Binary Mixtures of Ionic Liquids
free (by silver nitrate test). The ionic liquid, obtained after concen-
tration in vacuo, was dissolved in dichloromethane (100 mL) and
treated with active charcoal (1 wt%) overnight. Then, the solution
was filtered through a pad of neutral alumina and concentrated in
vacuo to give the ionic liquid as a pale yellow liquid (yield: 81%).
1H NMR (300 MHz; CDCl3, 258C, TMS): d=8.95 (s, 1H; CH), 7.35 (d,
mogeneous solvent media, as experienced by the probe reac-
tion.
On the whole, collected data evidence that each probe mol-
ecule may examine different environments and, according to
previous reports by Armstrong et al.,[29] the results obtained in
IL solution depend on studied reaction or tested compounds.
Furthermore, also as a consequence of the extension of the
cation surface, the site of reaction may not match the area
probed by the molecule.
3
3J(H,H)=8.1 Hz, 2H; CH), 5.55 (s, 2H; CH2), 4.22 (t, J(H,H)=7.5 Hz,
2H; CH2), 1.87 (m, 2H; CH2), 1.38 (m, 2H; CH2), 0.99 ppm (t,
3J(H,H)=7.5 Hz, 3H; CH3). 13C NMR (300 MHz; CDCl3, 258C, TMS):
d=151.4 (CCH), 147.5 (CCH), 144.8 (CCH), 143.5 (CCH), 136.2 (CCH),
123.0 (CCH), 122.3 (CCH), 117.1 (CF3), 112.0 (CF3), 50.4 (CH2), 40.6
(CH2), 31.8 (CH2), 19.3 (CH2), 13.1 ppm (CH3).
Finally, a careful analysis of our experimental data points out
that, in order to obtain neoteric solvents having peculiar fea-
tures compared to neat ILs, binary mixtures derived from com-
binations of different anions can be taken into account.
1-Benzyl-3-butylimidazolium tetrafluoroborate: 1-Benzyl-3-butylimi-
dazolium bromide (8.01 g, 27.1 mmol) was dissolved in dichloro-
methane (40 mL). The obtained solution was placed in an ice bath
and sodium tetrafluoroborate (2.97 g, 27.1 mmol) was added. The
reaction mixture was stirred at room temperature for 72 h, and
then left to stand for a further 24 h to favor separation of NaBr.
The mixture was filtered to remove NaBr and further filtered
through a pad of neutral alumina. The absence of residual bromide
was checked by means of a silver nitrate test. After concentration
in vacuo, the resulting ionic liquid was dissolved in anhydrous di-
chloromethane (100 mL), treated with active charcoal (1 wt%)
overnight, and subsequently filtered through a pad of neutral alu-
mina. Finally, removal of the solvent under reduced pressure yield-
ed the ionic liquid as a pale yellow liquid (yield: 82%). 1H NMR
(300 MHz; CDCl3, 258C, TMS): d=9.72 (s, 1H; CH), 7.44 (m, 2H;
CH), 7.35 (m, 5H; CH), 5.46 (s, 2H; CH2), 4.22 (t, 3J(H,H)=7.5 Hz,
3H; CH3), 1.85 (m, 2H; CH2), 1.34 (m, 2H; CH2), 0.96 ppm (t,
3J(H,H)=7.5 Hz, 3H; CH3). 13C NMR (300 MHz; CDCl3, 258C, TMS):
d=137.2 (CCH), 133.9 (CCH), 130.4 (CCH), 129.9 (CCH), 123.2 (CCH),
122.9 (CCH), 121.8 (CCH), 54.2 (CH2), 50.9 (CH2), 32.8 (CH2), 20.3
(CH2), 14.3 ppm (CH3).
Experimental Section
Materials: Commercially available acetone and piperidine were dis-
tilled before use. n-Butylimidazole, benzyl bromide, 2,3,4,5,6-penta-
fluorobenzyl bromide, and anhydrous 2-propanol were purchased
and used without further purification. The (Z)-phenylhydrazone of
3-benzoyl-5-phenyl-1,2,4-oxadiazole and the relevant triazole were
prepared according to previously reported procedures.[30] [Bzbim]-
[NTf2], [Bz(F)5bim][NTf2], and [Bzbim][BF4] were prepared by anion
metathesis of the corresponding bromides with LiNTf2 and NaBF4,
according to a reported procedure.[31] All ILs were dried on a
vacuum line at 708C for 2 h before use, then kept in a desiccator
under argon and over calcium chloride.
Each binary mixture was prepared by weighing the proper amount
of ILs into a small vial. To favor mixing, each mixture was vigorous-
ly shaken, sonicated for 1 min (45 kHz, 200 W), and then left to
equilibrate overnight before use. In all cases, mixtures appeared
homogeneous after this treatment.
Kinetic Measurements: All kinetic measurements were carried out
by using a UV/Vis spectrophotometer equipped with a Peltier con-
troller able to keep temperature constant within 0.18C. The sample
for a typical kinetic run was prepared by mixing in a quartz cuvette
(optical path 0.2 cm) 10 mL of a piperidine solution in acetone with
400 mL of a substrate solution in the IL binary mixture, previously
thermostated at 298 K. Substrate and piperidine concentrations
were kept constant (2.76ꢁ10À4 m and 1.20ꢁ10À2 m, respectively).
All binary mixtures were spectroscopically transparent at the work-
ing wavelength. Reactions were followed over at least three half-
lives. Apparent first-order kinetic constants were reproducible
within Æ5%. Kinetic data were analyzed by means of KALEIDA-
GRAPH 4.0 software package.
1-(2,3,4,5,6-Pentafluoro)-benzyl-3-butylimidazolium bromide: Butyl-
imidazole (3.68 g, 29.6 mmol) was dissolved in anhydrous 2-propa-
nol (50 mL). The obtained solution was placed in an oil bath at
908C. 2,3,4,5,6-Pentafluorobenzyl bromide (8.26 g, 29.6 mmol) was
dissolved in 2-propanol (50 mL), and the solution was added drop-
wise to the butylimidazole solution. The reaction mixture was
heated at 908C for 24 h. After cooling, the solution was concentrat-
ed in vacuo and the obtained white solid was washed several
times with diethyl ether. The obtained bromide salt was dissolved
in anhydrous methanol (100 mL) and the solution stirred overnight
at room temperature in the presence of active charcoal (1 wt%).
After filtration over neutral alumina and concentration in vacuo,
the desired salt was obtained as a hygroscopic white solid (yield:
94%), m.p. 88–918C. 1H NMR (300 MHz; CDCl3, 258C, TMS): d=
10.77 (s, 1H; CH), 7.27 (d, 3J(H,H)=15.0 Hz, 2H; CH), 5.85 (s, 2H;
RLS Measurements: Resonance light scattering measurements
were carried out on a spectrofluorophotometer operating in a syn-
chronous mode, with the excitation and emission wavelength set
to the same value. The RLS spectrum was recorded from 300 to
650 nm with both excitation and emission slit width set at 1.5 nm.
3
CH2), 4.28 (t, J(H,H)=7.5 Hz, 2H; CH2), 1.86 (m, 2H; CH2), 1.34 (m,
2H; CH2), 0.93 ppm (t, 3J(H,H)=7.5 Hz, 3H; CH3). 13C NMR
(300 MHz; CDCl3, 258C, TMS): d=147.5 (CCH), 144.7 (CCH), 143.6
(CCH), 139.9 (CCH), 138.2 (CCH), 122.6 (CCH), 121.8 (CCH), 50.4
(CH2), 41.0 (CH2), 32.0 (CH2), 19.5 (CH2), 13.4 ppm (CH3).
Nile Red UV/Vis Measurements: Nile Red absorbance was deter-
mined by injecting into a quartz cuvette (optical path 0.2 cm)
75 mL of a concentrated solution of spectroscopic probe in ace-
tone. After solvent removal under reduced pressure, 400 mL of the
IL binary mixture and 10 mL of acetone were added. Each sample
was kept at a temperature of 298 K for 30 min. A suitable operative
wavelength was chosen by means of difference in UV/Vis spectra
of Nile Red in each of the pure components of the mixture. The
probe concentration in each sample was 2.0ꢁ10À4 m.
1-(2,3,4,5,6-Pentafluoro)-benzyl-3-butylimidazolium bis(trifluorome-
thanesulfonyl)imide: 1-(2,3,4,5,6-Pentafluoro)-benzyl-3-butylimida-
zolium bromide (8.01 g, 20.8 mmol) was dissolved in dichlorome-
thane (40 mL). The obtained solution was placed in an ice bath
and lithium bis(trifluoromethanesulfonyl)imide (5.96 g, 20.8 mmol)
was added. The reaction mixture was stirred at room temperature
for 48 h. Then, it was filtered to remove LiBr and the organic solu-
tion was washed with water until the aqueous phase was halide
ChemPhysChem 0000, 00, 1 – 9
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D'Anna, Francesca
