292
INDUSTRIAL AND ENGINEERING CHEMISTRY
tive officials H. C. Urey, J. R. Dunning, W. F. Libby, and R . H. Crist. Other persons t o whom the authors are grateful are Raphael Rosen of the Standard Oil Company of S e w Jersey, R. D. Fowler of The Johns Hopkins University, W. S. Calcott and A. F. Benning of the D u Pont Company, L. A. Bigelow and P. M. Gross of Duke University, J. H. Simons of Pennsylvania State College, E: T. McBee and H. B. Hass of Purdue University, Manson Benedict of The Kellex Corporation, A. L. Henne of The Ohio State University, W. T. Miller of Cornel1 University, F. H. Reed and G. C . Finger of the University of Illinois, and Henry Eyring of Princeton University. This work was performed in partial fiilfillment of an Office of Scientific Resixarch and Development Contract.
Vol. 39, No. 3
LITERATURE CITED
(1) Fredenhagen, K., and Cadenbach, G., Ber.. 67, 928-36 (1934). (2) Fukuhara, S . , and Bigelom, L. A , , J . A m . Chem. Soc., 63, 2792, (1941).
(3) Miller, IT. T., Calfee, J . D . , and Bigelow, L. .A., Ibid., 59, 198 (1,937). (4) Sinioiii, J. H.. aid Block, L.P., Ihid.,61,2962 (1939).
PRESFXTED hefurc t h e Sgiiipo.iuni on rluorinc Chemistry l i s i l a i r r 50, Dirision of Industrial and Engineering Chemistry, 110th Meeting of tltc ~ V E R I C S C H E U I C ASOCIETY, L Chicago, Ill.
SYNTHESIS OF FLUOROCARBONS R. D. Fowler, W.B. Burford 111, J. 31. Hamilton, Jr.I, R. G. Sweet2, C. E. Weber3, J. S. Kasper'. and I. Litant4 T H E JOHNS H O P K l h S UhIVERSITY, BALTIMORE, >ID.
.4 PRACTICAL and general synthesis for completely fluorinated organic compounds was de\ eloped; it consists of reaction between cobalt trifluoride and vaporized hydrocarbons or fluorohydrocarbons at elelated temperatures. .-i number of pure fluorocarbons, ranging from perfluoron-butane to perfluorocetane, were produced and characterized. Certain reaction by-products were identified. Perfluoro-n-heptane was obtained in jields up to 789" from n-heptane, and perfluorodimethjlcjclohexane i n 8894 4 ields from bis(trifluorometh>1)beiizeiie. Crude yields for these two feed stocks were 91 aud 9 7 7 ~respectilely. ~
With high boiliup feed stocks, such as light lubricating oils, jieltls of fully fluorinated material in excess of 50% ere obtained. The Tariables of the reaction were studied, and iniproled equipment was designed on the basis of the results. These rariables included reaction temperature. dilution of the hjdrocarbon with inert gas, contact time, and degree of CoF3 exhaustion. 4 rough measurement was made of the heat of the reaction between fluorine and CoF2, and the result used to calculate the heat of the reaction between the resulting CoF3 aiid hjdrocarhons.
I
bons. There n-ere indications that these materials would be chemically inert, and there was interest in their possible use as fluids for the recoil mechanisms of large guns. Interest in the possibility of using these compounds for various purposes in the separation of uranium isotopes was also manifested; if these compounds could be made available on a large scale, it appeared that the separation of uranium isotopes would be greatly facilitated. Until October 1941 no pract'ical general method for the synthesis of perfluorocarbons had been reported in the literature. Several reviews of the subject had been written, among the more recent being those of Bockemueller (4) and Henne ( 1 4 ) . The syntheses reported could be divided roughly into two classes: those involving indirect techniques, such as a reaction between an organic halide and an inorganic fluoride, and those involving direct reaction between carbon and fluorine or the direct replacementof hydrogen by fluorine. The indirect techniques had been successful in introducing a fen fluorine atoms into organic molecules. Ruff and Keim (19) and Simons and Block (80) in 1930 and 1939, respectively, reported that the fluorination of elementary carbon resulted in the production of small amounts of fluorocarbons containing more than one carbon atom, in addition to the expected carbon tetrafluoride. A number of a t t e m p h had been made t o substitute hydrogen in hydrocarbons with fluorine by reaction between the hydrocarbons and elementary fluorine. Among the more successful were a vapor-phase method described by Bigelow (3)and a liquid-phase method described by Fredenhagen and Cadenbach ( 1 1 ) . In both of these cases, hon-ever, the
resulting products consisted of a coniplicated mixture of polymers and degradation products with only very small yields of the desired fluorocarbon. It was suggested by Roger Adanis and Ralph Connor that the n-ork of Ruff and Keirn and of Simons and Block he repeated in the hope of increasing the yields of heavier fluorocarbons. This was done. utilizing Sorite sugar charcoal, various other forms of carbon, and silicon carbide. The temperatures Tvere varied from 400" to 550" C., and the concentration of fluorine varied over a wide range by nitrogen dilution. However, in all cases S0-9070 of the product was a gas at room temperature, and the greater portion of the liquid product boiled helow 100" C . Although small amounts of higher fluorocarbons-including a little oily and a little waxlike material-were produced in these esperimentq, the results gave little promise of a practical synthei;is. Ruff (18) discovered a number of metallic fluorides in which the metal ion possessed a high ralence. These compound.; could be made only by the use of elementary fluorine, and Ruff showed that they were strong oxidizing agents. MnF3, AgF2, and CoF3 were three of these fluorides. They had been prepared in thi. laboratory previous to October 1941 and had heen used as fluorinating agents for converting CF,into CFs. It Peemed possible then that these compounds might react n-ith hydrocarbons to replace hydrogen by fluorine as does elementary fluorine, and that the reaction n-ould he 1e.s drastic. The replacement of hydrogen n-ith fluorine in hydrocarbons n-ould therefore essentially be accomplished by the uqe of elementary fluorine, hut the process v-ould be in two steps: fir-t, the fluorination of the lon-er metallic fluoridr to the hitrher:
]Present address, E . I. d u P o n t de Sernours & Company, Inc., KImington, Del. 2 Present address, The Linde Air Products Company, Tonawanda, N . T. Present address, General Electric Company, Schenectady, N. Y. 'Present address, New York University, S e w York, 1..Y .
and, second, the replacement of hydrogen with fluorine in the hydrocarbon by the higher fluoride:
S THE fall of 1941 work was undertaken in this laboratory on a general and practical method for the synthesis of fluorocar-
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
All three fluorides were found satisfactory. Efforts n-ere concentrated on CoF3 and MnF3because they were cheaper and somewhat easier to handle than AgFz. The present paper is limited to a discussion of CoF3 as a fluorinating agent according to the folloiving reactions: -CH?-
2CoF2 + Fz + 2CoF:j + ACoF3 --+ -CF2- + 2 H F + -1CoFy
(3) (4)
The reaction betn-een solid CoFQand liquid hydrocarbons is violent and could not be controlled. S o diluent inert t o CoF3 was available a t the time. The diluents used, CC1, and Freon 113, gave mixed chlorofluorocarbons, such as CsHtoF3Cl from hexane in carbon tetrachloride. Later, \i-ith fluorocarbons as diluents, several groups developed successful liquid-phase syntheses. An alternative method of dilution was to convert the hydrocarbon to a gas and mix it v-ith an inert gas such as nitrogen. I n the first successful vapor-phase experiment, a mixture of hexane vapor and nitrogen was passed over a bed of solid CoF3 in a heated copper tube, and the products were condensed in a trap a t -78" C. I n this experiment 86 grams of hexane were passed oT-er 325 grams of CoF3 a t 150" C. to give a product Tvith a density of 1.62 and a refractive index of 1.29. These encouraging results led to the design of better apparatus. Since the reaction is strongly exothermic, the heat of reaction was measured before the apparatus was designed. HEAT OF REACTION
For the reaction, ','z(-CH2-)
+ F, + '/2(--CF?-) + H F
(5)
an approximate heat was calculated from the bond strengths given by Pauling (17) as AH = - 104 kg.-cal. Since in this work reaction 5 is achieved in two steps,
'/z(-CHz-)
2CoFt + Fz + + 2COF3 + '/z(-CFz-)
+ H F f 2CoFz
(6)
(7)
the heat of reaction of either step can be calculated if the other is known. Reaction 6 was considered more amenable to measurement, and a rough, direct measurement was made. A bomb containing a weighed amount of freshly prepared CoF, was surrounded by a n oil bath contained in a Den-ar flask, and an electric heater vas adjusted to maintain a temperature of 200" C. Fluorine Tvas then admitted to the bomb and the steady temperature rise recorded for a period of about 10 minutes. After the fluorine was shut off, the system n-as readjusted to equilibrium a t 200" C. and the previously observed temperature increase duplicated as
I
Figure 1.
Schematic View of Reactor
293
nearly as possible by auxiliary electric heating. From this additional power input and the increase in the weight of the bomb, the heat of reaction 6 was determined to be 4 H = -52 * 3 kg.-cal. at 200" C. This value indicated that the heats of the two steps of the fluorination reaction were approximately equal. The heat of reaction for the fluorination of CoF2 as determined in the given experiment did not agree with the value of Jellinek and Koop (16), who reported a value of -159.2 kg.-cal. for reaction 6 a t 225 o C. Thi. value is in excess of the calculated value for reaction 5 and indicates that reaction 7 would be endothermic to the extent of +35.2 kg.-cal., contradictory to laboratory experience. SMALL SCALE REACTORS
The reactor used for preliminary investigations is s h o ~ mschematically in Figure 1. It consisted of a horizontal flat'tened copX 26 inches, the ends of n-hich xere closed with per tube 31,'? x brass plates n-ith lead gaskets. The tube was heated by electrical furnace H , and temperatures irere measured by thermocouples silver-soldered to the copper reactor. Commercial nitrogen &-asadmitted by valve A through flom-meter B to vaporizer E . The vaporizer rvas a vertical tube packed with steel wool and electrically heated. The liquid to be fluorinated lvas admitted to the vaporizer from graduated cylinder C by means of valve D. Three-n-ay valve G permitted connection of the reactor to a fluorine line for regeneration. The reaction products were condensed in cold trap J . The reactor was packed loosely with anhydrous CoCl? held in place by plugs of steel wool. The CoCI2 was converted t o CoF? by passing anhydrous hydrogen fluoride over it a t 400-450" C:. The resulting CoF, was a pink pon-der. This was then changed to buffcolored COF3 by passing F, over it a t 250' C. The run with hydrocarbon n-as started after sneeping n.ith nitrogen to remove the excess fluorine, and, when this was completed, the system was swept out for a half hour or more to remove all traces of reaction products. The reaction products, hydrogen fluoride, and crude fluorocarbon were condensed in a trap chilled to - 78' C. Since fluorocarbons are not, miscible with hydrogen fluoride, they were drawn off from the bottom of the trap. The crude product was washed with dilute sodium hydroxide and several times with water, dried with sodium sulfate, and distilled. The reactor was then refluorinated for the next hydrocarbon run. LARGE SCALE REACTORS
The preliminary experiments indicated the desirability of agitating the CoF3 to prevent caking and to facilitat,e temperature control and also suggested that the reactor be sufficiently long to permit gradation of temperature300° C. Physical properties of 1t0--3OO0 C. fractinn Reflux boiling point, C. Refractive index, n20 Density, d'S
1349 1300 49
1376 500 73
9.0 33.5 49.4 6 3
9.5 32.8 53.1 4.6
164 1.3171 1.974
165 1.3164 1.976
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
The crude from n-heptane yielded the following compounds :
TABLE VI. REACTION OF HYDROCARBOXS WITH CoF3 Starting 1Iaterial Pure Product Bis (trifluoromethyl) benzene (mixt. of 1,3- and 1,4-j Perfluorodirnethylcyclohexane n-Heptane Perfluoro-n-heptane XCT white oil ...... Diol 45 ........... n-Butane Perfluoro-n-butane n-Pentane Perfluoro-n-pentane Cyclopentane Perfluorocyclopentane Di methylcyclopentane Perfluorodimethylcyclopentane Ethylcyclopentane Perfluoroethylcyclopentane Renzotrifluoride Perfluoromethylcyclohexane o-Xylene Perfluoro-o-dimethylcyclohexane m-Xylene Perfluoro-m-dimethylcyclohexane p-Xylene Perfluoro-p-dimethylc yclohexane Mesitylene Perfluoro-1,3,5-trimethylcyclohexane Perfluorohexahrdroindan Indan Perfluorocetane Cetane Perfluorodicyclohexylether Diphenyl oxide a Averages of many runs under optimum conditions. h Rased on conversion of -CHzt o -CFz--. c Large handling losses. ri S o t distilled here.
Crude Yield, Yo 975 910
83: 68
51n.b 45c 67 46 83 68 88 63 66 55
..
54
43 40 32
Bi,(tiifluoromethyl)benzene, Hooker Electrochemical Company, Commercial grade. Mesitylene, Eastman Pure grade. Indan, Hooker Electrochemical Company, Hydrogenated grade. cr-;llethyliiaphtlialene, D u Pont Company, Telsicol 50-S. Cetane, Du Pont Company, Knock Rating grade. Diphenyl ether, DOLTChemical Company, Commercial grade. S C T K h i t e Oil, Standard Oilcompany of S e n Jersey, S o . 1338. Diol 45, Standard Oil Company of S e w Jersey, S o . 557 &$E 10. Mirando J , Standaid Oil Company of S e x Jersey PRODUCTS
Home of the products resulting from reaction of hydrocarbons with Cop3 are shonii in Tables 1-1and 1-11. The yield figures for the first four products in Table VI are averages of a large number of runs under optimum conditions, \Thereas the others :ne based on only one or two runs each; consequently there is no reasson to believe the latter represent optimum yields. It was found, in general, that when hydrocarbon vapor was passed over CoF,, there as always some incompletely fluorinated material. In the case oi the first, four materials of Table VI, this partially fluorinated material, which boiled higher in each case than the desired product, n'as repassed over cobalt trifluoride. This resulted in completion of the fluorination, and the additional amount of desired product was included in the yield calculations. Yield figures are based upon runs made in the large scale reactors. Large amounts of the crudes from n-heptane and bis(trifluor0niethy1)benzene were carefully fractionated. This resulted in the foilon-ing cuts: atarting Naterial n-Heptane I~iz(trifliiorometh~1) benzene
Reads,
Pure Product,
Tails,
"70
%
%
12 8
87
1
TABLE VII. Starting AIaterial n-Pentane Cyclopentane llimethylcyclopentsne Ethylcyclopentane Benzotrifluoride n-Heptane o-Xylene m-Xylene p-Xylene Bis(trifluoromethy1)benzene Mesitylene Indan Cetane Iliphenyl oxide
91
Yield of Pure Product, % Single pass Repass
..
io",b
1
SISGLEPASSCRUDES
~ ~ iR~~~~ l i of ~ F~in Pure Product, '70 Pure Product, O C. Calcd. Obsrd. ........ 29.4-29.5 .. 23.5-23.7 .. ........ 71.5-71.8 .. ........ 75.l-i5.2 ........ 76.3-76.4 76:O 76.7 * 0 . 3 82.4-82.6 78.4 78.3 * 0 . 3 .. ........ 102.1-102.4 101.7-101.9 .. ........ ........ 100.5-100.6 101.0-101.8 76:O 75.8 * 0.3 124.7-125.1 .. ........ 117.2-117.5 .. ..,. . , . , ........ 238-240 .. ........ 175-176 ..
.
297
d
88n 79Q
.. .. .. .. .. .. .. .. ..
Perfluoro-n-hexane Perfluorodimethylcyclopentane Perfluoroethylcyclopentane
1%
3
8
Perfluoro-n-heptane Perfluoro polymers
87 1
Some properties of a liquid fraction of these 1% of perfluoro polymers are: boiling range at 10 nim., 175-200' C.; refractive index (n"), 1.3405; density (dZ0),2.0915; and cryoscopic molecular weight, 916. ., .. .. .. No perfluorometh?-lcyclohexane or 15 perfluorocyclohexane appeared in the crude; this indicated that the most important side reaction was cyclization to form a five-membercd rather than a The rierfluorosix-membered ring.. ' dimethylcyclopentane n-a:: a mixture of isomers and ~ m not s resolved. The material obtained from benzotrifluoride contained no perfluorocyclohexane, but the material from bi.(trifluoromethyl)benzene contained about 3'3, of perAuoronietlivlcyclohexsne. This is indicated in the fullowing table, as ncll as the increased degradation when liydrocarbons v,we u ~ e da? feed stocks: 58
28 38 59 77 42 50 42 27 20 29
of Single Pass- Crude i'erfluuromethylI'erfluorodimethylcyclohexane cyclohexane 13 67 11 75 7 77 3 66 ~
Starting Material o-Xylene m-Xylene p-Xylene Bis(trifluoromethy1jbenzene
~
~
~~
In the case of mesitylene about 207, of perfiuoro-m-climethylcyclohexane lyas obtained; this shon-ed that degradation proceeded to a somewhat greater extent than with the xylenes. The material from a-methylnaphthalene consisted of three approximately equal cuts boiling in the ranges 140-145", 160-165 ', and 180-185" C. The 0-methylnaphthalene Tvas a t least 90% pure, and this apparent alteration of structui,e v-as rather unexpected. The material from diphenyl oxide contained about 30% perfluorocyclohexane; this indicated scission of the ether linkage. The pure product, however, had a molecular n-eight of about 380, ivhich compared favorably with that, of perfluorodimethycj-clohexylether. Little n-as known about the chemical nature of the variou5 lubricating oils used as feed stock. Extensive work was done on three such oils: XCT, Diol 45, and Mirando J . It was understood from the supplier that X C T oil was a distilled fraction of a Khite oil consisting largely of naphthenes and paraffins and having a boiling range in the neigliborliootl of 250-300O C. Diol -45 was an S.W-10 lubricating oil obtained froin n doniehtic naphthenic crude and was reported to Pure Heads, product, Tails, have a boiling range of 325-410" C. % Z % (The structural distribution in oils from 5 86 9 crudes similar to Diol 45 is approxi13 60 27 4 46 50 mately 20% aromatics, 25% naphthenes, 3 87 10 5 88 7 and 55y0 paraffin chains.) Mirando J 15 10 75 ivas an overhead fraction from a heavy 21 67 12 16 75 9 coastal-type oil high in naphthenes. Of 11 77 12 7 86 7 this fraction, OOy, n-as reported to boil 28 50 22 10 47 43 between 389-404 C. 73 17 The following table illustrates the 47 18 nature of the crudes from these oils.
E
INDUSTRIAL AND ENGINEERING CHEMISTRY
298 Boiling Range of Starting Material, C. < 160 (atm. pressure) 160 (atm.)-147 (10 mni ) 147-208 (10 m m . ) > 208 (10 mm.)
-~% in Desired Boiling Range
XCT 14 45
37 4
Diol 46 23 24 46 7
hlirando J 29 22 35 14
Vol. 39, No. 3
the nork desciihed in this paper, i. acknonledged. That author expresses appreciation to H. A. B. Dunning, \vhosw interest and financial support made that early n-ork pos-ihle. LITER4TLKE CITED
The fractions were increasingly viscous, the lo\\. boiling ones being thin oils and those boiling above 300” C. a t atmospheric pressure, brittle resins. Fractions of the three crudes having identical boiling ranges varied con.4derably in appearance arid physical properties, but the fractions \$-ere so broad that the differences may have resulted largely from differing distributions of material within a fraction. Thus the cut from the XCT crude boiling between 147-208” C. a t 10 mm. was markedly less viscous than the corresponding cuts from the Diol 45 and Mirando J crudes; but in the S C T crude most of this fraction canie over betveen 147175” C. a t 10 m i . , whereas m-ith Diol 45 and Mirando J much of the material boiled near the upper end of the cut. ACKNOWLEDGMENT
This work was instigated by the Sational Defense Research Committee and was carried out under Government Contract S o OEMsr-331. The early interest of Roger Adams and Ralph Connor is acknowledged. Many of the later portions of the work were performed for the U. S. Army Corps of Engineers, Manhattan District. Much help was obtained from A. F. Benning, F. €3 Downing, H. W. Elley, and W. S. Calcott of the Du Pont Company, and R. Rosen of the Standard Oil Company of S e w Jeraey. A. L. Henne was very helpful as were George Cady and -4.J’ Grosse. R. B. Barnes of American Cyanamid assisted in identifying the compounds resulting from some of the distillations. The interest of D. H. Andrews in the early work of R. D. Fowler on the preparation of fluorine and TF,, which led directly t o
(15) (16)
(17)
(18)
Beatty and Calingaert, ISD. ENG.CHEJI., 26, YO4 (1984). Bernstein and Miller, J . Am. Chem. Soc., 62, 948 (1940). Bigelow, Ibid., 63, 2792 (1941). Bockemueller, “Organische Fluorverbindungen”, Berlin, Verlag Chemie, 1936. Bromiloy and Quiggle, IND.ENG.CHEY.,25, 1136 (1933). Brown, Mitchell, and Fowler, Rev. Sci. Instruments, 12, 435 (1941). Burford, Fowler, Hamilton, Anderson, Weber, and Sweet, IND. ESG.CHEM.,39, 319 (1947). Elving and Ligett, IXD. ENG.CHEM.,A x . 4 ~ED., . 14,449 (1942). Fenske, IND.ENG.CHEM.,24, 482 (1932). Fowler, Burford, Anderson, Hamilton, and Weber, Ibid., 39, 206 (1947). Fredenhagen and Cadenbach, Ber., 67, 928 (1934). Grosse, private communication. Grosse, Wackher, and Linn. J . Phys. Chem., 44,275 (1940). Henne, in Gilman’s “Organic Chemistry”, Vol. I, 2nd ed.. p. 944. New York. John Wilev & Sons. h e . . 1943. Jellinek and Koop, Z.physik: Chem., A145, 305 (1929). Livingston, “Physicocliernical Experiments”, p. 56, N e w York, Macmillan Co., 1939. Pauling, “The Snture of the Chemical Bond”, 2nd ed., p. 53, Ithiea, Cornel1 Univ. Press, 1940. Ruff, “Die Chemie des Fluors”, p. 50, Berlin, Julius Springer, 1920.
(19) Ruff and Keim, 2. anwg. allgem. Chem., 192, 249 (1930).
(20) Simons and Blork, J . A m . Chem. SOC.,61, 2962 (1939).
PRESENTED before the Symposium on Fluorine Chemistry as paper 61, Division of Industrial and Engineering Chemistry, 110th Meeting of the A N E R X C CHEMICAL .~~ SOCIETY, 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. This report is soon to be published as Volume I of Division VI1 of t h e Manhattan ProjPct Technical Series.
PREPARATION OF BIS(TRIFLUOR0METHY UBENZENES E. T. McBee, H. B. Hass, P. E. Weimer. G. AI. Rothrock’. W. E. Burt2, R. 31. Robb3, and -4.R. Van Dyken4 PURDUE UNIVERSITY 4YD PURDUE RESE4RCH FOUYD4TIOY. L4FAYETTE. I V D .
COAIJIERCIALLY available xylene fractions, pure m xylene, and pure p-xylene were converted to bis(trich1oromethy1)benzenesby liquid-phase chlorination. The mixtures obtained therefrom were fluorinated with hydrogen fluoride alone and in the presence of antimony halides. Highest yields of bis(trifluoromethy1)benzenes were obtained by fluorination of 1,4-bis(trichloromethyl)benzenes. The conversion of xylene to bis(trifiuoromethy1)benzenes in a commercial mixture was about 4 l q c .
FTER it was demonstrated that fluorocarbons would be useful in the separation of uranium isotopes by gaseous diffusion, it became evident that the propertied of perfluorodimethylcyclohexane, CBFW, made it suitable for use in this process. The isomeric perfluorodimethylcyclohexanes can be prepared by the reaction of xylenes with either fluorine or certain metal fluorides, of which cobalt trifluoride (CoF,) is representative. As illustrated I Present address, E . I. d u P o n t de Nemours and Company, Inc., Buffalo, N. Y . 2 Present address, E t h y l Corporation, Detroit, Mich. 3 Present address, E. I. d u Pont de Nemours and Company,% Inc., Wilmington, Del. 4 Present address, University of Chicago, Chicago. Ill.
by Equations 1, 2, and 3, relatively large quantities of fluorine are required for these processes.
+
+
CsH,(CH,), 13Fz --f CsFio(CF,)z lOHF (1) csH~(cH,)s 26CoF3 +C,Fio(CFz)z IOHF 26C0Fz (2) 26COF2 4- 13F2 +26C0F3 (3) A process requiring less elemental fluorine for the production of perfluorodimethylcycloliexane was desired, since large scale production of fluorine appeared to be both difficult and espensive. Such a process would include the introduction of fluorine into the xylene molecule by a fluorinating agent which could be prepared without the use of fluorine. The chlorination of aromatic compounds containing methyl groups and subsequent fluorination of resulting trichloromethyl compounds is described in the patent literature ( I , 4, 5 , 7 ) . Hence, it was believed that, in the production of perfluorodimethylcyclohexane, it would be advantageous to convert xylene t o bis(trifluoromethyl)benzene, which could then be fluorinated with CoFa a t a corisiderable saving in fluorine. This sequence is illustrated by the following equations: C ~ H I ( C H ~ ) Z6C12 +C&(CC13)z 6HC1 (4) 6 H F --+ CkHd(CF3)z 6HC1 CGH,(CCI,)s (5)
+
+
+
+
+ +
+
