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T. Herzig et al. / Journal of Fluorine Chemistry 128 (2007) 612–618
was stirred at 60 8C for 3 h. During this time, lithium fluoride
(LiF) precipitated. LiF was removed from the liquid by
filtration. 2.03 g of anhydrous oxalic acid were added to the
obtained filtrate and the reaction was conducted at 60 8C for 1 h
with stirring. Finally, AN was evaporated at 60 8C under
vacuum, yielding 4.45 g (72.4%) product.
3.1.5.1. Analysis. 1H NMR (300.1 MHz, CD3CN, TMS): d
3.16 (4H, quartet, J = 7.3, 2CH2–CH3), 1.20 (6H, tt, J = 7.3,
3JHN = 1.9, 2CH2–CH3).
13C{1H} NMR (75.5 MHz, CD3CN, TMS): d 159.6 (s, CO),
1
51.7 (t, JCN = 3.3, N–CH2–CH3), 6.3 (s, CH3).
11B NMR (128.4 MHz, CD3CN, Et2OꢂBF3): d 3.6 (t,
1JBF = 2.7, BF2, 99.5%), ꢀ0.6 (s, BF4, 0.5%). The signal to
noise ratio for the [BF4]ꢀ signal was 207.
3.1.2.1. Analysis. 1H NMR (300.1 MHz, CD3CN, TMS): d
3.17 (8H, quartet, J = 7.3, 4CH2–CH3), 2.8 (s, unidentified
impurity), 2.2 (s, unidentified impurity), 1.2 (12H, tt, J = 7.27,
3JHN = 1.9, 4CH2–CH3).
19F NMR (282.4 MHz, CD3CN, CCl3F): d ꢀ150.1 (4F, s,
10BF4), ꢀ150.2 (4F, s, 11BF4, 4%), ꢀ152.3 (2F, s, 10BF2),
ꢀ152.3 (2F, m, 11BF2, 96%).
13C{1H} NMR (75.5 MHz, CD3CN, TMS): d 161.0 (s, CO),
[TEA][BF2Ox] was already mentioned in a patent [25] but
apart from a melting point in the range 20–30 8C no details
were given.
1
53.1 (t, JCN = 2.9, N–CH2–CH3), 7.7 (s, CH3).
11B NMR (128.4 MHz, CD3CN, Et2OꢂBF3): d 8.1 (s, B(Ox)2,
traces), 3.6 (t, 1JBF = 2.7, BF2, 87%), ꢀ0.6 (s, BF4, 13%).
3.1.6. Synthesis of 1-butyl-3-methylimidazolium
difluoromono[1,2-oxalato(2-)-O,O0]borate
([BMIM][BF2Ox] via SiCl4 (Fig. 1(ii))
3.1.3. Syntheses of 1-ethyl-3-methylimidazolium chloride
([EMIM]Cl) and 1-butyl-3-methylimidazolium chloride
([BMIM]Cl)
The synthesis was conducted according to [TEA][BF2Ox],
(3.1.5.), using [BMIM][BF4] (23.63 g, 0.104 mol), SiCl4
(6.0 ml, 0.052 mol), and anhydrous oxalic acid (9.41 g,
0.105 mol) giving a colourless ionic liquid (26.12 g, 90.1%).
[EMIM]Cl was synthesised according to a slightly modified
literature method [22,23] from 1-methylimidazole and ethyl
chloride. [BMIM]Cl was synthesised from 1-methylimidazole
and butyl chloride accordingly. The raw products were re-
crystallised from AN three times and finally dried 5 days at high
vacuum (about 1 ꢃ 10ꢀ6 mbar) yielding colourless crystals (79
and 84%, respectively). NMR data are according to expecta-
tions, showing no impurities.
3.1.6.1. Analysis. 1H NMR (300.1 MHz, CD3CN, TMS): d
8.59 (1H, s, C(2)H), 7.43 (1H, t, J = 1.8, C(4)H), 7.39 (1H, t,
J = 1.8, C(5)H), 4.15 (2H, t, J = 7.3, CH2), 3.86 (3H, s, CH3),
1.80 (2H, quintet, J = 7.5, CH2), 1.29 (2H, sextet, J = 7.5, CH2),
0.88 (3H, t, J = 7.3, CH3).
13C{1H} NMR (75.5 MHz, CD3CN, TMS): d 159.8 (s, CO),
135.8 (s, CH), 123.3 (s, CH), 121.9 (s, CH), 48.9 (s, CH2), 35.5
(s, CH3), 31.2 (s, CH2), 18.6 (s, CH2), 12.4 (s, CH3).
11B NMR (128.4 MHz, CD3CN, Et2OꢂBF3): d 3.6 (t,
1JBF = 2.4, BF2, 96%), ꢀ0.4 (s (br), BF4, 4%). The signal to
noise ratio for the [BF4]ꢀ signal was 20.
3.1.4. Synthesis of 1-butyl-3-methylimidazolium
tetrafluoroborate ([BMIM][BF4])
[BMIM][BF4] was synthesised according to Ref. [24] from
[BMIM]Cl and NaBF4. A solution of 610.3 g (5.56 mol) NaBF4
in 0.7 l H2O (Millipore) was added to a stirred solution of
962.2 g (5.51 mol) [BMIM]Cl in 1.3 l H2O. The resulting
biphasic system was separated and both layers were
individually extracted with dichloromethane (three times,
250 ml each). The combined dichloromethane solutions were
washed with water (four times, 50 ml) and then dried with
MgSO4 over night. After filtration and removing the
dichloromethane at reduced pressure, the product was dried
for 5 days at about 1 ꢃ 10ꢀ6 mbar. A colourless liquid was
obtained (1007 g, 81%). NMR data are in accordance with data
published in [24], showing no impurities.
19F NMR (282.4 MHz, CD3CN, CCl3F): d ꢀ152.3 (2F, s,
1
10BF2), ꢀ152.4 (2F, quartet, JFB = 2.4, 11BF2, 100%).
3.1.7. Synthesis of lithium difluoromono[1,2-oxalato(2-)-
O,O0]borate (Li[BF2Ox]) via SiCl4 (Fig. 1(ii))
The synthesis was conducted according to [TEA][BF2Ox]
(Section 3.1.5), using LiBF4 (13.06 g, 0.139 mol), SiCl4
(8.0 ml, 0.070 mol), and anhydrous oxalic acid (12.55 g,
0.139 mol) giving colourless crystals (17.25 g, 86.3%).
3.1.7.1. Analysis. 13C{1H} NMR (75.5 MHz, CD3CN, TMS):
d 160.3 (s, CO).
3.1.5. Synthesis of tetraethylammonium difluoromono[1,2-
oxalato(2-)-O,O0]borate ([TEA][BF2Ox]) via SiCl4
(Fig. 1(ii))
11B NMR (128.4 MHz, CD3CN, Et2OꢂBF3): d 3.6 (s, BF2,
98%), ꢀ0.8 (quintet, 1JBF = 4.1, BF4, 2%). The signal to noise
ratio for the [BF4]ꢀ signal was 190.
[TEA][BF4] (30.25 g, 0.139 mol) and anhydrous oxalic acid
(12.55 g, 0.139 mol) were dissolved in 300 ml AN in a 500 ml
flask. SiCl4 (8.0 ml, 0.070 mol) was added drop-wise to the
stirred solution over 6 h at room temperature. With the
beginning of the addition of SiCl4, a gas was generated. After
the addition of SiCl4, the reaction mixture was stirred over
night. The termination of the reaction was judged by confirming
that gas generation stopped completely. The next day AN was
evaporated at 40–50 8C under vacuum for 20 h giving
colourless crystals at room temperature (33.93 g, 91.4%).
19F NMR (282.4 MHz, CD3CN, CCl3F): d ꢀ153.0 (2F, s,
10BF2), ꢀ153.0 (2F, s, 11BF2, 96%), ꢀ153.6 (4F, s, 10BF4),
1
ꢀ153.6 (4F, quartet, JFB = 4.1, 11BF4, 4%).
3.1.8. Synthesis of 1-ethyl-3-methylimidazolium
difluoromono[1,2-oxalato(2-)-O,O0]borate
([EMIM][BF2Ox]) (Fig. 2)
In a typical experiment, an equimolar mixture of Li[BF2Ox]
and [EMIM]Cl in AN was stirred at room temperature for 15 h.