis of bromine trifluoride, (3) Determination of bromine the conditions for the reduction by hydrazine Bromine in the bromine trifluoride was hydrate were studied, using potassium bro- determined by the Mohr method after reduc- mate (KBrO3) as standard sample. As a result, ing with hydrazine hydrate(H2NNH2,H2O) the it was found that (1) an amount of alkali hypobromite and bromate ions in the solution necessary for the reduction, in proportion to to bromide ion. the potassium bromate present must be added III. RESULTS AND DISCUSSION to the sample solution; and (2) the reduction did not proceed except with boiling. 1. Products Resulting from the Hydrolysis The effect of the alkalinity of the sample of Bromine Trifluoride solution on the reduction was studied by the The products of the reaction between following method: bromine trifluoride and sodium hydroxide in The alkalinity of a mixture of 2 ml of 0.1 M the solution were analyzed by thorium nitrate potassium bromate solution and 10 mi of 1 N titration for fluoride ion and by iodimetry (=1/4M) hydrazine hydrate solution was ad- and arsenimetry for bromine compounds(3). justed with sodium hydroxide solution, and It was established that all of the fluorine the solution was boiled to expedite the re- from the bromine trifluoride had become duction. After removing the excess hydra- fluoride ion(F-) in the solution and bromine zine hydrate in the solution by thermal de- had converted to bromide(Br-), hypobromite composition, the quantity of bromide ion (BrO-) and bromate(BrO3-) ions. Bromide ion produced was determined by the Mohr

11 12 J. Nucl. Sci, Technol.

Table 2 Influence of Alkalinity of Sample sium bromate in the sample be roughly in Solution on the Reduction of KBrO3 the range between 8 and 70. These were the condition, found requisite for determining the amount of bromine in the purified bromine trifluoride after reduction of the hypobromite and bromate ions. The results of analysis under the above conditions are shown in Table 3. The experimental values of bromine are in good agreement with the calculated values, Table 3 Quantity of Bromine Determined by the Mohr Method, after Reduction of BrO- and BrOo

Note : Sample solution used: Mixture of 2 ml of O.1M-KBrO3, 10 ml of N-HZNNH2-H2O(=1/4M)and a given amount of NaOH method. The results obtained are shown in Table 2. It is seen that the alkalinity has a large influence on the reduction of bromate ion: The reduction ratio, i.e., the ratio of the amount of bromide ion determined to that -3 Note : Recovery ratio: Ratio of the determined quantity of bromine to that calculated of the initial amount in the potassium bromate, is proportional to the initial alkali- 3. Measured Ratio of Fluorine to Bromine nity of the sample solution. In Table 4 are given various experimental Thus, it is requisite for reduction that values obtained from the analysis of the the mole ratio of sodium hydroxide to potas- purified bromine trifluoride. It is seen that the

Table 4 Mole Ratio of Fluorine to Bromine, obtained from Analysis of Purified BrF3, and Recovery Ratio (ratio between quantity of BrF3 recovered and that of sample BrF3)

sum of the experimental values of bromine and fluorine is in good ageement with the 4. Summary of the Analytical Procedure amount of initial bromine trifluoride, and the As a result of the present study, the fol- ratio of fluorine to bromine is approximately lowing simple procedure was established for 2.97+-0.03. When unpurified bromine trifluo- the determination of bromine and fluorine in ride was analyzed by the same method, the bromine trifluoride: ratio was 2.84, These results indicate that (1) About 0.5~1g of solid bromine trifluoride vacuum distillation conducted by the method is decomposed in 200 ml of 2.5% sodium already described was effective in enhancing hydroxide solution containing about 0.4 g the purity of the bromine trifluoride. of hydrazine hydrate, in a 2l-polyethylene

12 Vol. 3, No.1 (Jan. 1966) 13

bottle closed by a lid. Motojima for his valuable advice. (2) Fluoride ion in the solution can be de- -REFERENCES- termined by thorium nitrate titration, using Alizarine Red S as indicator. (1)SIMONS, J.H.: "Fluorine Chemistry", Vol.II, (3) Bromine in the bromine trifluoride can p.110 (1954). be determined by the Mohr method, after (2)IVINS, R.O.: ANL-6362, 58 (1962). boiling the sample solution containing (3)FARKAS, L., LEWIN,M.: Anal. Chem., 19, 662 bromate ion and hydrazine hydrate, and (1947). (4)SIMONS, J.H.: "Fluorine Chemistry", Vol.I, p. then removing the excess hydrazine hy- 198 (1950). drate by thermal decomposition. (5)POLLAK, F.: Z. anorg. Chem., 196, 106 (1931). (6)BRISCOE, H.V.A., ELDRIGE,A.A., DYSON,G.M.: ACKNOWLEDGEMENTS Supplement to Mellor's Comprehensive Treatise on Inorganic and Theoretical Chemistry, Sup- The authors are much indebted to Dr. K. plement II , Part I , p. 750 (1956), Longmans.