RSC Advances
Paper
Scheme 1 Structure of the Brønsted acid-surfactant-combined ionic liquids.
15 ml ethyl acetate, and N,N-dimethyloctylamine (15.5 ml, and calculated through UV-visible spectrum. In the experiment,
0.06 mol) was dropped slowly into the previous solution. The 4-nitroaniline (pKa ¼ 0.99) was chosen as the basic indicators
mixture was stirred for 3 h at 55 ꢀC and the reaction mixture was and ethanol as the solvent. The maximum absorbance of
ltered to get the white precipitate. The precipitate was washed unprotonated form of 4-nitroaniline was observed at 371 nm in
with ethyl acetate and diethyl ether twice and dried at 100 ꢀC for ethanol. With the increase of acidity of the BASCs, the absor-
10 h, giving n-OctMe2N-PS as a white power.
bance of the unprotonated form of the basic indicator
n-OctMe2N-PS: yield: 95%, a white solid, mp: 178 ꢀC, 1H NMR decreased, whereas the protonated form of the indicator could
(400 M, D2O): d ¼ 0.68 (t, 3H), 1.09–1.17 (m, 10H), 1.57 (s, 2H), not be observed because of its small molar absorptivity and its
2.02 (m, 2H), 2.78 (t, 2H), 2.90 (s, 6H), 3.11–3.14 (m, 2H), 3.25– location, so the [I]s/[IH+]s can be determined from the differ-
3.28 (m, 2H), 13C NMR (100 M, D2O): 13.60, 18.27, 21.90, 22.16, ences of measured absorbance aer the addition of catalysts
25.56, 28.28, 31.14, 47.41, 62.07, 64.40.
and H0 can be calculated.
1
ꢀ
n-DodecMe2N-PS: yield: 96%, a white solid, mp: 244 C, H
NMR (400 MHz, D2O): d 0.81 (t, 3H), 1.23 (s, 18H), 1.69 (s, 2H),
2.11–2.15 (m, 2H), 2.86 (t, 2H), 3.052 (s, 6H), 3.23–3.27 (m, 2H),
3.39–3.44 (m, 2H), 13C NMR (100 MHz, D2O): d 13.88, 18.35,
22.22, 22.67, 26.11, 29.10, 29.52, 29.88, 29.74, 29.82, 29.97,
32.00, 47.41, 50.87, 61.92, 63.93.
2.4 General procedure for Mannich reaction catalyzed by
BASCs
In a typical procedure, to a reaction tube charged with catalyst
(0.1 mmol) in 1.5 ml of water was added aldehyde (1.0 mmol),
aniline (1.0 mmol), ketone (1.0 mmol). The mixture was then
stirred at 25 ꢀC. Aer completion, the precipitated product was
collected by centrifugation and decantation and the catalyst
solution could be reused directly in the next run without
purication.
The mixture of the zwitterion with equal mole of toluene-
sulfonic acid was stirred for 5 h at 110 ꢀC without solvent, aer
reaction, the white viscous emulsion was dried under vacuum at
ꢀ
100 C for 30 min, cooled and got a white solid product.
1
ꢀ
[DOPA][Tos]: yield: 97%, a white solid, mp: 76 C, H NMR
(400 MHz, D2O): 0.67 (t, 3H), 1.08–1.15 (m, 10H), 1.53–1.57 (m,
2H), 1.97–2.04 (m, 2H), 2.20 (s, 3H), 2.77 (t, 2H), 2.88 (s, 6H),
3.08–3.12 (m, 2H), 3.22–3.26 (m, 2H), 7.17 (d, 2H), 7.49 (d, 2H);
13C NMR (100 MHz, D2O): 13.78, 18.25, 20.71, 21.08, 23.37,
25.73, 28.55, 28.69, 31.40, 47.39, 50.48, 62.13, 64.41, 125.55,
129.41, 140.29, 141.84. ESI-MS: calcd for C20H37NS2O6 m/z [M ꢁ
C7H7SO3]+: 280.4; found: 280.4.
3. Results and discussion
3.1 Acidity of BASCs
The Hammett acidity (H0) function can effectively express the
acidity strength of an acid in organic solvents. The H0 of
the catalysts was summarized in Table 1. As shown in Table 1,
1
[DDPA][Tos]: yield: 96%, a white solid, mp: 86 ꢀC, H NMR
(400 MHz, DMSO-d): 0.86 (t, 3H), 1.25 (s, 18H), 1.64 (s, 2H), 1.94–
1.98 (m, 2H), 2.29 (s, 3H), 2.49 (t, 2H), 2.99 (s, 6H), 3.21–3.25
(m, 2H), 3.35–3.39 (m, 2H), 7.14 (d, 2H), 7.50 (d, 2H); 13C NMR
(100 MHz, DMSO-d): 13.93, 18.69, 20.77, 21.65, 22.09, 25.78,
28.88, 38.74, 38.95, 39.35, 39.57, 39.70, 39.99, 47.66, 49.95, 61.88,
62.93, 125.47, 128.53, 138.23, 144.69, 144.73. ESI-MS: calcd for
C24H45NS2O6 m/z [M ꢁ C7H7SO3]+: 336.5; found: 336.5.
Table 1 The H0 of different ionic liquids in ethanola
Entry
Catalyst system
Amax
[I](%)
[IH](%)
H0
1
2
3
4b
5
6
7
8
9
Blank
0.6556
0.4691
0.4488
—
0.4861
0.4649
0.4794
0.4527
0.4543
100
0
—
[MPSIM][Br]
[MPSIM][HSO4]
[MPSIM][H2PO4]
[MPSIM][Tos]
[MPSIM][CH3SO3]
[BPSIM][Tos]
[DOPA][Tos]
[DDPA][Tos]
71.50
68.46
—
74.15
70.91
73.12
69.05
69.29
28.50
31.54
—
25.85
29.09
26.88
30.95
30.71
1.39
1.33
—
1.45
1.37
1.42
1.34
1.34
2.3 The Hammett acidity of BASCs
The Hammett acidity (H0) function can be calculated by the
equation below: H0 ¼ pK(Iaq) + lg ([I]s/[IH+]s). Here, “I” repre-
sents the indicator base, [IH+]s and [I]s are respectively the
molar concentrations of the protonated and unprotonated
forms of the indicator. The value of [I]s/[IH+]s was determined
a
Condition for UV-vis spectra measurement: solvent: ethanol, indicator:
4-nitroaniline (pKa ¼ 0.99), 54 mmol lꢁ1; BASCs: 35 mmol lꢁ1, 25 ꢀC.
b
No protonation.
728 | RSC Adv., 2014, 4, 727–731
This journal is © The Royal Society of Chemistry 2014