March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY CARBON FORMATION
T h e carbon formed in these experiments was, surprisingly, a n activated char. It had decolorizing properties. Its density was a function of the temperature of t h e reaction, higher temperature producing a more dense form. It was not contaminated with tarry T~~~\Yere not found as products from the oxidation of either aromatic or aliphatic substances. All of t h e ‘Vithout gaseous Organic may be converted to products, depending only upon the use of sufficient oxygen. I n
367
most of the experiments reported in Table I, only a relatively small amount of oxygen was Present in the vessel and t h e reaction proceeded only as fer as this W A S used. LITERATURE CITED
60,492 (1938) (1) Simons, J. H., and Lewis, c. J. Am. Chem. (2) Simons, 3. H., and Passino, H . J., Ibid., 62.1624 (1940). J.9
PRESENTED before the Symposium on Fluorine Chemistry a8 paper 84, Divi: sion of Industrial and Engineering Chemistry, 110th Meeting of . ~ M F , R I C A N C H E ~ sOCIETY, ~ ~ C ~ chicago, ~ 111.
PROPERTIES OF FLUOROCARBONS Aristid V. Grosse’ and George H. Cady? WAR RESEARCH LABORATORIES. COLU>fBIA USIYERSITY, XEW YORK. S . Y.
THE main cheiiiical characteristic of fluorocarbons is due to the great stabilitj of the C-F bond. Thus, particularly in contrast to chlorocarbons, they show remarkable thermal stability and molecules with long carbon chains, similar to those of h?drocarboris and their cleri>atises, are possible. They are furthermore characterized by their great chemical inertness and resistance to oxidation. The physical properties of fluorocarbons are compared with those of hldrocarbons of the same carbon structure,
and a number of regularities obsened. Their boiling points arid \olatilities are close together, but the fluorocarbons ha\ e about double the density of hydrocarbons and remar1,ablj low- indices of refraction. O n the basis of present inforniation, it is not premature to c-oriclude that we are confronted here with a \ a \ t new field of inorganic “organic chemistr) ”, a field potentially as immense in size and as \aried, both in compounds and reactions, as that of ordinar? organic chemistry.
I
This was follon-ed shortly after by Co1umbi~’scatalytic nicthod and later by others. The first references to fluoro-olefin?, zucli as CF,=CF,, are found in early papers by Otto Ruff and X. L Henne. Since then our knowledge of fluoro-olefins has substantially increased. Fluorodiolefins, such as fluorobutadiene (C,Fs), were first isolated by R. T. Miller, and cyclo-olefins, such as fiuorocyclobutene (CdF,), by Henne. Representatives of fluoroaromatics, such as hexafluorobenzene (C,F,), have been synthesized by E. T. !tlcBee and co-TI-orkers. Table I lists all fluorocarbons knoivn t o dat>en-ith their physical properties.
S T H E fall of 1941 n-ork was started at Coluiiibia, anti extended to various other universitieq, having a? its objective
t h e development of certain liquid and solid compounds xi-ith special properties required by the Atomic Energy Project. From the behavior of those fluorocarbons, C,F,, n-hich were described by Sinions ( 2 6 ) ,Grosse suggested in 1940 that compounds of this chemical type might be satisfactory for the intended purpose. A4 few cubic centimeters of a mixture of liquid fluorocarbons, practically all of the available supply, were secured from Simons, tested ( 8 ) , and found t o be satisfactory. Further intensive research was indicated. As the result of a great cooperative effort by both university and industrial laboratories, a large number of new compounds containing only carbon and fluorine (fluorocarbons) were discovered. A large amount of data on their properties has accumulated, and the purpose of this paper is t o compare the fluorocarbons with hydrocarbons of the same carbon skeleton. On the basis of information now available, it is not premature t o conclude t h a t we are confronted here x i t h a vast new field of inorganic “organic chemistry”, which is potentially as immense and as varied as t h a t of ordinary organic chemistry. If we consider, in addition, the mixing of fluorocarbon compounds or their radicals with classical organic compounds or their respective radicals these potentialities become staggering. (Approximately 106 organic compounds are now known; in view of the stability of fluorocarbons and their derivatives, a similar number is possible. T h e number of possible “mixed” compounds is thus 1012.) At the time t h a t Ti-ork on the fluorocarbons Tvas started, only the first gaseous members of the fluorine paraffin series-namely, CF4,C2F6, C3F8,and C4F1g-and CF,=CF2, vere known as pure compounds, and some information ]vas available 011 one or t x o pure liquid fluorocarbons. B y the zummer of 1012 a large number of pure, liquid fluoroparaffins and -naphthenes, both monoand bicyclic, were available. The first practical and general way to produce them was the CoFz method of Foivler and associates (6) a t Johns Hopkins.
* Present address, Houdry Proceaa Corporation, Marcus 3
Hook, Pa. Present address, Lniversity of Kashingtcn, Seattle, Wash.
NOM E S C LATURE O F F LUOROCARDOXS
The classical nomenclature becomes cumbersome, particularly for compounds containing many atoms of fluorine and only a f e v of hydrogen. For example, CF3-CFH-CF,-CF2-CF2CF2-CFz-H 1%-ouldbe called lJ1,1,2,3,3,4,4,5,5,6,6,7,7-tetradecafluoroheptane. R e have found it convenient t o use the Greek letter phi as a symbol t o indicate complete substitution of all hydrogen atoms attached t o carbon by fluorine in the compound folloiving the symbol. For example, @-heptane is C7F18, :tnd the hydrofluorocarbon mentioned above is 1,6-dihydro-@-heptane. Similarly acyclohexane, pronounced phi-cyclohexane, i.: CFz-CFz /
F,C/
\\
CF,
\
/
CF~-CF~’
Bigelow’s C6Fl1H mould be named monohydro-@-cyclohesane, n hereas its regular Geneva organic name ~vouldbe 1,2,2,3,3,4,4,5,5,6,6-undecafluorocyclohexane.Further examples are @-benzoic acid (C6FsCOOH), @-ethyl alcohol (CzF,OH), and @-ethyl@-benzoate (C6F6-COOC2F5). The letter @ rvas chosen as the Greek equivalent for the Latin F, symbol of the element. We believe that this departure from organic nomenclature is rwrranted, particularly since we do not coniider this nexv field of chemistry a part of regular organic chemistry.
368
INDUSTRIAL AND ENGINEERING CHEMISTRY CHEMICAL PROPERTIES
The saturated fluorocarbons-that is, the fluoroparaffins (CnF2,,-2)and the fluoronaphthene$, monocyclic (C,F,,) and bicyclic (C,F,,_,)-may be produced in good yields (from 50-95%) by two general methods. The first was Fowler's two-rtep method (6). The compound t o be fluorinated is vaporized, diluted with nitrogen, and passed over a bed of CoF3 at 200-350" C. Substitut'ion takes place according t o the general equation :
+ 2CoF3 ---e-\-C-F
1C-H
/
/
-\C-H
/
+ 6F, bonds + 6 C-C
C';FIe (16 C-E'
7 CF4; AH bonds)
=
-551 kg.-cal.
+ 6 F-F
+ 381 kg.-cal. --+
bonds -+ 28 C-F bonds
2996 kg.-cal.
In vie\v of this highly negative value, LF (the free energy tle( v a s e ) should also be negative. Mixtures of fluorine and @-lieptane vapors do explode violently Ivhen ignited by a spark discharge, as found by Cady. It is therefore to be expected that fluorwarhoni will burn in fluorine, and vice versa, if admitted through a jet and ignited. Consequently precautions are neccsiary in handling fluorocarbons in t h e presence of free fluorine. The fluororarbons are readily attacked by metallic sodium and potassium a t temperatures around and above 400" C., as mentioned by Sinions (M). * SATURATED FLUOROCARBONS
/
The conversion of benzotrichloride (obtained by direct chlorination oftolueriej with hydrogen fluoride to benzotrifluoride, x i t h out or with catalysts (SbCI, or SbF,), was previously established. Similarly, the xylenes and mesitylene could be chlorinated and then converted with hydrogen fluoride to bis(trifluorometliy1)benzenes ("liexafluoroxylenes", 1 7 ) and tris(trifluoromethyl!benzenes ("nonafluoromesitylene"), respectively. Alllthese partially fluorinated compounds can be readily fluorinated by tlie two general methods (.?I, referred t o previously, t o completely fluorinated products with much greater yields than tlie original hydrocarbons. I n addition to the increase in yield, an advantage is thc g r w t decrease in elementary fluorine consumption (Le., 6 moles fluiirine for nonafluoromesitylene with a loss of only 1.5 moles a s h>-drogen fluoride compared t o 15 moles fluorine for mesitylme with a loss of 9 moles 3s iiydrogcm fluoride). I n addition, parafins can be converted substantially to fluorocarbons (19). For instance, n-heptane can 1~ c1ilorin:itcd photo. chemically and in the liquid plinse (19) up to G H ~ C l : ~1T7hen t r w t e d with hydrogen fluoride, the latter yields Cl:H1F&l~. l l u c l i higher fluorine substitution is possible ( 1 ) by internlittent clilorination during hydrogen fluoride treatment-namely, u p to crage composition of C7H2FL0.jCll.5.Final treatment of tlii pound by t h e tTvo general methods gives @-hept:ine; thus, consumption of elementary fluorine has been reduced from 16 molcs per mole heptane (Equation 1 below) to only 3.75 moles. The saturated fluorocarbons are chnrncterized ljy great stat,ility and inertness ton-ard even the most reartive chemicalSI
>C,
F
=0
--+ >c=0
+
\ S.I ' '
\
F
F1uoroc:irtjons are not attacked by nitric acid, conccntr:itc'tl (96%) and fuming sulfuric acid, nitrating mixture, acid chroniat(~, and permanganate solutions. The reaction product of thi, fluorinaticin of benzene (i,e.,@-cyclohexane) may be easily .seli:ir:itcd froni the last traces of unreacted benzene by nitrating the lattcr wit11 nitratiiig mixture and separating t h e dinitrobenzene froin the volatile C6F12. Fluorticarhons are stable totvard air and do not burn by 1 t i v m v l r c s . They crack, however, in the flame of a Bunscn t ) u n 1 i , 1 . . They do not decolorize bromine water and are stablc bromine and iodine. Fluorocarbons react in the presence of catalysts with hytlrcigc,it under pressure a t higher temperatures. For instance, Q-mt~thylcyclohexane (boiling a t 75.3" C.1 rcacts ivith hydrogen uritlvr about 100 atmosphi,res and nt 150" C. for 22 hours, in thc prvsence of iYiCr203and SiF, as catalyst, in a steel bomb.. .\ fen. moles of hydrogen fluoride form per mole of C7Fla. At the .smn(' time no noticeable cracking t o gases takes place. Higher boiling material (i.e,, from 75' to 95' C.) forms, having lower density, 1iighi.r refractive indices, and higher specific refraction than the original (Table 11).
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
369
TABLEI. LIST OF ISOLATED FLUOROCARBOSS KNOWSTO DATE Same
Forinula
0-LIethane @-Ethane @-Propane Q-n-Butane O-Isobutane
CF4 C2Fa CjFa CIFIO CIFN
O-n-HeDtane Q-Methylhesane and dimethylpentanes
C7Fia
Boiling Point a t lIeltiy 760 N n l . , C. Point, C.
C Skeleton
- 184
C
C-c C-c-C
-100.6
- 183
c-c-e-c
Glass Glass
C--c-C
Density (13
C.)
-128 1 96 (-184 i -78 2 1 8 5 ( - 7 8 ) -38 1 . 4 5 (0.2) - 4 . 7 1 . 4 7 (20) +3 .o ........
Reiractiye Viscosity Appearance Index a t 99.5' C . , ar Room Temp. ( t o C.) llillipoises
,
,
,
,
,
.,
.,..
............
............ a,
,
,
..,
, ,
, ,
..
............
Literature Reference
Colorle,s gas Colorle3s gas Colorless gas Colorless gas Colorless gas
(24)
Colorless liquid Colorless liquid
(6, 5 )
($4)
(26) (PO) (26)
C CTFls
c-e-c-e-e-C-c
CiF:e
rnethylpentanes
.....
A
1 , 7 0 3 8 (30)
1 . 2 5 7 2 (30) . . . .
. . . . . . . . . . . .
,
C
1
c-L-e-c-c < c
'
. . .
i A 1 c c
.....
'82
1 , 7 5 3 5 (30)
1.2676 (30)
.....
- 104
1,8002 (30)
1 , 2 7 3 3 (30)
1 . 9 8 (25)
1.324 (25)
I 0-2,2- & 2,4-Di-
82
0
c-c-c-e-c-c
Colorless liquid
I c-c-c-c-c I
@-2,2.3-Trimethy.lbutane
C~FK
*-2,2,4-Trimethylpentane
CsFla
9-n-Hexadecane
C,eFar
C
c-c-
-
C
c-C-e-c-c c c C--(C)1r-C
f115
................
................
fluorinations CbCyclopentane
,
., ,
Colorless liquid
I
c c
f 93
B.
CoFio
7
............
+240 r l l O h Y+85
-l-Methylnaphrhalane
CiiFzo
1.,
C'.
9 1- 100 100-11'
112-1:10 111 8 119 7 120.4
VAPORPRES~URE-. Ilcsenrc-li o n the detcrnii~iatici~i of v:ipor pre.i*urc's of various fluorocarbons is in progress at C'olunitiia. Hon-ever, no data are available as yet. R. D. Fowler at Johns Hopking ohtaincd the follorving results on @-n-heptanc,: Temp., ' C . Vapor pressure, nirn Hg
41.3 191.3
0 50
51.4 272.3
60 6 502 2
61.5 393.5
81.7 760.0
Figure 3 compares thme results n-ith those on the corrc~sponcling hydrocarbon. The slopes of the two curves seem to be about the same. ~ I E L T IPOISTR. SG Only a few data are availalilt~,and as usual the:- show less regularity than do boiling point data. Comparison of tlie mc~ltingpoints of synmcLtrica1 compounds, such as @-cyclohexane, and of straight-chain derivatives leads to the tentative conclusion that fluorocarbons melt wbutantially higher than the corrmponding hydrocarbons, except possi!)ly @methane. -411known values are compared below: Fluorocarbons
126"'
Vol. 39, No, 3
*-llethane *-Ethane *-Propnne a-n-Heptane O-n-Cetane @-Cyclopentane *-Cyclohexane @-Dicyclohexyl
11 P . , O C. - 184 -100 6 183 - 78 +I15 - 12 f 50 +75
ll.P., C. -183 -172.0 -187.1 - 90.6 +18.13 -93 8 +6.5 -20
A
-1 181 +4 +I3 198 f81 43 55
-
+-
Hydrocarbons llethnne Ethane Propane n-Heptane n-Cetane Cyclopentnne Cyclohexane Dicyclohesyl
The ni:iin reasoii for this effect ir probably the much higher atomic niass of Huorine as compared to hydrogen. DESSITI'AXD ~ I O L AT-OLLXES. R Table I and Figure 4 correlated our demity data. Both in @-paraffinand naphthene series the densities increase regularly with the number of rarhon atoms (Figure 4). The incrcme per carbon atom is, lion-ever, much larger than in hydrocarbon series. For instance, tlic incrcsase from C6F12 (die = 1.711) to C9Fls (d:' = 1.801 islarge in cornparison i o the change from CsHlz(d:3 = 0.780j to C9Hls (d:@ = 0.773). 1
C. i-
4
E
__
08CO
5---
n-PARAFFINS j 20"
z 0600, 3
The boiling points of all isomers are, for all practical purpose-, identical; the range in the hydrocarbon series is 21'. As Cady emphasizes, this is to be expected in view of the extraordinarily lo^ molecular attractive forces in fluorocarbons. The knowledge of boiling point of incompletely fluorinated heptanes is important for the purification of @-heptanes. Boiling points of hydro-@-heptanes lie above the value for C7Fm and also C7HI6. The semihj-drofluoroheptanes (i.e., C7FsHs) should boil around 150' C. Evidently hydrogen bonding is responsible for this phenomenon. Figure 2 illustrates the change in boiling point with number of substituting hydrogen or fluorine atoms,
_~_____--
'4
5
6
7
8
3
0
1
NUMBER O F C A T O M S I N M O L E C U L E
-i
2
1
3
Figure 4. Densities of Fluorocarbon6
REFRACTIVE INDEX .$SD IIOLlse. -1.I-.,Itept. from Dept. of Phz-sics, Columbia Vniv., t o L p i a n Briggs, Natl. Bur. Standards, June 25, 1941, p . 15 S.A.51. Lahs., Rept. A-211 (July 1912). Crosse, -1.V.. and Cady, G. H., S.d.51. Labs., Rept. A-312 (Sept. 1942). Grosse. .1.\-., and Linn, C. B., J . Am. Chem. SOC.,64, 2289-92 (1942). Grosse, A . T., Wackher, 11. C., and Linn, C . B., J . I'hys. Chem., 44, 290 (1940). Heline, -1.L., and Iluh, R. P., SJxlposiufn oil l'luorinc Chemistr?., .1.C.S., Chicago, 1946. Henne, A . L., and Zimnierschied, TV. J., I t i d . Ipatieff, V, N., and Grosse, A. I-,,J . Am. Chem. Soc., 58, 915 (1936). Brode, W. It., and Henne, A. L., Ihid.,56, 1726 Locke, 1;. G., (1934). 1 I r B e e anti Beclitol, 1x1.ESG.CHEM.,3
OF Y @ - C Y C L O H E X , LI SS EORG.LSIC ~ T A B L EIV. S O L U B I L I T SOLVESTS
(Boiling point, 45.2-53.4O C . ; solid t o about 9 0 5 zt rooiii reiiiperature' nk' of fraction used, 1.2622)
7-n::
Y
of:--Upper layer satd. with
.ippr ox. --AIID of:-5: CRFI? Pure Pure Dia?olved Cc. Solvent, Cc. solvent COFI? Solution liquid> a t 27' C . 1,3540 1.3470 0 0070 0 . 0920 Acetone, 2 1,4389 1.4060 0.03'29 0 1767 CHClab, 2 Benzenec, 2 0 0045 0 . 2312 1 ,4934 1.4889 0 0013 0 . 1927 1 4545 1 4532 CClIfI. 2 Trichloroethylenee, 2 1 ,4715 1 . 4 7 0 9 0.0006 0 "093 Completely niiscible a t ''70 c . C t her (CgHs)20 Completely miscible a t -.,1-0 a n d 0' c6frIj-cFd a In?oluble in water and methanol. b Completely miscible on heating t o about 50' C. c Solubility increases on warming t o 50° C . , although t w o layer; reiliain; no cooling, turbidity i n both layers. d Seuarated into two layers a t 0' C . : completely niscible at 27' C.;
C6FI?,
ny
'
and Wojcik, Ihid., 39, lch, Rohh, and Sgeyer,
5,~1.3657.
Completely miscible on warming to about 50" C. f 0.7% solubie a t 0' C.; corripletely miscible :if 27' C e
TABLE V. S O L U B I L I OF T YQ-WHEPTASE ASD H Y D R O - @ - H E I > T A S E ~ Temp.*
C.
%-Heptane0
0
-78
Solubility, G.:C. of Solvent I n anhydrous HF I n Hd) 3.14 0 23 0.4 ...
Trihydro-+-heptane (b.p. 121.6-130.0° C.) 0 10 Monohydro-*-heptane (b.p. 90-122O C . ) 25 ... 0.3 0 The solubility of *-heptane i n anhydrous H F is small but not negligib!e. It is significant t h a t trihydro-*-heptane is much more, soluble. I n I t a presence t h e solubility of *-heptane is increased, a n d this fact should be taken into account in recovering t h e latter from t h e reaction products.
...
5IcBee. Liiiclgren, and Ligett, Ihid.,39, 378 (1947). h1cHee. Schrej.er, Barnhart, Evans, Van Dyken et al., Ibid., 3 9 , : W 5 : McBee, Hotten, Evans, Alherts, Welch, Ligett, Pclireyer. and Krantz. Ibid.,39, 310 (1947). lIiller, Dittmaii, I I , , and Lewis, I:. E . , IiJid.. 3 8 , 670-7 (1946). Ruff, 0 . .d n g e i c . C'hem., 46, 739 (1933). Ruff, O., mid Breitichneider, O., %. anorg. Chtm., 210, 173 (1933). Sinionr. J . II., and Block, L. P., J . A m . Chem. SOC.,6 1 , 2962 (1939).
PRESESTED before t h e Synlpoaium on Fluorine Chemistry an paper 55, Division of Industrial and Engineering Chemistry, 110th Sleeting of . ~ E P . I C A S C H m f r c . h L SOCIETY, Chicago, Ill. T h e basis for this paper is t h e original report (9) submitted under OEce of Scientific Research and Developnient Contract OEAIsr-412. Additional d a t a disclosed during t h e cessions of the Symposium on Fluorine Chemistry are included where arailable. The \%-ark described in this paper is covered also in a comprehensive report of work with fluorine and fluorinated compounds undertaken in connection with t h e M a n h a t t a n Project. This report is soon to be published as Volume I of Division V I 1 of t h e M a n h a t t a n Project Technical Series.
