Reactions of oxalyl fluoride with electrophiles

Article abstract of DOI:10.1016/S0022-1139(01)00496-1

The reactions of oxalyl fluoride with electrophiles in the presence of alkali metal fluoride were carried out. In the reaction with CF₃CH₂OH (Tl = CF₃SO₂) or CH₃CH₂OTf, the synthesis of di-

Full text of DOI:10.1016/S0022-1139(01)00496-1

Journal of Fluorine Chemistry 113 /2002) 97±100
Reactions of oxalyl ¯uoride with electrophiles
b
a,*
Junji Murata , Masanori Tamura , Akira Sekiya
Department for the New Refrigerant and Other Substances, Research Institute of Innovative Technology for the Earth ꢀRITE),
c/o Central 5 AIST 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
b
a
b
National Institute of Advanced Industrial Science and Technology ꢀAIST), c/o Central 5 AIST 1-1-1 Higashi,
Tsukuba, Ibaraki 305-8565, Japan
Received 6 April 2001; received in revised form 18 June 2001; accepted 10 August 2001
Abstract
The reactions of oxalyl ¯uoride with electrophiles in the presence of alkali metal ¯uoride were carried out. In the reaction with
CF CH CH OTf, the synthesis of di-ether /ROCF CF OR) and mono-ether /ROCF COF) was achieved. The
3
2
OTf /Tf ˆ CF3SO2) or CH
3
2
2
2
2
difference of the reactivities between these two compounds was discussed from the result of DFT calculations. # 2002 Elsevier Science
B.V. All rights reserved.
Keywords: Oxalyl ¯uoride; Cesium ¯uoride; 1,2-Bis/2,2,2-tri¯uoroethoxy)-1,1,2,2-tetra¯uoroethane; DFT calculation
1
. Introduction
2. Results and discussion
We have developed hydro¯uoroethers /HFEs) as alter-
natives to chloro¯uorocarbons /CFCs) and hydrochloro-
uorocarbons /HCFCs) [1]. HFEs have almost zero ozone
depleting potential /ODP) due to no chlorine atom in the
molecules [2]. Many low global warming potential /GWP)
compounds belong to HFEs.
One of the ef®cient methods to prepare HFEs is the
reaction of per¯uoroalkyl acyl ¯uoride with electrophiles
in the presence of alkali metal ¯uoride [3]. In this view-
point, oxalyl ¯uoride [4±8] is an interesting reagent
because it has two carbonyl ¯uoride groups, which can
be transformed to ether groups, in the molecule. Mono-
ether is obtained from the reaction of one of carbonyl
2.1. Reactions of oxalyl fluoride with CF CH OTf
3
2
¯
The reactions of oxalyl ¯uoride /1) with CF CH OTf /2)
3 2
1
[12] in the presence of alkali metal ¯uoride gave not only
mono-ether /3) and di-ether /4) but also 1,1,1,2-tetra¯uor-
oethane /5) /Scheme 1). After the reaction, methanol was
added to the reaction mixture to change the reactive acyl
¯uoride of 3 to methyl ester.
In this reaction, CsF is more effective than KF /Table 1,
Entries 1 and 2). It is due to the difference of the stability of
the alkoxide salts; that is, the cesium alkoxide is more stable
than potassium alkoxide [13]. Even if the reaction was
carried out with KF at high temperature, the yield and the
selectivity were still low /Table 1, Entry 3). In the reaction
using CsF for a short period, the yields of the products were
low /Table 1, Entry 4). The selectivity of products depends
on the molar ratio of 1 and 2 and CsF /Table 1, Entries 5, 6
and 7). The more 1 was added, the more 3 was obtained. To
add an excess amount of CsF was not ef®cient because a
large amount of ¯uorinated product 5 was obtained. To
prepare alkoxide in advance, 1, CsF and diglyme were
¯
uoride groups, and di-ether is obtained from the reaction
of both groups. But few reactions of oxalyl ¯uoride to give
ethers have been reported [9±11]. Moreover, the yield of
di-ether was low or moderate, and the formation of mono-
ether was not reported although it should be an intermedi-
ate of di-ether. In this paper, the synthesis of mono- and
di-ether was achieved and the effect of the electrophiles
was discussed.
1
The preparation and reactivity of 2 have been reported by Burdon
and Mcloughlin [12]. In this paper, 2 was prepared by other method
and MS and NMRdata were shown in Section 3.
*
Corresponding author. Tel.: ‡81-298-56-3822; fax: ‡81-298-56-3944.
E-mail address: jmurata@mx6.nisiq.net /J. Murata).
0022-1139ꢀ02ꢀ$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 / 0 1 ) 0 0 4 9 6 - 1

98
J. Murata et al. / Journal of Fluorine Chemistry 113 ꢀ2002)97±100
3 2
Scheme 1. Reactions of oxalyl fluoride with CF CH OTf.
Table 1
a
3 2
Reactions of oxalyl fluoride with CF CH OTf
c
Entry MF
Molar ratio Temperature Time Yield /%) from 2
/h)
of 1:2:MF /8C)
3
4
5
1
2
3
4
5
6
7
8
CsF
KF
1:2:4
1:2:4
1:2:4
1:2:4
2:2:4
2:2:8
5:2:4
2:2:4
RT
RT
70
24
72
24
3
1
4
49
6
21
3
Scheme 2. Reactions of oxalyl fluoride with electrophiles.
KF
16
5
17
11
56
19
11
58
16
7
CsF
CsF
CsF
CsF
CsF
RT
RT
RT
RT
RT
of COF with 2. In using acetonitrile or THF as solvent,
2
the reaction did not proceed effectively /Table 2, Entries 4
and 5).
24
24
24
24
12
1
19
76
40
19
45
11
b
a
b
c
1
2
was added to the mixture of 2, MF and diglyme.
was added to the mixture of 1, MF and diglyme.
2.3. Reactions of oxalyl fluoride with electrophiles
Yields were determined by NMR.
The reactions of 1 with some electrophiles were carried out
Scheme 2, Table 3). In the reaction of 1 with CF CH OTs
/
3 2
mixed before adding 2. However, the yields of products were
unchanged /Table 1, Entries 5 and 8).
/Ts ˆ p-CH3C6H4SO2), CF CH OMs /Ms ˆ CH3SO2) or
3 2
3
2
CF CH I, neither 6 nor 7 were obtained /Table 3, Entries
2±4). In the reactions of 1 with CH CH OTf, the selectivity of
the products was different from that in the reaction with
3 2
2
.2. Solvent effect
CF CH OTf. In using 0.5 or 1.0 equimolar amount of 1 to
2
3
The reactions of 1 with 2 in various solvents were carried
CF CH OTf, di-ether /7) was the main product /Table 3,
3 2
out /Table 2). In the reaction of tri¯uoroacyl halide in the
presence of alkali metal ¯uoride, glyme-type solvents are
often used because the yields are usually high [14±16].
Diglyme and tetraglyme gave good yields of products
Entries 1 and 6). On the other hand, in the reaction of 1 with
CH CH OTf, mono-ether /6) was the main product in using
1.0 equimolar amount of 1 to CH CH OTf, and di-ether /7)
3
2
3
2
was the main product in using 0.5 equimolar amount of 1 to
CH CH OTf /Table 3, Entries 5 and 7).
/
Table 2, Entries 1 and 2). In using DMF as the solvent,
and 4 were detected by GC and NMR, however, there were
3
2
3
In the reactions of oxalyl ¯uoride with CF CH OTf and
3 2
many other products that were dif®cult to identify /Table 2,
Entry 3). In the complex product CF OCH CF was
detected. It has been reported that oxalyl ¯uoride decom-
CH CH OTf, the selective synthesis of mono- and di-ethers
3 2
was achieved. In the reaction with CH CH OTf, the selec-
2
3
2
3
3
tivity can be controlled by using theoretical amount of oxalyl
posed in the presence of KF and generated COF [17]. It was
2
considered that CF OCH CF was obtained by the reaction
2
3
3
Table 3
a
Reactions of oxalyl fluoride with electrophiles
c
Entry RX
Molar ratio
Temperature Yield /%) from RX
Table 2
Solvent effect on the reaction of oxalyl fluoride with CF
a
of 1:RX:CsF /8C)
3
2
CH OTf
6
7
8
c
Entry
Solvent
Recovery
Yield /%) from 2
1
2
3
4
5
6
7
CF
CF
CF
CF
3
3
3
3
CH
CH
CH
CH
2
2
2
2
OTf 1:1:2
RT
70
12
0
56
0
19
0
of 2 /%)
OTs 1:1:2
OMs 1:1:2
3
4
5
70
0
0
0
1
2
Diglyme
Tetraglyme
DMF
5
0
12
10
±
56
63
±
19
18
±
I
1:1:2
OTf 1:1:2
OTf 1:2:4
OTf 1:2:4
70
0
0
20
4
CH
3
CH
CH
CH
2
RT
RT
RT
71
1
18
49
78
b
b
b
3
0
CF
3
2
21
9
4
5
CH
3
CN
83
100
5
7
6
CH
3
2
9
THF
0
0
0
a
1
/2.0 mmol) was added to the mixture of RX /2.0 mmol), CsF
/4.0 mmol) and diglyme /5 ml).
a
1
mmol) and solvent /5 ml).
/2.0 mmol) was added to the mixture of 2 /2.0 mmol), CsF /4.0
b
1 /1.0 mmol) was added to the mixture of RX /2.0 mmol), CsF
/4.0 mmol) and diglyme /5 ml).
b
Complex products.
c
c
Yields were determined by NMR.
Yields were determined by NMR.

J. Murata et al. / Journal of Fluorine Chemistry 113 ꢀ2002)97±100
99
3 2 3 2
Scheme 3. Competitive reaction of oxalyl fluoride with CF CH OTf and CH CH OTf.
¯
uoride. But in the reaction with CF CH OTf, di-ether was
3
3. Experimental details
2
obtained predominantly even in the reaction with the same
molar amount of oxalyl ¯uoride, and an excess amount of
oxalyl ¯uoride was necessary to synthesize the mono-ether.
It is supposed that the mono-ether CF CH OCF COF could
All of the organic reagents and solvents were puri®ed prior
to use. Oxalyl ¯uoride was used without puri®cation. CsF and
KF were dried by heating at 300 8C under vacuum for 6 h and
3
2
2
1
19
form the alkoxide with CsF easier than the mono-ether
CH CH OCF COF by the electron withdrawing CF group.
stored in the dry box. H and F NMR were measured with
JNM-EX270 /JEOL, 270 MHz) using TMS and CFCl as an
3
2
2
3
3
internal standard and CDCl as a solvent. MS spectra were
3
2.4. Competitive reaction of oxalyl fluoride with
CF CH OTf and CH CH OTf
measured with the Hewlett-Packard 5790 series system
equipped with a jet separator for the 5890A GC.
3
2
3
2
To clarify the difference of reactivity of the two electro-
philes, the competitive reaction was carried out. The reaction
was carried out as follows: a small amount of oxalyl ¯uoride
3.1. Preparation of 2,2,2-trifluoroethyl
trifluoromethanesulfonate ꢀ2)
/
0.5 mmol) was added to the mixture of CF CH OTf
3
Under N atmosphere, sodium hydride /325 mmol) and
2
2
/
and diglyme /5 ml). As a result, the product derived from
2.0 mmol) and CH CH OTf /2.0 mmol) and CsF /4.0 mmol)
ether /150 ml) were placed in a 500 ml three-neck ¯ask with
a dropping funnel. 2,2,2-Tri¯uoroethanol /300 mmol) was
added over a period of 30 min at 0 8C. The reaction mixture
was warmed up to ambient temperature and stirred for 1 h.
Tri¯uoromethanesulfonyl chloride /294 mmol) was added
over a period of 30 min at 0 8C. The reaction mixture was
warmed up to ambient temperature again and stirred for 1 h.
The reaction mixture was poured into water and the organic
layer was separated. The aqueous layer was extracted with
ether /100 ml). The combined organic layer was washed
3
2
oxalyl ¯uoride was only CH CH OCF CF OCH CH /10)
3
2
2
2
2
3
/
Scheme 3). This result means that the electrophilic reactivity
of CH CH OTf toward the alkoxide from oxalyl ¯uoride and
3
2
CsF was much higher than that of CF CH OTf. It is con-
3
2
sidered that the higher electrophilicity of CH CH OTf made
2
3
the yields of mono- and di-ethers higher.
.5. DFT calculation
It is natural that the steric hindrance is one of the
2
with aqueous saturated NaHCO /50 ml) and dried with
3
MgSO . The product was puri®ed by distillation and
4
reasons for the difference of the electrophilic reactivity
between CF CH OTf and CH CH OTf. To consider the
0.225 mol /77%) of 2 was obtained.
1
19
H NMR: d: 4.71 /2H, q, J ˆ 7:4 Hz, CH ); F NMR: d:
3
2
3
2
2
electrostatic effect of the two electrophiles, density func-
tional theory /DFT) calculations were carried out. The
atomic positions in the molecule and their fractional charge
À74.5 /3F, br, CF SO ), À74.7 /3F, tq, J ˆ 7:4, 1.1 Hz,
‡ ‡
3 2 3 3 2
3
2
CF CH ); mꢀe: 163 /M À CF ), 133 /CF SO ), 99
‡
‡
‡
/CF CH O ), 83 /CF CH ), 69 /CF ).
3
2
3
2
3
Ã
values were obtained by using B3LYPꢀ6-31G and B3LYPꢀ
6
-311G/2d,p) with CHELPG method [18]. The calculation
showed the fractional charge of the methylene carbon atom
of CH CH OTf is more positive than that of CF CH OTf
3.2. A typical experimental procedure for the reaction
of oxalyl fluoride with electrophiles
3
2
3
2
/
of CF CH OTf and CH CH OTf depends on the fractional
charge of the carbon atom that is attacked by nucleophiles in
addition to the steric hindrance.
Scheme 4). It was concluded that the electrophilic reactivity
CsF /4.0 mmol) was placed in a stainless-steel reactor
equipped with a stop valve /volume: 25 ml) in the dry box
/Table 1, Entry 1). The reactor was heated under vacuum to
remove moisture from CsF and the reactor. CF CH OTf
3
2
3
2
3
2
/2.0 mmol) and diglyme /5 ml) were placed into the reactor
in the dry box. After cooling with liquid N , oxalyl ¯uoride
2
/1.0 mmol) was introduced to the reactor with a vacuum line.
The reactor was warmed up to ambient temperature and
stirred for 24 h. Products were fractionated through traps at
À78 and À196 8C. After fractionations, methanol /10 mmol)
was introduced to the À78 8C trap with a vacuum line. The
Scheme 4. Fractional charge of methylene carbon atom of CF
and CH CH OTf.
3 2
CH OTf
1
structures of the products were determined by GC±MS, H
3
2

100
J. Murata et al. / Journal of Fluorine Chemistry 113 ꢀ2002)97±100
and 19F NMR spectra. The ratio of the products was deter-
mined by H and 19F NMR spectra.
4. Conclusion
1
We have demonstrated the reactions of oxalyl ¯uoride
with electrophiles in the presence of alkali metal ¯uoride. In
the reaction of oxalyl ¯uoride with CF CH OTf or
3.2.1. Methyl ester of 3: methyl 2,2-difluoro-2-ꢀ2,2,2-
trifluoroethoxy)acetate
3
2
1
H NMR: d: 3.95 /3H, s), 4.32 /2H, q, J ˆ 7:9 Hz); 19F
CH CH OTf, the synthesis of mono-ether and di-ether
2
3
NMR: d: À74.8 /3F, tt, J ˆ 2:3, 7.9 Hz), À81.0 /2F, q,
was achieved. The reactivity of CH CH OTf toward alk-
3 2
‡
‡
J ˆ 2:3 Hz); mꢀe: 189 /M À F ), 149 /CF CH OCF ), 83
oxide is much higher than that of CF CH OTf. DFT calcu-
3 2
3
2
2
‡
‡
/
CF CH ), 69 /CF ).
2
lations supported the difference of the reactivity of the two
electrophiles.
3
3
3.2.2. 1,2-Bisꢀ2,2,2-trifluoroethoxy)-1,1,2,2-
tetrafluoroethane ꢀ4)
1
19
H NMR: d: 4.31 /4H, q, J ˆ 7:8 Hz); F NMR: d: À75.0
6F, tt, J ˆ 2:3, 7.8 Hz), À91.2 /4F, q, J ˆ 2:3 Hz); mꢀe: 279
Acknowledgements
/
/
/
‡
‡
‡
2
M À F ), 229 /M À CF ), 149 /CF CH OCF ), 83
This work was supported by the New Energy and Indus-
trial Technology Development Organization /NEDO).
3
3
2
‡
‡
CF CH ), 69 /CF ).
3
2
3
3.2.3. Methyl ester of 9: methyl 2-ethoxy-2,2-
difluoroacetate
References
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1
9
/
/
/
2H, q, J ˆ 7:1 Hz); F NMR: d: À80.1 /2F, s); mꢀe: 126
‡ ‡ ‡
4 3 2 2 3
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.2.4. 1,2-Diethoxy-1,1,2,2-tetrafluoroethane ꢀ10)
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9
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‡
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1
3
2
3
2
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[
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3
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3
2
into the reactor in the dry box. After cooling by liquid N2,
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with a vacuum line. The reactor was warmed up to ambient
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3
1
vacuum line. The ratio of the products was determined by H
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3
.4. Calculations
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[
Ã