Sulfonimidesversusketosulfonamides as epoxidized imidazolium counterions: Towards a new generation of ionic liquid monomers

Article abstract of DOI:10.1039/d0nj05126h

The design of novel ionic liquid monomers with attractive properties represents a real challenge in the field of poly(ionic liquid)s (PILs). Here, we describe a comparative study of the synthesis of original PIL precursors from various sulfonimides or ketosulfonamides as unprecedented counteranions of imidazolium ILs. These salts were submitted to the Prilezhaev reaction and a first insight into the intrinsic properties of these new epoxy monomers was unveiled, in particular the thermal stability of these advanced epoxy salts by comparison with traditional counterions.

Full text of DOI:10.1039/d0nj05126h

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Sulfonimides versus ketosulfonamides as
epoxidized imidazolium counterions: towards a
new generation of ionic liquid monomers†
Cite this: New J. Chem., 2021,
5, 2953
4
Received 18th October 2020,
Accepted 15th January 2021
a
a
a
a
b
a
C. Chardin,
A. Durand, K. Jarsale, J. Rouden, S. Livi * and J. Baudoux
*
´
DOI: 10.1039/d0nj05126h
rsc.li/njc
The design of novel ionic liquid monomers with attractive properties with halide counterions providing hydrophilic PILs with rela-
1
0
represents a real challenge in the field of poly(ionic liquid)s (PILs). tively limited thermal and chemical stabilities. Moreover, the
Here, we describe a comparative study of the synthesis of original halide counterion has a strong influence on the PIL solubility.
PIL precursors from various sulfonimides or ketosulfonamides as Indeed, the poly(1-vinyl-3-ethylimidazolium) bromide is water-
1
0b
unprecedented counteranions of imidazolium ILs. These salts were soluble in agreement with conventional ionic liquids.
By
submitted to the Prilezhaev reaction and a first insight into the contrast, the replacement of the halide by tetrafluoroborate
À À
4 6
) or hexafluorophosphate (PF ) anions led to cationic
intrinsic properties of these new epoxy monomers was unveiled, in (BF
particular the thermal stability of these advanced epoxy salts by PILs, which are totally insoluble in aqueous media but soluble
comparison with traditional counterions.
in aprotic polar solvents such as acetone, N,N-dimethyl-
formamide (DMF) or dimethyl sulfoxide (DMSO). Finally, NTf2
À
Bis(sulfonyl)imide is a very useful functional group that has promotes high PIL solubility in less polar solvents such as THF.
greatly contributed to the emergence of ionic liquids in recent Similar behavior has been observed for other cationic PILs
1
10a,11
years. Combined with an imidazolium cation, the anion of incorporating a pyridinium heterocycle.
Other parameters
bis(trifluoromethanesulfonyl)imide has been widely studied to such as the glass transition temperature (Tg) depend on the
synthesize various organic salts used as solvents with highly macromolecular architecture of the polymer. As a consequence,
attractive properties, such as excellent thermal and chemical the counteranion also plays a fundamental role. According to the
2
stabilities, low melting point and low viscosity. These organic literature, it is well-known that the Tg of poly(1-vinyl-3-
salts are usually prepared using efficient anionic metathesis ethylimidazolium) decreases after anionic metathesis of bromide
1
d
À
12
with the commercially available salt LiNTf
and then with NTf2 (from 235 1C to 60 1C). Moreover, the thermal
2
3
employed in many reactions. For example, they can be used stability of poly(1-vinyl-3-ethylimidazolium) is approximately
as a polymerization medium for the development of advanced 100 1C higher when the cation is associated with NTf
polymers, doping reagents or additives of polymers. More than bromide.
À
2
rather
4
,5
6
11,12
Despite these promising results, the
recently, they were considered as starting materials for making synthesis of tailor-made ionic liquid monomers combined with
7
poly(ionic liquid)s. In this context, the ion-pair backbone plays non-commercial counteranions remains little studied, whereas
a key role and governs the potential applications of the resulting access to new anionic partners could be achieved by (non-)
8
polymer materials. Thus, many research groups have prepared symmetrical sulfonimide or ketosulfonamide anions. Indeed,
quaternary nitrogen-based monomers (ammonium, pyrrolidi- some groups have reported and compared ionic liquids with
nium, pyridinium, imidazolium. . .) and among the wide variety asymmetric perfluoroanions (XSO
2
-N-SO
2 3
Y with X or Y = F, CF ,
1
3a–d
of poly(ionic liquids)s, the imidazolium core is currently the
2 5
C F , etc.)
and super-delocalized perfluorinated sulfonimide
9
13e
most widespread. All of these cations are commonly associated anions. These ionic liquids showed different viscosity, hydro-
phobicity, ionic conductivity, electrochemical or thermal
a
stability related to the two ends of the anion and its ability to
delocalize the charge. Very recently, Brennecke et al. have
observed higher O2 solubility in an ionic liquid containing
Laboratoire de Chimie Mol ´e culaire et Thio-organique, ENSICAEN,
Universit ´e de Caen Normandie, CNRS, 6 boulevard du Mar ´e chal Juin,
Caen 14050, France. E-mail: jerome.baudoux@ensicaen.fr
b
Universit ´e de Lyon, INSA Lyon, UMR CNRS 5223, IMP Ing ´e nierie des Mat ´e riaux
Polym `e res, Villeurbanne F-69621, France. E-mail: sebastien.livi@insa-lyon.fr
Electronic supplementary information (ESI) available: Synthesis and character-
À
perfluorinated ketosulfonamide compared to NTf2 . The density
and viscosity data remain marginal but similar results have been
†
À
3
1
13
19
noticed in a few cases, especially for [bmim] NTf
2 5
and Z = 51 mPa s) and [bmim] F C–SO N–CO–C F (r = 1.42 g cm
(r = 1.43 g cm
ization of imidazoliums by H, C and F NMR, Mass spectrometry, DSC, TGA
and IR. See DOI: 10.1039/d0nj05126h
2
3
3
2
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significant difference depending on the nature of the counter-
ion with partial hydrolysis of the salt 3c while the ring opening
by-product was observed during the epoxidation of the imida-
zolium bromide. These results clearly confirm the key role of
anions on the intrinsic properties of epoxy salts. Thus, we
undertook the epoxidation of ketosulfonamide salts 1a-b.
Concerning the salt denoted 1a, the use of mCPBA (1 equiv.)
showed only unreacted starting alkene by NMR monitoring
after 3 h 30 of reaction. The addition of a second equivalent of
mCPBA did not afford the expected epoxidized salt while a side
compound was detected by NMR. Next, the epoxidation of the
Scheme 1 Syntheses of imidazolium salts 2a-b and 3a–c from Im–Br.
14a
À
3
and Z = 52 mPa s at 298 K) or [emim] NTf2 (r = 1.52 g cm and salt 1a was investigated by adding DMDO (1 equiv.). After 3 h,
Z = 34 mPa s) and [emim] F C–SO N–CO–CF (r = 1.46 g cm and the NMR revealed the epoxidation of the alkene up to 70%, and
3 2 3
Z = 25 mPa s at 298 K). Ishida et al. measured a lower melting complete oxidation with the further addition of a slight excess
3
14b
À
point for perfluorinated ketosulfonamide versus NTf
2
for ionic of DMDO (0.3 equiv.). Despite this successful oxidation, a
liquids with planar chirality and an excellent thermal stability side-product was again observed over time. Under similar con-
15
(T
decomposition 4270 1C) was observed in almost all cases. These ditions, epoxidation of salt 1b with DMDO (1 equiv.) showed
encouraging data revealed the real potential of these anions and partial oxidation of the alkene (50%) without by-products. Once
16
recent studies have opened easy access to ketosulfonamides or again, the reaction was completed with additional DMDO
17
sulfonimides with particularly attractive methodologies from (0.5 equiv.) inducing mainly the oxidation of the alkene but also
simple substrates. Therefore, the aim of this work was to evaluate the appearance of by-products. Although the use of DMDO led to
À
these analogs of NTf
2
to confirm the potential of these types of the epoxidation of alkenes, the presence of impurities confirmed
À
anion as new epoxy precursors and more generally in PILs the poor stability of these epoxidized salts compared to NTf
chemistry.
Firstly, to prepare aliphatic or aromatic ketosulfonamides, saccharin as
we mixed stoichiometric amounts of benzoyl chloride and imidazolium. Thus, we oxidized imidazolium saccharinate 1c
sulfonamides in the presence of an excess amount of triethyl- with mCPBA (1 equiv.) and minor aromatic impurities appeared
amine (2.5 equiv.). The reaction with methanesulfonamide gave by NMR. In the literature, saccharin can react under acidic
mainly ketosulfonamide which can be isolated without purifi- conditions to give a sulfonic acid and a carboxylic acid or
cation in 53% yield. Under the same conditions, we used amide. In this process of oxidation, the high-resolution mass
benzenesulfonamide to prepare a biaryl ketosulfonamide in spectrometry confirmed the presence of the epoxide 2c (m/z =
moderate yield after recrystallization. These yields can be 215.1) and side-products 4c and 5b-c which could correspond to
2
.
To determine the structure of these side-products, we used
cyclic ketosulfonamide counteranion of
a
1
9
2
0
1
6
improved by using a substoichiometric amount of iodine.
the epoxide opened by saccharinate (m/z = 398.1) and derivatives
Thereafter, efficient deprotonation of ketosulfonamides by (m/z = 416.1 or 417.1) in accordance with acidic conditions in the
sodium hydride (1.1 equiv.) led to the corresponding anions presence of mCBA (Scheme 2). To confirm the poor stability of
with hydrogen gas as a sole by-product. At room temperature, these anions, we checked side reactions for the oxidation of 1a-b
these anions reacted as a one-pot sequence with homemade using DMDO. Once again, HRMS analyses showed the presence
imidazolium Im–Br to afford 1a-b in good yields. Thus, of imidazoliums 4a-b and 5a, which corroborate the slight
an effective and straightforward route (only two steps) was
developed to produce new ionic liquid monomers bearing a
terminal alkene avoiding tedious purification from readily
accessible reagents.
1
8
According to our recent works, imidazolium salts 1a-b
bearing a terminal alkene are promising precursors of epoxy
ionic liquid monomers 2a-b. To date, we have successfully
À
evaluated the epoxidation of several imidazoliums with NTf
2
exclusively (oxidant: meta-chloroperoxybenzoic acid ‘‘mCPBA’’
or dimethyldioxirane ‘‘DMDO’’). As a preliminary study, we
extended this recent methodology using other conventional
À
À
À
counteranions such as PF
6
, BF
4
or Br . TGA thermograms
of salts 3a–c (Scheme 1) clearly highlighted the better thermal
À
stability for the NTf2 salt 3a compared to 3b and 3c (see ESI†).
Thus, the thermal stability of these epoxidized salts can be
À
À
À
2
.
ranked according to the following order: BF
This ranking is consistent with conventional salts without the
epoxy group. From a chemical point of view, we detected a zolium ketosulfonamides.
4
o PF
6
o NTf
Scheme 2 Side-products detected by HRMS after epoxidation of imida-
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reactivity of the anion of ketosulfonamide towards the epoxide
even under neutral conditions (Scheme 2 and ESI†).
These oxidations revealed degradation of ketosulfonamide
counterions in the presence of strong oxidizing agents such as
mCPBA and DMDO. For salts 2a-b, the ketosulfonamide anion
is still too nucleophilic towards the epoxide. These results
showed the incompatibility of ketosulfonamide anions during
the epoxidation of an ionic liquid by mCPBA. Although the
epoxidation could be carried out with DMDO, the presence of
impurities limits their potential applications. Hence, we con-
tinued our investigation by studying the synthesis of the
original sulfonimides. The synthesis of these anions required
the preparation of sulfonyl chlorides and then sulfonamides
which lead potentially to non-symmetrical sulfonimides. We
started by the synthesis of symmetrical sulfonimide 8 bearing
Scheme 4 Synthesis of epoxidized sulfonimide salts 13a–c.
two p-methoxy aromatic rings (Scheme 3). 4-Methoxy- the oxidation of 12b-c with mCPBA (2 equiv.) required 24 h at
benzenesulfonyl chloride 6 was prepared by the reaction 40 1C to give 13b and 13c in 89% and 68% yield, respectively
between anisole and chlorosulfonic acid. Sulfonyl chloride 6 (Scheme 4).
was then transformed into sulfonamide 7 in quantitative yield.
Under basic conditions, this compound reacted with sulfonyl the NTf2 anion with the presence of a phenyl moiety as a
The fluorinated sulfonimide of salt 13c is fairly similar to
À
chloride 6 to afford sulfonimide 8. The anionic metathesis of unique difference. Thus, a comparison of the thermal behavior
imidazolium Im–Br with deprotonated sulfonimide 8 gave a can be carried out between these salts 10, 13a–c and a similar
À
salt 9 bearing a terminal alkene. Oxidation of this salt with the imidazolium salt incorporating the NTf
most efficient oxidant determined from our previous work, i.e. (Im–NTf
2
as a counteranion
, high
2
) (see ESI†). For this epoxidized salt Im–NTf
2
excess of DMDO, led quantitatively to salt 10 after 7 h in thermal stability (up to 310 1C) was observed with a maximal
acetone. This epoxidation clearly showed better stability of this degradation temperature between 410 and 460 1C. For imida-
anion compared to previous ketosulfonamide salts.
zolium combined with symmetrical biaryl sulfinimide anion
After the successful synthesis of epoxy ionic liquid 10 bearing a 10, two degradation peaks have been revealed at 110 1C
symmetrical biaryl sulfinimide counterion, we were interested (14 wt%) and 320 1C (50 wt%), respectively. The analysis of
in the preparation of non-symmetrical anions (Scheme 4). Due monoaryl salt 13a showed two decomposition temperatures at
to the important contribution of fluorine atoms on the final 120 1C (16 wt%), followed by a maximal degradation temperature
properties of ionic liquids, we used triflamide in the presence at around 379–414 1C. Consequently, the monoaryl sulfonimide
of various aromatic sulfonyl chlorides. Firstly, an ether group salt 13a appears more stable which may be due to the presence
was kept on the aromatic sulfonyl chlorides to give salt 11a, of fluorine atoms whereas the steric effects and the rigidity of the
possibly to incorporate a perfluorinated chain if necessary. We biaryl counterion destabilize salt 10. Finally, the TGA of salt 13b
also prepared the fluorinated sulfonamide salts 11b and 11c exhibits better thermal stability compared to salt 13c. In fact, salt
according to the previous strategy from an arylsulfonyl 13b had thermal stability of up to 300 1C with a mass loss of only
chloride and triflamide in the presence of an excess of NaH. 4%. The maximum degradation of salt 13b was noticed at high
The sulfonamide salts 11a–c were directly engaged in anionic temperature from 350 1C to 420 1C, which was close to the values
2
metathesis with imidazolium Im–Br to give products 12a–c with of the reference Im–NTf (410–460 1C). These results showed the
good yields. All ionic liquids were quantitatively oxidized with great potential of sulfonimides to synthesize tailor-made ionic
DMDO (2.4 equiv.) in 2 h at room temperature. Worthy of note, liquid monomers and their superiority over ketosulfonamides
with a better chemical and thermal stability. In addition, these
anions are easily adjustable without reducing their potential for
polymerization at processing temperatures of epoxy networks.
Finally, we synthesized ionic liquids carrying two epoxides
from sulfonimide salts 11b-c, which led to the best results in
the thermal analysis of salts 13b-c. The sequence was slightly
different from our previous study, the synthesis of salts 15a-b
required anionic metathesis with imidazolium diIm-Br to give
14a and 14b in 63% and 48% yield, respectively. In both cases, the
oxidation of the two alkenes was carried out with 3.3 equivalents of
DMDO to quantitatively obtain the corresponding diepoxides
15a and 15b (Scheme 5).
The TGA curves of diepoxides 15a and 15b have a similar
Scheme 3 Synthesis of symmetrical sulfonimide salt 10.
appearance to the monoepoxides 13b and 13c (see ESI†). A first
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3
4
5
6
7
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There are no conflicts to declare.
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