The production of N,N-butyl-d.-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP Tf2N, an ionic liquid) was desired to study the quenching of lanthanide fluorescence in this ionic liquid. Three steps to the ionic liquid were optimized with non-deuterated reactants. First, 1-methylpyrrolidine was quaternized with 1-bromobutane by an SN2reaction. Cation HPLC was used to determine percent conversion with yields >93%. Second, BMP Br was recrystallized using acetonitrile/ethyl acetate with yields >95%. Third, the anion was exchanged by mixing aqueous Li Tf2N and aqueous BMP Br producing the colorless BMP Tf2N as a separate layer with yields >95%. 'H and 13CNMR verified production of the ionic liquid. Nine extractions with 10:1 (v/v) water:ionic liquid were required to reduce bromide concentration in the aqueous phase below the anion HPLC detection limit of 1.6 ppm. A similar synthesis using perdeuterobutyl bromide proceeded smoothly producing a colorless ionic liquid with an overall 80% yield.

1. Journal of Undergraduate Chemistry Research, 2013, 12(3),75
SYNTHESIS OF N,N-BUTYL-D9
-METHYLPYRROLIDINIUM BIS(TRIFLUORO-
METHANESULFONYL)IMIDEt
Duane E. Weisshaar]", icole J. Altena*, Rachel S. Anderson*, Riley P. McManus*, Austin R. Letcher*, Mathew E.
Amundson*, and Gary W. Earl
Abstract
Chemistry Department, Augustana College, Sioux Falls, SD 57197, duane.weisshaar@augie.edu
The production of N,N-butyl-d.-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP Tf2N, an ionic liquid) was desired to
study the quenching of lanthanide fluorescence in this ionic liquid. Three steps to the ionic liquid were optimized with non-deuterated
reactants. First, 1-methylpyrrolidine was quaternized with 1-bromobutane by an SN2reaction. Cation HPLC was used to determine
percent conversion with yields >93%. Second, BMP Br was recrystallized using acetonitrile/ethyl acetate with yields >95%. Third,
the anion was exchanged by mixing aqueous Li Tf2N and aqueous BMP Br producing the colorless BMP Tf2N as a separate layer
with yields >95%. 'H and 13CNMR verified production of the ionic liquid. Nine extractions with 10:1 (v/v) water:ionic liquid were
required to reduce bromide concentration in the aqueous phase below the anion HPLC detection limit of 1.6 ppm. A similar synthesis
using perdeuterobutyl bromide proceeded smoothly producing a colorless ionic liquid with an overall 80% yield.
Keywords: Deuterated ionic liquid, Synthesis, Butylmethypyrrolidinium
Scheme 2.
:j: This work was previously presented as a poster at the 47thACS Midwest Regional Meeting, October 24-27, 2012, Omaha, NE.
Introduction
May et al. (I) have been studying the fluorescence of
lanthanides in the non-coordinating ionic liquid N,N-
butylmethylpyrrolidinium bis(trifluoromerhanesulfonyl)
imide (BMP Tf2 ). To investigate the quenching effects of
the solvent, that group desired deuterated analogs ofthe ionic
liquid and asked our group to synthesize them. (Changing
vibrational frequencies of the solvent molecules changes the
efficiency of fluorescence quenching.) It was decided that
the perdeuterobutyl analog would have sufficient deuteration
for the quenching study, so that became the primary target.
The initial effort was optimization of each step in the synthesis
using non-deuterated reactants to establish conditions that
maximized yield and purity.
The method of MacFarlane et at. (2) served as the starting
point for the synthesis. This method begins with an SN2
reaction of an alkyl halide with a tertiary amine (Scheme 1),
followed by an anion exchange reaction to produce the ionic
liquid (Scheme 2). BMP Tf2N should be a colorless
compound, but typically this synthesis produces a product
with varying degrees of color from a yellow to red liquid.
The most common strategy for removing the color is to heat
the ionic liquid with activated charcoal and filter (3).
Experimental
Reagents
The reagents from Sigma-Aldrich (St. Louis, MO) were:
acetonitrile (99.8%), I-bromobutane (99%), I-bromobutane-
d9 (98%), lithium bis(trifluoromethanesulfonyl)imide
-
Scheme 1.
-
o 0.e II ..•• II
+ Ll F3C-S-N-S-CF3
II €> II
o 0
(Li Tf2N) (99.95%), ammonium acetate (99.99%), and acetic
acid (99.99%). Additional reagents included: disodium 1,5-
naphthalenedisulfonate dihydrate (98%, Acros Organics, NJ),
l-methylpyrrolidine (99%, Fluka Analytical, St. Louis, MO),
methanol (99.99%, Pharmco-Aaper, Brookfield CT), ethyl
acetate (ACS Reagent, Pharmco-Aaper, Brookfield CT),
NMR solvent acetonitrile-d. (99.8%, Cambridge Isotope
Laboratories, Inc., Andover, MA), and compressed nitrogen
gas (Linweld, Sioux Falls, SD). All reagents were used as
received. HPLC water was produced by a 3-cartridge
Barnstead anopure II water purification system (Thermo
Fisher Scientific).
Safety
Lithium bis(trifluoromethanesulfonyl)imide is flammable
and corrosive. The l-brornobutane and l-methylpyrrolidine
are toxic, corrosive, and flammable. The 1,5-disodium
naphthalenedisulfonate (solid) is toxic and an irritant. These
were handled with gloves; goggles were worn at all times.
instrumentation
'H- and I3C-NMR spectra were obtained on a JEOL ECS-
400 (400 MHz) Spectrometer (Peabody, MA). UV-Vis spectra
were obtained on a Shimadzu Model UV-2450 UV-Vis
Spectrometer (Columbia, MD) using quartz cuvettes. Bromide
salts were - 0.2 M in acetonitrile and the ionic liquid was
neat.
The HPLC for cation analysis was constructed from
individual components that included the following: Series III
pump, SSI LP-21 pulse dampener, Rheodyne Model 7125
injector with 20 ~L sample loop, Model VD-4101 in-line
degasser (all from Chrom Tech, Inc., Minneapolis, MN), and
Waters Model 410 differential refractometer (Milford, CT).
A 150 x 4.6 mm, 5 urn Spherisorb SCX strong cation exchange
column (Waters Corp., Milford, CT) was used with an eluent
of 50 mM ammonium acetate and 100 mM acetic acid in
o 0II .... II $ e
F3C-S-N-S-CF3 + u XII e II
o 0

2. Journal of Undergraduate Chemistry Research, 2013, 12(3),76
Figure 1. Mini-reactor.
methanol at a flow rate of I mLiminute.
Anion analysis employed an Agilent LCI 100 HPLC with
photodiode array detector and Rheodyne Model 7125 injector
with 20 mL sample loop (Wilmington, DE) and a 150 x 4.1
mm, Sum Hamilton PRP-X100 strong anion exchange column
(Hamilton Co., Reno, NY). Indirect detection at 275 nm was
used with an aqueous 0.5 mM disodium 1,5-
naphthalenedisulfonate (NDS) mobile phase at a flow rate of
1 mL/min.
All mobile phases were filtered through Whatman GF/F
(0.7 mm) filters (Thermo Fisher Scientific) and the samples
were filtered through 0.2 mm polypropylene syringe filters
(Chrom Tech).
Step J - BMP Br Synthesis
Past experience synthesizing a variety of ionic liquids in
this lab has shown that removal of oxygen from the
quatemization reaction is critical for minimizing color in the
final product, but complete elimination of color is difficult.
To facilitate oxygen exclusion a small, stainless steel, high-
pressure reactor (mini-reactor, Figure I) was constructed from
a Hoke 30 mL sampling cylinder (part number 4HDY30, JEM
Technical, Long Lake, MN), a street T (Swagelok, Omaha
Valve & Fitting Co., La Vista, NE), and a Hoke 300-450 psi
pressure relief valve (part number 6711L4YC). A brass toggle
valve (Swageok) and straight-through quick disconnect body
(CPC, Cole-Parmer Instrument Co., Vernon Hills, IL) were
added to facilitate the 2flush. A Lollipop digital thermometer
(Control Company, Fischer Scientific, Hanover Park, IL)
wired to the outside of the mini-reactor tube monitored the
onset and subsidence of the exothermic reaction.
The liquid reagents were massed in a syringe and transferred
to the mini-reactor. In a typical synthesis, 1.7 g (0.02 mole,
-2 mL) I-methylpyrrolidine, 2.7 g (0.02 mole, -2 mL) 1-
bromo butane, and 10 mL acetonitrile were sealed in the mini-
reactor. Oxygen was removed from the vessel by executing
the following procedure at least 10 times: the vessel was
pressurized to 100 psi with N2, agitated for 15 seconds using
a test tube vortexer (CMS Super-Mixer, Morris Plains, J),
and then pressure was released. The tubes were immersed in
a constant temperature oil bath maintained at 70°C with a
125 W immersion heater (Cenco 1655 I-1, Fischer Scientific,
Hanover Park IL) controlled by a JKEM Model 150
Temperature Controller (St. Louis, MO). When the rate of
temperature increase monitored by the external thermometer
Cation HPLC BMP Br Reaction Mixture
BMP
0.00 10.00 15.00 20.00 25.00 30.00
Time (mln)
5.00
Figure 2. Cation HPLC of the quaternization reaction product
showing complete conversion to BMP: expected retention time
of 1-methylpyrrolidine (arrow) 12.5 min, retention time BMP 20.5
min.
indicated the exothermic reaction had begun (initiated around
40°C), the tube was removed from the heating bath) until the
exothermic reaction subsided (-10 minutes). The tube was
again immersed in the heating bath and maintained at 70°C
for 22 hours. After removing solvent and excess reactants by
by rotary evaporation, a pale yellow solid was collected with
greater than 93% yield. Sometimes yields were greater than
100% due to the hygroscopic nature of the material (deuterated
and non-deuterated).
Step 2- Purification
Early in this work, it was discovered that the non-deuterated
BMP Br recrystallized from an acetonitrile/ethyl acetate
mixture produced white, needle crystals, which could be anion
exchanged (next step) to produce a colorless ionic liquid. The
recrystallization approach proved to be more efficient than
the activated charcoal decolorizing process (3).
To recrystallize, the BMP Br was first dissolved in
acetonitrile (- 0.3 g/rnl.) and vacuum filtered to remove
insoluble components. To establish the appropriate solvent
mixture, ethyl acetate was added to the hot acetonitrile
solution until crystals just began to form, and then acetonitrile
was added drop-wise until the crystals just dissolved. The
solution was allowed to cool to room temperature and then
cooled further in an ice bath. (Cooling in two steps produced
larger crystals). The crystals were removed by vacuum
filtration and washed with ethyl acetate. A second crop of
crystals was recovered by a similar procedure after removing
solvent by rotary evaporation. A third crop of white crystals
could be harvested if the initial BMP Br was not too colored.
Deuteration on the butyl group did not affect the
recrystallization.
Step 3- Anion Exchange to Produce BMP TfJV
The recrystallized BMP Br was anion exchanged using
MacFarlane's (2) method with no modifications. Typically
1.3 g (5.6 mmol) BMP Br was dissolved in 2 mL of deionized
water, and 1.6 g (5.6 mmol) Li Tf2N was dissolved in a
separate 2 mL aliquot of deionized water. These two solutions
were then combined in a 10 mL Erlenmeyer flask and stirred
on a magnetic stirrer for three hours. The aqueous (upper)
layer was removed by pipet. To remove residual bromide,

3. Crude BMP Br Spectrum
0.8
0.6
~
~
=01
.c
!s 0.4
.c
<,< -
0.2
~
0
250 350 450 550 650
Wavelength (nm)
Figure 3. UV-Vis spectrum of 0.2 M crude BMP Br in acetonitrile.
The solution had a pale yellow color.
nine extractions with deionized H20 (10: I v/v H20:BMP
Tf2N) were required to reduce the bromide concentration in
the aqueous layer below the detection limit of the anion HPLC
(20 11M, 1.6 ppm). Yields for this step were typically above
95%. !he ionic ~iquid.appeared cloudy, presumably due to
emulsion formation with water. Rotary evaporation at room
temperature for -12 hours removed the cloudy appearance.
IH NMR (400 MHz, CD3CN) 8 3.36 (m, 4 H), 3.17 (m, 2 H),
2.90 (s, 1 H), 2.11 (m, 4 H), 1.68 (m, 2 H), 1.33 (hextet, J =
7.33 Hz, 2 H), 0.93 (t, J = 7.33 Hz, 3 H). l3C NMR (400
MHz, CD3CN) 8119.1 (q, J= 320 Hz, 2 C), 64.4 (2 C), 64.3,
48.2,25.3,21.3 (2 C), 19.4, 12.8.
NMR spec~a for the ionic liquid with the deuterated butyl
group were similar except the deuterium peaks on the butyl
group were absent from the NMR, and the butyl carbon peaks
were also attenuated as expected (4). The l3C peak for the
Tf2.N.carbons (119.1 ppm) appeared as a quartet due to
splitting by the three 19Fnuclei, not the usual singlet.
Results and Discussion
Halide Synthesis
The yields for BMP Br from the mini-reactor, based on
recovered masses, were greater than 93% with some
exceeding 100%. The yield for the deuterated BMP Br was
120%. Variable rotary evaporating efficiency and absorption
of water were the likely causes for yields greater than 100%.
Sinc~ the anion exchange step was carried out in aqueous
solution, the water was not an issue. HPLC analyses showed
no detectable amine left in the reaction mixture (Figure 2).
The crude BMP Br was a pale yellow color due to the
presence of unknown impurities, a typical result for this
synthesis (2,3). A UV-Vis spectrum of 0.2 M BMP Br in
acetonitrile (Figure 3) exhibited a peak at 280 nm and two
shoulders at 350 nm and 470 nm. The band at 470 nm
accounted for the pale yellow color ofthe product.
Recrystallization
Recrystallization ofthe deuterated and non-deuterated BMP
Br from ethyl acetate/acetonitrile produced white needles. The
470 nm band in the UV-Vis spectrum of 0.2 M BMP Br was
virtually absent, the absorbance at 280 nm was reduced to
0.04 and the absorbance at 350 nm bands was 0.02.
Journal of Undergraduate Chemistry Research, 2013, 12(3),77
Anion HPLC ofBMPTf2N Extractions
c
d
------------------------~
O+------,-----r------.------I
2.5 3 3.5
Time (min)
Figure 4. Anion HPLC of the aqueous layer after IL extraction
with water: extraction number a) 2, b) 3, c) 7, and d) 9.
4 4.5
Due to t~e hygroscopic nature of the crystals, an accurate
melting pomt could not be determined. A crystal sealed in a
melting point tube was not melted at 200°C when heating
was stopped to prevent bursting ofthe tube.
The overall yield from a single recrystallization was - 50%
but after optimizing the procedure and employing three
recrystallizations, overall yields of >95% were routinely
achieved.
Anion Exchange Synthesis
Anion ex.change with Li Tf2N yielded a colorless liquid
with a density of 1.45 ± 0.023 g/mL. Yields for the perfected
anion exchange step were - 90%. IH and l3C NMR verified
that BMP Tf2N formed with no evident impurities.
The spectrum of the neat deuterated BMP Tf2N did not
show the shoulder at 470 nm in the visible region, but did
exhibit the bands at 280 nm and 350 nm with absorbances of
1.0 and 0.4 respectively. This indicated that the impurities in
the crude BMP Br had not been completely removed.
However, their absence in the NMR suggested that their
concentrations were quite I?w. The deuterated BMP Tf2N
NMR, before rotary evaporation (to remove water), displayed
trace amounts of ethanol. The source of the ethanol impurity
is unknown, but due to the high cost of the deuterated
bromobutane, the synthesis was only executed once, therefore
the source of the impurity could not be investigated. Rotary
evaporation removed the ethanol.
The solubility of the ionic liquid was estimated through
cation HPLC. A chromatogram of the aqueous layer from
one of the ionic liquid extractions produced a peak height
approximately the same as an 18.4 roM standard BMP Br
indicating the solubility was - 20 mM. '
The aqueous layers from a series of extractions with 10:I
(v/v) water:ionic liquid were analyzed for residual bromide
by anion HPLC (Fig. 4). After the ninth extraction, the
bromide concentration was below the detection limit of -20
11Mbromide (1.6 ppm).

4. Journal of Undergraduate Chemistry Research, 2013, 12(3),78
Conclusion
The synthesis of N,N-butyl-d9-methylpyrrolidinium
bis(trifluoromethanesulfonyl)imide is described here, we
believe, for the first time. The May group reported that
fluorescence experiments using the non-deuterated BMP Tf2N
synthesized here matched results using the commercial ionic
liquid, so the synthesis method meets their requirements. The
deuterated ionic liquid also fulfilled the purpose the May
group was hoping to accomplish. Details of their fluorescence
study will be published elsewhere.
Acknowledgements
This material is based upon work supported by the National
Science FoundationiEPSCoR Grant No. 0903804 and by the
State of South Dakota and by the National Science Foundation
-Undergraduate Research Center program: CHE-0532242
"The Northern Plains Undergraduate Research Center
(NPURC). The NIH Grant Number 2 P20 RR016479 made
this publication possible from the INBRE Program of the
National Center for Research Resources. Its contents are
solely the responsibility of the authors and do not necessarily
represent the official views of NIH. Further thanks go to
Augustana's Roland Wright Chemistry Equipment
Endowment and Augustana College. Augustana's Brandon
Gustafson's patient assistance obtaining NMR spectra is
gratefully acknowledged.
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