J . Org. Chem. 1996, 61, 9605-9607
9605
In the search for an alternative route to the important
intermediates for many fluorochemicals, perfluoroalkyl
iodides,15 a new process for the preparation of RfI has
been discovered. This paper presents the results of the
reaction of fluoroolefins with solutions of the readily
available iodine monochloride in AHF.
Con ju ga te Electr op h ilic Iod oflu or in a tion of
F lu or oolefin s†
Viacheslav A. Petrov* and Carl G. Krespan
DuPont Central Research and Development,
Experimental Station, P.O. Box 80328,
Wilmington, Delaware 19880-0328
Resu lts a n d Discu ssion
Received J uly 9, 1996
The reactivity of iodine monochloride in iodofluorina-
tion of fluoroolefins depends significantly on the acidity
of the reaction media. For instance, reaction of ICl with
tetrafluoroethylene (TFE) in 99% anhydrous hydrogen
fluoride in the absence of catalyst produces a mixture of
ClCF2CF2I (1) and C2F5I (2), isolated in 48% and 19%
yields, respectively.16 The minor component in the
Conjugate electrophilic addition to a double bond of an
olefin is a process in which two fragments of halogen
fluoride, not connected to each other in the starting
material, are added across the double bond:1
(1)
C
C
A–C C–Z + X–Y
A–X +
+ Y–Z
ICl + CF2dCF2 25 °C, 16 h8 ClCF2CF2I + CF3CF2I (2)
HF
(1) 48%
(2) 19%
Many such reactions are known and are summarized in
several reviews.1-3 In the addition of halogen fluoride
across a hydrocarbon double bond, a typical reagent
combination includes an N-halogen compound (N-halo-
succinimides or hexachloromelamine) and anhydrous HF
(AHF) or another source of HF, such as the complex HF/
pyridine.4,5 Addition of halogen fluorides across the
electron poor double bond of fluoroolefins is generally
carried out using more powerful electrophiles, such as
mixture (iodide 2) is a product of conjugated iodofluori-
nation of TFE, but the major product (iodide 1) is the
result of a well-known thermal reaction of ICl with the
olefin.17
The presence of Lewis acids drastically changes the
course of this reaction, and the yield of desirable pen-
tafluoroethyl iodide (2) under the same conditions can
be increased to up to 91% by addition of 15-25 mol % of
boron trifluoride. In sharp contrast to the data reported
in refs 13 and 14, this reaction proceeds rapidly at
ambient temperature and produces only trace amounts
of the byproduct 1 (Table 1, entries 2, 3).
ClF2 or a combination of BrF3/Br2
or IF5/I2 as a
6-8
6,9
“stochiometric equivalent”2 of BrF or IF.
Recently it was found that the solution of an N-halo
compound in a superacid such as HOSO2F is an effective
reagent for conjugated addition of the elements X+ and
OSO2F- (X ) Cl, Br) across the double bond of terminal
fluoroolefins.10 Although this reaction does not involve
the formation of halogen fluorosulfate as an intermediate,
it is a good alternative route for the preparation of
corresponding fluorosulfates, otherwise only available by
addition of stable but potentially hazardous hypohalites
(XOSO2F) to fluoroolefins.11
ICl + CF2dCF2 25 °C, 16 h8
HF/BF3
ClCF2CF2I + CF3CF2I (3)
(1) 1%
(2) 78-91%
Only certain Lewis acids capable of significantly in-
creasing the acidity of hydrogen fluoride, such as SbF5,
TaF5, and NbF5, effectively catalyze the iodofluorination
of TFE. The lower yield of 2 with TaF5 (Table 1, entry
4) as a catalyst is probably due to low solubility of this
compound in HF.18 On the other hand, catalysts such
as AlCl3 and ZnCl2 are not active in this reaction, and
no significant difference in the ratio of 1 to 2 over that of
the control experiment (without the catalyst) was ob-
served in the reaction of TFE with ICl at 25 °C (Table 1,
entries 1, 6, 7).
The combination of X2/protic acid (HF2 or HOSO2F12
)
is usually not effective for this reaction, although it was
reported that iodine in the presence of certain oxidizing
agents in AHF is efficent for the synthesis of C2F5I and
i-C3F7I at 140-160 °C.13,14
† Publication No. 7384.
* Corresponding author.
(1) German, L. S.; Knunyants, I. L. Angew. Chem., Int. Ed. Engl.
1969, 8, 349.
(2) Bogouslavskaya, L. S.; Chuvatkin, N. N. In New Fluorinating
Agents in Organic Synthesis; German, L. S., Zemskov, S., Eds.;
Springer-Verlag: New York, 1989; pp 140-196, review on application
of halogen fluorides in organic synthesis.
(3) Belen’kii, G. G.; German, L. S. In Chemistry Reviews, Section B;
Vol’pin, M. E., Ed.; Soviet Scientific Reviews; Harwood Academic
Publishers GmbH: New York, 1984; pp 183-218.
(4) Olah, G.; Nojima, M.; Kekekas, I. Synthesis 1973, 779.
(5) Hamman, S.; Beguin, C. G. J . Fluorine Chem. 1979, 13, 163.
(6) Chambers, R. D.; Musgrave, W. K. R.; Savory, J . J . Chem. Soc.
1961, 3779.
(7) Yuminov, V. S.; Pushkina, L. N.; Sokolov, S. V. Zh. Obsh. Khim.
1967, 37, 375.
(8) Lo, E. S.; Readio, J . D.; Iserson, H. J . Org. Chem. 1970, 35, 2051.
(9) Hauptschein, M.; Braid, M. J . Am. Chem. Soc. 1961, 83, 2383.
(10) German, L. S.; Savicheva, G. I. Izv. Akad. Nauk SSSR Ser.
Khim. 1984, 479.
(11) Fokin, A. V.; Studnev, Yu. N. In Chemistry Reviews, Section B;
Vol’pin, M. E., Ed.; Soviet Scientific Reviews; Harwood Academic
Publishers GmbH: New York, 1984; pp 47-96.
(12) Fokin, A. V.; Studnev, Yu. N.; Rapkin, A. I.; Krotovich, I. N.;
Tamarinov, A. S.; Verinikin, O. V. Izv. Akad. Nauk SSSR Ser. Khim.
1985, 2298.
The reaction of chlorotrifluoroethylene (3) and ICl also
proceeds under mild conditions and leads to a mixture
of two isomeric iodides (4a ,b) in the ratio 67:33:
(13) Millauer, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 929.
(14) Millauer, H. Ger. Offen. 2,061,355, 1972; Chem. Abstr. 1972,
77, 87828n; Ger. Offen. 2,100,140, 1972; Chem. Abstr. 1972, 77,
125944g.
(15) Deev, L. E.; Nazarenko, T. I.; Pashkevich, K. I.; Ponomarev, V.
G. Uspekhi Khim. 1992, 61, 40, reviews the literature on the synthesis
and reactions of perfluoroalkyl iodides.
(16) The reactions discussed in this paper are covered in part by
U.S. Patent 5,421,028, 1996, to DuPont; Chem. Abstr. 1996, 123, P
313381p.
(17) Dyatkin, B. L.; Mochalina, E. P.; Knunyants, I. L. In Fluorine
Chemistry Reviews; Tarrant, P., Ed.; Marcel Dekker Inc.: New York,
1969; Vol. 3, p 45.
(18) Olah, G. A.; Prakash, G. K. S.; Sommer, J . Superacids; J ohn
Wiley & Sons: New York, 1985; pp 33-64.
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