Efficient preparation of new fluorinated lithium and ammonium sulfonimides

Article abstract of DOI:10.1021/jo800272q

(Chemical Equation Presented) An efficient preparation of new fluorinated lithium and ammonium sulfonimides, from the corresponding sulfonyl fluorides, is reported. These sulfonyl fluorides are reacted with benzylamine, then triflated. Due to the high lea

Full text of DOI:10.1021/jo800272q

at the high oxidation potentials of lithium ion batteries, it
corrodes the aluminum electrode collector connected to the
positive electrode.1 So, a growing interest is being paid to new
and efficient sulfonimide salts. It can be noticed that sulfon-
imides have also received attention in recent years as ionic
liquids,2 electrolytes for fuel cells,3 or acid catalysts.4 For all
these applications, it must be emphasized that fluorinated anions
are inescapable because of their very low basicity, nucleophi-
licity, and oxidability.
Efficient Preparation of New Fluorinated Lithium
and Ammonium Sulfonimides
Fabien Toulgoat,* Bernard. R. Langlois,*
Maurice Me´debielle, and Jean-Yves Sanchez†
ICBMS, Institut de Chimie et Biochimie Mole´culaires et
Supramole´culaires, Equipe SERCOF, 43 bouleVard du 11
noVembre 1918, Villeurbanne, F-69622, France, CNRS,
UMR5246, Villeurbanne, F-69622, France, UniVersite´ de
Lyon, Lyon, F-69622, France, UniVersite´ Lyon 1,
Lyon, F-69622, France, INSA-Lyon,
Villeurbanne, F-69622, France, and CPE Lyon,
Villeurbanne, F-69616, France
FIGURE 1. Structure of the desired sulfonimide salts.
ftoulgoat@yahoo.fr; langlois@uniV-lyon1.fr
ReceiVed February 03, 2008
As we recently developed new sulfonyl fluorides,5 we used
them to prepare a new class of sulfonimides (Figure 1) which
could provide electrolytes with better properties than LiTFSI.
Since the discovery of LiTFSI,6a a large number of perfluo-
roalkanesulfonimide salts7 have been prepared, but only few
of them contain an aromatic ring.8,9 The sulfonimide salts we
plan to describe here are complementary to them, as they are
constituted by an aromatic part separated by a linker from a
fluorinated moiety. This linker can be a sulfide function, that
brings some flexibility to the molecules, or a sulfone, which
enhances the electron withdrawing properties and the polarity
of the anion. The aromatic group could also allow the introduc-
tion of various substituents or functions enabling the preparation
of ionomers.
An efficient preparation of new fluorinated lithium and
ammonium sulfonimides, from the corresponding sulfonyl
fluorides, is reported. These sulfonyl fluorides are reacted
with benzylamine, then triflated. Due to the high leaving
ability of fluorinated sulfonimides, the formed N-benzylsul-
fonimides are simply debenzylated with an alcohol. Finally,
the intermediate oxonium sulfonimides are neutralized, in
situ, by various bases. The obtained sulfonimides are
potential electrolytes for lithium batteries or fuel cells.
Two main methods have been described to prepare fluoro-
alkanesulfonimides: the reaction of sulfonyl fluorides with
trifluoromethanesulfonamide in the presence of a base9,10 or with
the sodium salt of N-(trimethylsilyl)trifluoromethylsulfonamide.6,11
(2) Ionic Liquids in Synthesis; Wasserscheid, P., Welton, T., Eds.; Wiley-
VCH: Weinheim, 2003.
(3) (a) Souzy, R.; Ameduri, B.; Boutevin, B.; Gebel, G.; Capron, P. Solid
State Ionics 2005, 176, 2839–2848. (b) Souzy, R.; Ameduri, B. Prog. Polym.
Sci. 2005, 30, 644–687. (c) Belieres, J. P.; Gervasio, D.; Angell, C. A. Chem.
Commun. 2006, 4799, 4801.
(4) Olah, G. A., Prakash, G. K. S., Sommer J., Eds. Superacids; Wiley-
Interscience: New York, 1984.
(5) (a) Toulgoat, F.; Langlois, B. R.; Me´debielle, M.; Sanchez, J.-Y. J. Org.
Chem. 2007, 72, 9046–9052. (b) Sanchez, J.-Y.; Langlois, B.; Me´debielle, M.;
Toulgoat, F. FR20060006466, 2006.
Introduction
Nowadays, electricity production and storage is a major
challenge for reducing global warming. Lithium batteries are
already popular for small electronic devices but are not yet
adapted for future applications. To circumvent the current
drawbacks, new electrodes and new electrolytes have to be
designed.1 Considering electrolytes, LiPF6 is currently used, but
its development in batteries operating at 80-90 °C is hindered
by a moderate thermal and hydrolytic stability and by the
toxicity of its decomposition products. As for (CF3SO2)2NLi
(LiTFSI), its high conductivity and its high thermal and
electrochemical stabilities make it a promising salt. However,
(6) (a) Foropoulos, J.; DesMarteau, D. D. Inorg. Chem. 1984, 23, 3720–
3723. (b) DesMarteau, D. D.; Witz, M. J. Fluorine Chem. 1991, 52, 7–12.
(7) For example: (a) Waddell, J.; Howells, R. D.; Lamana, W. M.; Fanta,
A. D. US 5,874,616 (3M), 1999; Chem. Abstr. 1999, 130, 184069. (b) Armand,
M.; Choquette, Y.; Gauthier, M.; Michot, C. EP 850,920 (CNRS - Hydro
Quebec), 1998; Chem. Abstr. 1998, 129, 122975. (c) Nakano, T. JP 2000 082,494
(Sanyo Chemical Ind. Ltd.), 2000; Chem. Abstr. 2000, 132, 239412. (d)
DesMarteau, D. D. J. Fluorine Chem. 1995, 72, 203–208. (e) Feiring, A. E.;
Doyle, M. C.; Roelfos, M. G.; Farnahm, W. B.; Bekiarian, P. G.; Blau, H. A. K.
WO 99 45,048 (DuPont), 1999; Chem. Abstr. 1999, 131, 200299. (f) Michot,
A.; Armand, M. WO 99 38,842 (Hydro Quebec), 1999; Chem. Abstr. 1999, 131,
145247.
(8) Lu, K. US 2003 013,817, 2003; Chem. Abstr. 2003, 138, 107174.
(9) (a) Doyle, M. C.; Feiring, A. E.; Choi, S. K. WO 99 67,304 (DuPont),
1999; Chem. Abstr. 1999, 132, 50411. (b) Feiring, A. E.; Wonchoba, W. R. J.
Fluorine Chem. 2000, 105, 129–135. (c) Feiring, A. E.; Choi, S. K.; Doyle, M.;
Wonchoba, W. R. Macromolecules 2000, 33, 9262–9271.
† Laboratoire d’Electrochimie et de Physico-chimie des Mate´riaux et des
Interfaces - LEPMI, UMR 5631 CNRS-INPG-UJF, BP.75, 38402 Saint-Martin-
d’He`res, France.
(1) (a) Xu, K. Chem. ReV. 2004, 104, 4303–4417. (b) Alloin, F.; Benrabah,
D.; Sanchez, J-Y. J. Power Sources 1997, 68, 372–376.
(10) (a) Howells,R. D. ; Lamanna,W. M. ;Fanta,A. D. ; Waddell,J. E. WO
97 23,448 (3M), 1997; Chem. Abstr. 1997, 127, 136181. (b) Sakai, S.; Takase,
H.; Sakauchi, H. EP 1,029,850 (Central Glass Co. Ltd.) 2000; Chem. Abstr.
2000, 133, 192769.
10.1021/jo800272q CCC: $40.75
Published on Web 06/13/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 5613–5616 5613

TABLE 1. Synthesis of N-Benzylsulfonamides
SCHEME 1. First Attempts To Synthesize 2a
entry
RCF2
RCF2SO2F
product
yield (%)
1
2
3
4
C6H5SCF2CF2
C6H5SCF2
C6H5SO2CF2CF2
C6H5SO2CF2
1a
1b
1c
1d
4a
4b
4c
4d
77
90
83
78a
a Proportions determined by 19F NMR.
a Reaction performed between -20 °C and rt.
SCHEME 2. Proposed Retrosynthesis To Prepare Lithium
Sulfonimides
SCHEME 3. Side Formation of 5
TABLE 2. Synthesis of N-Benzylsulfonimides
Other methods can be mentioned, such as the reaction of
sulfonyl fluorides with ammonia,12 silazanes,13 or trifluoroac-
etamide.14 Unfortunately, when applied to our substrates, some
of these methods were not as efficient as expected.
Indeed, when reacting trifluoromethanesulfonamide with
sulfonyl fluoride 1a, in the presence of triethylamine, the
corresponding ammonium sulfonimide 2a was formed but along
a major amount of the corresponding sulfonate 3a resulting from
a competitive hydrolysis of 1a, whatever the precautions taken
(Scheme 1).
This coupling reaction was found to be very moisture
sensitive, and as CF3SO2NH2 or CF3SO2N(Na)TMS are very
poor nucleophiles, they could not kinetically compete with
moisture. Thus, we report here an improved synthesis to
circumvent this difficulty. A new strategy was considered: first,
creation of the sulfur-nitrogen bond, then introduction of the
SO2CF3 moiety. Benzylamine was chosen as the key nucleophile
to build the S-N bond since benzylamine is a good nucleophile
and the N-benzyl bond is known to be cleaved under a variety
of procedures (Scheme 2).
entry
RCF2
product
yielda (%)
1
2
3
4
C6H5SCF2CF2
C6H5SCF2
C6H5SO2CF2CF2
C6H5SO2CF2
6a
6b
6c
6d
92
89b
81
81
a Reaction performed with 1 equiv of DIEA and 1.5 equiv of triflic
anhydride unless otherwise noted. b With 1.1 equiv of DIEA, aqueous
workup before extraction of 6b from the residue.
It can be noticed that when 1d was reacted with benzylamine
at 50 °C, a side reaction occurred that led to the contamination
of 4d by N-benzylbenzenesulfonamide 5 (ratios 4d/5: 1/1.7).
This side reaction could result from the attack of benzylamine
on the very electrophilic sulfonyl group of 1d, followed by
expulsion of difluorocarbene, SO2, and a fluoride (Scheme 3).
Such a reaction exhibits some similarity with the generation of
a trifluoromethyl anion from t-BuOK and (trifluoromethane-
sulfonyl)benzene.15 Unfortunately, we were not able to obtain
any evidence of difluorocarbene formation. In contrast, this side
reaction was never observed with sulfonyl fluoride 1c.
Nevertheless, N-benzylsulfonamide 4d was obtained pure in
a 78% yield (Table 1, entry 4) when the reaction was performed
at lower temperatures (-20 °C to rt).
Results and Discussion
For the first step, benzylamine was used in excess and
N-benzylsulfonamides 4a-d were obtained in good to excellent
yields (Table 1) since hydrolysis was almost completely
suppressed. Compounds 4a-d were easily purified by
chromatography.
In a second step, N-benzylsulfonimides 6a-d were obtained
in excellent yields (Table 2) by subsequent reaction with triflic
anhydride in the presence of diisopropylethylamine (DIEA). The
formed ammonium triflates were easily separated from 6a-d,
which were extracted in pentane.
The deprotection of 6a-d was then examined. Usually,
N-benzyl bonds are cleaved by palladium-catalyzed hydro-
genolysis. Surprisingly, we observed that deprotection occurred
after addition of 6a-d to ethanol, prior introduction of hydrogen
(11) (a) For example: Hu, L.-Q.; DesMarteau, D. D. Inorg. Chem. 1993, 32,
5007–5010. (b) DesMarteau, D. D.; Pennington, W. T.; Montanari, V.; Thomas,
B. H. J. Fluorine Chem. 2003, 122, 57–61. (c) Geiculescu, O. E.; Xie, Y.;
Rajagopal, R.; Creager, S. E.; DesMarteau, D. D. J. Fluorine Chem. 2004, 125,
1179–1185.
(12) (a) Sakaguchi, H.; Fuji, K.; Sakai, S.; Kobayashi, Y.; Kita, Y. FR
2,724,380 (Central Glass Co. Ltd.) 1996; Chem. Abstr. 1996, 124, 342658. (b)
Morizaki, K.; Sasaki, M. JP 2000 086,617 (Kanto Denka Kogyo KK) 2000;
Chem. Abstr. 2000, 132, 236802.
(13) (a) Armand, M. FR 2,637,284 (Elf Aquitaine - Hydro Quebec), 1991;
Chem. Abstr. 1991, 113, 131568. (b) Furuya,M. ; Nakajima,H. JP 9,173,856
(Asahi Chemical Ind.) 1997.
(14) (a) Sogabe, K. JP 2001 233,849 (New Japan Chem. Co. Ltd.) 2001;
Chem. Abstr. 2001, 135, 195341. (b) Sogabe, K.; Hasegawa, Y.; Wada, Y.;
Kitamura, T.; Yanagida, S. Chem. Lett. 2000, 944–945.
(15) (a) Prakash, G. K. S.; Hu, J.; Olah, G. A. Org. Lett. 2003, 5, 3253–
3256. (b) Prakash, G. K. S.; Hu, J.; Mathew, T.; Olah, G. A. Angew. Chem., Int.
Ed 2003, 42, 5216–5219.
5614 J. Org. Chem. Vol. 73, No. 14, 2008

TABLE 3. Synthesis of Lithium Sulfonimides
recently, DesMarteau et al. prepared new ionic liquids by using
the methylating properties of N-methyl bis[(perfluoroalkyl)sul-
fonyl]imides at 70 °C.17 Nevertheless, they did not extend this
method to benzylation which, owing to our present results, can
be easily carried out at room temperature.
Our approach exhibits a wide scope since, in principle, it
allows the preparation of numerous sulfonimides associated with
a wide range of cations, depending upon the base used to
neutralize the oxonium salt 8 (Scheme 4). Indeed, tertiary and
quaternary ammonium sulfonimides can be also prepared from
trialkylamines or ammonium hydroxides as bases. For example,
triethylammonium sulfonimides 2a,b, which are potential
protonic electrolytes for fuel cells, were prepared from triethy-
lamine (Table 3, entries 5 and 6).
The use of other tertiary amines and quaternary ammonium
hydroxides are under study to get, respectively, new electrolytes
for fuel cells or new ionic liquids.
Another advantage of our method can be pointed out when
considering the final purification of lithium and ammonium
sulfonimides: the only byproduct is a benzyl ether, which is
easily separated from the desired salts. This constitutes a real
progress over the previous procedures which require the
separation of mixtures of organic salts.
yield (%) yield (%)
entry
base
RCF2
product
vs 6a-d
vs 1a-d
1
2
3
4
5
6
LiOH C6H5SCF2CF2
LiOH C6H5SCF2
LiOH C6H5SO2CF2CF2
LiOH C6H5SO2CF2
Et3N
Et3N
7a
7b
7c
7d
2a
2b
90
85
77
76
82
88
64
68
52
48
58
70
C6H5SCF2CF2
C6H5SCF2
SCHEME 4. Postulated Mechanism of the Debenzylation
Reaction
Conclusion
In conclusion, we have developed an original approach, easy
to scale up, to prepare new sulfonimide salts.18 This method is
based on two key steps: an efficient formation of a SO2-N bond
and an easy deprotection of a N-benzyl group. First, the reaction
between sulfonyl fluorides and benzylamine avoids hydrolysis
of the starting sulfonyl fluorides and provides N-benzylsulfona-
mides in very good yields. Then, the introduction of the SO2CF3
part with triflic anhydride was found to proceed very well.
Finally, N-deprotection was found to occur cleanly, under mild
conditions, without any metal (cost and pollution advantages)
and without any hydrogen (safety advantage). Moreover, this
last step allows the preparation of sulfonimides associated with
a wide range of cations. Therefore, this method was applied to
the synthesis of a series of new lithium sulfonimides, which
are potential electrolytes for lithium batteries, and extended to
that of triethylammonium sulfonimides, which are potential
electrolytes for fuel cells or potential ionic liquids. Data about
the end-use properties of these new organic salts will be
published in due time.
and palladium. Indeed, whereas 6a-d were insoluble in ethanol,
a complete dissolution was observed after 8 h and 19F NMR
analysis confirmed that a reaction occurred. Finally, after
addition of LiOH to the “solution” of 6a-d in ethanol, the
desired lithium salts 7a-d were readily obtained (Table 3,
entries 1-4). Although compounds 7a-d were obtained as
solids, it was not possible to measure their melting points due
to their high sensitivity to moisture.
Actually, this deprotection reaction results from a nucleophilic
substitution, at the benzylic center, of the sulfonimide group
by the alcoholic oxygen (Scheme 4). This substitution is strongly
favored by the presence of the electron-withdrawing fluorine
atoms, which greatly enhances the nucleofugal character of the
sulfonimide moiety. This mechanism has been experimentally
confirmed by isolation of benzyl ethers 9a,b after deprotection
of 6a-d in ethanol or 2-propanol.
This “one pot - 2 step” procedure was preferred to obtain
sulfonimide salts with high purities. Indeed, small amounts of
unidentified byproduct were observed when 6a-d were directly
treated with LiOH or LiOR. We assume that these undesired
reactions were due to the nature of LiOH or LiOR which can
abstract the benzylic protons or react on the sulfonyl groups of
the N-benzylsulfonimides. In contrast, ethanol is a less basic
and softer nucleophile, and thus, only nucleophilic substitution
was observed.
It must be mentioned that few old papers already described
the benzylation ability of N-benzyl-bis-trifluoromethanesulfon-
imide.16 Nevertheless, no attention was paid to the sulfonimide
part which was considered as a useless byproduct. More
Experimental Section
Synthesis of N-Benzyl-2-(phenylsulfanyl)-1,1,2,2-tetrafluoro-
ethanesulfonamide (4a). Freshly distilled benzylamine (4 mL, 37
mmol) was added at room temperature, under nitrogen, to a solution
of 1a (2.09 g, 7.2 mmol) in anhydrous 1,2-dichloroethane (20 mL).
The mixture was stirred at 50 °C for 20 h (1a conversion monitored
by TLC or 19F NMR). After the mixture was cooled to room
temperature, aqueous HCl (10%) was added. The aqueous phase
(16) (a) Hendrickson, J. B.; Bergeron, R.; Giga, A.; Sternbach, D. J. Am.
Chem. Soc. 1973, 95, 3412–3413. (b) DeChristopher, P. J.; Adamek, J. P.; Klein,
S.; Lyon, G. D.; Baumgarten, R. J. J. Org. Chem. 1975, 40, 3288–3291. (c)
Glass, R. S. Chem. Commun. 1971, 1546–1547. (d) Glass, R. S.; Swedo, R. J.
J. Org. Chem. 1978, 43, 2291–2293. (e) Mu¨ller, P.; Phuong, N. T. M. Tetrahedron
Lett. 1978, 47, 4727–4730.
(17) Zhang, J.; Martin, G. R.; DesMarteau, D. D. Chem. Commun. 2003,
2334–2335.
(18) Sanchez, J.-Y.; Langlois, B.; Me´debielle, M.; Toulgoat, F.; Alloin, F.;
Paillard, E.; Iojoiu, C. FR 20060006469, 2006.
J. Org. Chem. Vol. 73, No. 14, 2008 5615

was extracted with CH2Cl2 and the organic layer dried over MgSO4.
Filtration and solvent evaporation left a residue which was purified
by chromatography on silica gel (pentane to pentane/ethyl acetate
4/1). 4a was obtained as a white solid (2.14 g, 77%).
pension of 6a (0.51 g, 1 mmol) in ethanol (5 mL) was stirred at
room temperature for 8 h until clear. Then, LiOH ·H2O (42 mg, 1
mmol) was added, and the reaction mixture was stirred overnight.
After evaporation of the solvent, the residue was dissolved in ether
and filtered over Celite. Evaporation of the filtrate gave a solid
which was washed several times with pentane to deliver 7a as a
hygroscopic white solid (0.39 g, 90%).
Synthesis of N-Benzyl-N-(trifluoromethanesulfonyl)-2-(phe-
nylsulfanyl)-1,1,2,2-tetrafluoroethanesulfonamide (6a). Diiso-
propylethylamine (70 µL, 0.4 mmol) was added under nitrogen to
a solution of 4a (0.15 g, 0.4 mmol) in anhydrous CH2Cl2 (2.5 mL).
The reaction was cooled to -10 °C, and triflic anhydride (100 µL,
0.6 mmol) was added. The mixture was stirred for 30 min at this
temperature and then for 1 h at room temperature (reaction
monitored by 19F NMR in CDCl3). Solvent and volatile byproduct
were evaporated under reduced pressure. The residue was refluxed
in pentane, and before cooling to room temperature, the pentane
fractions were collected. This operation was repeated several times.
Evaporation of the combined pentane fractions left 6a as a white
solid (0.19 g, 92%).
Acknowledgment. Our work was granted by the “Re´gion
Rhoˆne Alpes” and ERAS Labo Co., which are gratefully
acknowledged. Dr. Roman Arvai, who prepared several batches
of starting material 1a, is also gratefully acknowledged.
Supporting Information Available: General methods, ex-
perimental procedures, compound characterization, and copies
of the NMR spectra data for all new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
Synthesis of Lithium N-(Trifluoromethanesulfonyl)-2-(phe-
nylsulfanyl)-1,1,2,2-tetrafluoroethanesulfonamide (7a). A sus-
JO800272Q
5616 J. Org. Chem. Vol. 73, No. 14, 2008