Full text of DOI:10.1016/S0022-1139(00)81696-6

112
Replacement of X by R corresponds to the possible mechanisms which
might apply to reactions in the presence of excess
The formation of
compounds could arise
in the following manner:
F
+
+
R
intra- or inter-
molecular exchange]
2 ----
[R f CF 2CR 2
[
The fact that compounds of the type
are not prepared could be
due to the increasingly unfavorable steric requirements, or a much greater
tendency for (or to yield
to yield
and for
(or
Presumably the steric requirements for attack of an ethyl Grignard
upon an ethylated intermediate are too great to allow the formation of the
olefins.
Attempts to trap a carbene by the use of olefins
methylethylene and cis-but-2-ene) or triethylsilane were unsuccessful.
Although fluorocarbenes have been successfully trapped by these means
failure to trap a carbene, however, does not rule out a carbene
mechanism since X-MgF (or
olefins or Carbene insertion into Mg-X bonds has been reported
and the order of reactivity of carbene insertion into metal-halogen bonds
was M-I M-Br M-Cl M-F No examples have been reported of
carbene insertion into an M-F bond.
The mechanistic schemes presented above may be likened to those
may be a better carbene trap than
suggested by
for the products they obtained from the reaction of
with or
halomethanes.
Hydrolysis of aliquots of ethereal solutions of
those to which or excess had been added) prior to thermal
and
and Villieras
to account
or
reagents
Of course, o-elimination was not possible with these
or
(even
decomposition (ca. -15 “C) provided a nearly quantitative amount of
This, coupled with the rapid rate of decomposition above -10
indicates that no stable intermediates are formed.

113
Experimental
Infrared spectra were obtained with a Beckman IR-12
meter. Analytical VPC was performed on an F M Model 500 Gas
graph using 3 m X 6 mm copper columns packed with either 15% SE-30 or
15% QF-1. Preparative VPC was performed on a Hewlett-Packard Model 776
Gas Chromatograph using 3.6 m X 1.8 cm stainless-steel columns packed
with 15% SE-30 or 15% QF-1 Chromosorb P, 60 80 mesh. Mass spectra
were recorded on an Atlas CH-4 spectrometer at 70
were obtained using a Varian A-60 instrument with TMS as an internal
standard, and NMR spectra were measured with a Varian HA-100
NMR spectra
instrument at 94.075 MHz using trichlorofluoromethane as the internal
standard.
General procedure
Into an oven-dried, nitrogen-flushed flask was placed the perfluoroalkyl
iodide and the required volume of
dried pentane) solvent as indicated in Table 1. The solution was cooled to
-78 and the alkyl Grignard reagent was added a syringe. Either the
ether or THF (or
cooling bath was retained and the reaction mixture was allowed to warm to
room temperature over a 6 8 h period, or the bath was removed in which
case the reaction mixture warmed to room temperature during 1 2 h
(similar results were obtained by either procedure). After stirring at room
temperature for the indicated time (Table
the reaction mixture was
hydrolyzed with 3
washed with water and dried over
hydrous
Distillation provided the crude products which were then
obtained in a pure state by preparative VPC (Tables 2 and 3). The boiling
points of
and
were too close to allow any separation
by distillation.
Magnesium bromide was prepared in ether by the reaction of ethylene
bromide with magnesium. Magnesium iodide was obtained from the reaction
of iodine with magnesium in ether at room temperature. The perfluoroalkyl
iodides were purified by spinning-band distillation of a telomer iodide
mixture of
and
obtained from the Thiokol
Corporation.
Acknowledgements
Support of this research by the National Science Foundation
34632) is gratefully acknowledged. We also thank Drs. R. H.
F. J. Marshall, 0. L. Chapman and E. S. Lo for assistance.
References
18; A. L. Henne
1) 35
73 (195
1 A. L. Henne and W. C. Francis, J . Amer. Chem.
and W. C. Francis, J . Amer. Chem. 75 (1953) 992.
2 R. N. Nature (London), 168 (1951) 1028.