Synthesis and properties of N,N′-dialkylimidazolium bis(nonafluorobutane-1-sulfonyl)imides: A new subfamily of ionic liquids

Article abstract of DOI:10.1016/j.tet.2006.01.015

A series of N,N′-dialkylimidazolium bis(nonafluorobutane-1-sulfonyl) imides was synthesized in high yields by quaternization of imidazole derivatives with various readily available alkylating reagents, followed by anion exchange with highly stable and non-hygroscopic potassium bis(nonafluorobutane-1- sulfonyl)imide. The latter was obtained by an improved method starting from ammonium chloride and nonafluorobutane-1-sulfonyl fluoride. The quaternary imidazolium salts thus obtained constitute a new subfamily of thermally stable and remarkably hydrophobic ionic liquids with melting points in the range 0-40°C and solubilities in water and organic solvents (aromatic hydrocarbons, dialkyl ethers) in the range of 0.5-1.5 wt%. The ionic liquids can be easily purified from ionic byproducts (e.g., halogenide salts) by aqueous extraction followed by thorough drying in a high vacuum without loss of yield. Due to the above features, these new ionic fluids may be considered as promising recyclable media in repeated catalytic processes.

Full text of DOI:10.1016/j.tet.2006.01.015

Tetrahedron 62 (2006) 3137–3145
Synthesis and properties of N,N0-dialkylimidazolium
bis(nonafluorobutane-1-sulfonyl)imides: a new subfamily
of ionic liquids
b
Ser Kiang Quek,a,b Ilya M. Lyapkaloa, and Han Vinh Huynh
*
aInstitute of Chemical and Engineering Sciences Ltd, 1 Pesek Road, Jurong Island, Singapore 627833
bDepartment of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
Received 18 October 2005; revised 23 November 2005; accepted 5 January 2006
Available online 13 February 2006
Abstract—A series of N,N0-dialkylimidazolium bis(nonafluorobutane-1-sulfonyl)imides was synthesized in high yields by quaternization of
imidazole derivatives with various readily available alkylating reagents, followed by anion exchange with highly stable and non-hygroscopic
potassium bis(nonafluorobutane-1-sulfonyl)imide. The latter was obtained by an improved method starting from ammonium chloride and
nonafluorobutane-1-sulfonyl fluoride. The quaternary imidazolium salts thus obtained constitute a new subfamily of thermally stable and
remarkably hydrophobic ionic liquids with melting points in the range 0–40 8C and solubilities in water and organic solvents (aromatic
hydrocarbons, dialkyl ethers) in the range of 0.5–1.5 wt%. The ionic liquids can be easily purified from ionic byproducts (e.g., halogenide
salts) by aqueous extraction followed by thorough drying in a high vacuum without loss of yield. Due to the above features, these new ionic
fluids may be considered as promising recyclable media in repeated catalytic processes.
q 2006 Elsevier Ltd. All rights reserved.
1. Introduction
To circumvent these difficulties, other types of anions were
introduced including n-alkyl sulfates, trifluoromethane-
sulfonates, bis(trifluoromethanesulfonyl)imides and tetra-
alkylborates. Alternative alkylating reagents, alkyl sulfates
and sulfonates were employed in place of ‘traditional’ alkyl
halogenides for synthesis of the N,N0-dialkylimidazolium
moieties in order to completely eliminate the possibility of
generating heavy halogenides (Cl2, Br2, I2). Special
attention has been paid to ionic liquids containing N,N0-
dialkylimidazolium cations combined with fluoroanions.
As recently reviewed,2 much diversity and availability of
fluorine-containing anions ensure a broad range of proper-
ties and applications of the respective ionic liquids.
Recently, N,N0-dialkylimidazolium bis(trifluoromethane-
sulfonyl)imides have received interest as remarkably
thermo- and chemically stable ionic liquids.2,3 In this
respect, the anions combining high stability of bis(trifluor-
omethanesulfonyl)imide with much higher hydrophobicity
due to higher fluorine content are of interest for design of
novel ionic liquids as special solvent components for bi- and
triphasic solvent systems. Herein, we report the synthesis
and properties of N,N0-dialkylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imides (1 and 3) and N,N0-dialkylimi-
dazolium nonafluorobutane-1-sulfonates (2) as new series
of ionic liquids (Fig. 1).
Low-melting salts containing lipophilic quaternary organic
cations, ionic liquids, have attracted much interest in the
area of electrochemistry as well as novel solvents and
reaction media.1 These fluids consisting of only ions were
found to have no detectible equilibrium vapor pressure. In
recognition of this remarkable property they were termed
as environmentally benign or ‘green’ solvents.1g Many
classical organic reactions were successfully modeled and
often optimized in these media.
The first generation of ionic liquids comprised mainly the
derivatives of inorganic halogen-ligated ate-complexes
such as BF24 , PF62 and AlCl24 as the anionic moieties.
These anions, especially the latter two, are prone to
releasing harmful and corrosive HF and HCl upon
interaction with traces of moisture, which in turn imposes
significant restrictions on applications of the corresponding
ionic liquids. Moreover, uncontrolled halogenide content
often affects and/or deteriorates transition metal catalysis.1h
Keywords: Nonafluorobutane-1-sulfonyl fluoride; Dialkyl imidazolium;
Bis(nonafluorobutane-1-sulfonyl)imide; Hydrophobicity; Ionic liquids.
Corresponding author. Tel.: C65 6796 3930; fax: C65 6316 6184;
e-mail: ilya_lyapkalo@ices.a-star.edu.sg
*
0040–4020/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.01.015

3138
S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
1: R1 = CH3, X = NNf2
2: R1 = CH3, X = ONf
features (appearance, progress) resulting in a similar yield
R1
Alkyl
N
N
X
of KONf B as under conditions b. The identity of the main
reaction product, KONf B7 in all four protocols described
above (see Scheme 1) was confirmed by FAB-MS analysis
as well as by 19F NMR measurements of the mixed samples
indicating complete overlap of all the relevant signals (see
Section 3).8
3: R1 = CH3(CH2)2, X = NNf2
1–3
Nf:CF3(CF2)3SO2
Figure 1.
2. Results and discussion
In the experiments with K2CO3, we noticed evolution
of CO2 gas during the reaction course and therefore
inferred the following mechanism for the salt B formation
(Scheme 2).
Our approach towards the synthesis of compounds 1–3 is
based on a two-step protocol, which comprises the
quaternization of imidazole derivatives with various readily
available alkylating reagents (alkyl bromides, chlorides,
sulfates) followed by anion exchange with highly stable
and non-hygroscopic potassium bis(nonafluorobutane-
1-sulfonyl)imide (A) or potassium nonafluorobutane-1-
sulfonate (B). We anticipated that the resulting salts 1–3
should be low-melting solids or even rt ionic liquids. They
would be hydrophobic enough to make possible reduction of
the residual halogenide content below detection limit by
repeated extraction with deionized water without significant
loss of yield at the purification step.
Presumably, acetamide remains mainly unreacted during
the entire reaction course, and NfF interacts directly with
K2CO3 owing to its affinity to anionic hard nucleophilic
centers.9 The lack of acetamide reactivity is attributed to the
insufficient basicity of K2CO3 or K3PO4 failing to produce a
sufficient equilibrial concentration of the reactive CH3-
C(O)NH2 species for the desired N-sulfonylation to take
place in favour of the direct interaction between NfF and
K2CO3 (see Scheme 2).
To circumvent the difficulties caused by using K2CO3 we
decided to develop a new protocol employing NH4Cl
instead of CH3C(O)NH2 and Et3N,10 which is fully
compatible with NfF in MeCN as a reaction solvent.11
This synthetic protocol proved to be successful and enabled
us to obtain the intermediate triethylammonium salt
Et3NH4NNf22 (Scheme 3).
An inspection of available literature data showed that the
potassium salt A could be synthesized directly from
trifluoroacetamide or acetamide using the convenient and
relatively inexpensive sulfonylating reagent, nonafluoro-
butane-1-sulfonyl fluoride (NfF),4 in the presence of
potassium carbonate.5 As acetamide is widely available and
cheap, it became a reactant of choice for the present study.
Subsequent treatment of the intermediate salt Et3-
NH4NNf22 with aqueous KOH furnishes the desired pure
potassium salt A as a white crystalline solid, which readily
precipitates out of the aqueous solution12 in good overall
yield (see Section 3).
However, in our hands, no anticipated potassium imide A
(KNNf2) was obtained as a main reaction product
(Scheme 1). Instead, potassium nonafluorobutane-1-sulfo-
nate (KONf) (B) was isolated in reasonably good yield
resulting from the reproduction of the literature procedure5
(conditions a). The same results were obtained at rt
employing either K2CO3 or more basic K3PO4 as an
auxiliary base6 in DMF as a solvent (modified conditions b).
Both KONf and KNNf2 were found to be thermally stable
and non-hygroscopic salts.13 They are poorly soluble in
water, KONf somewhat better than KNNf2. Remarkably,
both salts show good solubilities in a number of organic
solvents such as THF, MeCN, Me2CO, AcOEt, DMSO,
DMF, dioxane, 1,2-dimethoxyethane and alcohols although
they are virtually insoluble in chlorohydrocarbon- and
hydrocarbon solvents.
A control experiment carried out with K2CO3 in the absence
of acetamide (conditions c) revealed the same reaction
K NNf2
A
a or b or c
NfF
Nf:CF3(CF2)3SO2
K ONf
B
Having the requisite potassium salts A and B in hand, we
established the synthesis of the target N-methyl-N0-alkyl
imidazoliums 1 and 2 (Scheme 4). In a first step, an
alkylation of N-methyl imidazole with a slight excess
of RX0 was carried out upon heating without solvent
Scheme 1. a: CH3C(O)NH2, K2CO3 in THF 6 h at 65 8C, (62% yield);7 b:
CH3C(O)NH2, K2CO3 (73% yield) or K3PO4 (75% yield)7 in DMF at rt; c:
as in b employing K2CO3 but without CH3C(O)NH2, salt B (74% yield).
Nf
O
K O
O
slow
KF
fast
C O K
O
NfF
C O K
CO2
+
K ONf
+
B
Scheme 2.
Scheme 3.
Et3N in MeCN
aq KOH
2NfF
Et3NH NNf2
K NNf2 (81%)
NH4Cl
+
H2O/MeOH 10:1
–40° to 65°C, 17 h
A

S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
3139
R
R
K X (A or B)
R–X'
N
N
N
X
Me N
Me N
X'
Me N
CH2Cl2/H2O
rt
1: X = NNf2
2: X = ONf
Scheme 4.
Table 1. Synthesis and properties of N-methyl-N0-alkyl imidazolium bis(nonafluorobutane-1-sulfonyl)imides 1 and nonaflates 2
Entry
Reaction conditions
Product
Properties
RX0 (equiv)
T (8C)
Time (h)
X
Salt 1 or 2 (yield, %)
Mp (8C)
Decomposition (8C)
1
2
3
4
5
6
7
8
MeCH2OSO2Et
Me(CH2)2Br
Me(CH2)3Cl17
Me(CH2)4Br
Me2CH(CH2)2Br
Me2CHCH2Br
Me2CHBr
rta
70
90
70
70
70
70
70
70
90
70
70
17
4
24
3
NNf22
NNf22
NNf22
NNf22
NNf22
NNf22
NNf22
NNf22
ONf2
ONf2
ONf2
ONf2
1a (98)
!25b (31 8C)15
!4c
290
300
320
295
280
295
310
280
285
295
310
280
1b (98)
1c (O99)
1d (97)
1e (O99)
1f (O99)
1g (99)
1h (O99)
2a (82)
2b (82)
2c (81)
2d (79)
!25b
!25b
39–40
5
17
24
24
4
24
24
24
!4c
28–29 8C
MeCH2CH(Me)Br
Me(CH2)2Br
!4c
33–34
9
10
11
12
Me(CH2)3Cl17
Me2CHBr
MeCH2CH(Me)Br
!25b (20 8C)3
!25b
42–43
a An appreciable exothermic effect was observed during the alkylation.
b Crystallizes in a fridge (C4 8C) and melts at rt again.
c Crystallizes in a deep freezer (K18 8C) and melts in a fridge (C4 8C) again.
(see Table 1) followed by removal of volatiles (if any) in
high vacuum to give a nearly quantitative yield of the
corresponding N-methyl-N0-alkyl imidazolium salts.14
quantitatively. The first alkylation with n-propyl bromide
was carried out in MeCN and enabled the introduction of
only one propyl group with O95% selectivity. The second
alkylation conducted after removal of MeCN in0 vacuum
furnished the desirable unsymmetrical N,N -dialkyl
imidazolium moiety. This protocol culminated with
anion exchange with KNNf2 as described above resulting
in the isolation of the anticipated products 3a,b in high
yields and at least 95% purity according to 1H NMR
spectroscopic data.
The desired ionic fluids 1, 2 were then produced by anion
exchange with KX (A or B) in biphasic CH2Cl2/H2O
mixture followed by thorough washing of the organic phase
with deionized water until a negative halogenide test with
aqueous AgNO3 was achieved. Removal of CH2Cl2
followed by thorough drying in high vacuum enabled us
to obtain the ionic liquids 115 and 216 in high yields and
purities. The alkylation reaction conditions, yields and
properties of the N-methyl-N0-alkyl imidazolium salts 1
and 2 obtained are summarized in the Table 1.
The imidazolium salts 1–3 are thermally stable (up to 300—
320 8C), colourless or yellowish non-hygroscopic fluids or
low-melting crystalline solids (Table 1). They neither change
appearance nor gain weight upon exposure to atmospheric
moisture for at least 1 week. The NNf2-derivatives tend to
melt at lower temperatures than their ONf-counterpart.
Not surprisingly, symmetrical N,N0-dimethyl imidazolium
bis(nonafluorobutane-1-sulfonyl)imide has a higher melting
point (69 8C)15 compared to the unsymmetrically substituted
salts 1 and 3.
Unfortunately, among the few commercially available
N-alkyl imidazoles, only N-methyl imidazole is offered at
an affordable price. Hence, the ionic liquids obtained as
described above are limited invariably to imidazolium
derivatives comprising a N-methyl substituent.
To circumvent this limitation, we developed a one pot
sequential alkylation protocol starting from parent imida-
zole. The protocol is exemplified by the synthesis of the
products 3a,b (Scheme 5).
In general, all NNf2-derived ionic liquids presented in this
work have interesting specific properties. We believe that
the high content of perfluorobutyl groups in NNf2-derived
ionic liquids is accountable for their unique characteristics.
Unlike conventional ionic liquids, which are often miscible
with chlorohydrocarbon solvents, the salts 1 tend to form
Treatment of imidazole with MeONa in MeOH followed
by removal of the solvent gave sodium imidazolide
R
N
N
Me(CH2)2Br
MeCN, rt
i or ii
MeONa
MeOH
N– Na+
N
N
NNf2
NH
KNNf2
N
N
(CH2)2Me
(CH2)2Me
R = Et (3a, 99%)
R = n-Bu (3b, >99%)
Scheme 5. (i) (EtO)2SO2, 0 8C to rt, 17 h; (ii) Me(CH2)3Br, 70 8C, 3 h.

3140
S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
two-phase mixtures with chloroform. Thus, the salt 1h
forms a two-phase system upon mixing with CDCl3, with
the concentrations of 1h in the upper and lower phases 3.5
and 45.5 wt%, respectively. The mixture turns homo-
geneous upon heating and separates to two-phases upon
cooling down to rt.
(Lancaster) were dried in high vacuum before use. Et3N
(Riedel-de-Haen) was stored over KOH pellets.
3.1.1. Potassium bis(nonafluorobutane-1-sulfonyl)imide
(A). NH4Cl (13.9 g, 250 mmol) was placed into 1 L reaction
flask equipped with efficient magnetic stirring bar and dried
under high vacuum (hereafter HV) to remove traces of
moisture before MeCN (125 mL) and NfF (166.9 g,
550 mmol) were added. The resulting two-phase suspension
was cooled down to K40 8C, and Et3N (127.6 g,
1250 mmol) pre-cooled with liquid nitrogen was quickly
added to the reaction mixture upon vigorous stirring. After
gradual warming up to ambient temperature, the resulting
mixture was heated up to 65 8C and stirred at this
temperature overnight. After cooling down to ambient
temperature the bulk of MeCN was removed in vacuum.
The residue was partitioned between CH2Cl2 (400 mL)
and deionized water (200 mL). The organic layer was
then thoroughly washed with deionized water (3!200 mL)
until it showed a negative chloride test with aqueous
AgNO3. Volatiles were removed in vacuum to give the
intermediate Et3NH4NNf22 (165.85 g, 97% yield) as
a tawny crystalline solid, mp 42–43 8C, 1H NMR
The nature of the ionic liquids 1 is especially pronounced in
their remarkably low solubilities in typical organic solvents
(toluene, dialkyl ethers) and water. For example, the ionic
liquid 1c shows solubilities of 0.7 wt% in water, 0.3 wt% in
toluene and 1.2 wt% in diisopropyl ether, that is, it is
virtually immiscible with the above solvents. Specific
solvation effects in the salts 1 make them truly orthogonal
reaction media and should allow an easy recycling of
these ionic liquids by extractive removal of organic products
and inorganic salts with organic solvents and water,
respectively. This feature may turn out to be useful in the
design of new recoverable catalytic systems.18
3. Experimental
3.1. General
3
(400.23 MHz): d 1.33 (9H, t, JZ7.3 Hz, 3CH2CH3), 3.18
(6H, br q, 3JZ7.3 Hz, 3CH2CH3), 7.19 (1H, br s, NHC). 13
C
NMR (100.65 MHz): d 8.5 (CH2CH3), 47.2 (CH2CH3).
19F NMR (376.59 MHz): d K127.1 (4F, t*, JZ14.3 Hz,
2CF2-3), K122.1 (4F, mc, 2CF2-2), K113.9 (4F, t*, JZ
14.3 Hz, 2CF2-1), K81.9 (6F, tt, J1Z10.0 Hz, J2Z2.3 Hz,
2CF3); *further splitting due to the multiple 19F,19F
couplings.
NMR spectra were recorded on Bruker 400 UltraShield
instrument in CDCl3 as a solvent unless stated otherwise. 1H
and 13C chemical shifts are expressed as ppm downfield
from SiMe4 (dZ0) used as an internal standard. 19F
chemical shifts are given in ppm upfield from PhCF3
(dZK63.7 ppm)19 used as an internal standard. 13C signals
of the CF3(CF2)3 groups were not given due to very
complicated and overlapping heteronuclear 13C,19F coup-
ling patterns. 15N NMR signals of the 1-isopropyl-3-
methylimidazolium cation in the salt 1g are obtained
using insensitive nuclei enhanced by polarization (INEPT)
technique with the chemical shifts expressed as ppm upfield
from MeNO2 (dZ0) used as an external standard. Mass
spectra were registered with Finnigan MAT 95XP
(FAB-HRMS) and with Macromass Quattro microe API
(ESI-MS) spectrometers. Decomposition temperatures of
the salts B, 1 and 2 were determined with SDT 2960
Simultaneous DSC-TGA instrument. Microanalyses were
performed with Euro Elemental Analyser. Melting points
were determined using Bu¨chi Melting Point B-540
apparatus and are uncorrected.
Without further purification, Et3NH4NNf22 (165.9 g,
243 mmol) was dissolved in MeOH (30 mL) and added
dropwise to the solution of KOH (27.0 g, 590 mmol) in
water (300 mL) upon vigorous stirring. Instantaneous
precipitation of the desired KNNf2 A was observed. The
reaction mixture was stirred overnight before filtering the
precipitate. The crystalline residue was washed thoroughly
with cold deionized water until neutral pH followed by
drying on the sinter funnel and washing additionally with
CHCl3 (3!150 mL) to give the salt A (148.83 g, 81% yield)
as a white crystalline solid, mp 340–341 8C (decomp.). A,
19F NMR (376.59 MHz, DMSO-d6): d K128.2 (4F, t*,
JZ13.9 Hz, 2CF2-3), K123.5 (4F, mc, 2CF2-2), K115.8
(4F, t*, JZ13.5 Hz, 2CF2-1), K82.8 (6F, tt, J1Z9.8 Hz,
*
J2Z2.3 Hz, 2CF3); further splitting due to the multiple
19F,19F couplings. HRMS (FAB negative, Cs, 20 keV,
direct, glycerin, m/z), found: 579.9083. Calcd
(C8F18NO4SK2 ): 579.8976. Anal. Calcd for C8F18KNO4S2:
C, 15.52; F, 55.22; N, 2.26; S, 10.36. Found: C, 15.50; H, 0;
N, 2.32; S, 10.60.
The syntheses of the potassium salts A and B were carried
out under an atmosphere of argon in heat-gun dried reaction
flasks. Solvents for syntheses were dried following standard
procedures and freshly distilled prior to use: DMF (vacuum
distillation from CaH2), MeCN (distillation from CaH2),
THF (distillation from Na–K alloy/Ph2CO). Solvents for
extraction were distilled before use. Nonafluorobutane-
1-sulfonyl fluoride was obtained from Bayer AG; it can
also be purchased from commercial suppliers. N-Methyl
imidazole (Fluka) was distilled and stored over BaO.
3.1.2. Attempts to prepare the potassium salt (A) by
interaction of acetamide with NfF in the presence of
K2CO3 or K3PO4: potassium nonafluorobutanesulfonate
(B) (see Scheme 1).
The alkylating reagents (see Table 1), purchased from
Lancaster, Aldrich and Fluka were distilled before use.
a: according to the literature procedure:5 The synthesis was
attempted using CH3C(O)NH2 (0.827 g, 14.0 mmol),
K2CO3 (5.00 g, 36.0 mmol), THF (15 mL) and NfF (2!
4.23 g, 2!14 mmol). After heating for the designated time
(2!3 h) and removal of volatiles in vacuum, the mixed
K2CO3 (Fluka), K3PO4$H2O (Riedel-de-Haen), NH4Cl
(Merck), CH3C(O)NH2 (Acros Organics) and imidazole

S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
3141
solid residue was treated with Me2CO (25 mL) and filtered;
the insoluble precipitate on the sinter funnel was washed
with Me2CO, the combined filtrate was evaporated in
vacuum, MeOH (10 mL) was added to the residue, and the
resulting mixture was refluxed for a few minutes until the
crystalline residue was completely dissolved. The resulting
homogenous solution was diluted with CHCl3. The crystal-
line precipitate was filtered off and dried to give 5.40 g of
white crystalline solid, which was identified as potassium
nonaflate B (62% yield).
3.2.1. 1-Ethyl-3-methylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (1a). The title compound was
prepared from N-methylimidazole (1.314 g, 16.0 mmol),
(EtO)2SO2 (2.35 g, 15.2 mmol) and the salt A (9.00 g,
14.5 mmol) as described in GP1; yield 9.82 g (98%) as
a clear viscous slightly yellowish liquid. 1a, 1H NMR
(400.23 MHz, DMSO-d6): d 1.42 (3H, t, 3JZ7.3 Hz,
3
CH2CH3), 3.85 (3H, s, NCH3), 4.19 (2H, q, JZ7.3 Hz,
NCH2), 7.69 (1H, t, JZ1.8 Hz) and 7.78 (1H, t, JZ1.8 Hz)
(both CH]CH), 9.11 (1H, br s, N–CH]N). 13C NMR
(100.65 MHz, DMSO-d6): d 15.1 (CH2CH3), 35.7 (NCH3),
44.1 (NCH2), 122.0 and 123.6 (both CH]CH), 136.3
(N–CH]N). 19F NMR (376.59 MHz, DMSO-d6): d K128.1
(4F, t*, JZ14 Hz, 2CF2-3), K123.4(4F, mc, 2CF2-2), K115.7
(4F, br t, JZ14 Hz, 2CF2-1), K82.8 (6F, tt, J1Z9.7 Hz, J2Z
b: room temperature modification employing DMF as a
solvent: K2CO3 (81.8 g, 592 mmol) was dried at 200 8C in a
HV for 3 h and transferred into 500 mL reaction flask
equipped with efficient magnetic stirring bar. After flushing
with dry argon and cooling, DMF (160 mL), dry CH3-
C(O)NH2 (9.54 g, 161.5 mmol) and followed by NfF
(103.4 g, 342 mmol) were consecutively added at rt. The
reaction mixture was stirred for 40 h. During first 24 h,
evolution of CO2 was clearly observed. The isolation carried
out as described above furnished 84.42 g of white crystal-
line solid, which was identified as potassium nonaflate B
(73% yield). Likewise, the analogous reaction carried out
with K3PO4 in place of K2CO3 afforded the salt B in 75%
yield.
*
2.5 Hz, 2CF3); further splitting due to the multiple 19F,19F
couplings. MS (ESI positive, ion energy 0.3 eV), m/z (%):
111.03 [C6H11NC2 ] (100) and lighter fragments. MS (ESI
negative, ion energy 0.3 eV), m/z (%): 579.86
[(C4F9SO2)2NK] (100), 296.95 [C4F9SO2NK] (24.3) and
lighter fragments.
3.2.2. 1-Propyl-3-methylimidazolium bis(nonafluorobu-
tane-1-sulfonyl)imide (1b). The title compound was
prepared from N-methylimidazole (1.223 g, 14.9 mmol),
Me(CH2)2Br (1.93 g, 15.7 mmol) and the salt A (8.79 g,
14.2 mmol) as described in GP1; yield 9.85 g (98%) as a
c: a reference experiment in DMF conducted in the absence
of CH3C(O)NH2: The experiment was carried out with
K2CO3 (3.24 g, 23.4 mmol), DMF (15 mL) and NfF (4.75 g,
15.7 mmol) as described above, the progress and appear-
ance being identical. The workup and the isolation as
described above resulted in the salt B (3.72 g, 74% yield) as
a white crystalline solid, decomp. ca. 450 8C. B, 19F NMR
(376.59 MHz, DMSO-d6): d K128.1 (4F, t*, JZ13.5 Hz,
2CF2-3), K123.8 (4F, mc, 2CF2-2), K117.2 (4F, t*, JZ
13.5 Hz, 2CF2-1), K83.0 (6F, tt, J1Z9.8 Hz, J2Z2.9 Hz,
2CF3); *further splitting due to the multiple 19F,19F
couplings. HRMS (FAB negative, Cs, 20 keV, direct,
glycerin, m/z), found: 298.9449. Calcd (C4F9O3SK):
298.9419. Anal. Calcd for C4F9KO3S: C, 14.21; F, 50.56;
S, 9.48. Found: C, 14.48; H, 0; S, 9.75.
1
clear yellowish viscous liquid. 1b, H NMR (400.23 MHz,
DMSO-d6): d 0.87 (3H, t, 3JZ7.4 Hz, CH2CH3), 1.81 (2H,
sextet, 3JZ7.3 Hz, CH2CH3), 3.86 (3H, s, NCH3), 4.13 (2H,
t, 3JZ7.1 Hz, NCH2), 7.70 (1H, t, JZ1.8 Hz) and 7.76 (1H,
t, JZ1.8 Hz) (both CH]CH), 9.10 (1H, br s, N–CH]N).
13C NMR (100.65 MHz, DMSO-d6): d 10.3 (CH2CH3), 22.9
(CH2CH3), 35.7 (NCH3), 50.3 (NCH2), 122.3 and 123.7
(both CH]CH), 136.6 (N–CH]N). 19F NMR
(376.59 MHz, DMSO-d6): d K128.1 (4F, t*, JZ14 Hz,
2CF2-3), K123.3 (4F, mc, 2CF2-2), K115.6 (4F, br t, JZ
14 Hz, 2CF2-1), K82.8 (6F, tt, J1Z9.7 Hz, J2Z2.5 Hz,
2CF3); *further splitting due to the multiple 19F,19F
couplings. MS (ESI positive, ion energy 0.3 eV), m/z (%):
125 [C7H13NC2 ] (100) and lighter fragments. MS (ESI
negative, ion energy 0.3 eV), m/z (%): 580 [(C4F9SO2)2NK]
(100) and lighter fragments.
3.2. Synthesis of N-methyl-N0-alkyl imidazolium
bis(nonafluorobutane-1-sulfonyl)imides (1) and nona-
flates (2) (see Scheme 4): general procedure (GP1)
3.2.3. 1-Butyl-3-methylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (1c). The title compound was
prepared from N-methylimidazole (1.20 g, 14.6 mmol),
Me(CH2)3Cl (1.42 g, 15.3 mmol) and the salt A (8.61 g,
13.9 mmol) as described in GP1; yield 9.96 g (O99%) as
A mixture of N-methylimidazole (1.05 equiv) and the
alkylating reagent R0X (1.1 equiv) was stirred under the
conditions (temperature and time) specified in the Table 1.
The volatiles were then removed in HV, the residue was
dissolved in CH2Cl2 (typically 0.15–0.20 mmol/mL) and
transferred into the separating funnel containing a suspen-
sion of the salt A or B (0.85–1 equiv) in water (typically
0.25–0.30 mmol/mL). The content of the funnel was
vigorously shaken for 3–5 min so that no further precipitate
was present in the resulting two-phase mixture. The organic
layer was washed with dilute HCl (pH 1) and 3–4 times with
deionized water so that the last aqueous layer after
extraction should indicate pH 6–7 and give a negative
halogenide test with aqueous AgNO3. CH2Cl2 was removed
in vacuum, and the residue was vigorously stirred for
15–17 h at 40–50 8C under HV to give the desired molten
salt 1 or 2 in the designated yield (see Table 1).
a
clear yellowish viscous liquid. 1c, 1H NMR
3
(400.23 MHz): d 0.94 (3H, t, JZ7.4 Hz, CH2CH3), 1.36
(2H, sextet, 3JZ7.4 Hz, CH2CH3), 1.85 (2H, mc,
3
NCH2CH2), 3.93 (3H, s, NCH3), 4.18 (2H, t, JZ7.6 Hz,
NCH2), 7.38 (1H, t, JZ1.7 Hz) and 7.40 (1H, t, JZ1.7 Hz)
(both CH]CH), 8.71 (1H, br s, N–CH]N). 13C NMR
(100.65 MHz): d 12.6 (CH2CH3), 19.0 (CH2CH3), 31.8
(NCH2CH2), 35.8 (NCH3), 49.7 (NCH2), 122.3 and 123.6
(both CH]CH), 135.7 (N–CH]N). 19F NMR
(376.59 MHz): d K127.0 (4F, t*, JZ14 Hz, 2CF2-3),
K122.0 (4F, mc, 2CF2-2), K113.8 (4F, br t, JZ14 Hz,
2CF2-1), K82.0 (6F, tt, J1Z9.9 Hz, J2Z2.3 Hz, 2CF3);
*further splitting due to the multiple 19F,19F couplings.
MS (ESI positive, ion energy 0.3 eV), m/z (%): 139.1

3142
S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
[C8H15NC2 ] (100) and lighter fragments. MS (ESI negative,
ion energy 0.3 eV), m/z (%): 580.0 [(C4F9SO2)2NK] (100)
and lighter fragments.
135.9 (N–CH]N). 19F NMR (376.59 MHz): d K127.0 (4F,
t*, JZ14 Hz, 2CF2-3), K122.0 (4F, mc, 2CF2-2), K113.8
(4F, br t, JZ14 Hz, 2CF2-1), K82.0 (6F, tt, J1Z9.9 Hz,
*
J2Z2.3 Hz, 2CF3); further splitting due to the multiple
19F,19F couplings. MS (ESI positive, ion energy 0.3 eV), m/z
(%): 139.1 [C8H15NC2 ] (100) and lighter fragments. MS
(ESI negative, ion energy 0.3 eV), m/z (%): 580.0
[(C4F9SO2)2NK] (100) and lighter fragments.
3.2.4. 1-Pentyl-3-methylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (1d). The title compound was
prepared from N-methylimidazole (1.172 g, 14.3 mmol),
Me(CH2)4Br (2.27 g, 15.0 mmol) and the salt A (8.42 g,
13.6 mmol) as described in GP1; yield 9.66 g (97%) as a
clear yellowish viscous liquid. 1d, 1H NMR (400.23 MHz):
d 0.87 (3H, t, 3JZ7 Hz, CH2CH3), 1.23–1.38 (4H, m,
3.2.7. 1-Isopropyl-3-methylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (1g). The title compound was
prepared from N-methylimidazole (1.22 g, 14.9 mmol),
Me2CHBr (1.93 g, 15.7 mmol) and the salt A (8.79 g,
14.2 mmol) as described in GP1; yield 9.87 g (99%) as
a slightly yellowish deliquescent crystalline solid, mp
3
CH2CH2CH3), 1.84 (2H, quintet, JZ7.5 Hz, NCH2CH2),
3
3.91 (3H, s, NCH3), 4.14 (2H, t, JZ7.6 Hz, NCH2), 7.32
(1H, t, JZ1.8 Hz) and 7.33 (1H, t, JZ1.8 Hz) (both
CH]CH), 8.73 (1H, br s, N–CH]N). 13C NMR
(100.65 MHz): d 13.4 (CH2CH3), 21.8 (CH2CH3), 28.0
and 29.7 (both CH2) 36.0 (NCH3), 50.0 (NCH2), 122.2 and
123.7 (both CH]CH), 135.9 (N–CH]N). 19F NMR
(376.59 MHz): d K127.1 (4F, t*, JZ14 Hz, 2CF2-3),
K122.2 (4F, mc, 2CF2-2), K114.0 (4F, br t, JZ14 Hz,
2CF2-1), K82.0 (6F, tt, J1Z9.9 Hz, J2Z2 Hz, 2CF3);
*further splitting due to the multiple 19F,19F couplings.
MS (ESI positive, ion energy 0.3 eV), m/z (%): 153.172
[C9H17NC2 ] (100) and lighter fragments. MS (ESI negative,
ion energy 0.3 eV), m/z (%): 579.951 [(C4F9SO2)2NK]
(100) and lighter fragments.
1
28–29 8C. 1g, H NMR (400.23 MHz, DMSO-d6): d 1.48
(6H, d, 3JZ6.7 Hz, Me2CH), 3.85 (3H, s, NCH3), 4.63 (1H,
3
heptet, JZ6.7 Hz, NCHMe2), 7.71 (1H, t, JZ1.8 Hz) and
7.87 (1H, t, JZ1.8 Hz) (both CH]CH), 9.17 (1H, br s,
N–CH]N). 13C NMR (100.65 MHz, DMSO-d6): d 22.3
(Me2CH), 35.7 (NCH3), 52.2 (NCHMe2), 120.5 and 123.7
(both CH]CH), 135.4 (N–CH]N). 15N NMR
(40.57 MHz, DMSO-d6): d K183.6 and K210.4 (both
endocyclic N). 19F NMR (376.59 MHz, DMSO-d6): d
K128.1 (4F, t*, JZ14 Hz, 2CF2-3), K123.3 (4F, mc,
2CF2-2), K115.6 (4F, br t, JZ14 Hz, 2CF2-1), K82.8 (6F,
*
tt, J1Z9.8 Hz, J2Z2.6 Hz, 2CF3); further splitting due to
the multiple 19F,19F couplings. MS (ESI positive, ion energy
0.3 eV), m/z (%): 125.114 [C7H13NC2 ] (100) and lighter
fragments. MS (ESI negative, ion energy 0.3 eV), m/z (%):
579.950 [(C4F9SO2)2NK] (100) and lighter fragments.
3.2.5. 1-(3-Methyl-butyl)-3-methylimidazolium bis(nona-
fluorobutane-1-sulfonyl)imide (1e). The title compound
was prepared from N-methylimidazole (1.223 g,
14.9 mmol), Me2CH(CH2)2Br (1.93 g, 15.7 mmol) and the
salt A (8.42 g, 13.6 mmol) as described in GP1; yield 9.97 g
(O99%) as a yellowish crystalline solid, mp 39–40 8C. 1e,
1H NMR (400.23 MHz, DMSO-d6): d 0.92 (6H, d,
3JZ6.7 Hz, Me2CH), 1.52 (1H, nonet, 3JZ6.7 Hz,
Me2CH), 1.70 (2H, dt, 3J1Z7.8 Hz, 3J2Z6.7 Hz,
3.2.8. 1-sec-Butyl-3-methylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (1h). The title compound was
prepared from N-methylimidazole (1.20 g, 14.6 mmol),
MeCH2CH(Me)Br (2.10 g, 15.3 mmol) and the salt A
(7.25 g, 11.7 mmol) as described in GP1; yield 8.38 g
(O99%) as a clear viscous tawny liquid. 1h, 1H NMR
(400.23 MHz, DMSO-d6): d 0.78 (3H, t, 3JZ7.4 Hz,
CH3CH2), 1.47 (3H, d, 3JZ6.9 Hz, CH3CH), 1.80
(2H, mc, CH3CH2), 3.86 (3H, s, NCH3), 4.41 (1H, sextet,
3JZ6.9 Hz, NCH), 7.73 (1H, t, JZ1.7 Hz) and 7.86 (1H, t,
JZ1.7 Hz) (both CH]CH), 9.17 (1H, br s, N–CH]N). 13C
NMR (100.65 MHz, DMSO-d6): d 9.9 (CH2CH3), 20.2
(CH3CHN), 29.1 (CH2CH3), 35.8 (NCH3), 57.8 (NCH),
120.4 and 123.9 (both CH]CH), 135.7 (N–CH]N).
19F NMR (376.59 MHz, DMSO-d6): d K128.1 (4F, t*,
JZ14 Hz, 2CF2-3), K123.4 (4F, mc, 2CF2-2), K115.7
(4F, br t, JZ14 Hz, 2CF2-1), K82.8 (6F, tt, J1Z9.8 Hz,
3
NCH2CH2), 3.85 (3H, s, NCH3), 4.18 (2H, t, JZ7.6 Hz,
NCH2), 7.69 (1H, t, JZ1.8 Hz) and 7.78 (1H, t, JZ1.8 Hz)
(both CH]CH), 9.12 (1H, br s, N–CH]N). 13C NMR
(100.65 MHz, DMSO-d6): d 21.9 (Me2CH), 24.8 (Me2CH),
35.7 (NCH3), 38.2 (NCH2CH2), 47.2 (NCH2), 122.3 and
123.6 (both CH]CH), 136.5 (N–CH]N). 19F NMR
(376.59 MHz, DMSO-d6): d K128.1 (4F, t*, JZ14 Hz,
2CF2-3), K123.4 (4F, mc, 2CF2-2), K115.7 (4F, br t, JZ
14 Hz, 2CF2-1), K82.8 (6F, tt, J1Z9.8 Hz, J2Z2.6 Hz,
2CF3); *further splitting due to the multiple 19F,19F
couplings. MS (ESI positive, ion energy 0.3 eV), m/z (%):
153.2 [C9H17NC2 ] (100) and lighter fragments. MS
(ESI negative, ion energy 0.3 eV), m/z (%): 580.0
[(C4F9SO2)2NK] (100) and lighter fragments.
*
J2Z2.6 Hz, 2CF3); further splitting due to the multiple
19F,19F couplings. MS (ESI positive, ion energy 0.3 eV), m/z
(%): 139.1 [C8H15NC2 ] (100) and lighter fragments. MS
(ESI negative, ion energy 0.3 eV), m/z (%): 580.0
[(C4F9SO2)2NK] (100) and lighter fragments.
3.2.6. 1-Isobutyl-3-methylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (1f). The title compound was
prepared from N-methylimidazole (1.20 g, 14.6 mmol),
Me2CHCH2Br (1.42 g, 15.3 mmol) and the salt A (8.61 g,
13.9 mmol) as described in GP1; yield 9.99 g (O99%) as a
clear yellowish viscous liquid. 1f, 1H NMR (400.23 MHz):
d 0.94 (6H, d, 3JZ6.7 Hz, Me2CH), 2.15 (1H, nonet,
3JZ6.8 Hz, Me2CH), 3.95 (3H, s, NCH3), 4.00 (2H, t,
3JZ7.4 Hz, NCH2), 7.39 (1H, t, JZ1.8 Hz) and 7.41 (1H, t,
JZ1.8 Hz) (both CH]CH), 8.72 (1H, br s, N–CH]N). 13C
NMR (100.65 MHz): d 18.6 (Me2CH), 29.1 (Me2CH), 35.8
(NCH3), 56.7 (NCH2), 122.7 and 123.6 (both CH]CH),
3.2.9. 1-Propyl-3-methylimidazolium nonafluorobutane-
sulfonate (2a). The title compound was prepared from
N-methylimidazole (2.044 g, 24.9 mmol), Me(CH2)2Br
(3.21 g, 26.1 mmol) and the salt B (8.00 g, 23.7 mmol) as
described in GP1; yield 8.25 g (82%) as a slightly yellowish
crystalline solid, mp 33–34 8C. 2a, 1H NMR (400.23 MHz):
d 0.94 (3H, t, 3JZ7.4 Hz, CH2CH3), 1.90 (2H, sextet,
3JZ7.4 Hz, CH2CH3), 3.96 (3H, s, NCH3), 4.15 (2H, t,

S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
3143
3JZ7.4 Hz, NCH2), 7.41 (1H, t, JZ1.8 Hz) and 7.43 (1H, t,
JZ1.8 Hz) (both CH]CH), 9.09 (1H, br s, N–CH]N). 13C
NMR (100.65 MHz): d 10.4 (CH2CH3), 23.4 (CH2CH3),
36.3 (NCH3), 51.5 (NCH2), 122.1 and 123.6 (both
CH]CH), 136.9 (N–CH]N). 19F NMR (376.59 MHz): d
K127.1 (2F, t*, JZ14.2 Hz, 2CF2-3), K122.7 (2F, mc,
2CF2-2), K115.9 (2F, t*, JZ14.2 Hz, 2CF2-1), K82.0
(3F, tt, J1Z9.9 Hz, J2Z2.7 Hz, 2CF3); *further splitting due
to the multiple 19F,19F couplings. MS (ESI positive, ion
energy 0.3 eV), m/z (%): 125 [C7H13NC2 ] (100) and lighter
fragments. MS (ESI negative, ion energy 0.3 eV), m/z (%):
298.9 [C4F9SOK3 ] (100) and lighter fragments.
CH3CH2), 3.98 (3H, s, NCH3), 4.41 (1H, sextet, 3JZ6.9 Hz,
NCH), 7.41 (1H, t, JZ1.8 Hz) and 7.46 (1H, t, JZ1.8 Hz)
(both CH]CH), 9.17 (1H, br s, N–CH]N). 13C NMR
(100.65 MHz): d 9.9 (CH2CH3), 20.4 (CH3CHN), 29.8
(CH2CH3), 36.2 (NCH3), 59.1 (NCH), 120.2 and
123.8 (both CH]CH), 135.7 (N–CH]N). 19F NMR
(376.59 MHz): d K127.1 (2F, t*, JZ14.2 Hz, 2CF2-3),
K122.7 (2F, mc, 2CF2-2), K115.9 (2F, t*, JZ14.2 Hz,
2CF2-1), K82.0 (3F, tt, J1Z9.9 Hz, J2Z2.7 Hz, 2CF3);
*further splitting due to the multiple 19F,19F couplings. MS
(ESI positive, ion energy 0.3 eV), m/z (%): 139 [C8H15NC2 ]
(100) and lighter fragments. MS (ESI negative, ion energy
0.3 eV), m/z (%): 298.9 [C4F9SOK3 ] (100) and lighter
fragments. HRMS (FAB negative, Cs, 20 keV, direct,
glycerin, m/z), found: 298.9395. Calcd (C4F9O3SK):
298.9419.
3.2.10. 1-Butyl-3-methylimidazolium nonafluorobutane-
sulfonate (2b). The title compound was prepared from
N-methylimidazole (2.04 g, 24.9 mmol), Me(CH2)3Cl
(2.42 g, 26.1 mmol) and the salt B (8.00 g, 23.7 mmol) as
described in GP1; yield 8.52 g (82%) as a clear yellow
3.3. Synthesis of N-propyl-N0-alkyl imidazolium bis-
(nonafluorobutane-1-sulfonyl)imides (3) (see
Scheme 5): general procedure (GP2)
1
viscous liquid. 2b, H NMR (400.23 MHz): d 0.94 (3H, t,
3JZ7.4 Hz, CH2CH3), 1.35 (2H, sextet, 3JZ7.5 Hz,
CH2CH3), 1.85 (2H, mc, NCH2CH2), 3.96 (3H, s, NCH3),
4.19 (2H, t, 3JZ7.5 Hz, NCH2), 7.37 (1H, t, JZ1.8 Hz) and
7.41 (1H, t, JZ1.8 Hz) (both CH]CH), 9.13 (1H, br s,
N–CH]N). 13C NMR (100.65 MHz): d 13.1 (CH2CH3),
19.3 (CH2CH3), 31.9 (NCH2CH2), 36.2 (NCH3), 49.8
(NCH2), 122.2 and 123.6 (both CH]CH), 136.7 (N–
CH]N). 19F NMR (376.59 MHz): d K127.1 (2F, t*, JZ
14 Hz, 2CF2-3), K122.7 (2F, mc, 2CF2-2), K115.9 (2F, t*,
JZ14 Hz, 2CF2-1), K82.0 (3F, tt, J1Z9.9 Hz, J2Z2.7 Hz,
2CF3); *further splitting due to the multiple 19F,19F
couplings. MS (ESI positive, ion energy 0.3 eV), m/z (%):
139.1 [C8H15NC2 ] (100) and lighter fragments. MS (ESI
negative, ion energy 0.3 eV), m/z (%): 298.95 [C4F9SOK3 ]
(100) and lighter fragments.
Imidazole (1 equiv) was placed into the reaction flask and
dried in HV (0.05 mbar, rt) to remove traces of moisture
before adding a solution of MeONa (1.05 equiv) in MeOH
(4.026 mmol/g, prepared from MeOH and Na). The
reaction mixture was stirred for 15–20 min at rt, then
MeOH was removed in vacuum followed by drying the
residue in HV (0.05 mbar, rt) for 1 h. MeCN (0.5 mL per
1 mmol substrate) followed by the Me(CH2)2Br (1.0–
1.1 equiv) were added to the resulting sodium imidazolide
at 0 8C, and the reaction mixture was stirred for 5 h at 0 8C
and 15 h at ambient temperature. After the completion of
the first alkylation step (NMR-control), the volatiles were
removed in vacuum followed by the addition of the second
alkylating reagent. After the completion of the second
alkylation step (NMR-control), the residue was combined
with the salt A (0.95 equiv) in two-phase water/CH2Cl2
mixture and treated as described in GP1 furnishing the
compounds 3a,b.
3.2.11. 1-Isopropyl-3-methylimidazolium nonafluoro-
butanesulfonate (2c). The title compound was prepared
from N-methylimidazole (2.04 g, 24.9 mmol), Me2CHBr
(3.22 g, 26.2 mmol) and the salt B (8.00 g, 23.7 mmol) as
described in GP1; yield 8.14 g (81%) as a clear yellowish
1
viscous liquid. 2c, H NMR (400.23 MHz): d 1.56 (6H, d,
3.3.1. 1-Propyl-3-ethylimidazolium bis(nonafluoro-
butane-1-sulfonyl)imide (3a). The title compound was
prepared from imidazole (1.00 g, 14.7 mmol), MeONa
(0.83 g, 15.4 mmol) in MeOH (10 mL), Me(CH2)2Br
(1.80 g, 14.7 mmol) as a first alkylating reagent in MeCN
(8 mL), (EtO)2SO2 (2.16 g, 14.0 mmol) as a second
alkylating reagent employed at 0 8C to rt for 17 h, and the
salt A (8.61 g, 13.9 mmol), as described in GP2; yield 9.90 g
(99%) as a clear yellow viscous liquid. 3a, 1H NMR
3JZ6.7 Hz, Me2CH), 3.97 (3H, s, NCH3), 4.65 (1H, heptet,
3JZ6.7 Hz, NCHMe2), 7.42 (1H, t, JZ1.9 Hz) and 7.45
(1H, t, JZ1.9 Hz) (both CH]CH), 9.12 (1H, br s,
N–CH]N). 13C NMR (100.65 MHz): d 22.6 (Me2CH),
36.1 (NCH3), 53.3 (NCHMe2), 120.2 and 123.7 (both
CH]CH), 135.3 (N–CH]N). 19F NMR (376.59 MHz): d
K127.1 (2F, t*, JZ14.2 Hz, 2CF2-3), K122.7 (2F, mc,
2CF2-2), K115.9 (2F, t*, JZ14.2 Hz, 2CF2-1), K82.0
*
3
(3F, tt, J1Z10.0 Hz, J2Z2.8 Hz, 2CF3); further splitting
(400.23 MHz): d 0.94 (3H, t, JZ7.4 Hz, CH2CH2CH3),
due to the multiple 19F,19F couplings. MS (ESI positive, ion
energy 0.3 eV), m/z (%): 125 [C7H13NC2 ] (100) and lighter
fragments. MS (ESI negative, ion energy 0.3 eV), m/z (%):
298.9 [C4F9SOK3 ] (100) and lighter fragments.
3
1.52 (3H, t, 3JZ7.4 Hz, NCH2CH3), 1.89 (2H, sextet, JZ
7.4 Hz, CH2CH2CH3), 4.14 (2H, t, 3JZ7.4 Hz, NCH2CH2),
4.25 (2H, q, 3JZ7.4 Hz, NCH2CH3), 7.32 (1H, t, JZ
1.8 Hz) and 7.35 (1H, t, JZ1.8 Hz) (both CH]CH), 8.82
(1H, br s, N–CH]N). 13C NMR (100.65 MHz): d 10.2
(CH2CH2CH3), 15.0 (CH2CH2CH3), 23.4 (CH2CH2CH3),
45.2 (NCH2CH3), 51.5 (NCH2CH2), 121.9 and 122.3
(both CH]CH), 135.2 (N–CH]N). 19F NMR (376.59
MHz): d K127.1 (4F, t*, JZ14 Hz, 2CF2-3), K122.2 (4F,
mc, 2CF2-2), K114.0 (4F, br t, JZ14 Hz, 2CF2-1), K81.9
(6F, tt, J1Z9.9 Hz, J2Z2.4 Hz, 2CF3); *further splitting due
to the multiple 19F,19F couplings. MS (ESI positive, ion
energy 0.3 eV), m/z (%): 139.1 [C8H15NC2 ] (100) and lighter
3.2.12. 1-sec-Butyl-3-methylimidazolium nonafluoro-
butanesulfonate (2d). The title compound was prepared
from N-methylimidazole (2.04 g, 24.9 mmol), MeCH2-
CH(Me)Br (3.58 g, 26.1 mmol) and the salt B (6.74 g,
19.9 mmol) as described in GP1; yield 6.89 g (79%) as a
tawny crystalline solid, mp 42–43 8C. 2d, 1H NMR
3
(400.23 MHz): d 0.87 (3H, t, JZ7.4 Hz, CH3CH2), 1.55
(3H, d, 3JZ6.9 Hz, CH3CH), 1.86 (2H, quintet, 3JZ7.4 Hz,

3144
S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
4. NfF is available from many suppliers. It is produced in technical
scale by the electrochemical fluorination of 2,5-dihydrothio-
phene 1,1-dioxide. According to 19F NMR, our sample of NfF
contains 7 mol%of side product, perfluorosulfolane: Bu¨rger, H.;
Heyder, F.; Pawelke, G.; Niederpru¨m, H. J. Fluorine Chem.
1979, 13, 251–260.
fragments. MS (ESI negative, ion energy 0.3 eV), m/z (%):
580.0 [(C4F9SO2)2NK] (100) and lighter fragments. HRMS
(FAB negative, Cs, 20 keV, direct, glycerin, m/z), found:
579.8994. Calcd (C8F18NO4SK2 ): 579.8976.
3.3.2. 1-Butyl-3-propylimidazolium bis(nonafluorobu-
tane-1-sulfonyl)imide (3b). The title compound was
prepared from imidazole (1.021 g, 15.0 mmol), MeONa
(0.851 g, 15.8 mmol) in MeOH (10 mL), Me(CH2)2Br
(2.03 g, 16.5 mmol) as a first alkylating reagent in MeCN
(7.5 mL), Me(CH2)3Br (2.62 g, 19.1 mmol) as a second
alkylating reagent employed for 3 h at 70 8C, and the salt A
(8.30 g, 13.4 mmol), as described in GP2; yield 10.04 g
(O99%) as a yellowish crystalline solid, mp 36–37 8C. 3b,
1H NMR (400.23 MHz): d 0.936 and 0.940 (both 3H, t,
3JZ7.4 Hz, CH2CH3), 1.34 (2H, sextet, 3JZ7.4 Hz,
CH2CH3 of n-C4H9), 1.83 (2H, mc, NCH2CH2 of n-C4H9),
5. Sogabe, K.; Hasegawa, Y.; Wada, Y.; Kitamura, T.; Yanagida, S.
Chem. Lett. 2000, 29, 944–945.
6. pKa[HCOK3 ]aqZ10.33, pKa[HPO42K]aqZ12.32, Handbook of
Chemistry and Physics 81st ed., pp 8-44–8-45.
7. A careful analysis of the spectroscopic data of the products
obtained under the conditions a and b showed that they
consist of the salt B (60–70 mol%), CH3C(O)NNf2K4
(25–40 mol%) and KOSO2(CF2)4H (up to 11 mol%, MS
(ESI negative, ion energy 0.3 eV), m/z (%): 280.93
[H(CF2)4SO3]K). The latter salt may result from the
nucleophilic ring opening of perfluorosulfolane, see Ref. 4
and Lyapkalo, I. M.; Webel, M.; Reissig, H.-U. Eur. J. Org.
Chem. 2002, 1015–1025. No desired KNNf2 A is detected
in either of the experiments. CH3C(O)NNf2K4, 1H NMR
(400.23 MHz, DMSO-d6): 1.81 (3H, s, CH3). 19F NMR
3
1.89 (2H, sextet, JZ7.4 Hz, NCH2CH2 of n-C3H7), 4.14
3
and 4.17 (both 2H, t, JZ7.4 Hz, NCH2), 7.340 and 7.344
(both 1H, br s, CH]CH) 8.82 (1H, br s, N–CH]N). 13C
NMR (100.65 MHz): d 10.2 and 13.0 (both CH3), 19.2 and
23.4 (both CH2CH3), 32.0 (NCH2CH2 of n-C4H9), 49.9
and 51.5 (both NCH2), 122.3 (both CH]CH), 135.5
(N–CH]N). 19F NMR (376.59 MHz): d K127.1 (4F, t*,
JZ14 Hz, 2CF2-3), K122.2 (4F, mc, 2CF2-2), K114.0
(4F, br t, JZ14 Hz, 2CF2-1), K81.9 (6F, tt, J1Z9.9 Hz,
(376.59 MHz, DMSO-d6):
d K128.0 (2F, mc, CF2-3),
K123.5 (2F, mc, CF2-2), K115.8 (2F, mc, CF2-1), K82.75
(3F, tt, J1Z9.8 Hz, J2Z2.9 Hz, CF3). MS (ESI negative, ion
energy 0.3 eV), m/z (%): 339.94 [C4F9SO2NC(O)CH3]K.
8. In fact, microanalysis data given for KNNf2 (see Ref. 5) are in
a better consistency with the elemental composition of KONf!.
9. O-Sulfonylation of metal enolates or N-sulfonylation of
lithium dialkylamides with NfF occurs instantaneously even
at K78 8C, see: (a) Lyapkalo, I. M.; Webel, M.; Reissig, H.-U.
Synlett 2001, 1293–1295. (b) Lyapkalo, I. M.; Reissig, H.-U.;
*
J2Z2.3 Hz, 2CF3); further splitting due to the multiple
19F,19F couplings. MS (ESI positive, ion energy 0.3 eV), m/z
(%): 167 [C10H19NC2 ] (100) and lighter fragments. MS (ESI
negative, ion energy 0.3 eV), m/z (%): 580 [(C4F9SO2)2NK]
(100) and lighter fragments.
¨
Schafer, A.; Wagner, A. Helv. Chim. Acta 2002, 85,
4206–4215, respectively, whereas no evidences of F2 release
were noticed upon activation of NfF with highly nucleophilic
4-(N,N-dimethylamino)pyridine.
Acknowledgements
10. Et3N failed to produce the desired NNf22 ion when used
as a base for sulfonylation of amides RC(O)NH2 with NfF
(see Ref. 5).
We would like to thank Prof. Reissig (Free University of
Berlin) for the helpful discussion, which inspired this
research work. We are indebted to the Agency for Science
Technology and Research (A*STAR Singapore) for the
financial support and to Bayer AG (Germany) for the
generous donation of nonafluorobutane-1-sulfonyl fluoride.
We thank Dr C. Jacob (ICES) for obtaining the 15N NMR
spectrum of the salt 1g.
11. At the later stage of the optimization of KNNf2 synthesis, we
found out that a similar method was used for preparation of
LiNNf2 by heating of liquid NH3 with NfF in access of Et3N as
an auxiliary base and solvent at 90 8C in autoclave: Conte, L.;
Gambaretto, G. P.; Caporiccio, G.; Alessandrini, F.; Passerini,
S. J. Fluorine Chem. 2004, 125, pp 243–252. Our protocol
looks more convenient as it simplifies dosing of ammonia
(in form of solid NH4Cl) and is carried out at smoother
conditions in normal laboratory glassware giving a better yield
of the intermediate Et3NH4NNf22.
References and notes
12. The 19F NMR spectrum contains no detectable signal of
side product(s) that might result from perfluorosulfolane
(cf. Ref. 7).
1. (a) Wasserscheid, P. Org. Synth. Highlights V 2003, 105–117.
(b) Dzyuba, S. V.; Bartsch, R. A. Angew. Chem., Int. Ed. 2003,
42, 148–150. (c) Baudequin, C.; Baudoux, J.; Levillain, J.;
Cahard, D.; Gaumont, A.-C.; Plaquevent, J.-C. Tetrahedron:
Asymmetry 2003, 14, 3081–3093. (d) Xu, W.; Angell, C. A.
Science 2003, 302, 422–425. (e) Zhao, H. S.; Malhotra, V.
Aldrichim. Acta 2002, 35, 75–83. (f) Dupont, J.; de Souza,
R. F.; Suarez, P. A. Z. Chem. Rev. 2002, 102, 3667–3691. (g)
Earle, M. J.; Seddon, K. R. Pure Appl. Chem. 2000, 72,
1391–1398. (h) Wasserscheid, P.; Keim, W. Angew. Chem.,
Int. Ed. 2000, 39, 3772–3789. (i) Welton, T. Chem. Rev. 1999,
99, 2071–2083.
13. The samples of the salts neither change appearance nor gain in
wait upon storage in open vial for a long period of time.
14. The reaction progress was monitored by 1H NMR spectro-
scopy; in all the cases full conversion of the starting N-methyl
imidazole was observed. Up to 15–18 mol% of N-methyl
imidazolium bromide was detected by 1H NMR as a side
product resulting from HBr elimination from secondary
bromides. It was easily removed from ionic liquid by aqueous
extraction on the following anion exchange step. Although at
higher temperature primary branched and secondary alkyl
bromides react faster, a contribution of the E2 elimination
pathway increases significantly.
2. Hagiwara, R.; Ito, Y. J. Fluorine Chem. 2000, 105, 221–227.
ˆ
3. Bonhote, P.; Dias, A.-P.; Papageorgiou, N.; Kalyanasundaram,
¨
K.; Gratzel, M. Inorg. Chem. 1996, 35, 1168–1178.

S. K. Quek et al. / Tetrahedron 62 (2006) 3137–3145
3145
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