Synthesis of oxygen-containing spirobipyrrolidinium salts for high conductivity room temperature ionic liquids

Article abstract of DOI:10.1002/hlca.200900045

Synthesis of ionic liquids (IL) based on oxygen-containing spirobipyrrolidinium salts with BF₄ , BF₃C ₂F₅ , and NTf₂ as counterions was undertaken. Their physical and electrochemical properties were evaluated for suitability for Room Temperature Ionic Liquids (RTIL) application. Reduction in melting point occurred upon exchange of C(2) by an O-atom of spirobipyrrolidinium, without sacrificing the electrochemical stability; while introduction of alkyl groups between the N- and O-atoms led to incorporation of asymmetry, and hence reduced the melting points, and viscosity.

Full text of DOI:10.1002/hlca.200900045

1600
Helvetica Chimica Acta – Vol. 92 (2009)
Synthesis of Oxygen-Containing Spirobipyrrolidinium Salts for High
Conductivity Room Temperature Ionic Liquids
by Seiichiro Higashiyaa), Thamarai Selvi Devarajanb), Manisha V. Rane-Fondacaro*b),
Christopher Danglerb), Jeremy Snyderb), and Pradeep Haldarb)
a) Department of Chemistry, University at Albany, 1400 Washington Avenue, Albany, New York 12222,
USA
b) College of Nanoscale Science and Technology, University at Albany, 255 Fuller Road, Albany,
New York 12203, USA
Synthesis of ionic liquids (IL) based on oxygen-containing spirobipyrrolidinium salts with BF4,
BF3C2F5, and NTf2 as counterions was undertaken. Their physical and electrochemical properties were
evaluated for suitability for Room Temperature Ionic Liquids (RTIL) application. Reduction in melting
point occurred upon exchange of C(2) by an O-atom of spirobipyrrolidinium, without sacrificing the
electrochemical stability; while introduction of alkyl groups between the N- and O-atoms led to
incorporation of asymmetry, and hence reduced the melting points, and viscosity.
Introduction. – Improvement of energy density of electric double layer capacitors
(EDLCs) while maintaining the high power density, cycle life, and safety is one of the
most awaited technological developments for sustainable society [1 – 4]. Electrolytes
with wide operational (potential and temperature) window, high ion conductivity and
concentration are important for further improvement. Several aspects of aliphatic
room temperature ionic liquids (RTILs) meet these requirements; however, they have
relatively low conductivity. Reduction in melting point and viscosity, upon introduction
of O-atoms to aliphatic ammonium cations is well-known [5 – 9]. Meanwhile, 1,1’-
spirobipyrrolidinium (SBP) salts of type 1 (Table 1) generally show high conductivity
and solubility [10 – 18] and the application to EDLCs has been reported (for example
[11 – 14][19 – 34]). Therefore, simultaneous implementation of these characters in
cations depicted as type 2 in Table 1 would lower the melting point and increase the
conductivity of RTIL. In addition, introduction of alkyl groups in the molecules (R1 to
R3, Table 1) would lower the crystallinity by introduction of asymmetry and the ion-ion
interaction by shielding the localized positive charges. In this article, we report the
synthesis and characterization of oxygen-containing, alkyl group decorated spirobi-
pyrrolidinium salts.
Results and Discussion. – Synthesis of Oxygen-Containing Spirobipyrrolidinium
Salts of Type 2. There have been reports on the synthesis of oxygen-containing
spirobipyrrolidinium salts [35][36]. Cossar and Reynolds used acetal exchange
reaction of haloacetals with pyrrolidines. Our results show that a combination of
aldehydes and haloalcohols instead of haloacetals also works well, and it provides
flexibility in the synthesis (Scheme 1).
ꢀ 2009 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 92 (2009)
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Table 1. Type 1: 1,1’-Spirobipyrrolidinium; Type 2: Various Functionalities Modifying the Parent
Compounda)
Salt
X
R1
R2
R3
Aꢀ
Salt formation
b
SBP BF4
OP BF4
)
–
–
–
–
BF4
BF4
SBP Cl þ HBF4 ! SBP BF4
OP Cl þ HBF4 ! OP BF4
CH2
CH2
CH2
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
OP BF3C2F5
OP NTf2
2MOP BF4
BF3C2F5 OP BF4 þ KBF3C2F5 ! OP BF3C2F5
NTf2
BF4
OP Cl þ LiNTf2 ! OP NTf2
CH2 Me
2MOP Cl þ HBF4 ! 2MOP BF4
2MOP BF3C2F5 CH2 Me
BF3C2F5 2MOP BF4 þ KBF3C2F5 ! 2MOP BF3C2F5
2MOP NTf2
2EOP BF4
4MOP BF4
5MOP BF4
5MOP NTf2
SBO BF4
CH2 Me
CH2 Et
CH2
CH2
CH2
O
NTf2
BF4
BF4
2MOP BF4 þ LiNTf2 ! 2MOP NTf2
2EOP Cl þ HBF4 ! 2EOP BF4
4MOP Cl þ HBF4 ! 4MOP BF4
5MOP Cl þ HBF4 ! 5MOP BF4
5MOP BF4 þ LiNTf2 ! 5MOP NTf2
SBO Cl þ HBF4 ! SBO BF4
H
H
H
H
Me BF4
Me NTf2
H
BF4
a) The table provides a list of ammonium salts with corresponding anionic functionalities. For the way of
their preparation, see also Scheme 1. b) Type 1. Rest of the salts are of Type 2.
Scheme 1
In the presence of K2CO3 except in the cases of paraformaldehyde (R1 ¼ H),
pyrrolidine was added at low temperature to improve the purity of the crude products.
The crude chloride salts were washed with CH2Cl2. 2MOP Cl, 2EOP Cl, and SBO Cl
were further purified using a cation exchange column (Hþ-form), which removes most
of the color and basic by-products which cause the product to decompose at elevated
temperatures. The chloride salts were subsequently treated with HBF4 to generate BF4
salts. Further purification of 2MOP BF4 and 2EOP BF4 was performed by acidic
alumina column chromatography, which removed the protonated ammonium by-
products. BF3C2F5 and NTf2 salts were prepared from Cl or BF4 salts by the metathesis
with KBF3C2F5 [37 – 39] and LiNTf2, respectively. The molecular weights and melting
points are summarized in Table 2, along with the parent ammonium salt, 1,1’-
spirobipyrrolidinium (SBP) tetrafluoroborate (SBP BF4). The introduction of alkyl

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Salt
Helvetica Chimica Acta – Vol. 92 (2009)
Table 2. Characterization of Spiroammonium Salts
Mr
M.p. [8]
Conductivity [mScmꢀ1
]
Viscosity [cP]
a
a
SBP BF4
OP BF4
OP BF3C2F5
OP NTf2
2MOP BF4
2MOP BF3C2F5
2MOP NTf2
2EOP BF4
4MOP BF4
5MOP BF4
5MOP NTf2
SBO BF4
213.02
215.00
315.01
408.34
229.02
329.04
422.36
243.05
229.02
229.02
422.36
216.97
189
104
155
78
28
142
22
15
243
56
20
168
)
)
)
)
)
)
)
)
a
a
a
a
a
a
2.15
412.0
a
a
)
)
2.62
1.60
57.3
195.3
a
a
)
)
)
)
a
a
2.72
78.3
a
a
)
)
a) Solid at r.t., hence the property was not determined.
groups next to the O-atom greatly reduced the melting points and they were below 308
in cases of 2MOP BF4, 2MOP NTf2, 2EOP BF4, and 5MOP NTf2. The conductivity and
viscosity of these ionic liquids at 258 was 1.6 to 2.7 mS/cm as shown in Table 2. The ionic
liquids except 2EOP BF4 were purified by a low temperature recrystallization process
down to ꢀ 808 from MeOH, while 2EOP BF4 showed liquid-liquid phase separation
prior to the solidification with the contaminants. 2MOP BF4 also showed partial phase
separation by precipitating at the bottom of the flask along with crystallization from the
rest of the solution. The crystalline part was repetitively collected from the precipitate.
Conductivity in MeCN. The measured conductivity of the electrolytes in MeCN at
various concentrations at 258, and the results are shown in Fig. 1.
Most of the new BF4 salts exhibited highest conductivity around 2m, however, the
conductivity was considerably lower than for SBP BF4. The increased polarity of the
fixed ring O-atom, and the ion-ion interaction in OP BF4 was responsible for lowering
its conductivity. Conductivity measurement of SBO BF4 was not undertaken due to its
low solubility in MeCN (<0.35m).
Potential Window in MeCN. The potential window of electrolytes at 0.65m in MeCN
was measured using limiting current density of 1 mA/cm2 [10]. The results are
summarized in Table 3. A solution of 0.65m TEABF4 (tetraethylammonium tetra-
fluoroborate) in MeCN is the industry standard for ultracapacitors, and the perform-
ance of electrolytes developed in house was compared with 0.65m TEABF4/MeCN
(potential window ca. 5.5 V).
The cathodic stability of the BF4 salts of OP, 4MOP, and 5MOP was comparable
with SBP in MeCN, but for the 2MOP and 2EOP salts, it was slightly lower. The alkyl
group present between the N- and O-atoms was responsible for slight lowering of the
stability. The instability seems to be a result of the b-elimination from the alkyl group
between two electron-withdrawing atoms (Scheme 2).
Thermal Analysis. The thermal stability of the salts was estimated using
thermogravimetric analysis. The results are shown in Fig. 2.

Helvetica Chimica Acta – Vol. 92 (2009)
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Fig. 1. Conductivity of electrolytes at various concentrations in MeCN
Table 3. Potential Window of Oxygenated Spiroammonium Salts at 0.65m in MeCN
Salt
Cathodic limit [V]
Anodic limit [V]
Potential window [V]
SBP BF4
OP BF4
OP BF3C2F5
OP NTf2
2MOP BF4
2MOP BF3C2F5
2MOP NTf2
2EOP BF4
4MOP BF4
5MOP BF4
ꢀ 2.7
ꢀ 2.8
ꢀ 2.7
ꢀ 2.8
ꢀ 2.6
ꢀ 2.5
ꢀ 2.7
ꢀ 2.6
ꢀ 2.7
ꢀ 2.7
ꢀ 2.7
ꢀ 2.6
4.6
4.5
3.4
3.5
4.6
3.4
3.4
4.6
4.6
4.5
3.5
4.4
7.3
7.3
6.1
6.2
7.2
5.9
6.1
7.2
7.3
7.2
6.2
7.0
5MOP NTf2
SBO BF4
a
)
a) 0.3m (maximum solubility).
Scheme 2

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Helvetica Chimica Acta – Vol. 92 (2009)
Fig. 2. TGA Analysis of the synthesized salts
The onset of the weight loss of each of the BF4 salts occurred in the order of
2EOP < 2MOP ꢁ SBO < OP ꢁ 4MOP ꢁ 5MOP < SBP. This trend is similar to that of
the electrochemical stability. Reduction in thermal stability occurred upon introduction
of the O-atom to the ring. The salts of OP, 2EOP, 2MOP, 4MOP, and 5MOP left a
residue of carbonized material on the pan while the residue of SBP was colorless.
In summary, a variety of novel oxygen and alkyl group-containing spirobipyrro-
lidinium compounds were investigated for room temperature ionic liquid applications.
Six novel cations, namely, OP, 2EOP, 2MOP, 4MOP, 5MOP, and SBO, were synthesized
by employing aldehydes and haloalcohols. All together, eleven novel salts were
produced. Three types of anions, BFꢀ4 , BF3C2F5ꢀ, and NTf2ꢀ were applied. The BF4 and
NTf2 analogs were produced by conversion of chlorides, while the BF3C2F5 analogs
were generated by metathesis of BF4.
The melting points and voltage windows were determined from TGA and linear
sweep voltammetry. The melting point reduced from 1898 (SBP BF4) to below 1008 in
six salts, and was even below 308 (RTIL) in four salts.
Potential window measurement was performed at 0.65m solution dissolved in
MeCN for each salt. The parent compound SBP BF4 had a voltage window of 7.3 V. Six
out of eleven salts had a potential window ꢂ 7.0 V. The potential window varied from
5.9 to 7.3 V. The potential window of commercial workhorse 0.65m TEABF4 in MeCN
was ca. 5.5 V.
Conductivity measurement was performed at various concentrations (0.65 to 5.0m
in MeCN), and a conductivity maximum was observed around a 2m concentration for

Helvetica Chimica Acta – Vol. 92 (2009)
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all salts. The conductivity (at 2m) of all the salts was in the range ca. 48 – 55 mS/cm, as
compared with 65 mS/cm for SBP BF4.
The thermal stability of various salts was found to reduce from ca. 500 to 300 – 4208
range, which is more than adequate for most of the high temperature EDLC
applications.
Experimental Part
General. An overview of ions that were synthesized is shown in Table 1. Salt of LiNTf2 and aq. 50%
HBF4 were purchased from TCI and Acros Organics, resp. The cation chlorides were reacted with LiNTf2
and HBF4 to convert them into NTf2 and BF4 salts, resp. Aluminum oxide (activated, acidic, Brockmann
Grade I, 58 ꢂ) was purchased from Alfa Aesar. Regeneration of Hþ-form cation exchange resin (BioRad
AG MP-50 Hþ-form) was undertaken as follows. Addition of 1m NaOH to the column until the eluent
became basic, then H2O was added to neutralize the eluent, subsequently 1m HCl in MeOH/H2O (1:1)
was added until the eluent became acidic, 1m HCl (two bed volume), and then H2O until the eluent
became neutral.
Characterizations. Measurement of NMR spectra of salts in CD3OD unless specified, and the solvent
peaks of 1H- and 13C-NMR, and external CFCl3 peak of 19F-NMR were used as references for the
chemical shifts, resp. Linear sweep voltammetry of 0.65m electrolyte was performed using Princeton
Applied Research PARSTAT 2273A potentiostat with glassy carbon working electrode (AFE1E050GC
E1 Series Glassy Carbon electrode, Pine Research Instrumentation), Pt wire counter electrode, and Ag
wire quasi-reference electrode at a scan rate of 5 mV/s in a dry box and the potential window was
determined with a limiting current at 1 mA/cm2 [10]. Conductivity and viscosity were measured using
Radiometer Analytical CDM230 Conductivity Meter and Brookfield DV-II þ Pro, resp., at 258. TGA Data
was recorded on a TA Instruments TGA 2050 thermogravimetric analyzer under dynamic N2 flow (total
flow rate 100 cm3/min), using Pt pans and a ramp rate of 108/min. DSC Data was recorded on a TA
Instruments DSC 2920 differential scanning calorimeter at 1 atm under dynamic N2, using hermetically
sealed Al pans, with a ramp rate of 108/min.
Synthesis of KBF3C2F5. KBF3C2F5 was synthesized with slight modification of the previous method
[37]. CF3CF2Br (43.8 g, 0.22 mmol) was condensed on a cold finger and introduced to anh. Et2O
(400 ml). PhMgBr (3m in Et2O, 70 ml, 0.21 mol) was added dropwise to the mixture at a temp. below
ꢀ 658, and stirred for 1 h. After dropwise addition of (MeO)3B (24.9 g, 0.24 mol), the temp. was raised to
ꢀ 408, subsequently, the bath temp. was lowered to dry ice temp., and stirred for 2 h. The mixture was
decanted into cold 50% HF (100) in a high density polyethylene container, and stirred overnight at r.t.
Then, ice-cold aq. KOH (100 g in 100 ml H2O) was added while maintaining the temp. below 158. The
org. layer was separated. The aq. layer was extracted three times with Et2O. The combined org. layers
were dried over K2CO3 and MgSO4. Filtration removed the desiccant material, and the volatiles by
evaporation, the residual solid was washed with hexane and then recrystallized from i-PrOH/toluene to
give the salt (17.86 g, 33%).
Synthesis of 1,1’-Spirobipyrrolidinium Tetrafluoroborate (¼ 5-Azoniaspiro[4.4]nonane Tetrafluoro-
borate; SBP BF4). Synthesis of SBP BF4 was attempted according to the previous report using
pyrrolidine, 1,4-dibromobutane, K2CO3, and KBF4 in MeCN [40]. However, due to inefficient anion
exchange metathesis between Br and BF4, the anion was converted to Cl using cation exchange resin, and
subsequently converted to BF4 using HBF4 [23][41][42]. The resulting product was recrystallized from
i-PrOH several times.
Synthesis of 3-Oxazolidine-1’-spiropyrrolidinium Tetrafluoroborate (¼2-Oxa-5-azoniaspiro[4.4]no-
nane Tetrafluoroborate; OP BF4). Pyrrolidine (28.45 g, 0.40 mol), was added to a mixture of
paraformaldehyde (12.01 g, 0.40 mol), Et2O (150 ml), and 2-chloroethanol (32.20 g, 0.40 mol), and
mildly refluxed. Stirring overnight at r.t. resulted in layer separation. The top Et2O layer was discarded,
and the bottom layer was dissolved in H2O and subsequently filtered. CH2Cl2 was used to wash the
filtrate three times, and the aq. layer was evaporated, and the residue dried in vacuo at 1008 to yield a
crude chloride salt (OP Cl, 57.15 g, 0.35 mmol). It was converted to BF4 salt by adding 50% HBF4

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Helvetica Chimica Acta – Vol. 92 (2009)
(61.35 g, 0.35 mol) and MeOH (150 ml), followed by evaporation. EtOH (100 ml) was added and
subsequently evaporated to azeotropically remove moisture. The residue was recrystallized from MeOH,
and subsequently dissolved in MeCN and filtered through a membrane filter (Nylon, 0.22 m). The solvent
was evaporated, and the crude product was repeatedly recrystallized from MeOH and dried in vacuo at
1008 overnight to give OP BF4 (64.0 g, 74% overall yield). 1H-NMR: 4.87 (s, 2 H); 4.34 (t, J ¼ 7.3, 2 H);
3.81 (t, J ¼ 7.3, 2 H); 3.76 – 3.60 (m, 4 H); 2.24 (dd, J ¼ 7.8, 16.9, 4 H). 13C-NMR: 92.6; 67.4; 62.7; 60.7;
23.2. 19F-NMR: ꢀ 154.4 (m).
3-Oxazolidine-1’-spiropyrrolidinium Trifluoro(pentafluoroethyl)borate(1ꢀ) (¼2-Oxa-5-azoniaspir-
o[4.4]nonane Trifluoro(pentafluoroethyl)borate(1ꢀ); OP BF3C2F5). OP BF3C2F5 was synthesized by
the metathesis of OP BF4 (24.34 g, 0.116 mol) and KBF3C2F5 (26.17 g, 0.116 mol) by mixing the aq. solns.
CH2Cl2 was added to extract OP BF3C2F5. The org. layer was washed with two portions of H2O. The
solvent was removed by evaporation, and the residue was recrystallized from MeOH at ꢀ 808 to give the
product (17.2 g, 47%). 1H-NMR: 4.87 (s, 2 H); 4.33 (t, J ¼ 7.3, 2 H); 3.81 (t, J ¼ 7.3, 2 H); 3.74 – 3.62 (m,
4 H); 2.24 (dd, J ¼ 7.6, 17.2, 4 H). 13C-NMR: 92.5; 67.2; 62.7; 60.5; 23.0. 19F-NMR: ꢀ 85.9 (q, J ¼ 4.9); ꢀ
139.1 (q, J ¼ 20.0); ꢀ 156.6 (q, J ¼ 42.2).
3-Oxazolidine-1’-spiropyrrolidinium Bis[(trifluoromethyl)sulfonyl]azanide (¼2-Oxa-5-azoniaspir-
o[4.4]nonane Bis[(trifluoromethyl)sulfonyl]azanide; OP NTf2). OP NTf2 was prepared by the meta-
thesis of crude OP Cl (29.6 g, 0.181 mol) and LiNTf2 (51.9 g, 0.181 mol) in a similar way as described
1
above and recrystallized from MeOH at ꢀ 808 (63.0 g, 85%). H-NMR: 4.87 (s, 2 H); 4.33 (t, J ¼ 7.3,
2 H); 3.81 (t, J ¼ 7.1, 2 H); 3.76 – 3.58 (m, 4 H); 2.24 (dd, J ¼ 7.6, 17.2, 4 H). 13C-NMR: 121.3 (q, J ¼ 320.4);
92.7; 67.5; 62.9 (br.); 60.8 (br.); 23.3. 19F-NMR: ꢀ 81.1 (s).
Synthesis of 2-Methyl- (2MOP) and 2-Ethyl-3-oxazolidine-1’-spiropyrrolidinium (2EOP) Salts. 2-
Methyl-3-oxazolidine-1’-spiropyrrolidinium Tetrafluoroborate (¼1-Methyl-2-oxa-5-azoniaspiro[4.4]no-
nane Tetrafluoroborate; 2MOP BF4). Acetaldehyde (33.7 ml, 0.60 mol) was added to a chilled mixture of
K2CO3 (20.7 g, 0.15 mol), Et2O (150 ml), and 2-chloroethanol (48.3 g, 0.60 mol). To this mixture,
pyrrolidine (42.7 g, 0.60 mol) was added dropwise while constantly stirring. Overnight, the temp. of the
ice bath came to r.t. The volatile compounds were removed by evaporation, followed by addition of
CH2Cl2 (200 ml) and subsequent filtration. H2O (100 ml) was added, and the org. phase was removed.
CH2Cl2 was used to wash the aq. phase twice, followed by subsequent evaporation. The residue was
dissolved in H2O to apply to Hþ-form cation exchange column chromatography (CC; 300 ml). The
product was eluted with 0.2m aq. HCl (1 l) and the solvent was evaporated. The residue was dissolved in
EtOH, and the insoluble material was filtered off. The solvent was evaporated, and the residue was dried
in vacuo at r.t. to give the crude chloride salt (2MOP Cl, 77.9 g, 0.44 mol). The crude product was
dissolved in 50% HBF4 (77.3 g, 0.44 mol) and MeOH (200 ml) and subsequently evaporated. The residue
was dried in vacuo overnight at 508 and then dissolved in CH2Cl2 (200 ml) and applied to acidic alumina
CC (200 ml) and eluted with CH2Cl2 (800 ml). The eluent was evaporated, and the residue was dissolved
in H2O, then washed with 20% Et2O in CH2Cl2 three times. The aq. layer was evaporated and dried in
vacuo at 708 overnight to give a crude orange oil, 2MOP BF4 (71.6 g, 52%). Crude 2MOP BF4 (18.8 g)
was further purified by acidic alumina CC (150 ml) with CH2Cl2 eluent (600 ml). The eluent was
evaporated and the residue dissolved in H2O followed by washing with 20% Et2O in CH2Cl2. The aq.
phase was filtered, evaporated, and subsequently dried in vacuo at 708 overnight to give 2MOP BF4
(16.9 g). The product was dissolved in MeOH (800 ml) and allowed to crystallize at ꢀ 808. The soln.
separated into two phases. Most of the impurities settled down, while the product formed a turbid soln.
The turbid soln. was filtered using a chilled Bꢀchner funnel at 48, and the product dried in vacuo at 708
overnight. The filtrate soln. was poured back into the impure product to dissolve more salt to yield
additional crop. 1H-NMR: 5.09 (q, J ¼ 5.4, HꢀC(1)); 4.34 – 4,20 (m, 2 H); 3.96 – 3.71 (m, 2 H); 3.71 – 3.47
(m, 3 H); 3.47 – 3.33 (m, 1 H); 2.23 (br. s, 4 H); 1.58 (d, J ¼ 5.6, MeꢀC(1)). 13C-NMR: 99.0; 65.0; 61.5
(br.); 61.2 (br.); 57.5 (br.); 23.0; 22.6; 14.0. 19F-NMR: ꢀ 153.6 (m).
2-Methyl-3-oxazolidine-1’-spiropyrrolidinium Trifluoro(pentafluoroethyl)borate(1ꢀ) (¼1-Methyl-2-
oxa-5-azoniaspiro[4.4]nonane Trifluoro(pentafluoroethyl)borate(1ꢀ); 2MOP BF3C2F5) and 2-Methyl-3-
oxazolidine-1’-spiropyrrolidinium Bis[(trifluoromethyl)sulfonyl]azanide (¼1-Methyl-2-oxa-5-azonias-
piro[4.4]nonane Bis[(trifluoromethyl)sulfonyl]azanide; 2MOP NTf2). Equimolar amounts of crude
2MOP BF4 and KBF3C2F5 or LiNTf2, resp., were mixed in H2O/CH2Cl2. The org. phase was separated,

Helvetica Chimica Acta – Vol. 92 (2009)
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and the aq. phase was subsequently extracted with CH2Cl2 several times. The combined org. phase was
washed eight times with H2O. The solvent was evaporated, and the residue was dried in vacuo at 508 to
give each of the crude products (68 and 91%, resp.). 2MOP BF3C2F5 and 2MOP NTf2 were further
recrystallized from MeOH at ꢀ 208 and ꢀ 808, resp., and the crystals filtered at 48 and then dried in
vacuo at 708.
Data of 2MOP BF3C2F5. 1H-NMR: 5.08 (q, HꢀC(1)); 4.37 – 4.14 (m, 2 H); 3.93 – 3.69 (m, 2 H); 3.59
(td-like, 3 H); 3.44 – 3.32 (m, 1 H); 2.22 (br. s, 4 H); 1.58 (d, J ¼ 5.6, MeꢀC(1)). 13C-NMR: 99.3; 65.1; 61.6
(br.); 61.5 (br.); 57.7 (br.); 23.2; 22.7; 14.0. 19F-NMR: ꢀ 85.8 (q, J ¼ 4.9); ꢀ 138.9 (q, J ¼ 19.7); ꢀ 156.6
(q, J ¼ 41.8).
Data of 2MOP NTf2. 1H-NMR: 5.07 (q, J ¼ 5.6, HꢀC(1)); 4.36 – 4.18 (m, 2 H); 3.90 – 3.68 (m, 2 H);
3.69 – 3.48 (m, 3 H); 3.43 – 3.33 (m, 1 H); 2.22 (br. s, 4 H); 1.57 (d, J ¼ 5.6, MeꢀC(1)). 13C-NMR: 21.2 (q,
J ¼ 320.4); 65.2 (m); 61.2 (m); 57.3 (m); 23.0; 22.5; 14.0 (m). 19F-NMR: ꢀ 80.9 (s).
2-Ethyl-3-oxazolidine-1’-spiropyrrolidinium Tetrafluoroborate (¼1-Ethyl-2-oxa-5-azoniaspiro[4.4]-
nonane Tetrafluoroborate; 2EOP BF4). The same method using propionaldehyde instead of acetalde-
hyde produced a yield of 11% of 2EOP BF4. The recrystallization from MeOH or EtOH was not
successful. 1H-NMR: 4.87 (d, J ¼ 9.6, HꢀC(1)); 4.34 – 4.22 (m, 2 H); 3.85 – 3.73 (m, 2 H); 3.69 – 3.51 (m,
3 H); 3.44 – 3.30 (m, 1 H); 2.22 (br. s, 4 H); 2.06 – 1.91 (m, 1 H); 1.78 (ddd, J ¼ 7.1, 10.1, 13.6, 1 H); 1.10 (t,
J ¼ 7.6, Me). 13C-NMR: 102.8; 64.8; 61.8; 61.1; 57.9; 22.9; 22.2; 22.2; 9.8. 19F-NMR: ꢀ 152.9; ꢀ 153.0.
Synthesis of 4-Methyl-3-oxazolidine-1’-spiropyrrolidinium Tetrafluoroborate (¼ 3-Methyl-2-oxa-5-
azoniaspiro[4.4]nonane Tetrafluoroborate; 4MOP BF4). 2-Chloro-1-propanol was synthesized following
the procedure described in [43]. To a mixture of NaBH4 (14.19 g, 0.357 mol) and EtOH (150 ml), ethyl 2-
chloropropionate (68.29 g, 0.50 mol) was added dropwise while maintaining the temp. below 458. The
mixture was stirred for 30 min and subsequently acidified using 2m HCl (200 ml) soln. Addition of
CH2Cl2 (200 ml) separated the soln. into two layers. The org. phase was decanted and washed with H2O
(50 ml), followed by washing with aq. NaHCO3, and subsequently dried over anh. MgSO4. The solvent
was gently evaporated after filtering off the drying reagent. The residue was subjected to fractional
distillation (65 – 688/70 mmHg, 31.20 g, 65%). Pyrrolidine (36.82 g, 0.511 mol) was added to a mixture of
paraformaldehyde (15.35 g, 0.511 mol), Et2O (120 ml), and 2-chloro-1-propanol (48.78 g, 0.511 mol),
and refluxed overnight to form two layers. H2O was added to dissolve the salt, and the aq. layer was
separated, which was then washed with CH2Cl2 three times. The aq. phase was filtered and the solvent
evaporated. The residue was dried in vacuo at r.t. to give the crude chloride salt, 4MOP Cl (24.08 g, 27%).
50% HBF4 (23.8 g, 0.136 mol) and MeOH (70 ml) were added to the crude product, and the solvent was
evaporated. EtOH (50 ml) was added and subsequently evaporated. This process was repeated twice.
The resulting residue was recrystallized from EtOH (200 ml) at ꢀ 208 to give 4MOP BF4 (26.4 g, 85%) as
a viscous solid. The product was further recrystallized from MeOH. 1H-NMR: 4.87 (br. s, CH2(1)); 4.53 (t,
J ¼ 8.3, 1 H); 4.13 (qt, J ¼ 7.1, H ꢀC(3)); 3.88 – 3.81 (m, 1 H); 3.73 – 3.64 (m, 1 H); 3.64 – 3.53 (m, 2 H);
3.51 – 3.43 (m, 1 H); 2.29 – 2.11 (m, 4 H); 1.47 (d, J ¼ 6.6, Me). 13C-NMR: 91.7; 73.4; 67.1; 61.7; 55.0; 22.9;
22.3; 12.8. 19F-NMR: ꢀ 154.4; ꢀ 154.5.
Synthesis of 5-Methyl-3-oxazolidine-1’-spiropyrrolidinium (5MOP) Salts. 5-Methyl-3-oxazolidine-1’-
spiropyrrolidinium Tetrafluoroborate (¼4-Methyl-2-oxa-5-azoniaspiro[4.4]nonane Tetrafluoroborate;
5MOP BF4). Synthesis of crude 5MOP Cl was undertaken in a manner similar to OP Cl. The reaction
between 1-chloro-2-propanol (technical grade, 75% purity, 18.91 g, 0.20 mol), paraformaldehyde (6.01 g,
0.20 mol), and pyrrolidine (14.22 g, 0.20 mol) in Et2O (50 ml) gave crude 5MOP Cl as a waxy gel (29.53 g,
83%). 5MOP Cl was subsequently converted to 5MOP BF4 with 50% HBF4 (29.18 g, 0.166 mol) in
MeOH (80 ml) followed by three sets of EtOH-evaporation procedure. Drying in vacuo overnight at r.t.
gave the crude solid product (36.9 g, 81%), which was further recrystallized from MeOH at ꢀ 808 in the
same manner as 2MOP BF4. The product was dried in vacuo at 808 to yield 5MOP BF4 (25.9 g, 55%).
1H-NMR showed that the product contained about 6 mol-% of 4MOP BF4 derived from the technical
grade 1-chloro-2-propanol, and further recrystallization from MeOH did not remove 4MOP BF4.
1H-NMR: 5.03 (d, J ¼ 6.1, HꢀC(1)); 4.79 (d, J ¼ 5.6, HꢀC(1)); 4.59 (qdd, J ¼ 6.8, HꢀC(4)); 3.96 (dd, J ¼
7.3, 11.9, HꢀC(3)); 3.80 – 3.55 (m, 4 H); 3.35 (dd, J ¼ 8.1, 11.6, HꢀC(3)); 2.38 – 2.07 (m, 4 H); 1.44 (d, J ¼
6.1, Me). 13C-NMR: 92.2; 76.4; 66.5; 64.1; 62.4; 23.1; 23.0; 18.6. 19F-NMR: ꢀ 154.1; ꢀ 154.2.

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Helvetica Chimica Acta – Vol. 92 (2009)
5-Methyl-3-oxazolidine-1’-spiropyrrolidinium Bis[(trifluoromethyl)sulfonyl]azanide (¼4-Methyl-2-
oxa-5-azoniaspiro[4.4]nonane Bis[(trifluoromethyl)sulfonyl]azanide; 5MOP NTf2). 5MOP NTf2 was
synthesized using metathesis of 5MOP BF4 and LiNTf2 in the same manner as the synthesis of 2MOP
NTf2 in 91% yield, and the product was further recrystallized from MeOH at ꢀ 808, in the same manner
as 2MOP BF4. 1H-NMR: 5.04 (d, J ¼ 5.6, HꢀC(1)); 4.79 (d, J ¼ 6.1, HꢀC(1)); 4.59 (qdd, J ¼ 6.9,
HꢀC(4)); 3.95 (dd, J ¼ 7.1, 11.6, HꢀC(3)); 3.79 – 3.58 (m, 4 H); 3.35 (dd, J ¼ 8.6, 11.6, HꢀC(3)); 2.30 –
2.14 (m, 4 H); 1.45 (d, J ¼ 6.6, Me). 13C-NMR: 121.2 (q, J ¼ 320.5, 1 H); 92.3 (br.); 76.4; 66.6 (m); 64.3
(m); 62.6 (m); 23.0; 23.0; 18.6; 18.6. 19F-NMR: ꢀ 81.1 (s).
Synthesis of 3,3’-Spirobioxazolidinium Tetrafluoroborate (¼2,7-Dioxa-5-azoniaspiro[4.4]nonane
Tetrafluoroborate; SBO BF4). 1,3-Oxazolidine was synthesized from paraformaldehyde (15.02 g,
0.50 mol) and 2-aminoethanol (30.54 g, 0.50 mol) [44]. The reaction between paraformaldehyde and
aminoethanol yielded 1,3,5-tris(2-hydroxyethyl)hexahydro-1,3,5-triazine [45], which was thermally
cracked to yield 1,3-oxazolidine. The crude distillate (34.4 g, 94%) was collected in a trap chilled at ꢀ
788 and was used without further purification. Crude 1,3-oxazolidine (34.4 g, 0.47 mol) was added to
paraformaldehyde (14.11 g, 0.47 mol) and 2-chloroethanol (37.8 g, 0.47 mol) in Et2O (120 ml) at ꢀ 788.
The temp. was raised to 08 and then slowly to r.t. overnight while stirring continuously. The volatile
materials were removed by evaporation, and the residue was dissolved in H2O. The insoluble material
was filtered, and the filtrate was washed three times with CH2Cl2, and then applied to a column of Hþ-
form cation exchange resin (250 ml). The column was washed with H2O to neutralize the eluent, and
subsequently eluted with 1 to 2m HCl. Solvent evaporation yielded a crude SBO Cl (51.04 g, 66%,
0.31 mol), which was converted to SBO BF4 with 50% HBF4 (54.17 g, 0.31 mol) in MeOH (100 ml) to
immediately generate a white precipitate. The product was filtered and subsequently recrystallized from
H2O, and dried in vacuo at 1008 to yield SBO BF4 (23.55 g, 35%). 1H-NMR ((D6)DMSO): 5.27 (d, J ¼
5.6, 2 H); 5.13 (d, J ¼ 5.6, 2 H); 4.50 (t, J ¼ 7.1, 4 H); 4.19 – 4.07 (m, 4 H). 13C-NMR ((D6)DMSO): 90.0
(m); 66.1 (m); 56.6 (m). 19F-NMR: ꢀ 148.7; ꢀ 148.7.
We would like to thank the Chemistry Department for providing processing and characterization
facilities.
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Received February 11, 2009