EPA-650/4-74-010
April 1974
Environmental Monitoring Series
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EPA-650/4-74-010
SYNTHESIS OF
TRIFLUOROMETHYLSULFUR PENTAFLUORIDE
(CF3SF5)
by
Edward A. Tyczkowski
Armageddon Chemical Company
431 Salem Street
Durham, N. C. 27703
Contract No. 68-02-0680
Project No. FY 72
Program Element No. 1AA010
EPA Project Officer: Andrew E. O'Keeffe
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D. C. 20460
April 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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1
Table of Contents
Page
1 .0 Introduction 2
2.0 Summary 3
3.0 Discussion 4
4.0 Experimental 8
4. 1 Preparation of Bts(trifluoromethyl)disulfide 8
4.2 Safety Note 8
4. 3 Preparation Trifluoromethylsulfur Pentafluoride 9
4.4 Vent Gas Combustor 10
4.5 Analysis of CF 3 SF 5 11
5.0 References 12
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2
1.0 Introduction
The object of this work was to prepare 100 lb. of trifluoromethylsulfur
pentafluoride (CF 3 SF 5 ), which was to be tested to determine its potential as
a meteorological tracer. The gas was to be delivered in lots of 10 lb. more
or less and was to meet the following quality requirements using thermal
conductivity gas chromatographic analysis:
SF 6 Less than 10% of the amount of CF 3 SF 5 present
SF 4 Less than 0.01% of the amount of CF 3 SF 5 present
SF 2 Less than 0.01% of the amount of CF 3 SF 5 present
HF Less than 0.01% of the amount ofCF 3 SF 5 present
CF 4 Less than 0.01% of the amount of CF 3 SF 5 present
CH 3 SH Less than 0.01% of the amount of CF 3 SF 5 present
CS 2 Less than 0.01% of the amount of CF 3 SF 5 present
In producing the gas every possible precaution to minimize the release
of CF 3 SF 5 to the atmosphere was to be made.
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2.0 Summary
A quantity of 100 lb. of CF 3 SF 5 was prepared by the cobalt trifluoride
fluorination of bis(trifluoromethyl)disulflde (CF 3 SSCF 3 ). It was purified by
alkaline sulfite scrubbing and fractional distillation to meet the quality
requirements. Precautions were taken to minimize release to the atmosphere,
but about 2 lbs. were lost due to a leaking cylinder valve. Otherwise, there
were no losses of any consequence.
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3.0 Discussion
There were three known methods available to u.s at the start for the
preparation of CF 3 SF ; fluorination of CS 2 or CH 3 SH by cobalt trtfluortde (1),
by electrolytic fluorination (2), or by direct fluorination (1,3). Cobalt trifluoride
is a solid which Is readily entrained in a gas stream causing plugging of the
reactor. It has to be regenerated by fluorine periodically. The process is
generally messy and difficult to operate, and of poor yield. Electrolytic
fluorination involves the use of liquid HF as the electrolyte and is extremely
hazardous to work with, even more so than fluorine itself in some respects.
The process is tricky to operate and control, requires cooling of the cell, and
is generally a difficult process, although yields in some cases are quite high.
Direct fluorination is a fairly simple straightforward gas reaction, and with a
jet reactor (4,6) the yields can be quite good. Fluorine is available in cylinders
and is much easier to use now than formerly, although It still requires considerabi
care. Direct fluorination, therefore, appeared to be the most generally suitable
method available at the start.
Methyl mercaptan, dimethyl sulfide, and carbon disulfide have all been
reacted with fluorine to prepare CF 3 SF 5 (l,3):
CH3SH + 6F2 = CF3SF5 + 4HF
CH3SCH3 + 9F2 = CF3SF5 + CF4 + 6HF
CS2 + 7F2 = CF3SF5 + SF6
Methyl mercaptan requires the least amount of fluorine. The other two require
cleavage of a C-S bond, which would certainly occur in a poorly controlled
reaction. In a well controlled reaction, however, such as provided by a jet
reactor (4,6) less cleavage should occur and the yield of CF 3 SF 5 should
decrease. Under optimum conditions, therefore, methyl mercaptan should give
the highest yield for a given amount of fluorine.
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5
The reactor used in the original preparation of CF 3 SF 5 was a metal
packed cylinder, which gave a yield of 10% (1). SimIlar reactors also gave
low yields of similar perfluoro-compourids (3,5,6). The jet reactor, however,
has given yields of over 80% in some cases (4). Therefore, it was expected
that a well controlled reaction using a jet reactor would give fairly high
yields of CF 3 SF 5 from methyl mercaptan.
For the above reasons, therefore, we proposed to prepare CF 3 SF 5 by
the direct fluorination of methyl mercaptan using a jet fluorination reactor.
Such a reactor -was constructed of copper tubing and readily available
commercial fittings. It was tested by fluorinating propane, since we knew from
previous experience that C 3 F 8 could be made in high yield in this manner:
C 3 H 8 + 8 F 2 = C 3 F 8 + 8HF.
Also, this reaction allowed us to check our entire reaction, scrubbing and
condensing system for leaks without fear of losing any CF 3 SF 5 to the atmosphere.
Accordingly, several runs were made with propane, varying flow rates,
temperatures, fluorination and dilution ratios until the optimum conditions were
found for preparing C 3 F 8 . Under these conditions C 3 F 8 could be prepared in
about 85% yield at about 2400 at rates of about 0.7 lb./hr. The reactor,
therefore, performed exactly as expected.
Next, we tried to fluorinate OH 3 SH under similar conditions, but the
results were completely unexpected. Whereas the C 3 H 8 /F 2 flame was easily
blown out into a homogeneous gas phase reaction, the CH 3 SH/F 2 flame could
not be blown out at the highest jet velocities arid dilution ratios we were
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able to obtain. The yield of CF 3 SF 5 was 15—20%, which Is a considerable
improvement over the original preparation (1) but still not enough for a
practical manufacturing process. Numerous variations in the Jet design and
operating conditions were made, all without significant improvement in the
yield. Both CS 2 and CF 3 SSCF 3 were also used as starting materials, but in
neither case was any significant improvement in the yield of CF 3 SF 5 made.
Direct fluorination, therefore, was abandoned as a preparative method, and
other possible methods were investigated.
The C0F 3 preparation of CF 3 SF 5 from CS 2 or CH 3 SH was not attractive
because the yields were still too low for a practical process (1). The reaction
of CF 3 SSCF 3 with CoF 3 , however, was reported to give CF 3 SF 5 (7) and looked
more promising, since 3/8 of the required fluorine was already present.
Accordingly, we made a small C0F 3 reactor and tested the reaction. It was
found that CF 3 SF 5 was formed in about 70% yield at lOO 0 and that by raising
the temperature to 170 it could be converted to CF 3 SF 5 . These results were
quite satisfactory, and this method, therefore, was chosen for scale up.
A conventional C0F 3 reactor of the rotating paddle wheel type was built
and used to prepare CF 3 SF 5 :
CF 3 SSCF 3 + 1OCoF 3 2 CF 3 SF 5 + lOCoF 2 .
The CF 3 SSCF 3 was prepared by the NaF fluorination of CC1 3 SCL in Suifolane (8),
and was fed into the C0F 3 reactor as gas. The temperature of the reactor rose
from about 600 at the entrance to a maximum of about 1600 near the exit. Under
these conditions we were able to prepare CF 3 SF 5 in 66% yield at a rate of about
1/2 lb./hr. The crude product was scrubbed with alkaline sulfite solution and
condensed by dry ice. Distillation of the crude product in a low temperature
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still gave pure product which met the quality requirements without difficulty.
The pure CF 3 SF 5 was collected In steel cylinders and shipped In increments
of about 10 lb. until the requIred 100 lb. was prepared.
The requirement to minimize release to the atmosphere was met by
installing a heated bath at the scrubber exit to degas the waste scrubber
solution and by passing all waste gas streams from the reactor, gas
chromatograph, traps, cylinders, etc. to a vent gas combustor where they
were burned to products such as HF, SO 2 and CO 2 .
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4.0 Experimental
4. 1 Preparation of Bis(trifluoromethyl) disulfide
CF 3 SSCF 3 was prepared by fluorinating CC1 3 SC1 with NaF in Sulfolane following
the method of Tullock & Coffman (8). C d 3 SC1 (9) was added gradually to a stirred
suspension of NaF in anhydrous Sulfolane, the mixture was heated gradually to
0
about 200 over about 6 hours, arid the gaseous product was collected in a
dry ice cooled trap. Distillation of the crude product through a 3 X 1” ID
Helipak column with a dry ice cooled head gave CF 3 SSCF 3 as the major product,
0
b. 34 , which was used without further purification in the next slep. In a
typical run in a 22 1. flask, 5 kg. CCI 3 SCI were fluorinated to 720 gm. of the
disulfide for an average yield of 27% in fair agreement with the original work (8).
It was important to maintain anhydrous conditions for this reaction. The
0
solvent was dried over CaH 2 , and the NaF was baked in an oven at 150 overnight.
Even with these precautions, however, there was considerable etching of the glass
apparatus, and numerous flasks and condensers were destroyed during this work.
4.2 Safety Note
Great care should be taken to avoid exposure to any of these intermediates.
CCI 3 SC I if very toxic (9) and is a potent lachrymator. CF 3 SSCF 3 is reported to
be extremely toxic as well as CF 3 SC I(10) which is the major by-product of the
reaction. No doubt there are other toxic materials in the reaction mixture.
Particular care should be taken in disposing of the reaction residue. It is
highly lachrymatory and contains many toxic materials. It should be drowned
in water and flushed away as rapidly as possible.
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4 3 PreparatIon of Tr1f1uoromethyls dfur Penta fluoride
CP 3 SF 5 was prepared by fluorirtating CF 3 SSC1’ 3 in a CoF 3 reactor of
conventional design as described by Stacey & Tatlow (11). Our reactor was
made of a section of steel pipe 6” ID X 40” long and held a charge of about
36 lb. CoF 3 which was stirred with steel paddles. Temperature was controlled
by heating tapes and cooling coils wrapped around It arid the temperature was
monitored by 6 thermocouples attached to a 6-point temperature recorder. The
temperature increased along the length of the reactor from about 600 at the
entrance to about l60 near the exit. The CF 3 SSCF 3 was fed th gas phase
from a steel cylinder heated to about 600 in a water bath. The gaseous
product was scrubbed with alkaline sulfite to remove HF, F 2 , OF 2 , SF 4 , SF 2 ,
and any other di- or tetravalent sulfur compounds. The countercurrent scrubber
consisted of a 10’ long section of 3” polypropylene pipe packed with 5/8”
plastic pall rings and mounted vertically. Scrubber solution of 5% NaOH and
2% Na 2 SO 3 was pumped from a 52 gallon polyethylene tank to the top of the
scrubber and was controlled by a needle valve and rotameter. The exit liquid
passed through a boiling water bath to degas it to prevent loss of CF 3 SF 5 to the
atmosphere, then through a phase separator to collect any high boiling products,
and finally to the drain. The product gas entered through a 3/8” ID Teflon
tube near the bottom and exited at the top.
The scrubbed product gas was led directly to a dry Ice cooled condenser
of the cold finger type, and the liquefied product was collected in a 5 1.
distilling flask. After storing overnight in a dry ice chest the flask and its
contents were transferred directly to the still.
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The product was purified by distillation through a 3’ X 1” ID Helipak
column with a dry ice cooled head. The distillate was collected and packaged
in steel cylinders. In a typical run, about 500 gm. of CF 3 SSCF 3 was
fluorinated over a period of 3 hrs. to give about 700 gm. CF 3 SF 5 for an
average yield of about 65%.
The CoF 3 was regenerated by passing in elemental F 2 at 1500_2500.
One difficulty which caused considerable trouble initially was the
continual plugging of the scrubber inlet by dust carried over from the reactor.
This was overcome by installing a 12,000 volt electrostatic dust precipitator
at the reactor exit as recommended by Fowler et al (12). We agree with their
statement that such a dust precipitator is a necessity for smooth operation.
4.4 Vent Gas Combustor
The combustor consisted of a shielded pre-mixed gas flame with a
jet-pumped air supply. Into this air supply was fed all vent gases from the
reactor, scrubber, still, gas chromatograph, etc. Any waste CF3SF5 from
cylinders or analytical samples was also vented into this air supply. In
this way all waste CF 3 SF 5 had to pass through the flame front of a very hot
gas flame and was burned to HF, CO 2 . SO 2 , etc.
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Note: Results are given as percent peek area without corrections for thermal
conductivity differences.
* Sample lost.
4.5
Ana’ysis of CF 3 SF 5
1
0.9
0.4
98.2
Liquid phase samples were taken from the shipping
cylinders and
analyzed by gas chromatography using a 6’ X 1/4” OD silica
gel column
at
2000. The results are summarized in the following table:
ANALYTICAL RESULTS
Shipment No. L 4 5* 6 1
IQ.
.11
Amount, lb. 8.0 10.7 9.6 10.5 10.8 9.6
9.9 9.7
10.2
10.1
SF 6 , % 1.2 0.8 0.8 — 0.9 1.3
1.0 0.6
0.8
0.9
CF 3 SF 5 f % 97.3 98.6 98.0 — 96.8 97.3
97.7 97.7
98.9
98.8
CF 2 C I 2 , % — 1.3 — 0.4 — 1.2 1.0
0.8 1.2
Unknown A, % — 0.3 0.6 0.8 — 1.2 0.4
0.5 0.5
0.3
0.3
Unknown B, %
Unknown C, %
Unknown D, %
! tTt’ t’ 01
F0
0.5
0.3
0.3
0.2
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5.0 References
1) G. A. Silvey & G. H. Cady, J. Am. Chem. Soc. 72,3624 (1950)
2) S. Nagase, Fluorine Chemistry Reviews, Vol. 1, Marcel Dekker
(New York), 1967, pp. 77—106
3) E. A. Tyczkowski & L. A. Bigelow, J.Am. Chem. Soc. 75, 3523 (1953)
4) E. A. Tyczkowski & L. A. Bigelow, J. Am. Chem. Soc. , 3007 (1955)
5) L. A. Bigelow, Chem. Rev. 4Q, 51 (1947)
6) J. M. Tedder, Advances in Fluorine Chemistry, Vo’. 2,
Butterworth & Co. (London), 1961, pp. 104-137
7) G. A. R. Brandt, H. J. Emeleus & R. N. Haszeldine, J. Chem.
Soc. 1952 . 2198
8) C. W. Tullock & D. D. Coffman, J. Org. Chem. 2016 (1960)
9) Stauffer Chemical Co.
10) PCR, Inc., Gainesville, Florida
11) M. Stacey & J. C. Tatlow, Advances in Fluorine Chemistry,
Vol. 1, Butterworth & Company (London) 1960, pp. 166-19 8
12) R. D. Fowler, et al, Preparation, Properties and Technology of
Fluorine and Organic Fluoro - Compounds, Ed. Slesser and Schram,
McGraw-Hill, (New York) 1951.
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TECHNICAL REPORT DATA
(Please read inwuctions on the rei erse before coin pleting)
1. REPORT NO. 2
EPA-650/4-74-010
3 RECIPIENT’S ACCESSIOFNO.
4. TITLE AND SUBTITLE
SYW11- SIS OF TRIFLUOW METHYLSULFUR
PENTAFLUORIDE (CF 3 SF 5 )
5 REPORT DATE
April 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Edward A. Tyczkowski
8. PERFORMING ORGANIZATION REPORT NO.
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Armageddon Chemical Company
431 Salem Street
Durham, NC 27703
10 PROGRAM ELEMENT NO.
LAAO1 O
Ii CONTRACT/GRANT NO
68-02-0680
12 SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
National Environmental Research Center
Chemistry and Physics Laboratory
Research Triangle Park, North Carolina 27711
13 TYPE OF REPORT AND PERIOD COVERED
Final 8/24/72 to 1/12/74
14SPONSORING AGENCY CODE
16. SUPPLEMENTARY NOTES
16.
One hundred pounds of CF 3 SF 5 were synthesized via the route:
2000
CCl 3 SC + Naf’ Sulfolane
(B) CF 3 SSCF 3 +
CF 3 SSCF 3 + NaC1
Yield was approximately 27% in step A and 65% in Step B.
Report includes experimental details of the above, together with a synopsis of
res .dts obtained with several alternate syntheses of the same product.
This report was submitted in fulfillment of Contract No. 68-02—0680 by
Armageddon Chemical Company under the sp ’onsorship of the Environmental Pro1 ection
Agency. Work was completed as of January 12, 1974.
I?. KEY WORDS AND DOCUMENT ANALYSIS
— — DESCRIPTORS
rrifluoromethylsuifur Pentafluoride
obalt Trifluoride
us (trifluoromethyl) disulfide
1 luorinat ion
b.IDENTIF IERS/OPEN ENDED TERMS
C. COSATI Field/Group
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‘
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Unclassified
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17
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Unclassified
22. PRICE
(A)
C0F 3 l70 , CF 3 SF 5 +CoF 2 .
(PA Form 2220-1 (9-73)
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