J. Am. Chem. Soc. 1998, 120, 7117-7118
The Thermal Decomposition of Perfluoroesters
7117
Koichi Murata,† Hajimu Kawa,‡ and Richard J. Lagow*,†
Department of Chemistry and Biochemistry
The UniVersity of Texas at Austin
Austin, Texas 78712-1167
Exfluor Research Corporation, 2350 Doublecreek DriVe
Round Rock, Texas 78664
ReceiVed March 5, 1998
Certain hydrocarbon esters are known to decompose into
carboxylic acids and olefins at elevated temperatures. Mechanistic
studies revealed that the decomposition proceeds intramolecularly
via the transition state TS-1 with the migration of one of the
â-hydrogen atoms.1
Figure 1. Prepared perfluoroesters.
Table 1. Conditions, Products, and Yields of the Decomposition
Reaction of Perfluoroesters
This knowledge led to the development of new thermally stable
synthetic oils based on hydrocarbon esters which do not have
â-hydrogens in the alkoxy group.2 Perfluorinated esters, which
do not have hydrogen atoms to cause the above-mentioned
intramolecular reactions, can also be considered to be thermally
stable. In this Communication, we wish to report that certain
perfluoroesters do decompose at elevated temperatures in a fashion
quite different from hydrocarbon esters.
Currently, perfluoroesters have become important intermediates
in the recent commercial technology to produce various perfluo-
rocarboxylic acids in large quantities. The technology involves
the direct fluorination of hydrocarbon esters in a liquid-phase
fluorination system.3-5 One of the most significant advantages
of this technology is that very pure, isomer-free perfluoroesters,
which are further hydrolyzed to perfluorocarboxylic acids, can
be prepared in high yields.
Various perfluoroesters were prepared from corresponding
hydrocarbon esters by the direct fluorination technique above.
The perfluoroesters which were prepared are shown in Figure 1.
The fluorination was carried out according to the previously
published procedure,5 and the obtained perfluoroesters were
carefully purified by distillation under vacuum. Typically, the
direct fluorination was carried out by slowly feeding a solution
of approximately 5 g of appropriate hydrocarbon ester in 200
mL of 1,1,2-trichlorotrifluoroethane over 4 h into a reactor charged
with 500 mL of 1,1,2-trichlorotrifluoroethane. Simultaneously,
a 20% F2/He gas mixture (500 mL/min) was fed into the reactor
at 25 °C. In the case of perfluoroester 6, 100 g of sodium fluoride
powder was added to the reactor as a hydrogen fluoride scavenger
to protect the ether linkages. The other perfluoroesters were
obtained in good yields (>70%) without sodium fluoride.
a Yield not available. b Recover 7 (27%).
Perfluoroester 8 was also prepared from perfluorododecanoyl
chloride and sodium perfluoro-tert-butoxide.6
The thermal decomposition was performed in a small Pyrex
glass distillation apparatus under a dry argon atmosphere.
Extreme care was taken to prevent the purified perfluoroesters
from being exposed to moisture during the transfer to the
apparatus. The reaction vessel was carefully heated using a
heating mantle to allow the volatile products to distill out slowly.
The condition of the decomposition was found to depend on
the number of fluorine atoms located at the R-position of the
alkoxy group. The decomposition temperatures of the perfluo-
roesters are summarized in Table 1. All the perfluoroesters which
had two fluorine atoms at the R-position (1-6) immediately
decomposed over a narrow range of temperatures (232-254 °C).
It these cases, the decomposition temperature does not depend
very much on the size or the structure of the perfluoroester.
Perfluoroester 7, which has a branching at the R-position, slowly
decomposed at 224 °C into perfluorohexanoyl fluoride and
perfluoro-2-undecanone, while perfluoroester 8, which has no
fluorine atoms at the R-position, showed no signs of the
decomposition after being refluxed (235 °C) for 24 h.
† The University of Texas.
‡ Exfluor Research.
(1) Taylor, R. In The Chemistry of Functional Groups, Supplement B, The
Chemistry of Acid DeriVatiVes; Patai, S., Ed.; John Wiley & Sons: Chichester,
UK, 1979; Part 2, Chapter 15.
(2) Randles, S. J. In Synthetic Lubricants and High-Performance Functional
Fluids; Shubkin, R. L., Ed.; Chemical Industries 48; Marcel Dekker: New
York, 1993; p 41.
(3) Lagow, R. J.; Margrave, J. L. Prog. Inorg. Chem. 1979, 26, 161.
(4) Lagow, R. J. In Kirk-Othmer Encyclopedia of Chemical Technology,
4th ed.; Howe-Grant, M., Ed.; John Wiley & Sons: New York, 1994; Vol.
11, p 482.
(5) Bierschenk, T. R.; Juhlke, T. J.; Kawa, H.; Lagow, R. J. U.S. Patent
5,093,432, 1992.
To explore this decomposition reaction further, AM1 semiem-
pirical calculations7 were performed using a very simplified model
compound, perfluoro(ethyl acetate) (9), as shown in Scheme 1.
(6) De Pasquale, R. J. J. Org. Chem. 1973, 38, 3025.
(7) Dewer, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P. J. Am.
Chem. Soc. 1985, 107, 3902.
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Published on Web 07/03/1998