Acetylation in an ionic liquid
637
benzenesulfonate (Na[p-CBS]) were applied to react with
1-butyl-3-methylimidazolium chloride for ion exchange,
the similar procedures were followed as mentioned above.
Finally, [bmim][BS] and [bmim][m-NBS] were obtained as
pale yellow viscous liquids. [bmim][p-CBS] was obtained
as a waxy yellow solid. [bmim][BF4] was synthesized as
reported in Ref. [28].
the di-acylated products were obtained without
mono-acetylation. The acetylation of amines (sensi-
tive to acid catalysts) and phenols (sensitive to base
catalysts) could also be carried out smoothly in
[bmim][OTs]–[bmim][BF4] (entries 11–19). Hence,
due to the neutral feature of the [bmim][OTs]–
[bmim][BF4] system, this method could be widely
applicable for acetylation involving reactants or pro-
ducts instable under acidic or basic reaction condi-
tions [26].
Conclusively, we developed an ionic catalytic sys-
tem of [bmim][OTs]–[bmim][BF4], which can effi-
ciently catalyze the acetylation with the advantages
of wide scope of substrates (alcohols, phenols, and
amines) under neutral conditions, excellent recycl-
ability, non-metal contamination, facile separation
work-up, and insensitivity to air and water. The ac-
celeration of acetylation catalyzed by [bmim][OTs]–
[bmim][BF4] could be explained by the synergistic
effects from the [bmim]þ cation as a weak acid ca-
talyst and the OTsꢀ anion as a nucleophilic (Lewis
base) catalyst.
1-Butyl-3-methylimidazolium tosylate
([bmim][OTs], C15H22N2O3S)
Mp 67ꢁC; ESI-MS: m=z ¼ 171 [bmimþ], 139 [OTsꢀ]; 1H
NMR (500 MHz, D2O): ꢀ ¼ 0.8 (m, CH3), 1.3 (m, NþCH2-
CH2CH2CH3), 1.8 (m, NþCH2CH2CH2CH3), 2.4 (s, Ar–CH3),
3.8 (s, N–CH3), 4.1 (m, NþCH2), 7.3 and 7.6 (2d, 2ꢃ2H,
J ¼ 8 Hz, –Ph), 7.4 (s, NCHCHNþ), 8.6 (s, NCHNþ) ppm;
IR (KBr disc): ꢁꢀ¼ 3149 (m), 3100 (m), 2960 (m), 2872
(m), 1645 (m), 1570 (m), 1461 (m), 1380 (m), 1192 (s),
1037 (s) cmꢀ1
.
1-Butyl-3-methylimidazolium benzenesulfonate
([bmim][BS], C14H20N2O3S)
ESI-MS: m=z ¼ 171 [bmimþ], 125 [BSꢀ]; 1H NMR (500 MHz,
CDCl3): ꢀ ¼ 0.9 (m, 3H, CH3), 1.3 (m, 2H, NþCH2CH2-
CH2CH3), 1.8 (m, 2H, NþCH2CH2CH2CH3), 4.0 (s, 3H, N–
CH3), 4.2 (m, 2H, NþCH2), 7.2, 7.3, 7.9 (m, 2H, 1H, 2H,
–Ph), 7.3 (m, 2H, NCHCHNþ), 10.2 (s, 1H, NCHNþ) ppm;
IR (KBr disc): ꢁꢀ¼ 3149 (m), 3112 (m), 2961 (m), 2872 (m),
1655 (m), 1570 (m), 1471 (m), 1379 (m), 1192 (s), 1037
Experimental
(s) cmꢀ1
.
˚
N-Methylimidazole was dried with 5 A molecular sieve over-
night and purified by distillation before use. The other chemi-
cal reagents were of analytical grade and used as received. The
IR spectra were recorded on a Nicolet NEXUS 670 spectro-
1-Butyl-3-methylimidazolium p-chlorobenzenesulfonate
([bmim][p-CBS], C14H19N2O3SCl)
Mp 64ꢁC; ESI-MS: m=z ¼ 171 [bmimþ], 191 [p-CBSꢀ];
1H NMR (500MHz, D2O): ꢀ ¼ 0.8 (m, 3H, CH3), 1.2 (m,
2H, NþCH2CH2CH2CH3), 1.7 (m, 2H, NþCH2CH2CH2CH3),
3.8 (s, 3H, N–CH3), 4.1 (m, 2H, NþCH2), 7.3 (s, 2H, NCH-
CHNþ), 7.5 and 7.7 (d, 2ꢃ2H, J ¼ 8 Hz, –Ph) ppm; IR (KBr
disc): ꢁꢀ¼ 3145 (m), 3086 (m), 2961 (m), 2871 (m), 1662 (m),
1
meter. The H NMR and 13C NMR (298K) spectra were re-
corded on a Bruker Avance 500 spectrometer. All reactions
were analysed directly using a SHIMADZU GC-14B Gas
Chromatograph equipped with a HP-1 column and a flame
ionization detector. Products were identified by GC-MS
(Agilent 6890 Series, MS=Agilent 5973 Network). Electro-
spray ionization mass spectrometry (ESI-MS) analyses were
performed on Agilent 1100LC=MSDVL. All reactions were
run in an Argonaut Advantage Series 2410 Personal Screening
Synthesizer.
1571 (m), 1473 (m), 1389 (m), 1227 (s), 1186 (s) cmꢀ1
.
1-Butyl-3-methylimidazolium m-nitrobenzenesulfonate
([bmim][m-NBS], C14H19N3O5S)
ESI-MS: m=z ¼ 171 [bmimþ], 201.9 [m-NBSꢀ]; 1H NMR
(500MHz, D2O): ꢀ ¼ 0.8 (m, 3H, CH3), 1.2 (m, 2H, NþCH2-
CH2CH2CH3), 1.7 (m, 2H, NþCH2CH2CH2CH3), 3.8 (s, 3H,
N–CH3), 4.1 (m, 2H, NþCH2), 7.3 (s, 2H, NCHCHNþ), 7.7,
8.1, 8.3, 8.5 (4ꢃ1H, –Ph), 8.6 (s, 1H, NCHNþ) ppm. IR (KBr
disc): ꢁꢀ¼ 3145 (m), 3081 (m), 2961 (m), 2870 (m), 1609
(m), 1569 (m), 1532 (s), 1464 (m), 1349 (s), 1237 (s), 1193
Syntheses of imidazolium salts with differently substituted
benzenesulfonates as anions
A solution of 17.4 g 1-butyl-3-methylimidazolium chloride
[27] (0.1mol) in 100 cm3 deionized water was treated with
17.1g sodium toluene-4-sulfonate (0.1mol, Na[OTs]). After
stirred for 2 h at ambient temperature, the solution was stripped
of water by heating in vacuo. To the obtained slurry solid
100 cm3 CH2Cl2 were added and the mixture was stirred vig-
orously at ambient temperature for 6 h. The resultant filtrate
was treated with active carbon. After filtration and removal of
solvent in vacuo, [bmim][OTs] was obtained as a waxy yellow
solid.
(s) cmꢀ1
.
Acetylation procedure and recycling of the [bmim][OTs]–
[bmim][BF4] system
To [bmim][OTs] (0.31 g, 0.001mol) was added 1 cm3 [bmim]-
[BF4]. After stirring for 5 min, the IL solution was mixed with
1.08g benzyl alcohol (10 mmol) (or other substrates) and
2.04g acetic anhydride (20 mmol). The resultant homoge-
When sodium benzenesulfonate (Na[BS]), sodium 3-
nitrobenzenesulfonate (Na[m-NBS]), and sodium 4-chloro-