A convenient synthesis of triflate anion ionic liquids and their properties

Article abstract of DOI:10.3390/molecules17055319

A solvent- and halogen-free synthesis of high purity triflate ionic liquids via direct alkylation of organic bases (amines, phosphines or heterocyclic compounds) with methyl and ethyl trifluoromethanesulfonate (methyl and ethyl triflate) has been developed. Cheap and non-toxic dimethyl and diethyl carbonate serve as source for the methyl and ethyl groups in the preparation of methyl and ethyl triflate by this invented process. The properties of ionic liquids containing the triflate anion are determined and discussed.

Full text of DOI:10.3390/molecules17055319

Molecules 2012, 17, 5319-5338; doi:10.3390/molecules17055319
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
A Convenient Synthesis of Triflate Anion Ionic Liquids and
Their Properties
1
,
2
3
3
4
Nikolai V. Ignat’ev *, Peter Barthen , Andryi Kucheryna , Helge Willner and Peter Sartori
1
Merck KGaA, PM-ABE, Ionic Liquids Research Laboratory, Frankfurter Str. 250,
Darmstadt D-64293, Germany
2
Inorganic Chemistry, Henrich-Heine-University Düsseldorf, Universitätsstrasse 1,
Düsseldorf D-40225, Germany; E-Mail: peter.barthen@uni-duesseldorf.de
3
Inorganic Chemistry, Bergische University Wuppertal, Gauss Str. 20, Wuppertal D-42119,
Germany; E-Mails: andriy.kucheryna@uni-wuppertal.de (A.K.); willner@uni-wuppertal.de (H.W.)
Professor Emeritus, Inorganic Chemistry, University Duisburg-Essen, Lotharstrasse 1,
Duisburg D-47048, Germany; E-Mail: peter.sartori@online.de
4
*
Author to whom correspondence should be addressed; E-Mail: nikolai.ignatiev@merckgroup.com;
Tel.: +49-151-1454-3102; Fax: +49-6151-728-587.
Received: 7 March 2012; in revised form: 13 April 2012 / Accepted: 13 April 2012 /
Published: 7 May 2012
Abstract: A solvent- and halogen-free synthesis of high purity triflate ionic liquids via
direct alkylation of organic bases (amines, phosphines or heterocyclic compounds) with
methyl and ethyl trifluoromethanesulfonate (methyl and ethyl triflate) has been developed.
Cheap and non-toxic dimethyl and diethyl carbonate serve as source for the methyl and
ethyl groups in the preparation of methyl and ethyl triflate by this invented process. The
properties of ionic liquids containing the triflate anion are determined and discussed.
Keywords: methyl triflate; ethyl triflate; ionic liquids; viscosity
1
. Introduction
Ionic liquids (ILs) with the triflate anion ([CF SO ] ; OTf) are of interest for practical application in
−
3
3
various fields [1–4]. Triflate ionic liquids are hydrolytically stable and in many cases they are the
−
preferred reaction media in comparison to ionic liquids with the hydrolytically unstable [PF
6
] or
−
[BF
4
] anions. For example, the Claisen rearrangement of aromatic allyl esters in [EtDBU][OTf]

Molecules 2012, 17
5320
results in the formation of 2,3-dihydrobenzofuran derivatives in up to 91% yield. The same reaction in
[BMIM][PF ] or [BMIM][BF ] gives only 9–12% yield [5]. Recently it was demonstrated that
6 4
[
BMIM][OTf] is also a suitable reaction medium for fluorolactonization of unsaturated carboxylic
acids [6]. The combination of [BMIM][OTf] with triflic acid (CF SO H, cat.) provides good
3
3
conditions for the Schmidt reaction, i.e., the conversion of aryl alkyl ketones to the corresponding
carboxamides [7]. In triflate ionic liquids polymerization of methyl methacrylate (MMA) generally
yields the highest molecular weight [8]. These examples demonstrate the utility of triflate ionic liquids
in organic synthesis or in polymer chemistry, but there are further applications for triflate ILs. Due to
their high thermal and electrochemical stability these ionic liquids are of interest as heat transfer
materials, lubricants and as components of electrolytes for electrochemical cells. The purity of ionic
liquids is particularly important for their use in electrochemistry, and quality control should be always
in the focus during the preparation of ILs for this application [2].
Typically triflate ionic liquids are prepared by means of the metathesis reaction of the corresponding
chlorides, bromides or methylsulfates with metal triflates, CF SO OM, for instance M = K [9,10], Na [11],
3
2
Li [12], Ag [13], with ammonium triflate [14] or triflic acid, CF SO H [15]. The ionic liquids prepared
3
3
by means of this methodology have to be purified from the side products: metal chlorides or bromides,
or HCl. The side products then need to be disposed of. The reactions referred above were carried out in
organic solvents such as dichloromethane, chloroform, acetone, or methanol, but if we are considering
ionic liquids as replacements for volatile organic solvents to perform chemical reactions, then logically
the ionic liquids themselves should be produced without the use of organic solvents [16]. Mikami
wrote “It is also important to underline that to justify the green solvents label, ionic liquids have to be
prepared in an ecological way, without the generation of a large amount of waste material” [17].
Recently, the syntheses of ionic liquids under solvent free conditions were tested by application of
microwave (MW), power ultrasound (US) and combined MW/US irradiation [18,19]. The authors have
carried out the one pot synthesis of triflate ionic liquids by reacting pyridine or N-methylpyrrolidine, or
N-methylimidazole with 1-chlorobutane or 1-chlorooctane in the presence of potassium triflate, KOTf.
The reaction mixture was heated under MW-irradiation up to 180 °C after an initial step (10–15 min at
1
20 °C). This reaction gives the corresponding ionic liquids in 60% to 79% yield [18]. KCl is formed
as a side product in this reaction. Replacement of 1-chloroalkanes by 1-bromoalkanes reduced the
reaction temperature to 80–90 °C [19]. The yield of ionic liquids increased up to 90%, but KBr is
formed as a side product. The final products prepared by means of this methodology have to be
purified using organic solvents (acetone, dichloromethane, diethyl ether) to reduce the halogen
(
chloride or bromide) impurities [18,19].
According to an assessment recently carried out by Deetlefs and Seddon [20] applications of
microwave (MW), ultrasound (US) or combined MW/US irradiation to the syntheses of ionic liquids
do not meet the principles of green chemistry to the full extent. This technology provides only
low-medium atom economy and has a poor E-factor value. Preparation of ionic liquids by alkylation of
organic substances with a suitable alkylating reagent is much “greener” in comparison to the
metathesis protocol.
3 3 0
Trifluoromethanesulfonic acid (triflic acid, CF SO H) is a very strong acid (H = −14.1 at 22 °C) [21].
It has a broad application as a catalyst [22] in Friedel-Crafts alkylation and acylation, Diels-Alder
reactions, aldol condensations, hydrogenation of alkenes, cyclization and polymerization processes.

Molecules 2012, 17
5321
Triflic acid is the starting material for the production of all variety of triflates, i.e., metal salts, organic
salts, triflic anhydride and alkytriflates, CF SO OR. Methyl trfiflate, CF SO OCH , was first
3
2
3
2
3
synthesised by Gramstadt and Haszeldine by the reaction of silver triflate with methyl iodide [23]
Scheme 1).
(
Scheme 1. Synthesis of methyl triflate by the reaction of silver triflate with methyl iodide [23].
Later on Booth et al. [24] used triflic anhydride as a starting material for the synthesis of methyl
triflate, CF SO OCH , via reaction with methanol (Scheme 2).
3
2
3
Scheme 2. Synthesis of methyl triflate by the reaction of triflic anhydride with methanol [24].
(
CF SO ) O + CH OH
CF SO OCH
+
CF SO OH
3 2
3
2 2
3
3
2
3
Yield: 70-80%
This method can be used to prepare various alkyl triflates, CF
3
2
SO OR, [25,26], but it is not very
economical because half of the triflic anhydride is lost. The yield of methyl triflate in this reaction is
also not satisfying. A simpler and less expensive procedure for methyl triflate preparation was
developed Beard et al. [27] (Scheme 3), but additional efforts are required to utilize the side product,
sulphuric acid, contaminated with toxic dimethylsulfate.
Scheme 3. Synthesis of methyl triflate by the reaction of triflic acid with dimethylsulfate [27].
2
. Results and Discussion
Recently Merck KGaA (Darmstadt, Germany) has developed a new protocol for the preparation of
methyl triflate [28] (Scheme 4).
Scheme 4. Synthesis of methyl triflate by the reaction of triflic anhydride with dimethylcarbonate [28].
Commercial available dimethyl carbonate serves as source for the methyl groups in this reaction.
3 2 3
This invented method provides a very convenient access to methyl triflate, CF SO OCH . This
chemical is formed in a very good yield and CO is the only side product in this process. Traces of
2
triflic acid (which is typically present in the commercial triflic anhydride) are enough to catalyse the
conversion of triflic acid anhydride and dimethyl carbonate into methyl triflate (Scheme 4). The
possible mechanism of this reaction can be described as follows (Scheme 5).

Molecules 2012, 17
Scheme 5. Proposed mechanism of the reaction of triflic anhydride with dimethylcarbonate
5322
catalyzed by triflic acid.
CH3
O
-
OCH3
H OSO CF
OH
2
3
1
O
C
+ HOSO CF3
O
C
CF SO OCH + O C
3 2 3
2
OCH3
OCH3
OCH3
In the first step triflic acid protonates dimethyl carbonate (Equation 1) inducing the methyl cation
transfer to the triflate anion resulting in methyl triflate (Equations 1 and 2). Triflic acid is regenerated
in the reaction of triflic anhydride with the water which is formed by decomposition of carbonic
acid (Scheme 5, Equation 3). According to this mechanism the triflic acid anhydride plays a role as
water scavenger.
The disadvantage of this method is the use of the relatively expensive starting material triflic acid
anhydride. To reduce the production costs the combination of triflic acid and acyl or aryl chlorides can
be used instead of triflic acid anhydride in this process (Scheme 6) [29]. Acyl or aryl chlorides
(
for instance cheap and readily available benzoyl chloride) play the role of scavenger of the alcohol
and water which are generated as intermediates during the process.
Scheme 6. Syntheses of methyl and ethyl triflate by the reaction of triflic acid with
dimethyl- and diethyl-carbonate in the presence of benzoyl chloride [29].
This method provides a very convenient and simple access not only to methyl triflate, but also to
ethyl triflate (Scheme 6). Ethyl triflate or methyl triflate can easily be distilled out of the reaction
mixture. The residue consists of ethyl or methyl benzoate, which are valuable products as well.
Ethyl triflate and methyl triflate are broadly used in synthetic organic chemistry to alkylate various
substrates: N-heterocycles [30–33]; S,N-heterocycles [34]; organophosphorus compounds [35,36];
imines [37]; enol silyl ethers [38] and aromatic compounds [23,24].
1
-Methylimidazole reacts with methyl triflate in dichloromethane yielding 1,3-dimethyl-
imidazolium triflate [39]. Bonhöte et al. [40] have described the alkylation of 1-alkylimidazoles
Alk = CH , C H , C H ) with methyl or ethyl triflate in refluxing 1,1,1-trichloroethane. The yield of
(
3
2
5
4
9
triflate ILs was good, but the use of chlorinated solvent was a drawback in this method.

Molecules 2012, 17
5323
The alkylation ability of methyl triflate is comparable to that of the Meerwein salt [41]. We have
used the alkylation power of methyl triflate to convert ionic liquids with chloride or bromide counter-
anions to the corresponding ILs with triflate anion (Scheme 7) [42,43].
Scheme 7. Preparation of triflate ionic liquids from corresponding chlorides or bromides [42,43].
R.T.
+
CF SO OCH
+
CH Br
3
3
2
3
0.5 h
N
R
N
R
Br-
-
[CF SO ]
3
3
R = C H C H
4 9
2
5,
Yield: quantitative
This is a very convenient method to prepare triflate ionic liquids with various substituents R and R'.
The reaction progresses very fast at room temperature under solvent free conditions. The gaseous
3 3
CH Cl or very volatile CH Br are the only side products in this process. Trimethylsilyl triflate is less
active in these reactions, but more convenient to handle [42,43]. The side product, trimethylchlorosilane,
can be easily utilised.
To avoid the formation of any side products, the direct alkylation of amines, phosphines or
heterocyclic compounds with ethyl or methyl triflate is favored (Scheme 8) [28,29]. This water and
halogen free process gives the possibility to prepare triflate ionic liquids of very high quality with
residual water below 10 ppm and non-detectable halogenide impurities. This is particularly important
for the electrochemical applications of ionic liquids [2].
Scheme 8. Preparation of triflate ionic liquids by means of alkylation with methyl or ethyl triflate.
This method can be applied to the alkylation of trialkylamines, trialkylphosphines, N,N,N',N'-tetra-
methylguanidine and N,N,N',N'-tetramethylurea (see Experimental section). The synthesis can be
carried out under solvent free conditions at 0 °C. The product yield is close to quantitative. It means
that atom economy is very high (close to 100%) and the E-factor has an excellent value [20]. If a solid
material is formed during the alkylation process (for example N,N-dimethylpyrrolidium triflate),
diluting the reaction mixture with hexane, which can be easily regenerated, is favored.

Molecules 2012, 17
5324
2
-Methyl-5-ethylpyridine and the 2,4,6-trimethylpyridine can be methylated with methyl triflate in
quantitative yield (Scheme 9). But, if the steric hindrance is too strong, for example, in the case of
,4,6-tris(t-butyl)pyridine, the reaction proceeds very slowly and the product yield is low (see
Experimental section).
2
Scheme 9. Alkylation of substituted pyridines with methyl triflate.
Ionic liquids with the triflate anion possess high thermal stability (see Figure 1 and Table 1), good
electrochemical stability (see Figure 2 and Table 2) and fairly low viscosity (see Tables 3 and 4).
Figure 1. TGA of N-butyl-N-methylpyrrolidinium trifluoromethanesulfonate. Scan rate: 10 °C/min.
Table 1. Isothermal TGA measurements at 200 °C and 250 °C.
Weight loss (% per day, Weight loss (% per day,
Ionic Liquid
24 h), TGA isothermal
24 h), TGA isothermal
mode at 200 °C
mode at 250 °C
1
1
-Butyl-1-methylpyrrolidinium [CF
3
SO
SO
3
]
]
0.28
0.55
2.8
5.9
-Butyl-3-methylimidazolium [CF
3
3

Molecules 2012, 17
Figure 2. Cyclic voltammogram of N-butyl-N-methylpyrrolidinium trifluoromethanesulfonate.
5325
Scan rate: 20 mV/s.
Table 2. Electrochemical stability of triflate ionic liquids in comparison to the ionic liquids
with [(C
2
F
5
)
3
PF
3
] and [BF
Ionic Liquid
Tetrabutylammonium [(C
Methyl-trioctyl-ammonium [CF
-Butyl-1-methylpyrrolidinium [CF
-Butyl-3-methylimidazolium [CF
-Ethyl-3-methylimidazolium [CF
-Ethyl-3-methylimidazolium [BF
4
] anions.
E
(ox), V
3.7
3.4
3.4
3.0
2.8
2.6
E
(red), V
−3.3
−3.4
−3.2
−2.6
−2.5
−2.6
Window, V
2
F
5
)
3
PF
SO
SO
SO
SO
3
]
7.0
6.8
6.6
5.6
5.3
5.2
3
3
]
1
1
1
3
3
]
]
]
3
3
3
3
1
4
]
Table 3. Viscosity of 1-ethyl-3-methylimidazolium triflate (EMIM OTF) in comparison to
EMIM ionic liquids with alkylsulfate anions, [ROSO
2
O] [36].
Dynamic Viscosity, mPa·s
0 °C 40 °C 60 °C 80 °C
Cation
Anion
2
[
CH OSO ]
84
52
117
261
37
26
47
90
20
15
24
40
12
10
14
22
3
3
3 3
[CF SO ]
C H
2
N
N
CH3
5
[C
C
2
H
H
5
OSO
OSO
3
]
]
[
4
9
3
3 3 3 3
In spite of its higher molecular weight [EMIM][CF SO ] is less viscous than [EMIM][CH OSO ]
(
Table 3). The triflate anion is less coordinating than the CH OSO -anion. Weaker interaction between
3
3
3 3
the [CF SO ] anion and the EMIM-cation reduces the viscosity of triflate ionic liquids in comparison
to methylsulfate ILs [44]. Nevertheless, triflate ILs are more viscous than ionic liquids with weekly
coordinating anions such as [(C F ) PF ] [45] and [(CF SO ) N] (Table 4). The viscosity of triflate
2
5 3
3
3
2 2
ionic liquids is influenced by water or organic solvents impurities (decrease of viscosity) and
metal triflate impurities (increase of the viscosity value), which can remain in the triflate ILs after
metathesis reaction.

Molecules 2012, 17
Table 4. Viscosity and density of 1-hexyl-3-methylimidazolium triflate in comparison to
5326
ionic liquids with other anions.
Kinematic
Viscosity
20 °C), mm /s
Density
(20 °C),
g/cm
Dynamic
Viscosity
(20 °C), mPa·s
Ionic Liquid
2
3
(
1
-Hexyl-3-methylimidazolium Chloride
-Hexyl-3-methylimidazolium [PF
-Hexyl-3-methylimidazolium [BF
7453
548
195
160
74
1.05
1.30
1.15
1.24
1.56
1.38
7826
712
224
198
115
90
1
1
6
]
4
]
1
-Hexyl-3-methylimidazolium [CF
-Hexyl-3-methylimidazolium [(C
-Hexyl-3-methylimidazolium [(CF
3
3
SO ]
1
1
2
F
5
)
3
PF
3
]
3
SO
2
)
2
N]
65
The possible applications of triflate ionic liquids themselves or in combination with Brønsted acids
for dehydration of alcohols, deprotection of ketals or synthesis of chromane derivatives are described
in the cited patents applications [46–48].
3. Experimental
3.1. Chemicals
Commercially available chemicals have been used. Triflic acid and triflic acid anhydride was
provided by Merck KGaA (Darmstadt, Germany) company and used without further purification.
Methyl trifluoromethanesulfonate (methyl triflate) and ethyl trifluoromethanesulfonate (ethyl triflate)
were obtained and distilled as described below and stored under a nitrogen atmosphere. Heterocyclic
bases were distilled over CaH and stored under a nitrogen atmosphere.
2
3
.2. Analytical Procedures
3.2.1. NMR Spectroscopy
NMR samples were measured in 5 mm precision glass NMR tube (Wilmad 507 or 528 PPT) at
4 °C. NMR spectra were recorded in the deuterium-locked mode on a Bruker Avance III spectrometer
2
1
19
equipped with a 9.3980 T cryomagnet. The H- and F-NMR spectra were acquired using a 5 mm
1
19
13
H/ F combination probe operating at 400.17 and 376.54 MHz respectively. C-NMR spectra were
obtained using a 5 mm broad-band inverse probe operating at 100.61 MHz. Spectra were recorded
1
using various memory sizes, optimal acquisition times, and relaxation delays (0.5–2 s). The H-NMR
chemical shifts were referenced with respect to tetramethylsilane (TMS) using the chemical shifts
1
3
for the solvents CH
2 2 3
Cl (5.32 ppm) and CH CN (1.95 ppm). The C-NMR chemical shifts were
referenced with respect to TMS using the chemical shifts for the solvents CH
2
Cl (53.5 ppm) and
2
1
9
CH
3
CN (118.7 ppm). The F-NMR spectra were referenced with respect to CFCl using either the
3
6 6 6 5 3 3
internal standards C F (−162.9 ppm) or C H CF (−63.9 ppm) or externally to a neat CFCl reference
sample at 24 °C.

Molecules 2012, 17
.2.2. Elemental Analysis
5327
3
Elemental analysis was performed using a HEKATECH EA 3000 elemental analyser (HEKAtech
GmbH, Wegberg, Germany) with Callidus software.
3
.2.3. Thermal Analyses
The thermal analyses were performed using a NETZSCH 409C STA (Selb, Germany).
.2.4. Viscosity
3
Viscosity and density of ionic liquids were measured on the viscosimeter SVM 3000 (Anton Paar,
Graz, Austria).
3
.2.5. Cyclic Voltammetry
For electrochemical stability measurements an Autolab PGSTAT 30 (Metrohm Autolab B.V.,
Utrecht, The Netherlands) was used. Cyclic voltammograms were recorded for 0.5 M solutions in
CH CN at glassy carbon (gc) working electrode; auxiliary electrode was Pt and Ag/AgNO (CH CN)
3
3
3
was used as reference electrode. The purity (quality) of triflate ionic liquids was proven by measuring of
residual water (Karl-Fischer titration; 831 KF-Coulometer, Metrohm, Filderstadt, Germany) and
chloride or bromide (ion-chromotography, Metrohm Advanced IC System; stationary phase: Metrosep
A SUPP4-150). Contents of residual water and halides were below 100 ppm.
3
.3. Syntheses
Methyl Trifluoromethanesulfonate (CF
3
2 3
SO OCH )
Method (a): Trifluoromethanesulfonic acid anhydride (2,300 g, 8.15 mol) was slowly added to freshly
distilled dimethyl carbonate (808 g, 8.97 mol) under vigorous stirring at 25 °C. The solution was heated
(
2 2 4
approximately at 70 °C) until a moderate stream of CO runs through the H SO -filled bubbler.
Stirring was continued for 48 h at 70 °C. The excess of dimethyl carbonate (b.p. 90 °C) was distilled
off over a short column under a dry atmosphere. The yield of the colourless raw product is close to
1
00%. Purification by fractionated distillation gives 2,515 g (15.33 mol, 94% yield) of methyl
1
19
trifluoromethanesulfonate (b.p. 94–96 °C); H-NMR (CD CN) δ, ppm: 3.75 s; F-NMR (CD CN) δ,
3
3
ppm: −76.3 s.
Method (b): Trifluoromethanesulfonic acid (3,000 g, 19.99 mol) was slowly added to freshly
distilled benzoyl chloride (2,810 g, 19.99 mol) with mechanical stirring under a very slight positive N
2
pressure. After the addition was completed (45 min), the solution was heated to 80 °C. Freshly distilled
dimethyl carbonate (1,715 g, 19.04 mol) was dropped slowly into the solution under vigorous stirring
2 2 4
over a period of 7 h. During the addition a stream of CO and HCl passed through the H SO -filled
bubbler. Stirring was continued for 4 h at 85 °C to complete the reaction. The raw product was distilled
off with a short column under a dry atmosphere until the head-temperature increased above 115 °C.
The yield of the colourless raw product is close to 100%. Purification by fractional distillation gives

Molecules 2012, 17
5328
1
2
,906 g (17.12 mol, 93% yield) of methyl trifluoromethanesulfonate (b.p. 94–96 °C); H-NMR
1
9
(CD
3
CN), δ, ppm: 3.76 s; F-NMR (CD
3
CN), δ, ppm: δ −76.3 s.
OC
Ethyl Trifluoromethanesulfonate (CF
3
SO
2
2 5
H )
Trifluoromethanesulfonic acid (918 g, 6.12 mol) was slowly added to freshly distilled benzoyl
chloride (860 g, 6.12 mol) under a very slight positive N pressure with mechanical stirring. After the
2
addition was completed (20 min), the solution was heated to 95 °C. Freshly distilled diethyl carbonate
(690 g, 5.83 mol) was then dropped slowly into the solution under vigorous stirring over a period of 3 h.
During the addition a gas stream of of CO and HCl passed through the H SO -filled bubbler. Stirring
2
2
4
was continued for 1 h at 100 °C to complete the reaction. The raw product was distilled off immediately
over a short column under a dry atmosphere until the head-temperature raised above 125 °C. The yield of
the colourless raw product was 92%. Purification by fractional distillation gives 874 g (4.91 mol, 84%)
1
of ethyl trifluoromethanesulfonate (b. p. 112–114 °C); H-NMR (CD CN), δ, ppm: 1.03 t (3H, CH ,
3
3
3
3
19
J
H,H = 7.2 Hz), 4.19 q (2H, CH
,3-Dimethylimidazolium Trifluoromethanesulfonate [C
Freshly distilled methyl trifluoromethanesulfonate (1,486 g, 9.06 mol) was dropped slowly into a
2
, JH,H = 7.2 Hz); F-NMR (CD
3
CN), δ, ppm: −76.4 s.
1
5 9 2 3 3
H N ][CF SO ]
mechanically stirred solution of N-methylimidazole (730 g, 8.89 mol) in hexane (1,000 mL) over a
period of 16 h (1,300 g were dropped in at 0 °C and 159 g at 25 °C). Stirring (700 rpm) was continued
for 12 h at 25 °C to complete the reaction. During this time the product precipitated as a colourless
solid. The solvent and the excess of methyl trifluoromethanesulfonate (27 g, 0.17 mol) were decanted
and finally the product was evaporated at 0.01 mbar and 25 °C for 6 h. 1,3-Dimethylimidazolium-
trifluoromethanesulfonate was obtained as a colourless solid (2,189 g, 8.89 mol, quantitative yield,
1
19
m.p.: 56 °C); H-NMR (CD
3
CN), δ, ppm: 3.85 s (6H, 2CH
3
), 7.37 s (2H), 8.52 s (1H); F-NMR
CN), δ, ppm: 35.4 q, 120.8 q (CF S), 123.2 d,
6 9 3 2 3
H O N F S: C, 29.27; H, 3.68; N, 11.38; S, 13.02. Found: C, 30.03;
1
3
(
CD CN), δ, ppm: −79.3 s (3F, CF
3
3
S); C-NMR (CD
3
3
m, 136.5 d, m; Anal. Calcd. for C
H, 4.10; N, 11.57; S, 13.50.
1
6 11 2 3 3
-Ethyl-3-methylimidazolium Trifluoromethanesulfonate [C H N ][CF SO ]
Freshly distilled ethyl trifluoromethanesulfonate (895 g, 5.02 mol) was dropped slowly into
magnetically stirred N-methylimidazole (400 g, 4.87 mol) at 0 °C over a period of 6 h. Stirring
1,000 rpm) was continued for 12 h at 30 °C to complete the reaction. Finally the excess of ethyl
(
trifluoromethanesulfonate (27 g, 0.15 mol) was evaporated at 0.01 mbar and 25 °C. The product (1,268 g,
1
4
.87 mol, quantitative yield) was obtained as a clear and colourless liquid; H-NMR (CD CN), δ, ppm:
3
3
3
1
.44 t (3H, CH
3
, JH,H = 7.3 Hz), 3.86 s (3H, CH
3
), 4.20 q (2H, CH
2
, JH,H = 7.3 Hz), 7.44 s (1H), 7.50
1
9
13
s (1H), 8.70 s (1H); F-NMR (CD
3
CN), δ, ppm: −79.3 s (3F, CF
3
S); C-NMR (CD
3
CN), δ, ppm: 14.3
q, 35.4 q, 44.5 t, 120.8 q (CF S), 121.7 d,m, 123.3 d,m, 135.9 d,m; Anal. Calcd. for C H O N F S: C,
3
7
11
3
2 3
3
2.31; H, 4.26; N, 10.76; S, 12.32. Found: C, 32.47; H, 4.50; N, 10.86; S, 12.39.

Molecules 2012, 17
-Butyl-3-methylimidazolium Trifluoromethanesulfonate [C H N ][CF SO ]
5329
1
8
15
2
3
3
Method (a): Freshly distilled methyl trifluoromethanesulfonate (1,341 g, 8.17 mol) was dropped
slowly into magnetically stirred N-butylimidazole (1,000 g, 8.05 mol) during 14 h at 0 °C. Stirring
1,000 rpm) was continued for 3 h at 25 °C to complete the reaction. Finally the excess of methyl
(
trifluoromethanesulfonate (20 g, 0.12 mol) was evaporated at 0.01 mbar and 25 °C within 10 h. The
product (2,321 g, 8.05 mol, quantitative yield) was obtained as a clear and nearly colourless liquid;
1
3
H-NMR (CD
.86 s (3H, CH
CD CN), δ, ppm: −79.3 s (3F, CF
3
CN), δ, ppm: 0.93 t (3H, CH
3
, JH,H = 7.3 Hz), 1.33 m (2H, CH
2
), 1.82 m (2H, CH
2
),
3
19
3
3
), 4.17 q (2H, CH
2
, JH,H = 7.3 Hz), 7.42 s (1H), 7.47 s (1H), 8.68 s (1H); F-NMR
1
3
(
3
3
S); C-NMR (CD
3
CN), δ, ppm: 12.4 q, 18.6 t, 31.3 t, 35.5 q,
4
5
8.9 t, 120.8 q (CF S), 122.0 d,m, 123.3 d,m, 136.0 d,m; Anal. Calcd. for C H O N F S: C, 37.50; H,
3
9
15
3
2 3
.24; N, 9.72; S, 11.12. Found: C, 37.30; H, 5.39; N, 9.60; S, 10.53.
Method (b): A mixture of 1-butyl-3-methylimidazolium chloride (1.04 g, 5.95 mmol) and methyl
triflate (CF SO OCH , 1.67 g, 10.2 mmol) was stirred at room temperature for 30 min. The residue
3
2
3
was dried for 30 min in vacuum at 0.13 mbar and 120 °C (oil-bath temperature), giving 1.71 g
a quantitative yield) of 1-butyl-3-methylimidazolium triflate. The product was characterised by NMR
(
spectroscopy. The spectra are identical to those of the product obtained by Method (a).
Method (c): A mixture of 1-butyl-3-methylimidazolium chloride (1.67 g, 9.56 mmol) and trimethylsilyl
triflate ([CF
residue was dried for 30 min in vacuum at 0.13 mbar and 120 °C (oil-bath temperature), giving 2.75 g
a quantitative yield) of 1-butyl-3-methylimidazolium triflate. The product was characterised by means
of NMR spectroscopy. The spectra are identical to those of the product obtained by Method (a).
3 2 3 3
SO OSi(CH ) , 2.36 g, 10.6 mmol] was stirred at room temperature for 30 min. The
(
1
19 2 3 3
-Hexyl-3-methylimidazolium-trifluoromethanesulfonate [C10H N ][CF SO ]
Method (a): A mixture of 1-hexyl-3-methylimidazolium chloride (1.80 g, 8.88 mmol) and methyl
triflate (CF SO OCH , 1.52 g, 9.26 mmol) was stirred at room temperature for 30 min. NMR
3
2
3
measurements show the completeness of the reaction. The residue was dried for 30 min under vacuum
at 0.13 mbar and 120 °C (oil-bath temperature), giving 2.80 g (a quantitative yield) of 1-hexyl-3-
1
methylimidazolium triflate; H-NMR (CD
3
CN), δ, ppm: 0.87 m (3H, CH
3
), 1.29 m (6H, 3CH
2
), 1.81 m
(
2H, CH ), 3.82 s (3H, CH ), 4.11 t (2H, CH ), 7.35 d,d (1H, CH), 7.39 d,d (1H, CH), 8.55 br.s (1H,
2 3 2
3
19
3 3
CH), JH,H = 6.9 Hz, JH,H = 1.5 Hz; F-NMR (CD CN), δ, ppm: −78.1 s (3F, SCF ).
Method (b): A mixture of 1-hexyl-3-methylimidazolium chloride (1.81 g, 8.93 mmol) and
trimethylsilyl triflate [CF SO OSi(CH , 2.62 g, 9.26 mmol] was stirred at room temperature for 4 h.
3
2
3 3
)
The residue was dried for 30 min under vacuum at 0.13 mbar and 120 °C (oil-bath temperature),
giving 2.81 g (a quantitative yield) of 1-hexyl-3-methylimidazolium triflate. The product was
characterised by means of NMR spectroscopy. The spectra are identical to those of the product
obtained by Method (a).

Molecules 2012, 17
-Octyl-1-methylimidazolium-trifluoromethanesulfonate [C H N ][CF SO ]
5330
3
1
2
23
2
3
3
Freshly distilled methyl trifluoromethanesulfonate (1,010 g, 6.15 mol) was dropped slowly into
magnetically stirred N-octylimidazole (1,100 g, 6.10 mol) over a period of 10 h at 0 °C. Stirring
1,000 rpm) was continued for 2 h at 20 °C and 1 hour at 40 °C to complete the reaction. Finally the
(
excess of methyl trifluoromethanesulfonate (9 g, 0.05 mol) was evaporated at 0.01 mbar and 25 °C
within 10 h. The product (2101 g, 6.10 mol, quantitative yield) was obtained as a clear and nearly
1
3
colourless liquid; H-NMR (CD CN), δ, ppm: 0.89 t (3H, CH , J = 7.0 Hz), 1.30 m (10H, 5CH2),
3
3
H,H
3
1
.84 m (2H, CH
2
), 3.86 s (3H, CH
3
), 4.15 t (2H, CH
2
, JH,H = 7.3 Hz), 7.41 s (1H), 7.46 s (1H), 8.63 s
1
9
13
(
1H); F-NMR (CD
3
CN), δ, ppm: −79.3 s (3F, CF
3
S); C-NMR (CD
3
CN), δ, ppm: 14.7 q, 23.7 t,
2
7.0 t, 29.9 t, 30.1 t, 31.0 t, 32.8 t, 37.1 q, 50.8 t, 120.8 q (CF S), 123.6 d, m, 125.0 d, m, 137.5 d, m;
3
23 3 2 3
Anal. Calcd. for C13H O N F S: C, 45.34; H, 6.73; N, 8.13; S, 9.31. Found: C, 45.29; H, 6.78; N,
7
.77; S, 8.61.
1
-Butyl-3-ethylimidazolium-trifluoromethanesulfonate [C H N ][CF SO ]
9
17
2
3
3
Freshly distilled ethyl trifluoromethanesulfonate (1,240 g, 6.96 mol) was dropped slowly into
magnetically stirred N-butylimidazole (840 g, 6.76 mol) during 9 h at 0 °C. Stirring (1,000 rpm) was
continued for 12 h at 30 °C to complete the reaction. Finally the excess of ethyl trifluoromethanesulfonate
(
35 g, 0.20 mol) was evaporated at 0.01 mbar and 25 °C. The product (2,045 g, 6.76 mol, quantitative
1
yield) was obtained as a clear and colourless liquid; H-NMR (CD
3
3
CN), δ, ppm: 0.94 t (3H, CH
3
,
3
J
H,H = 7.3 Hz), 1.34 m (2H, CH
2
), 1.48 t (3H, CH
3
, JH,H = 7.3 Hz), 1.83 m (2H, CH
2
), 4.17 t (2H,
3
3
CH
1
2
, JH,H = 7.3 Hz), 4.21 q (2H, CH
2
, JH,H = 7.3 Hz ), 7.48 s (1H), 7.49 s (1H), 8.73 s (1H);
9
13
F-NMR (CD
3
CN), δ, ppm: −79.3 s (3F, CF
3
S); C-NMR (CD
3
CN), δ, ppm: 12.4 q, 14.2 q, 31.3 t,
S: C,
4
4.5 t, 49.0 t, 120.8 q (CF
3
S), 121.8 d,m, 122.4 d,m, 135.0 d,m; Anal. Calcd. for C10
H
17
O
3
N
2
F
3
3
9.73; H, 5.67; N, 9.27; S, 10.61. Found: C, 39.13; H, 5.43; N, 9.32; S, 10.63.
7 3 3
N,N-Dimethylpyrrolidinium Trifluoromethanesulfonate [C H14N][CF SO ]
Freshly distilled methyl trifluoromethanesulfonate (272 g, 1.66 mol) was added slowly (within 45 min)
to the stirred solution of N-methylpyrrolidine (141.1 g, 1.66 mol) in dry hexane (800 mL) at 0 °C.
After that the reaction mixture was heated and kept reflux for 15 min (oil-bath temperature is 70–75 °C).
After cooling to room temperature a white precipitate was filtered off, washed twice with hexane
(
100 mL) and dried under vacuum (0.3 mbar) at 110 °C for 3 h. The N,N-dimethylpyrrolidinium
1
trifluoromethanesulfonate was obtained as a white solid material (409 g, 99%); H-NMR (CD
3
CN), δ,
CN), δ, ppm: −78.0 s
S: C, 33.73; H, 5.66; N, 5.62; S, 12.86. Found: C, 33.66; H,
1
9
ppm: 2.17 m (4H, 2CH
3F, CF S); Anal. Calcd. for C
.68; N, 5.60; S, 13.06.
2
), 3.07 s (6H, 2CH
3 2 3
), 3.45 m (4H, 2CH ); F-NMR (CD
(
3
7
H
14
F
3
NO
3
5
9 3 3
N-Butyl-N-methylpyrrolidinium Trifluoromethanesulfonate [C H20N][CF SO ]
Freshly distilled methyl trifluoromethanesulfonate (990 g, 6.03 mol) was dropped slowly into
magnetically stirred N-butylpyrrolidine (764 g, 6.00 mol) over a period of 24 h at 0 °C. Stirring
(
1,000 rpm) was continued for 3 h at 25 °C to complete the reaction. Finally the excess of methyl

Molecules 2012, 17
5331
trifluoromethanesulfonate (5 g, 0.03 mol) was evaporated at 0.01 mbar and 25 °C within 10 h. The
product (1,749 g, 6.00 mol, quantitative yield) was obtained as a clear and nearly colourless liquid;
1
3
H-NMR (CD
3 3 2 2
CN), δ, ppm: 0.97 t (3H, CH , JH,H = 7.4 Hz), 1.38 m (2H, CH ), 1.73 m (2H, CH ),
1
9
2
.16 m (4H, 2CH ), 2.98 s (3H, CH ), 3.28 m (2H, CH ), 3.45 m (4H, CH ); F-NMR (CD CN), δ,
2
3
2
2
3
13
ppm: −79.2 s (3F, CF
t, 120.8 q (CF S) ; Anal. Calcd. for C10
0.85; H, 6.81; N, 4.96; S, 10.42.
3
S); C-NMR (CD
3
CN), δ, ppm: 12.5 q, 19.1 t, 21.0 t, 25.0 t, 47.8 q, 63.6 t, 63.9
NF S: C, 41.23; H, 6.92; N, 4.81; S, 11.01. Found: C,
3
H
20
O
3
3
4
N,N-Dimethylpiperidinium Trifluoromethanesulfonate [C H N][CF SO ]
8
16
3
3
Freshly distilled methyl trifluoromethanesulfonate (12.83 g, 78.2 mmol) was added slowly (within
45 min) to the stirred solution of N-methylpiperidine (7.76 g, 78.2 mol) in dry hexane (150 mL) at
room temperature. The warm reaction mixture was left stirring for 30 min and then cooled down to
room temperature. The white precipitate was filtered off, washed twice with hexane (10 mL) and
dried under 0.3 mbar vacuum at 80 °C to give a white solid material (19.72 g, 96%). The melting point
1
after crystallisation from methanol was 255–256 °C; H-NMR (CD CN), δ, ppm: 1.79 m (6H, 3CH ),
3
2
1
9
3
.02 s (6H, 2CH
3
), 3.27 m (4H, 2CH
2
); F-NMR (CD
3
CN), δ, ppm: −78.1 s (3F, CF
3
S); Anal. Calcd.
for C NO
8
H
16
F
3
3
S: C, 36.50; H, 6.13; N, 5.32; S, 12.18. Found: C, 33.44; H, 6.07; N, 5.31; S, 12.20.
N-Methyl-3-butylpyridinium Trifluoromethanesulfonate [C
9
H20N][CF
3
SO
3
]
Freshly distilled methyl trifluoromethanesulfonate (23.00 g, 0.14 mol) was dropped slowly into
magnetically stirred 3-butylpyridine (18.13 g, 0.13 mol) over a 2 hour period at 0 °C. Stirring
(
800–1,000 rpm) was continued for 1 h at 25 °C to complete the reaction. Finally the excess of methyl
trifluoromethanesulfonate (1.00 g, 0.01 mol) was evaporated at 0.01 mbar and 25 °C within 5 h.
The title compound (40.13 g, 0.13 mol, quantitative yield) was obtained as a clear and pale yellow
1
3
liquid; H-NMR (CD
3
2
CN), δ, ppm: 0.90 t (3H, CH
3
, JH,H = 7.3 Hz), 1.34 m (2H, CH
2
), 1.64 m (2H,
3
CH ), 2.82 t (2H, CH
2
, JH,H = 7.8 Hz,), 4.37 s (3H, CH
3
), 7.93 m (1H, CH), 8.40 m (1H, CH), 8.67 m
1
9
(
1H, CH), 8.75 s (1H, CH); F-NMR (CD CN), δ, ppm: −77.9 s (3F, CF S).
3
3
7 3 3
N-Ethylpyridinium Trifluoromethanesulfonate [C H10N][CF SO ]
Method (a): A mixture of N-ethylpyridinium bromide (1.56 g, 8.29 mmol) and methyl triflate
(
CF SO OCH , 1.67 g, 10.2 mmol) was stirred at room temperature for 30 min. The residue was dried
3
2
3
for 30 min under vacuum (0.13 mbar) at 120 °C (oil-bath temperature), giving 2.13 g (a quantitative
1
yield) of N-ethylpyridinium triflate; H-NMR (CD
3
CN), δ, ppm: 1.58 t (3H, CH
3
), 4.59 q (2H, CH
2
),
3
3
3
8
.02 m (2H, 2CH), 8.49 t,t (1H, CH), 8.78 d (2H, 2CH), JH,H = 7.3 Hz, JH,H = 7.6 Hz, JH,H = 6.1 Hz,
4
19
J
3 3
H,H = 1.2 Hz; F-NMR (CD CN), δ, ppm: −78.0 s (3F, CF ).
Method (b): A mixture of N-ethylpyridinium bromide (1.85 g, 9.84 mmol) and trimethylsilyl triflate
CF SO OSi(CH , 2.54 g, 11.4 mmol) was stirred at room temperature for 4 h. The residue was dried
[
3
2
3 3
)
for 30 min under vacuum (0.13 mbar) at 120 °C (oil-bath temperature), giving 2.53 g (a quantitative
yield) of N-ethylpyridinium triflate. The product was characterised by means of NMR spectroscopy.
The spectra are identical to those of the product obtained using Method (a).

Molecules 2012, 17
5332
N-Butylpyridinium Trifluoromethanesulfonate [C H N][CF SO ]
9
14
3
3
Method (a): A mixture of N-butylpyridinium bromide (4.31 g, 19.9 mmol) and of methyl triflate
CF SO OCH , 4.41 g, 26.9 mmol) was stirred at room temperature for 30 min. The residue was dried
(
3
2
3
for 30 min under vacuum (0.13 mbar) at 120 °C (oil-bath temperature), giving 5.68 g (a quantitative
1
yield) of N-butylpyridinium triflate; H-NMR (CD CN), δ, ppm: 0.93 t (3H, CH ), 1.35 m (2H, CH ),
3
3
2
3
1
.93 m (2H, CH
2
3
), 4.53 t (2H, CH
2
), 8.02 m (2H, 2CH), 8.50 t (1H, CH), 8.74 d (2H, 2CH), JH,H = 7.4 Hz,
3
3
19
J
H,H = 7.6 Hz, JH,H = 7.9 Hz, JH,H = 6.1 Hz; F-NMR (CD
3
CN), δ, ppm: −78.0 s (3F, CF
3
).
Method (b): A mixture of N-butylpyridinium bromide (1.42 g, 6.57 mmol) and of trimethylsilyl
triflate [CF SO OSi(CH , 1.73 g, 7.78 mmol) was stirred at room temperature for 4 h. The residue
was dried for 30 min under vacuum (0.13 mbar) at 120 °C (oil-bath temperature), giving 1.87 g
a quantitative yield) of N-butylpyridinium triflate. The product was characterised by means of NMR
spectroscopy. The spectra are identical to those described in the experiment (a).
3
2
3 3
)
(
1
,2-Dimethyl-5-ethylpyridinium-trifluoromethanesulfonate
Freshly distilled methyl trifluoromethanesulfonate (45.0 g, 0.27 mol) was dropped slowly into
magnetically stirred 5-ethyl-2-methylpyridine (32.0 g, 0.26 mol) over a period of 4 h at 0 °C. Stirring
1,000 rpm) was continued for 3 h at 25 °C to complete the reaction. Finally the excess of methyl
(
trifluoromethanesulfonate (1.7 g, 0.01 mol) was evaporated at 0.01 mbar and 25 °C within 10 h. The
product (75.3 g, 0.26 mol, quantitative yield) was obtained as a clear and nearly colourless liquid;
1
3
3 2 3 3
H-NMR (CD CN), δ, ppm: 1.29 t (3H, JH,H = 7.6 Hz, CH CH ), 2.73 s (3H, CH ), 2.81 t (2H,
3
J
H,H = 7.6 Hz , CH
2
CH
3
), 4.17 s (3H, CH
3
), 7.80 d (1H, JH,H = 8.2), 8.24 d (1H, JH,H = 8.2), 8.56 s
1
9
13
(
1H). F-NMR (CD
4.9 t, 45.5 q, 121.1 q (CF
NF S: C, 42.10; H, 4.95; N, 4.91; S, 11.24. Found: C, 41.55; H, 4.83; N, 4.90; S, 11.40.
3
CN), δ, ppm: −79.2 s (3F, CF
3
S); C-NMR (CD
3
CN), δ, ppm: 13.7 q , 19.2 q,
2
3
S), 129.0 d, 143.1 d, 144.8 d, 145.8 s, 153.3 s Anal. Calcd. for
C
10
H
14
O
3
3
1
9 3 3
,2,4,6-Tetramethylpyridinium Trifluoromethanesulfonate [C H14N][CF SO ]
Freshly distilled methyl trifluoromethanesulfonate (15.0 g, 0.09 mol) was dropped slowly into a
magnetically stirred solution of 2,4,6-trimethylpyridine (10.0 g, 0.08 mol) in hexane (100 mL) over a
period of 2 h at 25 °C. With the first drops a colourless solid material precipitated. Stirring (1,200 rpm)
was continued for 1 h at 25 °C to complete the reaction. The deposit was isolated by filtration and
washed twice with fresh hexane. Finally the product was evaporated at 0.01 mbar and 25 °C for 2 h.
1
,2,4,6-Tetramethylpyridinium trifluoromethanesulfonate (23.5 g, 0.08 mol, quantitative yield) was
1
obtained as a colourless solid (m.p.: 145 °C); H-NMR (CD CN), δ, ppm: 2.51 s (3H, CH ), 2.71 s
3
3
1
9
(6H, 2CH
3
), 3.94 s (3H, CH
3
), 7.56 s (2H, 2CH); F-NMR (376.54 MHz, CD
3
CN), δ, ppm: −79.3 s
1
3
(
3F, CF S); C-NMR (CD
3
3
3
CN), δ, ppm: 21.8 q, 22.2 q, 40.9 q, 122.5 q (CF S), 129.1 d, 156.3 s, 159.1
s; Anal. Calcd. for C H O NF S: C, 42.10; H, 4.95; N, 4.91; S, 11.24. Found: C, 42.59; H, 5.17; N,
1
0
14
3
3
4
.98; S, 11.68.

Molecules 2012, 17
-Methyl-2,4,6,-tris(t-butyl)pyridnium Trifluoromethanesulfonate [C H N][CF SO ]
5333
1
1
8
32
3
3
Freshly distilled methyl trifluoromethanesulfonate (10.0 g, 60 mmol) was added to solid 2,4,6-tris(t-
butyl)pyridine (1.0 g, 4 mmol). The suspension was heated to reflux (bath 100 °C) and forms a
solution at 70 °C. After 8 h of stirring the solution was cooled down to room temperature (a suspension
is formed again at 70 °C). The raw solid material contains only 6 % of the expected product. After two
recrystallizations from dichloromethane/hexane (1/10, vol/vol), the colourless solid product obtained
was evaporated at 0.01 mbar and 25 °C within 8 h to give the product (0.07 g, 0.2 mmol, 4% yield) as
1
a colourless solid (m.p.: 186 °C); H-NMR (CD CN), δ, ppm: 1,55 s (9H, 3CH ), 1.66 s (18H, 6CH ),
3
3
3
1
9
4
.36 s (3H, NCH
3
), 7.92 s (2H, 2CH); F-NMR (CD
3
CN), δ, ppm: −79.3 s (3F, CF
3
S); Anal. Calcd.
for C H O NF S: C, 55.45; H, 7.84; N, 3.40; S, 7.79. Found: C, 54.11; H, 7.80; N, 3.69; S, 7.75.
1
9
32
3
3
8 17 3 3 3 3
Methyl trioctylammonium Trifluoromethanesulfonate [(C H ) NCH ][CF SO ]
Freshly distilled methyl trifluoromethanesulfonate (715 g, 4.36 mol) was dropped slowly into a
magnetically stirred solution of trioctylamine (1,526 g, 4.31 mol) in dichloromethane (700 mL) within
24 h at 0 °C. Stirring (1,000 rpm) was continued for 3 h at 25 °C to complete the reaction.
Dichloromethane (b.p. 40 °C) was distilled of under atmospheric pressure. Residual dichloromethane
and the excess of methyl trifluoromethanesulfonate (7 g, 0.05 mol) were evaporated at 0.01 mbar within
14 h. During the evaporation the temperature was increased slowly to 65 °C to avoid the crystallization
of the product. Methyl trioctylammonium trifluoromethanesulfonate (2,234 g, 4.31 mol, quantitative
1
yield) was obtained as a colourless solid (m.p.: 52 °C); H-NMR (CD
3
CN), δ, ppm: 0.92 t (9H, 3CH
), 3.16 m (6H, 3CH );
CN), δ, ppm: 13.1 q, 21.4 t, 22.0 t,
S); Anal. Calcd. for C26 NF S: C, 60.31;
H, 10.51; N, 2.71; S, 6.19. Found: C, 59.82; H, 10.51; N, 2.76; S, 6.26.
3
,
3
J
H,H = 6.7 Hz), 1.34 m (30H, 15CH
2
), 1.67 m (6H, 3CH
2
), 2.92 s (3H, NCH
3
2
1
9
13
F-NMR (CD
3
CN), δ, ppm: −79.1 (s, 3F, CF
3
S); C-NMR (CD
3
2
5.5 t, 28.3 t, 28.4 t, 31.1 t, 47.6 q, 61.2 t, 120.9 q (CF
3
H
54
O
3
3
2 5 3 3 3 3
Methyl triethylphosphonium Trifluoromethanesulfonate [(C H ) PCH ][CF SO ]
Freshly distilled methyl trifluoromethanesulfonate (11.19 g, 68.2 mmol) was added slowly (within
0 min) to a stirred solution of triethylphosphine (8.05 g, 68.2 mmol) in dry hexane (150 mL) at room
1
temperature. The warm reaction mixture was left stirring for 30 min and cooled down to room
temperature. The white precipitate was filtered off, washed twice with hexane (10 mL) and dried under
vacuum (0.3 mbar) at 60 °C to give the title compound (19.02 g, 99% yield) as a white solid material;
1
3
3
H-NMR (acetone-d
6
): δ, ppm: 1.30 d,t, (9H, 3CH
3
J
H,H = 7.7 Hz, JP,H = 18.8 Hz), 1.95 d (3H, PCH
3
,
2
2
19
J
P,H = 13.7 Hz), 2.40 d,q (6H, 3CH
2
, JP,H = 13.8 Hz); F-NMR (CD
3
CN), δ, ppm: −77.8 s (3F,
CF
3
S); Anal. Calcd. for C
8
H
18
F
3
O
3
PS: C, 34.04; H, 6.43; S, 11.36. Found: C, 33.72; H, 6.57; S, 11.14.
Trihexyl tetradecylphosphonium Trifluoromethanesulfonate [(C
6
H13) SO
3
PC14
H
29][CF
3
3
]
Method (a): A mixture of trihexyl tetradecylphosphonium chloride (1.75 g, 3.37 mmol) and methyl
triflate (CF SO OCH , 2.59 g, 15.8 mmol) was stirred at room temperature for 30 min. The residue
3
2
3
was dried for 30 min under vacuum (0.13 mbar) at 120 °C (oil-bath temperature), giving 2.13 g
1
(
quantitative yield) of trihexyl tetradecylphosphonium triflate; H-NMR (CD
3
CN), δ, ppm: 0.84–0.94 m

Molecules 2012, 17
5334
(
12H, 4CH ), 1.24–1.37 m (32H, 16CH ), 1.37–1.57 m (16H, 8CH ), 1.99–2.09 m (8H, 4CH );
3
2
2
2
1
9
31
1
F-NMR (CD
3
CN), δ, ppm: −78.0 s (3F, SCF
3
); P{ H}-NMR (CD
3
CN), δ, ppm: 33.5 s.
Method (b): A mixture of trihexyl tetradecylphosphonium chloride (1.64 g, 3.16 mmol) and
trimethylsilyl triflate [CF SO OSi(CH ) , 0.91 g, 4.09 mmol) was stirred at room temperature for 4 h.
3
2
3 3
The residue was dried for 30 min under vacuum (0.13 mbar) at 120 °C (oil-bath temperature) to give
.00 g (a quantitative yield) of the title compound, which was characterised by NMR spectroscopy.
2
The spectra were identical to those of the product obtained by Method (a).
N"-Ethyl-N,N,N',N'-tetramethylguanidinium Trifluoromethanesulfonate [(CH ) NC(NHC H )N(CH ) ]
3
2
2
5
3 2
3 3
[CF SO ]
Freshly distilled ethyl trifluoromethanesulfonate (870 g, 4.88 mol) was dropped slowly into
magnetically stirred N,N,N',N'-tetramethylguanidine (560 g, 4.86 mol) during 9 h at 0 °C. Stirring
1,000 rpm) was continued for 12 h at 30 °C to complete the reaction. Finally the excess of ethyl
trifluoromethanesulfonate (4 g, 0.02 mol) was evaporated at 0.01 mbar and 25 °C. The product (1,426 g,
(
4
.86 mol, quantitative yield) was obtained as a clear and colourless liquid; [(CH ) NC(C H NH)
3
2
2
5
1
3
N(CH
3
)
2
][CF
3
SO
3
]: H-NMR (CD
3
CN), δ, ppm: 1.12 t (3H, JH,H = 7.1 Hz, CH
2
CH
3
), 2.88 s (12H,
CN), δ, ppm:
3
19
2[N(CH
3
)
2
]), 3.25 q (2H, , JH,H = 7.1 Hz, CH
2
CH
3
), 6.46 s (1H, NH); F-NMR (CD
3
13
−
79.1 s (3F, CF
3
S); C-NMR (CD
3
CN), δ, ppm: 12.1 q (CH
2
CH
NH)N(CH
), 2.92 s (12H, [N(CH
3
), 39.1 q (N(CH
3
)
2
), 43.2 t
1
(
CH
2
3
CH
3
), 120.8 q (CF
3
S), 163.0 s; [(CH
3
)(CH
2
CH
3
)NC(CH
3
3
)
2
][CF SO
3
3
]: H-NMR
3
(
CD
CN), δ, ppm: 1.20 t (3H, JH,H = 7.1 Hz, CH
2
CH
3
3
)
2
]), 3.25 q (2H,
3
19
13
J
H,H = 7.1 Hz, CH
2
CH
CN), δ, ppm: 14.2 q (CH
NC(C
3
), 6.46 s (1H, NH); F-NMR (CD
3
CN), δ, ppm: −79.1 s (3F, CF
), 39.7 t (CH CH ), 120.8 q (CF
3 2
]: [(CH )(CH CH )NC(CH NH)N(CH )
3
S); C-NMR
(CD
3
2
CH
3
), 38.9 q (N(CH
3
)
2
2
3
3
S), 161.3 s; The
] was 2.3:1;
ratio of isomers [(CH
Anal. Calcd. for C
5.35; S, 10.90.
3
)
2
2
H
5
NH)N(CH
3
)
2
3
2
3
3
8
18 3 3 3
H O N F S: C, 32.76; H, 6.19; N, 14.33; S, 10.93. Found: C, 32.72; H, 6.67; N,
1
N,N,N',N'-Tetramethyl-O-methylisouronium Trifluoromethanesulfonate [(CH ) NC(OCH )N(CH ) ]
3
2
3
3 2
3 3
[CF SO ]
Freshly distilled methyl trifluoromethanesulfonate (765 g, 4.66 mol) was dropped slowly into
magnetically stirred N,N,N',N'-tetramethylurea (534 g, 4.60 mol) over a period of 9 h at 20 °C. Stirring
1,000 rpm) was continued for 12 h at 25 °C to complete the reaction. Finally the excess of
methyltrifluoromethanesulfonate (10 g, 0.06 mol) was evaporated at 0.01 mbar and 25 °C. The product
(
(
1,288 g, 4.60 mol, quantitative yield) was obtained as a clear and colourless liquid; [(CH ) N)
3 2
2
1
COCH
1
3
][CF
3
SO
3
]: H-NMR (CD
3
CN), δ, ppm: 3.11 s (12H, 2[N(CH
3
)
2
]), 4.10 s (3H, OCH
3
);
9
13
F-NMR (CD
3
CN), δ, ppm: −79.2 s (3F, CF
3
S); C-NMR (CD
3
CN), δ, ppm: 40.7 q (N(CH
3
)
2
), 62.9 q
(
OCH ), 120.8 q (CF S); Anal. Calcd. for C H O N F S: C, 30.00; H, 5.39; N, 10.00; S, 11.44.
3 3 7 15 4 2 3
Found: C, 29.64; H, 5.34; N, 9.92; S, 10.93.

Molecules 2012, 17
. Conclusions
New economical syntheses of methyl and ethyl triflate from dimethyl- and diethyl carbonate and
5335
4
triflic acid has been developed. These chemicals were used in solvent and halogen free syntheses of
high purity triflate ionic liquids via direct alkylation of organic bases: amines, phosphines or
heterocyclic compounds. Ionic liquids with the triflate anion possess high thermal and electrochemical
stability and fairly low viscosity.
Acknowledgement
The authors thank A. Amann (Merck KGaA, Darmstadt, Germany) and J. Hübner (Bergische
University Wuppertal, Germany) for the analytics of the ionic liquids and viscosity, thermal and
electrochemical stability measurements.
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©
2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
http://creativecommons.org/licenses/by/3.0/).
(