condenser, would permit extended operation of this process. T h e flow system can isomerize relatively impure carborane without difficulty, as compared with the closed system, which requires purified carborane to avoid difficulties during the reaction. Acknowledgment
T h e authors are grateful to H. A. Schroeder and N. Semenuk for helpful discussions and acknowledge the support of this work by the Office of Naval Research. literature Cited
(I) Alexander, R. P., Schroeder, H., Znorg. Chem.
2, 1107-10 (1963). (2) Alexander, R. P., Schroeder, H., U. S. Patent Ser. 323,394 (1963). (3) Bobinski, J., J . Chem. Educ. 41, 9, 500-1 (1964). (4) Fein, M., Bobinski, J., Mayes, N., Schwartz, N. N., Cohen, M . S., Znorg. Chem. 2, 1111-15 (1963). (5) Fein, M., Grafstein, D., Paustian, J. E., Bobinski, J., Lichstein, B. M., Mayes, N.,Schwartz, N. N., Cohen, M. S., Ibid., 2, 1115-19 (1963). (6) Grafstein, D., Bobinski, J., Dvorak, J., Paustian, J. E., Smith, H. F., Karlan, S., Vogel, C., Fein, M., Ibid., 2, 1125-8 (1963). (7) Grafstein, D., Bobinski, J., Dvorak, J., Smith, H. F., Schwartz, N. N., Cohen, M. S., Fein, M . , Ibid., 2, 1120-5 (1963). (8) Grafstein, D., Dvorak, J., Brit. Patent 959,919 (June 3, 1964). (9) Grafstein. D.. Dvorak. J.. Inore. Chem. 2.1128-33 (19631. (10) Green, J., Mayes, N., Cohe"n, M. S.,'J. Polymer Sci.; Pt. A 2, 3113-33 (1964).
(11) Green, J., Mayes, N., Kotloby, P., Cohen, M. S.,Ibid., Pt. A 2, 3135-46 (1964). (12) Green, J., Mayes, N., Kotloby, P., Fein, M., O'Brien, E. L., Cohen, M. S., Zbid., Pt. B 2, 109-13 (1964). (13) Heying, T. L., Ager, J. W., Clark, S. L., Alexander, R. P., Papetti, S., Reid, J. A., Trotz, S. I., Znorg. Chem. 2, 1097-105 (1963). (14) Heying, T. L., Ager, J. W., Clark, S. L., Mangold, D. J., Goldstein, H. L., Hillman, M., Polak, R. J., Szymanski, J. W., Ibid., 2, 1089-92 (1963). (15) Papetti, S., Heying,T. L., Zbid., 2, 1105-7 (1963). (16) Zbid., 3, 1448 (1964). (17) Papetti, S., Heying, T. L., J . A m . Chem. Sac. 86, 2295 (1964). (18) Papetti, S., Schaeffer, B. B., Gray, A. P., Heying, T. L., "New Series of Organoboranes. VII. Preparation of Polym-carboranylenesiloxanes,"J . Polymer Sci:,in press. (19) Papetti, S., Schaeffer, B. B., Troscianiec, H. T., Heying, T. L., Znorg. Chem. 3, 1444 (1964). (20) Polak, R. J., Obenland, C., IND. ENG.CHEM.PROD.RES. DEVELOP. 3, 234-8 (1964). (21) Schroeder, H., Heying, T. L.i Reiner, J. R., Inorg. Chem. 2, 1092-6 (1963). (22) Schroeder, H., Reiner, J. R., Alexander, R. P., Heying, T. L., Zbid., 3,1464-5 (1964). (23) Schroeder, H.,Vickers, G. D., Zbid., 2, 1317-18 (1963). (24) Smith, H. D., Jr., Obenland, C., Papetti, S., Zbid., 5 , 1013-15 (1966). (25) Thiokol Chemical Co., Netherlands Patent 84,817 (June 1965). (26) Zakharin, L. I., Stanko, V. I., Brattsev, V. A., Chapovskii, Yu. A., Struchkov, Yu. I., Izu. Akad. Nauk SSSR, Ser. Khim. 11, 2069 (1963). RECEIVED for review July 20, 1966 ACCEPTED October 17, 1966
VAPOR P H A S E BROMINATION 0 F 1,l-DI FLUOROETHAN E RALPH A. DAVIS AND M A X R. BROADWORTH Halogens Research Laboratory, The Daw Chemical Co., Midland, Mich. The direct thermal bromination of ethylidene fluoride using an excess of bromine a t 600"to 650" C. has been used to produce a combined product of 1,2,2-tribromo-l ,1 -difluoroethane and 1,2,2,2-tetrabromo-l,1 difluoroethane in good yields. The use of bromine-ethylidene fluoride mole ratios of 1 . 1 or less at 450' C. resulted in a conversion to 1 -bromo-1 ,I -difluoroethane of 75%, but a t 575" to 600" C. gave conversions to vinylidene fluoride of 65 to 75%. The reaction probably proceeded by elimination of HBr, followed b y bromination of the double bond. The reaction may b e run stepwise to produce either 1,2-dibromo-l,1difluoroethane or lI2,2-tribromo-l ,1 -difluoroethane as the principal product.
-
HIS work was undertaken to develop methods of making Tbromofluoroethanes, desired as intermediates for the preparation of compounds for pharmacological testing. Although the thermal bromination and chlorination of l,l,l-trifluoroethane have been reported (5-7), only the chlorination of 1,l-difluoroethane has been reported (7, 3 ) . I t was found that if ethylidene fluoride was thermally chlorinated with a n excess of chlorine, competing reactions took place. I n addition to the loss of HF by thermal splitting, chlorinolysis and coupling reactions also occurred. These side reactions were circumvented by chlorination in the presence of ultraviolet light as well as heat (7, 3 ) . Ethylidene fluoride was chlorinated in the presence of ultraviolet light to yield essentially 1-chloro-l,1-difluoroethane ( 2 ) by using aqueous hydrochloric acid as a n internal cooling medium in the reaction zone to regulate the temperature a t 80' to 120' C. T h e present work, however, was confined entirely to thermal bromination.
Experimental
Three slightly different procedures were used for the bromination of ethylidene fluoride. However, the apparatus and setup of Figure 1 were used for all three. Minor changes were made to adapt the equipment to the procedure used.
Method I. The bromination was carried out with an excess of bromine. 1,l-Difluoroethane was metered through a bromine vaporizer, where the bromine was held at a constant temperature and level to control the mole ratio. The mixed gases were then passed through a heated "4 X 30 inch Vycor tube reactor packed with 7-mm. Vycor rings. The exit gases were passed through an air-cooled pot, water scrubber, 10% NasCOa scrubber, and wet ice-cooled receiver, and were finally collected in a receiver cooled with dry ice. T h e products, after washing with caustic to remove free bromine, were analyzed by distillation and vapor phase chromatography, T h e reactor temperature was varied from 400' to 700' C. and ) examined. mole ratios of 3 to 1 to 5 to 1 (Brz to C H F ~ C H Iwere VOL. 5
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HEATED TRANSFER LINE
Figure 1 . Apparatus for bromination of 1 , I -difluoroethane
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REGULATED HEATING MANTLE
Method 11. The same equipment was used, but the Br2 to CHF2CH3 mole ratios were maintained at 1.1 or less, and the gases which contained vinylidene fluoride passed through the trap cooled with dry ice and were absorbed in liquid bromine and analyzed. The CBrF2CH2Br produced in this final bromination reaction was calculated as CH2=CFz. Reaction temperature was varied from 450' to 600' C.
A run at 700' C. and 2.8 seconds at a lower mole ratio (3.9) resulted in a large decrease in the amount of CBrF&HBrz produced and a very slight decrease in CBrF2CBr3. For comparison with the results in Table I, the conversion to CBrF2CH3 was 15 mole %; CBrF2CH2Br, 7.2 mole %; CBrF2CHBr2,15.1 mole %; CBrFtCBr3, 42.9 mole yo. If one assumes that the reaction is proceeding by HBr Titration of the water scrubber indicated that H F eliminaelimination, it is possible to explain this result by the ease of tion was less than 3 or 4% and probably accounted for less dehydrobromination of the various compounds. [One rethan 2% of the starting ethylidene fluoride. viewer comments that the dehydrohalogenation is probably Method 111. The crude 1,2-dibromo-l,l-difluoroethane free radical-initiated and this could explain the higher perproduced by Method I1 was pyrolyzed at 600' C. in the same centage of CBrFzCH3at 700' C. us. 550' to GOO0 C.] Since equipment to give difluorobromoethylene, which also reacted with liquid bromine to give 1,2,2-tribromo-l,l-difluoroethane. one would expect CBrFzCHs to be the most difficult to dehyThe products from this final reaction were washed with 10% drobrominate and CBrFzCHBrz the least ( 6 ) , CBrF2CBr3 will caustic and separated by distillation. All l,Z-dibromo-l,lbe formed at the expense of CBrF2CHBr2 even though the difluoroethane or lower boiling materials were recycled to the lower brominated materials are not converted. pyrolysis. A few runs made in nickel reaction tubes with inert packings, such as CaF2 or MgFa pellets, showed no significant difference Results and Discussion when compared with the runs made in Vycor tubes using Since the threshold temperature for thermal bromination packing made of Vycor. usually lies between 400' and 500' C., a temperature study To determine the effect of lower mole ratios, a series of runs was made starting at 500' C. and increased in 50' increments was carried out at a mole ratio of 1.1 or less at temperatures of each run to a temperature of 650' C. In this series of runs 450' to 600' C. (Table 11). At 450' C. bromination pro(Table I) an excess of bromine was used. The mole ratio of ceeded rapidly converting 75% of the ethylidene fluoride to bromine to ethylidene fluoride was 5.0 to 1 or slightly greater. CBrFzCH3 and only 5y0to CBrF2CHZBr. As the reactor temperature was increased from 500" to 650" C., 60 I I I 1 the product composition changed from predominantly monoW C and dibrominated products to essentially all tri- and tetra0 5 50 . brominated compounds. 0 a The conversions to each of the bromides at the various m reaction temperatures are plotted in Figure 2. This shows clearly that the amount of CBrF2CH3and CBrFzCH2Br in the z 0 product diminishes rapidly as the temperature increases. v) a W At the same time, the CBrF2CBr3 content increases steadily > 2 as the reaction temperature is raised, but the CBrF2CHBr2 8 content remains somewhat constant at about 30%. It is s apparent that it is difficult to brominate CHFzCHa, using a n excess of bromine, and produce CBrFzCHBrz as the predominant product without producing large quantities of either 500 550 600 650 CBrF2CBr3 or CBrF2CH2Br. REACTOR TEMPERATURE, OC. The conversion and yield to combined tribromo and tetraFigure 2. Conversion of 1 , l -difluoroethane vs. rebromo products are in the range of 80 to 87y0,, and no evidence actor temperature at Br2/CHF2CH3 mole ratios of 5 of brominolysis or coupling reactions was detected. to 1 or greater
e
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I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Table 1.
Bromination of CHFzCH3
(Bre/organic mole ratios greater than 5.0. Vycor tube and packing)
Temp.,
c.
500 550 600 650 650
CHFgCHa, Moles 1.82 2.17 2.12 2.4 2.4
Br2, .Moles 10.1 10.8 11.6 1.3.0 13.4
Residence Time. RecovSecered M o l e yo Conversion to onds CHFzCHs, % CBrFzCHa CFzBrCH2Br CBrFzCHBrZ 2.6 0.4 39.1 20.8 16.4 2.6 9.5 27.9 29.0 2.2 5.4 6.7 31.8 2.7 25.4 2.1 2.9 29.2
Mole Ratio Brz/ Org. 5.5 5.0 5.5 5.4 5.6
Mole CF2BrCBr3 2.6 12.5 37.5 56.3 54.6
Yield CFzBrCHBr2 f CFzBrCBra 48.0 66.7 78.7 81.7 86.3
%
Recovery 79.3 79 81.4 81.7 86 .7
Table II. Bromination of CHF2-CH3
(Br2/organic mole ratio less than 1.0. Vycor tube) Residence Time, Seconds CF2=CHz 5.8 0.3 4.8 38 5.2 65.2 4.2 66 4.8 76.6a
Mole Ratio T;mp., CHF2CH3, Br2, Brz/ Moles C. Moles Org. 450 6.35 7.05 1.1 1.37 0.73 500 1.88 550 3.73 3.73 1.0 575 5.2 4.9 0.93 600 3.14 2.13 0.68 a VPC analysis of product stream.
RecovTotal Br? ered Recov- RecovYield M o l e yo Conversion to CHFzCH3, ery, ery, CF2=CHz, CFzBrCHs CFZBrCHzBr CFzBrCHBrz 70 7 0 % 70 16.7 96.9 ,. 75 4.9 29 99 .. 9i:o 32 12.9 2.1 80.7 97 76.6 7.4 88.9 100 84.2 10.6 3.7 1.2 14.P 8.5~
As the reactor temperature was raised to GOOo C. a higher and higher proportion of this material is dehydrobrominated, until a t 575' to GOOo C., 65 to 700/, is converted to vinylidene fluoride. I n comparison, 1-chloro-1,l-difluoroethanehas been dehydrochlorinated at 870' C. and 2.0-second retention time to produce 67% CFFCHZ and 13.5% CClF=CHz (4). T h e CCIF=CHz is formed by H F elimination at these high reaction temperatures. The 1-bromo-1,l -difluoroethane, on the other hand, does not undergo any large amount of dehydrofluorination a t pyrolysis temperature because of the greater ease of dehydrobromination and the corresponding lower temperature required for pyrolysis. As a result, it is possible to produce vinylidene fluoride in one step by the thermal bromination of 1,l-difluoroethane. I t appeared that 1,2-dibromo-l,l-difluoroethane or 1,2,2tribromo-1 ,1-difluoroethane could be produced as the major product if the following !sequence of reactions was followed:
+ l . O B r z - - - - - + CBrFzCH3 + C F p C H z CBrFzCH3+ CFz=CHz + liq. Brz CBrF2CH3 + CBrFzCHzBr CBrFzCH3 + CBrFzCHzBr CFFCHZ + CHF2CH3
-
GOO0 C .
(1)
30° C.
(from Reaction 1) CFFCHZ
600' C .
+ CFs=CH13r + liq. Brz
CFZ=CHBr
(2)
30' C.
CBrFZCH2Br
+ CFzBrCHBrz
T h e products can be separated by distillation and any CBrFzCHzBr recycled to Reaction 2, or in the case of Reaction 1, the CBrF2CHscan be recycled. Following the outline of Reaction 1, 19.15 moles of 1,ldifluoroethane reacted with 20.73 moles of bromine at 575' C. and a contact time of 3.8 seconds. T h e product consisted of CFzHCHa, 4.2 mole 7 0 . CFzBrCH3, 8.9 mole yo; CFzBrCH2Br, 80.4 mole %; and CFZBrCHBrz, 0.6 mole yo (percentage based on the 19.15 moles of CHFz-CHS charged). This gave a yield 92.5% of CBrFzCHZBr.
A composite mixture (18.28 moles) containing 8.4 mole yo CBrF&H3, 86.6 mole % CFZBrCHzBr, 3.9 mole % CFZBrCHBr2, and 1.1 mole TOCBrF&Br3, was pyrolyzed at GOOo C. a t a contact time of 2.8 seconds as indicated in Reaction 2, the products being absorbed in liquid bromine. Analysis of the product indicated the following recoveries and conversions based on the moles of material charged: CBrFzCHZBr, 22.6 mole %; CBrF2CHBr2, 67 mole %; CBrF2CBr3, 4.3 mole %. If conversion and yield of CBrFzCHBrz are calculated on the basis of the CBrFzCHzBr content of the starting mixture, the conversion is 77% and the yield is 92%. These results show that the reaction can be run stepwise as postulated in Reactions 1 and 2 to produce either CBrFzCH2Br or CBrFgCHBrz as the predominant product in high yields. Conclusions
Conditions have been found under which the thermal bromination of ethylidene fluoride gives good yields of CBrF2CH3, C F F C H ~ , or a mixture of CBrFzCHBrZ and CBrFZCBx-3. The reaction appears to proceed by HBr elimination as the predominant reaction once the first bromine has been introduced and the composition of the product can be changed by varying the reaction conditions and reactant ratios. T h e bromination and dehydrobromination reactions can also be or run as separate steps to give CBrF2CHzBr, CF-CHBr, CBrFzCHBrz as the major product. literature Cited (1) Calfee, J. D., Florio, P. A., U. S. Patent 2,469,290 (1949). (2) Zbid., 2,499,129 (1950). ( 3 ) Calfee, J. D., Smith, L. B., Zbid., 2,566,163(1951). (4) Feasley, C. F., Stover, W. A., Zbid., 2,627,529 (1947). (5) McBee, E. T., Can. Patent 516,572 (1955). (6) McBee, E. T., Hass, H. B., Bittenbender, W. A., Weesner, W. E., Toland, W. G., Hausch, W. R., Frost, L. W., 2nd. Enp. Chem. 39, 409 (1947). (7) McBee, E. T., Hass, H. B., Toland, W. G., Truchan, A,, Zbid., 39, 420 (1947).
RECEIVED for review March 7, 1966 ACCEPTEDAugust 8, 1966 VOL. 5
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