Production of
BIS(TRIFLUOR0METHYUBENZENE R. L. ItIurray, W.S. Beanblossom, and B. H. Wojcik HOOKER ELECTROCHE1IIC4L COMPANY, NIAG4R4 FALLS, N. Y .
ASED on information obtained from a review of the litera-
were ret for u 2 " product n-ith a boiling point of 137.5-139.5" C. Snmpleq of syleiie were chlorinated t o varl-ing degrees in order t o determine optimum conditions for conversion to the hexafluoride. The results obtained indicated that chlorination to a gravity of 1.600-1.605 a t 25" C. (67.7% Cln) gave the best yields of desired product. The following table shows the effect of chlorine content on yields of bis(trifluoromethy1) benzene:
ture ( 1 , Z ) and research FTork performed a t Purdue University under the guidance of E. T. McBee, a method was developed for the production of bis(trifluoromethy1)benzene in conimercial quantities. The reactions involved in the manufacturing process are the chlorination of xylene:
1.550 1,575 1.600 1,605
and fluorination (halogen exchange) of bi~(tricliloromettiy1) benzene
Hexafluoroxylene Tield, 70 26 49 54 54.6
62.6 65.0 67.7 67.6
Partial rectifiration of the hexachloride h p vacuum distillation h hydrogen fluoride did not prior to its treatment ~ i t anhydroui result in any advantage. FLUORINATIOS OF BIS(TRICHLORO1IETHYL)BENZESE
Such information as \J-as available on the preparation of tlw hexafluoride proved to be inadequate for translation to plant operation. Additional data accumulated during development studies pertained to the chlorination of xylene, the fluorination of bis(trichloroniethyl) benzene, rectification of the crude product, and recovery of useful by-products.
A laboratory study showed that the fluorination could be succe.sfully carried out in an autoclave a t 110-120' C. and 13001500 pounds per square inch. iigitation was found to be desirable and the use of a 50% theoretical excess of hydrogen fluoride proved beneficial (Table 11). Steel was noted as a suitable material for the construction of the autoclave whcn anhydrous conditions were maintained. For pilot plant studies a 20-gallon high-pressure standard hydrogenation autoclave was used. rl number of difliculticn were en-
CHLORINATION OF XYLENE
The customary techniques for side-chain chlorination were applicable t o xylene with only a few adjustments. Cleanliness and freedom from metallic contamination were of primary importance in the production of bis(trichloromethy1)benzene suitable for conversion to the corresponding fluoride. The procurement of high quality xylene for this program presented a real problem. Commercial 3 coal tar xylene varies considerably in composition, which depends not only on the source but also the initial temperature of the 3" cut. A recent publication (5) lists the following as the composition of commercial xylene:
TABLE
Source
A
H
Ethylbenzene p-Xylene m-Xylene o-Xylene
Per Cent 7-9 18-19 68-70 3-5
Boiling Point, 136.2 138.5 139.3 144.0
O
I.
C.
Siiice specifications for the final product did not require the production of any particular isoiner, it seemed desirable to ascertain the behavior of the individual isomers for optimum yields. The para isomer was noted to give the best yields and the meta was next, whereas none of the hexafluoride was obtained from the ortho isomer under the conditions employed for the reactions. The yields of bis(trifluoromethy1j benzene from the individual isomers were p-xylene 80-8570, m-xylene 70-7570, and o-xylene 0%. Thus it vias apparent that the best results might be realized from a xylene fraction with a boiling range of 138-139" C. This was further substantiated by examination of various xylene cuts supplied by the manufacturers (Table Ij, Since the quantity of 1 xylene which could be made available was not sufficient t o meet production demands, specifications
b:V.&LI-.ITIOS
OF
CO5fJfERCI.iL
I\;YLESE
Hexachloroxplene Yp. gr. n t 25' C. 5 CIS 1 600 67.1 1.605 67.8 1.600 67.1 66.7 1.600 1 620 66 6 1 595 66 0 1 600 67 0 67 4 1 610 67 9 1 610 68.2 1 610
Distn. Ifange, ' C . 137 0-139.5 137,7-139.5 138 3-139 9 139.1-140.7 136.3-139.3 138 0-139 2 138 5-139.0 138 8-139.3 139 1-139.7 130 4-140.5
FRACTIONS HexaAuoroxyiene Yield, % 46 0 61.0 63.0 54.0 44.6 62.0 60 0 54.4 52.8 47 6
TABLE 11. L.~BOR.ITORY COSVERSIOSS OF BIS(TRICHLOROMETHYL)B E X Z E S E TO
Exceas H F , 70 10 100 25 50 50 85 85 85 85 85 85 a b C
302
BI~(TRIFLL?ORO~fETHYI,) BESZEKE
Reaction Time. Hr. 12 12 1' 12 21 4 16 3 0.75 0.10 6
Reaction Temp., C . 100 100 100 100 100 100 220 150 125 150 160
0.5% SbCh used as catalyet. 5,0q0 SbCh uFed as catalyst. Agitation omitted in this run.
Pressure. T.b./Sq. I n . 1000 1000
...
950 950
29'50 1875 1600 2500 1800
1-ield Rased on EICX, 70 46 F,7 45 56
59 61 59 53,8 57" 56 b 26C
March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
countered with this unit, particularly with the valves and the stuffing box around the agitator shaft. Using needle valves with a spool-type seat eliniinated valve trouble. The design of a proper stuffing box against a mixture of gaseous hydrogen fluoride and hydrogen chloride a t 1300-1500 pounds per square inch was a major undertaking. Standard high grade packing material failed completely after three or four runs. Polytetrafluoroethylene showed signs of promise but it also failed after several runs because it crept along the shaft. K i t h the a>sistance of BlawKnox engineers, a stuffing box vias designed which allowed for the protection of the packing by a pressure oil seal. This proved t o be a step in the right direction. Hoivever, it iyas not until Teflon (polytetrafluoroethylcne) was employed as the bottom ring in the packing assembly that real progress vas made. llpparently the
303
slight creepage of the bottom Teflon ring served as a lubricant and as a protecting surface for the main packing material. With a combination of the oil pressure seal and the packing aseinbly it was possible to make as many as 600 runs before repacking was necessary. Figure 1 is a drawing of the 110-gallon steel autoclave designed for batch fluorination. Two significant laboratory experiments mere made which unfortunately were not developed in time to be incorporated into plant operation. I n one case KF.HF complex salts Ivere found to be satisfactory for the conversion of the hexachloride to the fluoride. It is likely t'hat a succesful application of these complex salts to the fluorination step might have decreased the hydrogen fluoride consumption. I n another seritx of experiments it was established that antimony pentachloride functioned as a catalyst or perhaps as a fluorine transfer agent when used in conjunction with hydrogen fluoride; this permitted the conversion to take place at atmospheric pressures and 100-125" C. By the addition of catalytic amounts of antimony trifluoride to the hexachloroxylene being fluorinated, the reaction period was decreased from 90 to 15-20 minutes. The use of antimony salts in plant operation was not encouraged as routine practice because these salts presented a serious valve-seat erosion or caorrosion prolileni during the venting and discharging of the autoclave. RECTIFICATIOR OF CRUDE PR0I)UCT
The crude product from the fluorination step, after neutralization with a dilute caustic solution and filtration to remove the sodium salts, consisted essentially of the follon-ing components:
Boilinsc P$int,
C.
101--102
Residue
LL Figure 1.
Fluorination Autoclave
Vt. ?c Based on Charge of Bis(trich1oromethq-1)benzene
0.5
113--116.5
29-42
131--140 140.- 150 170--173 175--185
Trace 8-12
,
..
Trnre
4-7 20-26:
By means of a simple steam dihtillation from an iron vehsel, this mixture n - a ~ ieadily separated into two fractions. The clear, almost colorless distillate contained all of the benaotrifluoride and hexafluoroxylene and virtually all of the chlorofluoro derivatives. The brown-to-black viscous residue was discarded. Attempts to fractionate the steam distillate directly after drying over soda ash were not always successful. This was attributed to trares of
INDUSTRIAL AND ENGINEERING CHEMISTRY
304
Vol. 39, No. 3
VENT
I
I
STF4M
Pressure Fluorination of I I C S
Figure 2 . IIeruchloroxylene Hydrogen fluoride
1
110-12O0 C.
1300-1500 Ih. 'sq. in.
unstable intermediates such as may result from incomplete fluorination. To circumvent erratic fractionation it was nceessary first to vacuum distill the hexafluoroxylene from the chlorofluoro derivatives and then submit it to careful fractionation through a ten-plate column operated a t atmospheric pressure?. 9 s a final rectification st,ep the hexafluoroxylene was treat,ed with soda ash to remove traces of acids. RECOVERY O F USEFUL Bl-PRODUCTS
Nost of the hydrogen chloride formed in the chloriiintio~iof xylene was employed without any rect>ificatioriin another proces.. The hydrogen chloride-hydrogen fluoride mixture, obtained on venting the autoclaves after fluorination, was converted to calcium salts, xhich were discarded. Experimental work showed that a good portion of the hydrogen fluoride present in the vent gases could have been recovered and re-used. The mono- and dichlorohexafluoroxylenes proved to be useful material since they could be successfully converted to the perhalo derivative.< by subsequent treatment with cobalt trifluoride. .1 simplc vacuum distillation was sufficient t o put these material.; into usable condition. These products were not separated into pure chemical individuals but into concentrates with approximately 10"boiling ranges; that is, the monochloro fraction boiled a t 110150" C. and the dichloro fraction a t 170-180" C. a t atmospheric pressures. PRODUCTION
The procedures described in the folloiving text Tvere employed for the coinniercial production of hexafluoroxylenc:
A commercial grade of coal tar xylene boiling at 137.5-130.3" C'. (1960 pounds) was charged into a standard 500-g:illon chlorinator equipped with three light wells, a chlorine ncll linc., ii reflux condenser, and suitable controls. The xylene in the reactor was heated to 90-100" C. before the feed of chlorinc \vas started a t a rate of approximately 75 pounds per hour. Soon after chlorina-
r L
Hydrogen chloride Ilexafluoro~ylene
tion started, chlorine addition was gradually increased to a rate of 150 pounds. The time required to reach this rate depended on the capacity of the reflux condensers, The reaction temperature for the first 24 hours was maintained slightly below 100" C. by passing cooling water through the jacket of the chlorinator. Thereafter t,he temperature was allowed to increase gradually until, a t the end of 65 hours of chlorination, mater cooling was replaced with steam heating so that the temperature could be maintained a t 160" C. The specific gravity of the xylene undcrgoing elilorination increased about 15 points per hour for the first 35-40 hours and then gradually decreased to 3 points per, hour toivard the end of the reaction. Chlorination was continued until a specific gravity of 1.600 a t 2;' C. was reached. The product obtained a t the end of a 91-hour reaction period had a orine content of 67.753. The (5530 pounds), based on id the chlorine efficiency ene charged, amounted t o 96 9 noted as being approximately The hexachloroxylene (515 pounds) made by this process was charged into a Ilo-gallon steel autoclave designed for operation a t 2500 pounds per square inch. I t \vas equipped xvith a turbinetype agitator, internal heating or cooling coils, and an external jacket for the same purpose. The liquid hydrogen fluoride (290 pounds, 50% over theory) was added t o the chloroxylene, through a pump under slight pressure, since vent valves attached to the autoclave were closed to minimize hydrogen fluoride losses. K i t h the agitator in motion steam heat was applied through the coils. The pressure in the autoclave increased gradually until, at 110-120" C., after a00-minute reaction period, it reachcd 13001500 pounds per square inch. The reaction mixt,ure was then cooled to 30" C. by applying water to the coils and the autoclave jacket. By careful venting through a 2000-gallon steel blowdown tank the pressure was dropped to 100-200 pounds per square inch. The autoclave !vas then discharged into the blowdown tank while the gaseous hydrogen chloride-hydrogen fluoride mixture passed on to the diiposal plant. The blowdown tank served several functions: It minimized entrainment losses, allowed for the rapid discharge of the autoclave while still under partial pressure, and finally acted as a reservoir for the crude material from which the hydrogen chloride and hydrogcn fluoride could gradually escape. T o ensure complete removal of the acids from the fluorinated Inatcrial prior to subsequent processing, the latter was carefully neutralized with a 10% caustic solution and filtered. This material was next subjected to a simple steam distillation from & 500-gallon iron still. Benzotrifluoride, hexafluoroxylcne, and the
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
chlorofluoroxylenes (275 pounds) were thus separated from a residue (119 pounds) of unknown composition, which was discarded. The fluorinated bodies (276 pounds) in the steam distillate were carefully separated from the water. Distillation under 28 inches of vacuum and up to 80" C. in a simple iron still served as a means of isolating the desired material (225 pounds) from most of the chlorofluoroxylenes and unstable intermediates (60 pounds), The hexafluoroxylene fraction (225 pounds) was further rectified by distillation through a ten-plate column, whereby a product boiling a t 113-116.6" C. (208 pounds) was collected. I n the final operation this material was treated with 1% by weight of soda ash to remove traces of acidic constituents. Bis(trifluoromethy1)benzene was thus prepared in yields ranging from 40 to 657" based on theory for hexachlorouylcne, and i t possessed the following specifications: Refractive index a t 20° C. Density a t 25' C . Distillation range, O C . Water content Color Benzotrifluoride content,
1.378--1,351 1.390-1.400 113-116.5 Si1 TVater white, rlenr Less than 1 . 5
Mono- and dichloro-bis( trifluoromethyl) benzenes were not isolated as pure individuals but were separated into two con-
centrates by vacuum distillation. fluorination of hexachloroxylene.
305 Figure 2 is a flow sheet of the
ACKNOFLEDGMENT
The authors express their thanks to the Manhattan District, United States Corps of Engineers, who helped in the guidance of this project and whose financial support made it possible. The authors also wish to thank Raphael Rosen and E. T . PllcBee and associates a t Purdue University for many helpful suggestions. LITER-ITURE CITED
(1) I. G . Farbenindustrie -4.-G., Brit. Patent 464,%9 (1935). (2) Ibid., 465.885 ( 1 9 3 7 ) . J . Gen. Chem. (I,-.S.S.R.),6, 748-56 (3) Kizhner, X., and Krasova, Y., (1936) PRESESTEDbefore the Symposium on Fluorine Chemistry a s paper 68, Division of Industrial and Engineering Chemistry, 110th Meeting of t h e AMERICANCHEMICALSOCIETY,Chicago, Ill. The work described in this paper is covered also in a comprehensive report of work with fluorine and fluorinated compounds undertaken in connection with the Manhattan Project. r h i s report is soon t o be published as Yolume I of Division VI1 of the M a n h a t t a n Project Technical Series.
Prepnration of fluorine=contnining
POLYHALOHEPTENES E. T. McBee, R. C. Schreyer', '6-. S. Barnhart, L. R. Evans', A. R. Van Dylren?, H. B. Hass, Z. D. Welch, TV. E. Burt3, G. M. Rothrock4, R. E. Hatton;, R . RIezey, T. S. Taylor, D. W. Pearce, A. A. Alberts, C. I. G o c h e n o d , R . AI. Robb', P. E. Weimer, R . E. Burns, W.V. Clipp7,IC. W. Krantz', I. B. Silverberg8, and R. Tekel PURDUE UYIVERSITY kVD PURDUE RESEARCH FOUYDATION, L-IFkYETTE, IND.
POLlCHLOROHEPTANES containing about 8370 chlorine, corresponding to the average formula C,H,Cll,, were prepared by the liquid-phase photochemical chlorination of heptane in a temperature range starting at 25" C. and gradually increasing to 100" C. These polychloroheptanes were converted to polychloropolyfluoroheptenes containing about 29% chlorine and about 47%0 fluorine (C7HzC13F8) by treatment with hydrogen fluoride and antimony pentahalides. The antimony residues can be re-used effecti\ ely in subsequent fluorinations if they are maintained anhydrous and are chlorinated prior to re-use. Polyhaloheptenes corresponding to the formulas C,H,Fl,, C?€I,ClF,,,C,H&l,Flo, and C1HzC13F9 were isolated from fluorinated products.
HEX it became apparent t h a t perfluoroheptane would be useful in a process for the separation of uranium isotopes by gaseous diffusion, methods for the preparation of this fluorocarbon were in immediate demand. The fluorination of n-heptane with fluorine in the presence of copper gauze and with CoF3 were studied extensively a t Columbia and Johns Hopkins Universities. 1 Present address, E. I. d u P o n t de Kemours & Company, Inc., Wilmington, Del. * Present address, 3Ietallurgical Laboratory, University of Chicago, Chicago, Ill Present address, E t h y l Corporation, Detroit, Mich. Present address, E. I. du P o n t d e Semours & Company. Inc., Buffalo, J
li.Y.
However, a method requiring l e v elemental fluorine T\ as desired because large scale production of fluorine appeared to he extremely difficult and expensive. A general method for introducing fluorine into an organic molecule is the replacement of established chlorine, bromine, or iodine with fluorine, using an inorganic fluoride requiring 110 elemental fluorine for its preparation ( I ) . 9 series of reactions leading to perfluoroheptane by the chlorination of n-heptane and subsequent fluorination of the polychloroheptanes was therefore investigated. The investigation was carried out according to the following general sequence. %-Heptane n a s chlorinated to a mixture of polychloroheptanes containing about 837, chlorine. These polychloroheptanes n ere converted to polychloropolyfluoroheptenes by treatment n ith hydrogen fluoride and antimony pentahalides. The polychloropolyfluoroheptenes R ere then converted to perhaloheptanes by the action of either COP3 or 4gFz. The amount of chlorine in the product from the latter reaction waq dependent upon the composition of starting materials and reacPresent address, Monsanto Chemical Company, St. Louis, hlo. address, Hooker Electrochemical Company, Niagara Falls,
' Present
N. Y. Present address, Huntington College, Huntington, Ind. 8 Present address, Cilco, Inc., Black Lick, Pa.
