Synthesis of fluorinated dimethyl carbonates by direct fluorination

Article abstract of DOI:10.1081/SCC-120030685

Growing interest has been focused on the development of florinated solvents for lithium batteries, because they have a number of benefits such as excellent oxidation durability, wide liquidus ranges, and nonflammability. Flourination of dimethyl carbonate (DMC) is carried out using molecular flourine (15 vol.% F₂/N₂) at 5°C, and the flourinated derivatives of the DMC are identified and characterized. The selectivity of monoflourinated dimethyl carbonate (MFDMC) is ca. 90% at early stage of the flourination. The successive electrophilic substitution of a hydrogen with a fluorine is found to proceed for the direct fluorination of the DMC.

Full text of DOI:10.1081/SCC-120030685

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Synthesis of Fluorinated Dimethyl Carbonates by
Direct Fluorination
a
a
a
b
Masahiro Takehara , Susumu Watanabe , Noritoshi Nanbu , Makoto Ue & Yukio
a
Sasaki
a
Department of Applied Chemistry, Faculty of Engineering , Tokyo Polytechnic
University , 1583 Iiyama, Atsugi, Kanagawa, 243‐0297, Japan
b
Mitsubishi Chemical Group Science and Technology Research Center, Inc. , Inashiki,
Ibaraki, Japan
Published online: 21 Aug 2006.
To cite this article: Masahiro Takehara , Susumu Watanabe , Noritoshi Nanbu , Makoto Ue & Yukio Sasaki (2004) Synthesis
of Fluorinated Dimethyl Carbonates by Direct Fluorination, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:8, 1367-1375, DOI: 10.1081/SCC-120030685
To link to this article: http://dx.doi.org/10.1081/SCC-120030685
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w
SYNTHETIC COMMUNICATIONS
Vol. 34, No. 8, pp. 1367–1375, 2004
Synthesis of Fluorinated Dimethyl
Carbonates by Direct Fluorination
1
Masahiro Takehara, Susumu Watanabe,
Noritoshi Nanbu, * Makoto Ue, and Yukio Sasaki *
1
1
,
2
1,
1
Department of Applied Chemistry, Faculty of Engineering, Tokyo
Polytechnic University, Atsugi, Kanagawa, Japan
2
Mitsubishi Chemical Group Science and Technology Research Center,
Inc., Inashiki, Ibaraki, Japan
ABSTRACT
Growing interest has been focused on the development of fluorinated
solvents for lithium batteries, because they have a number of benefits
such as excellent oxidation durability, wide liquidus ranges, and nonflamma-
bility. Fluorination of dimethyl carbonate (DMC) is carried out using
2 2
molecular fluorine (15 vol.% F /N ) at 58C, and the fluorinated deriva-
tives of the DMC are identified and characterized. The selectivity of
monofluorinated dimethyl carbonate (MFDMC) is ca. 90% at early
stage of the fluorination. The successive electrophilic substitution of a
*
Correspondence: Noritoshi Nanbu and Yukio Sasaki, Department of Applied
Chemistry, Faculty of Engineering, Tokyo Polytechnic University, 1583 Iiyama,
Atsugi, Kanagawa 243-0297, Japan; Fax: þ81-46-242-3000; E-mail: nanbu@chem.t-
kougei.ac.jp or sasaki@chem.t-kougei.ac.jp.
1
367
DOI: 10.1081/SCC-120030685
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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1
368
Takehara et al.
hydrogen with a fluorine is found to proceed for the direct fluorination of
the DMC.
Key Words: Direct fluorination; Dimethyl carbonate; Fluorinated
dimethyl carbonate; Lithium battery.
INTRODUCTION
There has been a growing demand for the development of novel solvents
for the high-performance electrochemical devices. One of the strategies for
finding novel solvents is the introduction of fluorine atoms into the solvent
molecules. This is because the fluorinated solvents can improve various pro-
perties such as oxidation durability, liquidus ranges, and nonflammability.
[1]
Since the molecular fluorine is very reactive, direct fluorination can afford
various fluorinated compounds, which are hardly obtained by conventional
methods, under solvent-free conditions. The fluorination can be performed
safely at low temperatures using F gas that is generated by electrolysis
2
and diluted with an inert gas. Dimethyl carbonate (DMC) is one of the low-
viscosity chain esters commonly used in electrochemical energy storage
[2–4]
devices such as lithium batteries.
[1]
We previously reported direct fluorination of g-butyrolactone (g-BL) that
is also commonly used in the electrochemical devices. The direct fluorination
gives b-fluoro-g-butyrolactone and g-fluoro-g-butyrolactone besides a-fluoro-
g-butyrolactone. Similar direct fluorination is applied to 1,2-dimethoxyethane
[
5,6]
[7]
[7,8]
(DME),
attempt has been made to conduct direct fluorination of acyclic esters, though
propylene carbonate (PC), and ethylene carbonate (EC).
No
[9,10]
perfluorodimethyl carbonate
[11]
and gem-difluorinated DMC (gem-DFDMC
in Sch. 1), where two fluorine atoms and an oxygen atom are attached to the same
carbon atom, are synthesized by different methods. There are some reports of
electrochemical fluorination of substrates such as N-containing carboxylic
[
12]
[13]
[14,15]
[16]
acids, amino alcohols, chain ethers,
and cyclic ethers.
A fluorine atom is highly electronegative and shows a very low electronic
polarizability and high enthalpy of ionization. Perfluorination or polyfluorination
of solvents results in a lowering of their polarity. On the other hand, partial fluor-
ination of solvents can lead to an increase of the polarity, though the amount of
polarization depends on the position where the substitution takes place. It is
desirable to develop partially fluorinated solvents for the high-performance
electrochemical devices. We report here direct fluorination of DMC.
Figure 1 shows a gas chromatograph of the reaction mixture obtained
after the introduction of F gas for 24 hr. There appeared four peaks except
for a peak due to DMC, a starting material. The result of GC-MS (CI) for
2

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Synthesis of Fluorinated DMCs by Direct Fluorination
1369

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1
370
Takehara et al.
Figure 1. Gas chromatograph of the reaction mixture obtained after the introduction
of F gas for 24 hr.
2
a
the reaction mixture indicates that these peaks can be ascribed to molecular
ions and that direct fluorination of DMC occurred without the fragmentation
of the DMC chain.
A peak ascribable to the DMC, whose molecular weight is 90, was
observed at the retention time of 2.3 min. A peak due to monofluorinated
DMC (MFDMC), whose molecular weight is 108, appeared at 3.5 min. Two
peaks attributable to difluorinated DMCs, whose molecular weights are 126,
were detected at 2.1 and 4.9 min. According to the analysis of GC-MS (EI)
b
spectra, the peak at 4.9 min can be ascribed to DFDMC, while the peak at
2.1 min can be accounted for gem-DFDMC. Furthermore, a peak responsible
for trifluorinated DMC (TFDMC), whose molecular weight is 144, is observed
at 3.1 min. The MFDMC purified by fractional distillation was also identified
c
1
13
19
by techniques of elemental analysis and H, C, and F NMR spectroscopy.
d
a
þ
þ
GC-MS (CI) (m/z): DMC, 91 [M þ H] ; MFDMC, 109 [M þ H] ; DFDMC, 127
þ
þ
þ
[M þ H] ; gem-DFDMC, 127 [M þ H] ; TFDMC, 145 [M þ H] .
b
þ
þ
þ
3
O (73.14);
GC-MS (EI) (m/z): DMC, 90 [M] (11.42), 59 COOCH
3
(100), 31 CH
þ
þ
þ
MFDMC, 77 COOCH (84.25), 33 CH
þ
COOCH F (15.74), 33 CH F (100); gem-DFDMC, 95 COOCHF (2.38), 59
2
F (4.33), 59 COOCH
þ
3
2
F (100); DFDMC, 77
þ
2
2
2
þ
þ
þ
þ
COOCH
þ
3
(30), 51 CHF
2
(100), 31 CH
þ
3
O
(30.95); TFDMC, 33 CH
þ
2
F
(46.27), 51
CHF (3.52).
c
Anal. Calcd for C H FO : C, 33.3%; H, 4.7%; F, 17.6%. Found: C, 33.4%; H, 3.9%; F,
2
(100), 77 COOCH
2
F
(7.05), 95 COOCHF
2
3
5
3
1
7.5%.

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Synthesis of Fluorinated DMCs by Direct Fluorination
1371
The DFDMC and the gem-DFDMC are isomeric with each other. It is
interesting to note that the retention time of the DFDMC (4.9 min) is consider-
ably longer than that of the DMC (2.3 min), but that the retention time of the
gem-DFDMC (2.1 min) is slightly shorter. The retention time reflects the
boiling point of the solvent, which relates to the attractive forces between
molecules. The boiling points of gem-DFDMC, DMC, TFDMC, MFDMC,
and DFDMC were 858C, 908C, 1008C, 1088C, 1208C, respectively. The
DFDMC molecule contains two carbon atoms, each of which is attached to
a fluorine atom and an oxygen atom, whereas two fluorine atoms and an
oxygen atom are bound to the same carbon atom in the gem-DFDMC mol-
ecule. A fluorine and an oxygen atom are highly electronegative and show
very low electronic polarizability and high enthalpy of ionization. Accord-
ingly, the polarity of the DFDMC can be substantially higher than that of
the gem-DFDMC, whose electronic polarizability may be also small as com-
pared to that of the DMC. It is expected that the drastic increase of the reten-
tion time (the boiling point) observed for the DFDMC can be ascribed to the
dipole–dipole interaction, which includes the hydrogen bonding, as well as
the dispersion or London interaction between molecules.
In general, as molecular weight increases, so too do the molecular size
and surface area. With increasing them, the dispersion or London interactions
[17]
between molecules increase.
Therefore, more energy (a higher tempera-
ture) is required to separate molecules from one another. In spite of higher
molecular weight of the TFDMC, the retention time of the TFDMC
(
(
3.1 min) was shorter than those of the MFDMC (3.5 min) and the DFDMC
4.9 min). Trifluorination of the DMC can induce a lowering of polarity as
compared to the monofluorination and the difluorination. On the other hand,
the retention time of the TFDMC was longer than that of the DMC
(2.3 min), because the molecular weight and polarity of the TFDMC are higher
than those of the DMC.
Figure 2 shows the variation of yields of the fluorinated derivatives of
DMC with reaction time. Monofluorination of DMC preferentially proceeded,
and the maximum yield of MFDMC (ca. 60%) was attained at 16 hr after the
introduction of F gas. The selectivity of the MFDMC was ca. 90% at early
2
stage of the fluorination. The selectivity is defined as the ratio of the amount
of the resulting MFDMC to that of the DMC consumed by the reaction. The
yields and selectivity were estimated from the ratios of the areas of peaks
observed on a gas chromatograph. The yields of two difluorinated DMCs
d1
2
H NMR (1% TMS/CDCl
3
, 500.00 MHz): d 4.23 (s, 3H), 6.08 (d, JHF ¼ 51.5 Hz,
1
3
1
2
1
H). C NMR (1% TMS/CDCl , 125.65 MHz): d 55.10, 96.97 (d, J ¼ 219.0 Hz),
3
CF
9
2
54.68. F NMR (2% CF COOD/D O, 470.40 MHz): d 2158.05 (t, J ¼ 51.5 Hz).
3
2
FH

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372
Takehara et al.
Figure 2. Yields of the fluorinated derivatives of DMC and selectivity of MFDMC as
a function of reaction time.
increased with the decrease of the yield and selectivity of MFDMC beyond
16 hr. No significant formation of these two difluorinated DMCs was observed
at early stage. These findings indicate that the two difluorinated DMCs can
result from the MFDMC. The yield of TFDMC was also extremely low at
early stage. This yield exceeds that of gem-DFDMC after ca. 21 hr, while
that of DFDMC continues to increase. Therefore, we can think that trifluori-
nation of the DMC mainly occurs through the gem-DFDMC. On the other
hand, no significant formation of another TFDMC, where three fluorine
atoms are situated on the same carbon atom, was observed. The yield of the
DFDMC was higher than that of the gem-DFDMC over an investigated period
of time. It appears that a fluorine molecule acts as an electrophile and that
electron withdrawing groups deactivate nearby C–H bonds toward the
[
18,19]
electrophilic attack.
is summarized in Sch. 2.
The process of the direct fluorination of the DMC
In conclusion, the selectivity of the MFDMC was ca. 90% at early stage of
direct fluorination. The successive electrophilic substitution of a hydrogen
with a fluorine was found to proceed for the direct fluorination of DMC.
Difluorination of the DMC accompanies the consumption of the MFDMC.
Tifluorination of the DMC mainly occurred through the gem-DFDMC, in
which two fluorine atoms and an oxygen atom are attached to the same carbon
atom. It is of interest to investigate the electrolytic properties of these

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Synthesis of Fluorinated DMCs by Direct Fluorination
1373

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1
374
Takehara et al.
fluorinated DMCs and to clarify the relationship between the successive
substitution and the properties.
EXPERIMENTAL
Direct fluorination of DMC is depicted in Sch. 1. In a PFA vessel (500mL)
equipped with gas inlet and outlet 50.0g (0.556 mol) of DMC was placed, and
the atmosphere in the reactor was replaced with N gas. F gas generated by
2
2
TM
.
electrolysis of KF 2HF (Fluorodec 30, Toyo Tanso Co. Ltd.) was diluted
with N gas to 15vol.% and poured over the surface of DMC in the reactor
2
21
22
21
at 22.4mL min (6.00 ꢀ 10 mol hr ). The DMC solution was stirred and
maintained at 58C with cooling. The fluorinated derivatives of the DMC
were identified and characterized by means of gas chromatography coupled
with mass spectrometry (CG-MS analysis). The CG-MS analysis based on
a
b
chemical ionization (CI) and electron ionization (EI) were performed on
JEOL JMS-SX102A equipped with a TC-WAX column (0.25 mmw ꢀ 30m,
df ¼ 0.25mm). Perfluorokerosene (PFK) was used as the internal standard.
21
The temperature in the capillary column was increased at a rate of 108C min
from 508C to 1008C. Although the capillary column was heated at a rate of
2
1
2
08C min from 1008C to 2008C, no peaks were observed on the gas chroma-
tograph. The boiling points of gem-DFDMC, DMC, TFDMC, MFDMC, and
DFDMC were 858C, 908C, 1008C, 1088C, 1208C, respectively.
MFDMC was separated from the reaction mixture obtained after the
introduction of F gas for ca. 10 hr. Hydrogen fluoride, HF, can be formed
2
as a by-product by the substitution. Since the fluorinated DMC solution was
immiscible with water, the reaction mixture was washed with water and
followed by washing aqueous solution containing Na CO for removal of
2
3
the HF. The fluorinated DMC solution was dehydrated with purified mol-
ecular sieve 4 A for ca. 24 hr. We have isolated the MFDMC from the mix-
ture of the DMC and the fluorinated DMCs in a 45% yield using fractional
distillation at atmospheric pressure. It should be noted that this yield is
essentially the same as that shown in Fig. 2. That is to say, almost all of
the MFDMC formed by the direct fluorination of the DMC was successfully
separated. The purity of the MFDMC determined by means of GC
1
13
19
(
GC-1700, Shimadzu) was 99.7%. H, C, and F NMR spectra of the
d
purified MFDMC were recorded on a JEOL JNM-LA500 FT-NMR
spectrometer.
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Received in Japan September 30, 2003

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