The reaction of difluorodioxirane with caesium trifluoromethoxide

Article abstract of DOI:10.1039/a904090k

The reaction of difluorodioxirane with caesium trifluoromethoxide in the presence of CsF forms CF₃OOC(O)F and the new compounds CF₃O(OCF₂O)(n)OC(O)F (n = 1~3); ¹³C labeling shows that the dioxirane undergoes ring opening at the O-O bond.

Full text of DOI:10.1039/a904090k

The reaction of difluorodioxirane with caesium trifluoromethoxide
Qun Huang and Darryl D. DesMarteau*
Department of Chemistry, Box 341905, Clemson University, Clemson, S.C. 29634-1905, USA.
E-mail: fluorin@clemson.edu
Received (in Corvallis, OR, USA) 17th May 1999, Accepted 19th July 1999
The reaction of difluorodioxirane with caesium trifluor-
3
omethoxide in the presence of CsF forms CF OOC(O)F and
13
3 2 n
the new compounds CF O(OCF O) OC(O)F (n = 1 ~ 3); C
labeling shows that the dioxirane undergoes ring opening at
the O–O bond.
We were able to show that the reaction occurred at the oxygen
atom of the difluorodioxirane by using 13C labeled COF
(5)].§¶
[eqn.
2
Dioxiranes are powerful oxygen transfer reagents which have
been studied extensively over the last twenty years.1 Epoxida-
tions, heteroatom oxidations and C–H insertion reactions are the
most investigated reactions of dioxiranes. The heteroatom
–3
oxidations are generally explained by an S
heteroatom lone pair (A:) on the dioxirane peroxide bond [eqn.
N
2 type attack of the
4
(1)].
A reasonable mechanistic proposal is given in Scheme 1. The
well-known trifluoromethoxy anion is first formed by the
8
reaction of carbonyl fluoride with caesium fluoride. Then an
The mechanism is based on the fact that oxygen-type
N
S 2-type attack of this anion on the dioxirane peroxide bond
occurs to give CF OOCF O , which loses fluoride to form 2,
nucleophiles catalytically decompose dioxiranes with evolution
2
9
of molecular oxygen [eqn. (2)].5
3 2
or reacts further with the dioxirane to form the new oligomeric
peroxides 3–5. The 13C distribution in the products makes it
2
clear that the predominate reaction is the attack of CF
3
O on the
dioxirane at oxygen and not at the more electropositive carbon.
10
Previously we had suggested that reaction of 1 with CsF might
2
form CF
3
OO and 2 could then be formed by reaction with
13
COF . However this path would lead to the C label in the
2
Until now, no peroxide related product has been detected in
these reactions. Our recent investigation of difluorodioxirane 1
chemistry provides direct evidence of this mechanism.
carbonyl group, contrary to what is observed. The small amount
of 13C present in the carbonyl carbon arises from secondary
reactions of the products, which have been confirmed by
additional 13C labeling experiments. These results will be
described in a future publication.
Difluorodioxirane is one of the most stable dioxiranes
known. The first successful synthesis of 1 was based on the
reaction of its isomer fluorocarbonyl hypofluorite [FC(O)OF]
6
with ClF in the presence of CsF. † As expected, 1 is a powerful
oxidant and can undergo reactions that are typical of dioxiranes.
It readily transfers oxygen to alkenes, forming epoxides and
6
COF
2
in high yield. Beside this, little is known about the
reactivity of 1. Here we report a very unusual result from the
reaction of 1 with COF in the presence of CsF.
2
Difluorodioxirane was originally prepared by passing a 1+1
6
(
v/v) mixture of FC(O)OF and ClF over a CsF catalyst. We
have improved this method by using Cl
KHF .‡ A 1+1 (v/v) mixture of FC(O)OF and Cl
through a Teflon tube containing the new catalyst KHF
provided 1 in moderate but higher yields (30–50%) [eqn. (3)].
Also the dioxirane 1 prepared by this procedure is easily
purified by vacuum fractional condensation as a mixture of 1
2
and the new catalyst
Scheme 1
2
2
passed
2
Remarkably the 19F chemical shifts for 2–5 can be assigned
from a mixture of the compounds. The NMR data is presented
in Fig. 1 for pure 2 and 3 and for 4 and 5 taken from a mixture
of 3–5. Compound 2 is unequivocally identified by comparison
with known samples prepared by other routes. For 3–5 the
(
2
70–90%) and COF (10–30%). The mechanism of this reaction
6
is assumed to be the same as previously proposed.
chemical shifts for the CF
characteristic and show a large shift relative to CF
OCF O functions in fluorocarbon ethers. While the chemical
3
OO and the OOCF
2
OO groups are
3
O and
2
shift differences between 2–5 are small, at 188 MHz all the
signals except the C(O)F are separated and the expected peak
19
The O–O bond length in 1 is 157.6 pm, and is the longest O–
O bond ever calculated and measured. The relatively weak O–
O bond should be easily broken but to date no direct evidence
was available for this. Recent studies on the reaction of 1 with
integration for each compound is observed. Finally F bound to
7
13
12
19
C and C exhibits substantial isotopic shifts in the F NMR
1
13
C
in addition to the large JF– coupling, making it trivial to
discern the presence of 13C.
COF
2
in the presence of CsF show that dioxirane reacts by ring
A variety of other novel fluorocarbon peroxides can be
formed by related reactions with other nucleophiles and the
opening at the O–O bond [eqn. (4)].
Chem. Commun., 1999, 1671–1672
1671

the 2196 °C trap, contaminated with a small amount of COF
2
. Selected data
1
for 1: 292.4 (s), d
report of the 19F NMR data in ref. 6 is in error.
Two 500 ml ss cylinders fitted with ss valves were connected to the
F
220.7 (d, JC–F = 283.3) d
C
119.5 (t). The original
§
vacuum line through a PFA tee closed by an ss valve. The cylinders were
evacuated and one was filled with 7 mmol of fluorine gas and the other with
13
7
mmol of 13CO (99% C). At 22 °C, the cylinders valves were then opened
13
to the closed and evacuated tee in the order fluorine/ CO. After 4 h, the
contents of the two cylinders were passed through the tee into a trap cooled
to 2196 °C under dynamic vacuum. Unreacted F
the 2196 °C trap and through a soda lime scrubber. The contents of the
196 °C trap were then passed through 2140 and 2196 °C traps under
and 13CO passed through
2
2
13
dynamic vacuum to give pure COF (3.5 mmol, 50%) in the 2196 °C trap.
2
13
1
Selected data for COF
2
: d 220.7 (d, JC–F 311.3); nmax
cm 1882.1, 1208.2, 957.9, 749.5, 648.6.
2
The reactions of 1 with COF were carried out in a 150 ml ss
and 13COF
C
133.8 (t); d
F
/
2
1
¶
2
cylinder which contained 2 g of dry powdered CsF. Compound 1 (0.3 mmol)
and carbonyl fluoride (0.3 mmol) were then vacuum transferred into the
cylinder cooled to 2196 °C. The mixture was then allowed to warm to 250
°
C over 1 h and remained at 250 °C for 16–20 h. The products were
separated by vacuum fractional condensation through traps at 290, 2110,
2
130 and 2196 °C. The 290 °C fraction consisted of 3, 4 and 5 (0.03
Fig. 1 19F NMR data for 2–5 (CCl
lock, 188 MHz). Data for 4 and 5 come from a mixture of 3–5.
4
3 2
solvent, CFCl reference, external D O
mmol), the 2110 °C fraction consisted of 3 (0.03 mmol), the 2130 °C
fraction consisted of 2 (0.07 mmol) and the 2196 °C fraction consisted of
2
COF (0.3 mmol). Compounds 2–5 were identified by NMR (see Fig. 1) and
chemistry of difluorodioxirane is proving to be quite extraor-
dinary.
1
IR. Selected data for 2: d
C
122.6 (q, CF
3
, JC–F 271.6); 141.2 [d, C(O)F,
1
21
J
C–F 302.9]; nmax/cm 1874, 1254, 1209, 1153, 1005, 930, 750, 614.
We are grateful to Ausimont SPA (Italy) for financial support
of this work and to W. Navarrini of Ausimont for technical
support.
1
2
R. W. Murray, Chem. Rev., 1989, 89, 1187.
R. Curci, A. Dinoi and M. F. Rubino, Pure Appl. Chem., 1995, 67,
8
11.
W. Adam and A. Smerz, Bull. Soc. Chim. Belg., 1996, 105, 581.
4 W. Adam and D. Golsh, Angew. Chem., Int. Ed. Engl., 1993, 32, 737.
3
Notes and references
5
6
A. Lange and H. Brauer, J. Chem. Soc., Perkin Trans. 2, 1996, 805.
A. Russo and D. D. DesMarteau, Angew. Chem., Int. Ed. Engl., 1993,
†
CAUTION! The chemicals employed in this work are hazardous and
should only be used by experienced personnel familiar with the safe
handling of toxic strong oxidizers.
3
2, 905.
7
8
9
H. Burger, P. Weinrath, G. A. Arguello, B. Julicher, H. Willner, D. D.
DesMarteau and A. Russo, J. Mol. Spectrosc., 1994, 167, 607.
W. B. Farnham, B. E. Smart, W. J. Middleton, J. C. Calabrese and D. A.
Dixon, J. Am. Chem. Soc. 1985, 107, 4565.
‡
In a typical reaction a mixture of equimolar amounts (0.5–3.0 mmol) of
FC(O)OF and Cl at 23 °C were passed at reduced pressure through a Teflon
FEP tube (35 3 1 cm outer diameter) containing 20 g of pelletized KHF
catalyst. The calculated flow rate of the mixture through the tube was 0.37
2
2
D. D. DesMarteau, Inorg. Chem., 1970, 9, 2179.
3
21
cm
s . The effluent exited into a trap cooled to 2196 °C and under
1
0 A. Russo and D. D. DesMarteau, Inorg. Chem., 1995, 34, 6221.
dynamic vacuum. The gases condensed at 2196 °C were vacuum distilled
several times through traps at 2145 and 2196 °C. This procedure gave 1 in
Communication 9/04090K
1672
Chem. Commun., 1999, 1671–1672