8
28
W. Xu et al.
Then, the synthetic TSILs were tested for liquid–liquid extrac-
2þ
85 %). d (CDCl , 400 MHz) 10.32 (1H, s), 7.62 (1H, s), 7.50
H
3
2
tion of Cu , Ni , and Co from water. TSILs 3a and 3b both
þ
2þ
(1H, s), 4.40 (2H, t, J 7.2), 4.34 (2H, t, J 7.6), 3.43–3.40 (4H, m),
2.03–1.84 (6H, m), 1.51–1.23 (12H, m), 0.87 (3H, t, J 6.8). dC
(CDCl , 100 MHz) 136.3, 122.1, 121.8, 49.9, 49.6, 33.7, 32.3,
2
þ
showed high extraction efficiency for the three metal ions. Cu
2þ
2þ
showed higher distribution coefficient relative to Ni and Co
the distribution coefficient could reach up to 19990 when
3
–
32.1, 31.5, 30.1, 30.0, 28.9, 27.2, 26.1, 25.1, 22.4, 14.0. m/z
þ
using TSIL 3b. TSIL 3b presented superior capability to 3a
under the conditions employed to extract the three metal ions,
and may be ascribed to the extra nitrogen atom in the alkyl chain
of piperazine, and thus higher affinity to the metal ions was
obtained. The synthetic TSILs were pH sensitive; higher per-
(ESI) 345 ([M] ). m/z 345.1733. HRMS (ESI) Anal. Calc. for
þ
C H BrN ([M] ) 345.1728.
1
7
32
2
Task-Specific Ionic Liquids (3)
Compound (0.14 g, 0.35 mmol), mono-substituted
2
þ
2
centage extraction was observed at higher pH values for Cu
,
2
þ
2þ
piperazine (0.44 mmol; for the synthesis of mono-substituted
piperazine, see Supplementary Material), anhydrous aceto-
nitrile (8 mL), and potassium carbonate (0.30 g, 2.2 mmol) were
added in a 100-mL round-bottom flask. Then, the reaction
Ni , and Co under our operating conditions. And the ther-
modynamic parameters indicated that the extraction process was
exothermic and spontaneous in nature. The results of the
experiments suggest that the synthetic TSILs can be used as
potential extracting solvents for copper, nickel, and cobalt.
mixture was refluxed under N atmosphere for 72 h. The mixture
2
was then cooled to room temperature and filtered. The filtrate
was concentrated and the residue was purified by washing
with anhydrous diethyl ether (3 ꢁ 5 mL), and dried under
vacuum to give functionalized ionic liquids as a light yellow
oil. Functionalized ionic liquids (1.11 mmol), lithium bis(tri-
fluoromethanesulfonyl)imide (0.32 g, 1.11 mmol), and Milli-Q
water (18.2 MO cm; 10 mL) were stirred at room temperature for
Experimental
Materials
Chemicals were of reagent grade and used without further
1
purification unless otherwise stated. The H NMR (400 MHz)
1
and C NMR (100 MHz) spectra were recorded with a Bruker
3
1
2 h to exchange the anions. Dichloromethane (15 mL) was then
added to extract the product, and washed with Milli-Q water
3 ꢁ 10 mL). The organic layer was dried with anhydrous
Na SO . The solvent was removed by rotary evaporation to
DPX 400 using CDCl as solvent and TMS as internal standard
3
at room temperature. High-resolution mass spectrometry
(HRMS) and electrospray ionization mass spectrometry (ESI–
MS) were conducted using the ESI-mode. Silica gel (300–400
mesh) was used for flash chromatography. The metal ion con-
centrations were measured by a PGENERAL TAS-990 atomic
absorption spectrophotometer fitted with copper, cobalt, and
nickel hollow cathode lamps. The instrument was set at
(
2
4
give final TSILs 3.
TSIL 3a. Light yellow oil (0.211 g, 88 %). dH (CDCl3,
4
3
1
00 MHz) 8.56 (1H, s), 7.32–7.26 (2H, m), 4.17–4.13 (4H, m),
.46–3.41 (2H, m), 2.33–2.23 (6H, m), 1.87–1.71 (6H, m), 1.50–
.42 (4H, m), 1.33–1.25 (18H, m), 0.93–0.85 (6H, m). dC
3
24.7 nm for copper, 240.7 nm for cobalt, and 320.0 nm for
(CDCl , 100 MHz) 134.8, 122.1, 122.1, 120.2 (q, J
3
310),
C–F
nickel. A centrifuge (SORVALL fresco) was used to separate
ionic liquid and aqueous phase.
5
2
8.5, 58.3, 53.1, 50.1, 50.0, 46.5, 31.6, 30.0, 29.9, 29.0, 28.9,
8.8, 27.3, 26.8, 26.6, 26.1, 26.0, 22.6, 20.8, 14.1. m/z (ESI) 405
þ
([M] ). m/z 405.3953. HRMS (ESI) Anal. Calc. for C H N
49
2
5
4
Synthesis of Task-Specific Ionic Liquids
þ
([M] ) 405.3952.
TSIL 3b. Light yellow oil (0.225 g, 90 %). dH (CDCl3,
1
-Octylimidazole (1)
Imidazole (3.41 g, 50 mmol) and NaH (1.34 g, 54 mmol)
were dissolved in THF (10 mL) under N in an ice bath for
400 MHz) 8.59 (1H, s), 7.31 (1H, s), 7.28 (1H, s), 4.16 (6H, t,
J 7.6), 2.99 (2H, m), 2.65 (2H, m), 2.45–2.27 (8H, m), 2.21
(6H, s), 1.86 (6H, m), 1.68–1.64 (2H, m), 1.37–1.22 (14H, m),
2
4
5
5 min, followed by addition of 1-bromooctane (9.65 g,
0 mmol). The solution was stirred for 24 h at room temperature
0.88–0.85 (3H, m). d (CDCl , 100 MHz)135.3, 122.5, 122.5,
C 3
and then concentrated under reduced pressure after filtration.
The residue was purified by flash chromatography (SiO2;
petroleum ether/ethyl acetate ¼ 5 : 1 as eluent) to give 1 as a
light yellow oil (5.97 g, 60 %). d (CDCl , 400 MHz) 7.42 (1H,
120.6 (q, JC–F 301), 58.6, 58.3, 57.0, 53.5, 53.4, 50.5, 50.3, 45.7,
32.0, 30.3, 30.2, 29.4, 29.2, 27.2, 26.9, 26.5, 26.4, 25.3, 23.0,
þ
14.5. m/z (ESI) 434 ([M] ). m/z 434.4197. HRMS (ESI) Anal.
Calc. for C26
þ
H
52
N
([M] ) 434.4217.
H
3
5
s), 7.01 (1H, s), 6.87 (1H, s), 3.89 (2H, t, J 8.0), 1.76–1.73 (2H,
m), 1.31–1.25 (10H, m), 0.87 (3H, t, J 7.2). dC (CDCl3,
Liquid–Liquid Extraction of Metal Ions
1
2
00 MHz) 136.2, 128.4, 118.1, 46.4, 31.2, 30.6, 28.6, 28.5,
þ
Liquid–liquid extraction of metal ions was carried out starting
2þ
6.0, 22.1, 13.6. m/z (ESI) 181 ([M þ H] ). m/z 181.1708.
2þ
2þ
from aqueous solutions containing Cu , Ni , and Co . The
initial pH was adjusted with hydrochloric acid from 1 to 5.
Product 3a or 3b was dissolved in [Bmim][NTf ] to achieve a
þ
HRMS (ESI) Anal. Calc. for C H N ([M þ H] ) 181.1705.
1
1 21 2
2
3
-(6-Bromohexyl)-1-octyl-imidazolium Bromide (2)
ꢀ1
concentration of 175 mmol L . Then, 20 mL of TSIL/IL was
1
,6-Dibromohexane (10.00 g, 42 mmol) was dissolved in
mixed with 200 mL of the above mentioned metal ion solutions
ꢀ
1
anhydrous acetonitrile (10 mL) and introduced into a three-neck
round-bottom flask. After the solution was heated gently to
reflux, a solution of 1 (0.50 g, 2.80 mmol) in anhydrous aceto-
(initial concentration of 200 mg L ) of various pH values, and
stirred for 1 h while keeping the temperature at 308C. Then, the
mixture was centrifuged at 2000 g for 5 min and the residual
concentration of the metal ions was determined.
nitrile (5 mL) was added dropwise under N atmosphere. The
2
reaction mixture was stirred for 24 h at reflux and then cooled to
room temperature. The solvent was removed to give a residue,
which was purified by washing with anhydrous diethyl ether
Uptake experiments examining the effect of tempera-
ture were performed by adding 200 mL metal ion solution
(200 mg L ) of which the pH was 3.0 into tubes containing
20 mL TSIL/IL, and incubated at 30, 40, 50, or 608C with
constant stirring for 1 h.
ꢀ
1
(3 ꢁ 5 mL), and concentrated under reduced pressure. The resi-
due was dried under vacuum to afford 2 as a puce oil (1.01 g,