Synthesis of task-specific imidazolium ionic liquid as an efficient catalyst in acetylation of alcohols, phenols, and amines

Article abstract of DOI:10.1007/s11696-020-01150-0

Herein, we report the synthesis of task-specific amino-functionalized imidazolium ionic liquid, acetate1-(2-tert-butoxycarbonylamino-ethyl)-3-methyl-3H-imidazol-1-ium; (Boc-NH-EMIM.OAc), as an efficient catalyst for the acetylation of alcohols, phenols, and amines in the presence of acetic anhydride (acetylating reagent). Remarkably, acetic anhydride in the presence of 10?molpercent of catalyst (Boc-NH-EMIM.OAc) under solvent-free conditions showed excellent acetylation activity in shorter duration of time. On the basis of this, a general procedure for acetylation of alcohols, phenols, and amines has been developed. The ionic liquid (Boc-NH-EMIM.OAc) can be readily recovered and reused successfully up to four consecutive cycles without any significant loss of its catalytic activity. We have been able to show that this acetylating method has many advantages. It gives high yields, takes shorter time, and develops the possibility of benign environmental-friendly process.

Full text of DOI:10.1007/s11696-020-01150-0

Chemical Papers
https://doi.org/10.1007/s11696-020-01150-0
ORIGINAL PAPER
Synthesis of task‑specifc imidazolium ionic liquid as an efcient
catalyst in acetylation of alcohols, phenols, and amines
Snehkrishn A. Chaubey1 · Roli Mishra1
Received: 17 October 2019 / Accepted: 30 March 2020
© Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract
Herein, we report the synthesis of task-specifc amino-functionalized imidazolium ionic liquid, acetate1-(2-tert-butoxy-
carbonylamino-ethyl)-3-methyl-3H-imidazol-1-ium; (Boc-NH-EMIM.OAc), as an efcient catalyst for the acetylation of
alcohols, phenols, and amines in the presence of acetic anhydride (acetylating reagent). Remarkably, acetic anhydride in the
presence of 10 mol% of catalyst (Boc-NH-EMIM.OAc) under solvent-free conditions showed excellent acetylation activity
in shorter duration of time. On the basis of this, a general procedure for acetylation of alcohols, phenols, and amines has been
developed. The ionic liquid (Boc-NH-EMIM.OAc) can be readily recovered and reused successfully up to four consecutive
cycles without any signifcant loss of its catalytic activity. We have been able to show that this acetylating method has many
advantages. It gives high yields, takes shorter time, and develops the possibility of benign environmental-friendly process.
Keywords Amino-functional imidazolium ionic liquids · Acetylation · Catalyst · Acetic anhydride · Solvent-free condition ·
Boc-NH-EMIM.OAc
Introduction
Cu and Sn) trifates (Ishihara et al. 1996; Orita et al. 2001;
Chandra et al. 2002) have been also found to be efective
catalysts for acetylation. In spite of the accomplishment in
the above-stated acetylation procedures, there are numerous
drawbacks in them because some of the catalysts utilized are
complex, costly, and toxic. The word "complex" refers to
metal complexes. Thus, there is an urgent need to overcome
the above constraints in the acetylation procedures.
The acetylation/acylation reactions are very versatile reac-
tions, and acetylated alcohols, phenols, and amines are
important building blocks in organic synthesis during oxi-
dation, peptide coupling, and glycosidation reactions for
peptide synthesis, nucleotides, oligonucleotides, steroids,
and other natural products. Signifcantly, the protection of
alcohols, phenols, thiols, and amino groups attracts attention
of the scientifc community from both academic and indus-
trial felds (Von Larock 1989). Numerous methodologies
have been developed for the acetylation of alcohols, which
involves the use of bases such as pyridine, triethyl amine and
dimethylamino pyridine (Höfe et al. 1978; Scriven 1983).
Several Lewis acids such as ZnCl2 (Baker and Ammerman
1995), CoCl2 (Iqbal and Srivastava 1992), and metal (Sc, Bi,
To avoid the use of toxic substance and the generation of
waste in chemical reactions, the use of green procedure of
synthesis is a good choice. From both environmental and
economical point of view, using ionic liquids as media for
organic reactions has attracted signifcant interests as ionic
liquids are considered to be environmentally acceptable and
safe. Recently, there are a lot of reports on the value of ILs
as solvents and catalysts (Song et al. 2013; Jiang et al. 2008).
This class of compounds has huge scope in chemical syn-
thesis due to their diverse properties like low melting point
(<100 °C) salts, typically liquid at room temperature, solva-
tion of wide range of both organic and inorganic compounds,
high thermal stability, low vapor pressure, recyclability, and
ease of handling (Tan et al. 2009; Armand et al. 2009; Liu
et al. 2008; Jutz et al. 2011). Along with these properties, ILs
are also known as designer solvents (MacFarlane and For-
syth 2003) because their properties can be altered according
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-020-01150-0) contains
supplementary material, which is available to authorized users.
* Roli Mishra
rolimishra2@gmail.com; roli.mishra@iar.ac.in
1
Department of Physical Sciences, Institute of Advanced
Research, Gandhinagar, Gujarat 382426, India
Vol.:(0123456789)
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Chemical Papers
to the need of applications by simple tuning of cations and/
or anions. These entire properties make ILs very appropriate
candidates for the development of environmentally benign
chemical processes and greener substitutes to traditional
volatile organic solvents in chemical transformations.
The literature illustrates only a few reports on acetyla-
tion reactions involving the ionic liquids as solvents or/and
catalysts or both (Liu et al. 2008; Shen and Ji 2009; Wang
et al. 2009; López et al. 2011). Recently, in the search of
new environment friendly method, Lewis acid based ionic
liquids (Wang et al. 2008; Abbott et al. 2005), and Brönsted
acidic ionic liquids (Wuts and Greene 2007; Hajipour et al.
2009) have been successfully used as the catalysts for the
acetylation of alcohols and phenols. Previously, our group
has reported Lewis Acid-Based Ionic Liquid (EMIM·AlCl4)
as mild and efcient catalyst for tritylation of alcohols with
triphenyl methyl alcohol (Tr-OH) and 4-monomethoxyl tri-
tyl alcohol (MMTr-OH) (Chaubey et al. 2018). Moreover,
acyl imidazolium derivatives have been used as acetylating
agents in protection of alcohols (Leclercq et al. 2010; Con-
nors and Pandit 1978; Saha et al. 1989; Pandit and Connors
1982; Kamijo et al. 1983; Nakatsuji et al. 2006). There have
also been reports on the acylation of alcohols (Yang et al.
2007) and cellulose (Abe et al. 2016) using acetic anhydride,
catalyzed by task-oriented ionic liquid, 1-ethyl 3-methyl-
imidazolium acetate [EMIM.OAc]. Acetylation of alcohols,
phenols, and amines with acetic anhydride by using the
succinimide-N-sulphonic acid catalyst at room temperature
under solvent-free conditions has been reported by Shirini
and Khaligh (2013). Though these available methods fur-
nished good results, they drawbacks like long reaction time,
formation of by-product, and being expensive. Therefore,
there is still a great need for simple, mild, easy-to-handle,
and environment-friendly catalysts to produce acetyl esters.
Several toxicity studies of ionic liquids have been previously
reported (Mena et al. 2020; Bubalo et al. 2017; Zanoni et.al.
2019; Mishra et.al. 2019).
The activities of various ionic liquids in acetylation
reaction and the efects of process constraints like reaction
time, temperature, catalyst-to-reactant ratio, and catalyst
recyclability are investigated. The application of the ionic
liquids with an amino-functional group (NH2-EMIM.X−;
X=Br, BF4, PF6) has been explored as a medium to absorb
CO2 from natural gas, catalyst for Knoevenagel reactions,
and stable dispersion of multiwalled carbon nanotubes.
Considering aforementioned discussion and our unrelent-
ing eforts for developing profcient ionic liquid-based
catalyst (Chaubey et al. 2018), we have investigated the
present amino-functional imidazolium ionic liquid-cat-
alyzed acetylation of alcohol, phenol, and amine in the
presence of acetic anhydride as an acetylating reagent to
the corresponding acetates. In order to demonstrate the
advantages of this process, Table 1 compares the results
obtained from the O-acetyl protection of benzyl alcohol by
our method with some of those reported in the literature
(Cai et al. 2006; Song et al. 2005; Zhou et al. 2009; Kurnia
et al. 2011).
Recently, ionic liquids have gained recognition as envi-
ronmentally friendly. Keeping this rationale in mind, we
have designed and synthesized ionic liquids Boc-NH-
EMIM.OAc as a catalyst. To the best of our knowledge,
there is no evidence of using the ionic liquid Boc-NH-
EMIM.OAc as organocatalyst for the acetylation reaction
of alcohols, phenols, and amines using acetic anhydride.
Through this communication, we report a fast, simpler,
and efcient procedure for the acetylation of alcohols, phe-
nols, and amines with acetic anhydride in the presence of
ionic liquid Boc-NH-EMIM.OAc under solvent-free con-
ditions. Our catalyst is recyclable up to four cycles without
any loss of catalytic activity. It is pertinent to indicate
that in this report we have not attempted to evaluate the
toxicity issues.
Table 1 Comparisons of
Entry
Imidazolium ILs
Time (min)/Temp (°C)/Yield
References
the publish procedure for
the acetylation of alcohols
(imidazolium ionic liquid) with
the present method
1
2
3
4
5
6
7
8
9
[BMIM] [OTs]+[BMIM][BF4]S
[BMIM] [BS]+[BMIM][BF4]S
[BMIM][p-CBS]+[BMIM][BF4]S
[BMIM][m-NBS]+[BMIM][BF4]S
[BMIM][BF4]C–S
5/50/99
5/50/99
5/50/99
5/50/99
1140/RT/99
20–200/RT/88–94
5/RT/93
5/RT/99
5/RT/99
Cai et al. (2006)
Song et al. (2005)
Zhou et al. (2009)
Kurnia et al. (2011)
[BMIM][FeCl4]C–S
[EMIM][OAc]C–S
[EMIM][HSO4]C–S
[BocNH-EMIM][OAc]C
Present work
S, ionic liquid used as solvent only; C, ionic liquid used as catalyst only; C–S, ionic liquid used as solvent
and catalyst both
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Chemical Papers
product was purifed by washing with ethyl acetate. Chlo-
Results and discussion
ride ion was exchanged with sodium acetate (NaOAc). The
1
structure was confrmed by IR, HNMR, 13CNMR, and
Ionic liquid 1-(N-Boc-2-ethylamine)-3-methylimidazo-
lium acetate (Boc-NH-EMIM.OAc) was prepared by reac-
tion of N-methylimidazole with N-boc-bromoethylamine
followed by anion exchange with sodium acetate (NaOAc)
as a viscous dark brown liquid (Scheme 1). N-butyl-N-
methylpiperidinium acetate (MBPIP.OAc) was prepared by
treating to a solution of N-methylpiperidine with chlorobu-
tane. The reaction mixture was refuxed under a nitrogen
atmosphere at 70 °C, and after completion of reaction,
white solid precipitate of desired product was formed. The
MS (ESI).
A number of experiments were carried out to optimize
the reaction conditions for acetylation, viz. the efects of
solvents, kinds of ionic liquid, mol% of ionic liquid, and
types of substrate. In the beginning of this study, 4-meth-
oxy benzyl alcohol (1 mmol) as model substrate was
treated with acetic anhydride (1.5 mmol) in the presence
and the absence of base/catalyst for duration of time at
room temperature to compare the catalytic performance
of the NaOAc, [BMIM] BF4, [BMIM] PF6, and [BMIM]
N
N
BocHN
BocHN
N
N
N
Anion exchange
N
Br
OAc
BocHN
NaOAc, H2O, 24 h
°
2
Br
70 C; 48 h
1
[BocNH-EMIM] [OAc]
Cl
Anion exchange
Cl
OAc
°
NaOAc, H2O, 24 h
N
16 h at 50 C
N
N
3
4
MBPIP.OAc
Scheme 1. Synthesis of [Boc-NH-EMIM][OAc] and N-butyl-N-methylpiperidinium acetate (MBPIP.OAc) catalyst
Table 2 Optimization of catalyst for acetylation reaction of p-methoxy benzyl alcohol
Entry
Catalyst
Catalyst (mmol %)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
10
No catalyst
NaOAc
[BMIM]BF4
BMIM]PF6
[BMIM]Br
[BMIM]OAc
[Boc-NH-EMIM]Br
[Boc-NH-EMIM].OAc
4MBP.OAc
–
120
120
120
120
120
90
120
5
30
–
10
10
10
10
10
10
10
10
10
20
35
40
25
35
45
98
50
45
MBPIP.OAc
30
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Chemical Papers
Br. It was observed that without catalyst no acetylated
product was detected (Table 2, entry 1). In the presence
of CH3COONa the acetylation reaction occurs slowly
(Table 2, entry 2). It is, further, observed that [BMIM]
BF4, [BMIM] PF6 and [BMIM] Br also demonstrated poor
yields of acetylated product (Table 2, entries 3, 4, and 5).
On the other hand, the reaction was accelerated obviously
when BMIM.OAc was used for the acetylation reaction
(Table 2, entries 6). It may be due to the catalytic nature
of ionic liquids. Based on the observed results in Table 2,
a suitable mechanism is proposed for the acetylation of
alcohols in Fig. 1 (benzyl alcohol as a model substrate).
This outcome encourages us to design more acetate based
ionic liquids viz. Boc-NH-EMIM.OAc and MBPIP.OAc.
Positive charge is delocalized over the aromatic ring in imi-
dazolium ILs, while it is localized in piperidinium ILs. This
charge distribution of the cations plays a major role in the
acidity of ILs. Due to high acidity of imidazolium-based ILs
compared to piperidinium-based ILs nucleophilic behavior
of anion will be weaker in imidazolium. Keeping this ration-
ale in mind, we have explored N-butyl-N-methylpiperidin-
ium acetate (MBPIP.OAc).
Boc-NH-EMIM.OAc was used as model ionic liquid-based
catalyst for acetylation reactions.
In order to determine the efects of solvents on acetylation
reactions, we investigated the acetylation reactions in difer-
ent solvent systems (DCM, chloroform, toluene, CH3CN,
and DMF) and the results are presented in (Table 3). It was
observed that under neat condition (in the absence of sol-
vents) acetylation reactions worked extremely well and fur-
nished good yields of acetylated products (Table 3).
Boc-NH-EMIM.OAc catalyst amount varied up to
20 mol% to examine its efects on acetylation yields. The
results clearly show that the decrease in the loading of Boc-
NH-EMIM.OAc from 10 to 5 mol% resulted in lower yields
of the products (Table 3, entry 7 vs 6), whereas on increasing
the amount of Boc-NH-EMIM.OAc from 10 to 15 mol%,
there was no efect on the yields of the products (Table 3,
entry 7 vs 8). The highest yield of acetylated product was
accomplished at 10 mol% catalysts (Table 3, entry 4). Fur-
ther enhancement in the catalyst amount did not improve the
yield of the acetylated product as it is evident from Table 3
(entry 9). This is accredited to the increased viscosity of
the solution, leading to the reduced interaction among the
reactants and the ILs.
It was found that Boc-NH-EMIM.OAc demonstrated
outstanding catalytic activities, gave yields of 98% at room
temperature in shorter time (Table 2, entry 8) compared to
other acetate ILs viz. 4MBP.OAc (1-butyl-4-methylpyri-
dinium acetate, N-butyl-N-methylpiperidinium acetate
(MBPIP.OAc), [BMIM] BF4, [BMIM] PF6, and [BMIM]
Br. The other ILs ([BMIM] BF4, [BMIM] PF6, [BMIM]
Br) furnished lower yields of acetylated products. Thus
This is also important to explore the reusability of the
Boc-NH-EMIM.OAc as the catalyst since it may have pos-
sibly considerable impact on the overall economy of catalyst.
We have also found that the catalyst used for the acetylation
was easily regenerated by washing with diethyl ether. The
entire acetylated products went into the organic layer, but the
ionic liquid catalyst which was left at the bottom was dried
Fig. 1 Proposed mechanism
for the acetylation of alcohols
(benzyl alcohol as a model
substrate)
O
O
+
N
N
NHBoc
O
O
OH
O
O
O
O
O
N
N
NHBoc
N
N
NHBoc
O
O
H
H
OH
O
O
O
O
O
O
O
HO
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Chemical Papers
Table 3 Optimization of the reaction conditions (solvent and mol% of catalyst)
Catalyst
[Boc-NH-EMIM] [OAc]
OH
OAc
Ac2O
r.t
H3CO
H3CO
Entry
Solvent
Catalyst (mol%)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
DCM
CHCl3
10
10
10
10
10
10
05
15
20
40
40
60
90
60
5
5
5
5
30
35
45
10
55
98
65
96
96
CH3CN
Toluene
DMF
No solvent
No solvent
No solvent
No solvent
Table 4 Recycling of [Boc-NH-EMIM][OAc] during the acetylation
products in high yields (Table 5, entries 1, 8–10). The
acetylation of benzylic alcohols, phenols, and aromatic
amines with electron-withdrawing groups, viz. nitro,
chloro, fuoro, and aldehyde and ketone substituents, was
also scrutinized. However, electron-withdrawing groups
impeded the reactions and the yields of the acetylated
products were 85 to 92% (Table 5, entries 2–3, 14–16,
18). Satirically hindered alcohols furnished correspond-
ing acetylated products relatively in lower yields (Table 5,
entries 4, 7). Substrate 11 was selectively converted to
the corresponding acetylated products without afecting
the base-labile-protecting Fmoc group (Table 5, entry 11).
The acetylation of lithocholic and deoxycholic acid
was performed in the presence of 5 mol% ionic liquid; the
desired acetylated products 3α-12α-diacetoxy-5β-cholan-
24-oic acid methyl ester (12) and 3α-Acetoxy-5β-cholan-
24-oic acid methyl ester (13) were obtained in 65–75%
yield in 90 min. Indeed, the yields of 3α-12α-diacetoxy-
5β-cholan-24-oic acid methyl ester (12) and 3α-acetoxy-
5β-cholan-24-oic acid methyl ester (13) were increased
to 80–85%, using 10 mol% ILs with full conversion in a
relatively shorter time of 15 min (Table 5; entry 12, 13).
This catalyst was not only applicable to primary alcohols
but also underwent smoothly in case of secondary alcohols
(Table 5; entries 5–7, 10, 12–13). The alcohols were trans-
formed into the corresponding acetates in excellent yields
without any difculty in shorter times (Table 5; 1–13).
Phenols and amines were also acetylated in good to excel-
lent yields (Table 5; 14–20). As a result of our investiga-
tions, we have demonstrated [Boc-NH-EMIM] [OAc] as an
efcient catalyst for the acetylation of alcohols, phenols,
and amines. It is apparent the current procedure is more
profcient than the compared procedures with reference to
of alcohol
Acetic anhydride
(10 mol%), rt,
H3CO
H3CO
OAc
OH
Cycle (Reuse)
Time (min)
Yield (%)
1
2
5
5
7
5
10
5
20
5
120
98
95
97
92
95
85
90
20
75
3
4
5
at 50 °C for 4 h to get recycled catalyst. No aqueous workup
was required. Experiments were run with recycled catalyst
to test whether this catalyst can be reused. The result showed
that catalyst could be reused up to four cycles without sig-
nifcant loss of activities (Table 4).
In order to generalize the use of Boc-NH-EMIM.OAc
as an efcient catalyst for acetylation of structurally difer-
ent alcohols, phenols, and amines with acetic anhydride,
10 mol% of Boc-NH-EMIM.OAc was treated at room tem-
perature. The results obtained are shown in Table 5. In all
cases, the acetylated products were obtained in good to
excellent yields.
Regarding acetylation of the benzylic alcohols, an elec-
tron-donating group at the aromatic nucleus accelerated
the reaction and aforded the corresponding acetylated
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Chemical Papers
Table 5 Acetylation of primary
and secondary alcohol, phenol
and amine
Entry
1
Substrate
H3CO
Product
H3CO
Time (min) Yield (%)
OH
OAc
5
98
OH
OAc
8
89
2
F
F
OAc
OH
8
86
85
3
4
Cl
Cl
10
OAc
OAc
OH
OH
10
5
92
92
80
5
6
7
O
O
O
OAc
O
OH
O
O
OAc
OH
10
5
8
7
94
95
96
8
9
AcO
OAc
HO
OH
OAc
OH
OH
OAc
10
OH
OAc
FmocHN
HO
11
12
5
95
80
FmocHN
AcO
15
15
HO
O
AcO
O
OCH3
OCH3
OCH3
OCH3
13
85
O
O
HO
AcO
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Chemical Papers
Table 5 (continued)
Entry
14
Substrate
OH
Product
F
Time (min) Yield (%)
F
OAc
2
78
NO2
NO2
OCH3
OAc
OCH3
OH
15
3
86
OHC
O
OHC
O
NHAc
NH2
16
17
18
5
5
85
95
87
NH2
NHAc
NHAc
NHAc
NH2
NH2
5
5
Cl
Cl
96
19
20
O
O
20
88
HO
HO
NH2
NHAc
conditions, recyclability of catalyst, reaction times, and/
or the products’ yields.
The ionic liquid [Boc-NH-EMIM] [OAc] was prepared
by metathesis of [Boc-NH-EMIM] [Br] with sodium acetate.
[Boc-NH-EMIM] [Br] salt was dissolved in deionized water
and aqueous CH3COONa (equimolar) was added drop-wise
under stirring at RT for 18 h and water was removed under
vacuum. To the viscous crude ionic liquid Boc-NH-EMIM.
OAc, acetonitrile was added and fltered to remove NaBr.
Acetonitrile potion was removed under reduced pressure
to get desired product and washed once with diethyl ether
to remove organic impurities. This was, then, dried under
high vacuum (with heating at 40 °C) for at least 2–3 h to
minimize the moisture content. FTIR (ATR, νcm−1): 3287,
2360, 2131, 1598, 1448, 1357, 1175, 1096, 979, 926, 814,
657, 545, 445, 414; 1H NMR (400 MHz, DMSOd6): δ 9.11
(s, 1H), 7.70 (s, 1H), 7.55 (s, 1H), 6.86 (s, 1H), 4.17–4.29
(t, 2H), 3.84 (s, 1H), 3.63 (s, 1H), 3.15–3.3 (s, 1H), 2.07
(s, 1H), 1.89 (s, 2H), 1.56 (s, 1H), 1.32 (S, 9H); 13C NMR
(100 MHz, DMSOd6): δ=155.6, 137.3, 128.3, 123.1, 120.4,
78.2, 64.1, 49.1, 39.5, 38.9, 35.6, 32.7, 28.5, 21.0; ESI-MS
Synthesis of 1-(N-Boc-2-ethylamine)-3-methylimidazo-
lium acetate (2) N-methyl imidazole (0.782 ml, 9.82 mmol,
1.1 eq.) was added to N-Boc-2-bromoethylamine (2.720 g,
8.92 mmol) in CH3CN and was stirred at 70 ºC for 48 h. The
progress of reactions was monitored by TLC and taken to
completion. Bromide salt (3) was washed with ethyl acetate
and dichloromethane. The solvent was removed by decanta-
tion, and the residue was purifed by column chromatography
method on silica gel, using acetone and methanol as eluent
to give desired 1-(N-Boc-2-ethylamine)-3-methylimidazo-
lium bromide Boc-NH-EMIM.Br (1) as yellowish colour
viscous liquid in 84% (2.32 g) yield (Scheme 1, Compound
3). 1H NMR (DMSO-d6, 400 MHz): δ 9.30 (s, 1H, Im), 8.20
(s, 1H, Im), 7.75 (s, 2H, Im), 7.34–7.33 (s, 1H, Im-NH),
7.15–7.14 (d, 1H, NH), 4.28–4.20 (m, 2H, CH2), 3.85 (s,
3H, Im-CH3), 3.72 (s, 2H, CH2), 3.44–3.33 (m, 2H), 1.57
(s, 1H), 1.31 (s, 9H, Boc). 13C NMR (100 MHz, DMSO-d6)
δ: 155.6, 136.9, 124.7, 123.0, 121.4, 78.0, 64.0, 48.9, 38.9,
+
calcd for [C11H20N3O2 ] 226.1550, found 226.1498.
+
35.6, 33.7, 29.0, 28.0. ESI-MS calcd for [C11H20N3O2 ]
Synthesis of N-butyl-N-methylpiperidinium acetate
226.155, found 226.283.
(MBPIP.OAc) To N-methyl piperidine (1.21 ml, 10 mmol) in
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Chemical Papers
pressure tube, bromobutane (1.180 ml, 11 mmol) was added
slowly with continuous stirring at 25 °C. Mixture was stirred
for 16 h at 50 °C in nitrogen atmosphere. The solution was
washed with dry diethyl ether and remaining residue evapo-
rated on a rotavapour. MBPIP.Br was treated with sodium
acetate in similar fashion as described compound 2. A solid
precipitate of NaCl was removed by fltration. White liquid
product was kept under high vaccum at 50 °C for 3 h (yield;
95%). The product N-butyl-N-methylpiperidinium acetate
(100 MHz, CDCl3): δ 170.4, 140.5, 128.3, 127.8, 126.5,
29.7, 29.2, 21.2, 19.1, 9.8.
Acetic acid 2,5-dioxo-cyclopentyl ester (entry 6) FTIR
(ATR, νcm−1): 2986, 2371, 1714, 1374, 1163, 1051, 824,
1
644, 507; H NMR (400 MHz, CDCl3): δ = 2.83 (s, 4H),
2.34 (s, 3H); 13C NMR (100 MHz, CDCl3): 169.0, 165.6,
29.7, 25.6, 17.6.
Acetic acid 2-oxo-1,2-diphenyl-ethyl ester (entry 7) FTIR
(ATR, νcm−1): 3062, 2360, 1693, 1597, 1448, 1372, 1225,
1
1
(4) was confirmed by H NMR (400 MHz, DMSO-d6):
1055, 971, 862, 755, 695, 582, 526; H NMR (400 MHz,
δ=3.39–3.32 (m, 6H), 3.09 (s, 3H), 2.05 (s, 3H), 1.78 (s,
br, 3H), 1.67–1.45 (m, 4H), 1.33–1.24 (m, 2H), 0.91 (t, 3H.
J=7.2 Hz). FTIR (ATR, νcm−1): 2959, 2874, 1474, 1353,
1225, 1050, 940, 673, 576, cm−1.
CDCl3): δ 7.47 (d, J = 4.0 Hz, 2H), 7.45–7.40 (m, 2H),
7.39–7.33 (m, 4H), 6.86 (s, 1H), 2.20 (s, 3H); 13C NMR
(100 MHz, CDCl3): 193.8, 170.5, 134.7, 133.6, 128.9, 77.7,
29.5, 21.7, 14.2.
General procedure for Acetylation of alcohols To mix-
ture of an alcohols (10.0 mmol), acetic anhydride (Ac2O)
(15 mmol; 1.5 equivalent) and 10 mol % of catalyst [Boc-
NHCH2CH2MIM] [OAc] was stirred at room temperature.
Completion of reactions was monitored through TLC. After
completion of the reactions, the reaction mixture evaporated
under vacuum till dryness. The residue was extracted with
diethyl ether and concentrated. The crude products were
purifed by column chromatography on neutral alumina
using hexanes/ethyl acetate as the eluent to give correspond-
ing products. Acetic acid 4-methoxy-benzyl ester (entry 1)
FTIR (ATR, νcm−1): 2956, 2838, 2360, 1733, 1612, 1515,
Acetic acid 2-acetoxymethyl-ethyl ester (entry 8) FTIR
(ATR, νcm−1): 2963, 2289, 1738, 1371, 1212, 1045, 957,
1
847; H NMR (400 MHz, CDCl3): δ 5.27–5.22 (m, 2H),
4.31–4.27 (m, 1H), 4.18–4.13 (m, 1H), 2.09 (s, 9H);
13CNMR (100 MHz, CDCl3): 170.2, 69.0, 62.2, 29.6, 20.7.
Acetic acid octyl ester (entry 9) FTIR (ATR, νcm−1):
2926, 2860, 1739, 1462, 1369, 1234, 1038, 960, 724, 640;
1H NMR (400 MHz, CDCl3): δ 4.05 (t, J = 6.8 Hz, 2H),
2.04 (s, 3H), 1.65–1.60 (m, 2H), 1.58–1.27 (m, 10H), 0.90
(t, J=6.8, Hz, m, 3H); 13C NMR (100 MHz, CDCl3): 171.2,
64.6, 31.9, 31.7, 29.7, 29.3, 29.2, 29.1, 28.6, 25.9, 22.6,
21.0, 14.0.
1
1221, 1024, 958, 813, 756, 607, 561, 518, 431, 408; H
Acetic acid cyclohexyl ester (entry 10) 1H NMR
(400 MHz, CDCl3): δ 4.76–4.70 (m, 1H), 2.02 (s, 3H),
1.86–180 (m, 4H), 174–1.70 (m, 6H), 1.57–1.44 (m, 2H);
13C NMR (100 MHz, CDCl3): 170.6, 72.7, 35.5, 31.6, 29.7,
25.4, 23.8, 22.6, 21.4.
NMR (400 MHz, CDCl3): δ=7.30–7.25 (m, 2H), 6.90–6.87
(m, 2H), 5.04 (s, 2H), 2.09 (s, 3H); 13C NMR (100 MHz,
CDCl3): δ 170.9, 159.6, 130.1, 128.1, 113.9, 113.8, 66.1,
55.3, 29.7, 21.0
Acetic acid 4-fuoro-benzyl ester (entry 2) FTIR (ATR,
Acetic acid 2-(9H-fuoren-9-ylmethoxycarbonylamino)-
ethyl ester (entry 11) FTIR (ATR, νcm−1): 3319, 2930,
2364, 1720, 1550, 1441, 1258, 1157, 1055, 956, 613, 471;
1H NMR (400 MHz, CDCl3): 7.77–7.26 (m, 8H); 4.474.42
(m, 3H), 4.23–4.00 (m, 2H), 3.78–3.32 (m, 2H), 2.07 (s,
3H); 13C NMR (100 MHz, CDCl3): δ 177.0, 143.8, 141.4,
127.7, 127.1, 125.0, 120.1, 47.4, 40.2, 20.9.
νcm−1): 2360, 1737, 1605, 1511, 1379, 1221, 1158,
1
1027, 822, 766, 607, 551; H NMR (400 MHz, CDCl3):
δ=7.32–7.07 (m, 2H), 7.06–7.02 (m, 2H), 5.06 (s, 2H), 2.09
(s, 3H); 13C NMR (100 MHz, CDCl3): δ 170.8, 163.9, 161.4,
131.8, 130.3, 130.2, 115.6, 115.3, 65.5,20.9.
Acetic acid 4-chloro-benzyl ester (entry 3) FTIR (ATR,
νcm−1): 2359, 1735, 1599, 1493, 1377, 1222, 1092, 1014,
803, 530; 1H NMR (400 MHz, CDCl3): δ=7.34–7.32 (m,
2H), 7.29–7.25 (m, 2H), 5.06 (s, 2H), 2.09 (s, 3H); 13C NMR
(100 MHz, CDCl3): δ 170.7, 134.4, 134.1, 129.6, 128.7,
65.4, 29.7, 20.9.
3α-12α-Diacetoxy-5β-cholan-24-oic Acid methyl ester
(12) 1H NMR (400 MHz, CDCl3): 5.07 (d, 1H, J=2.8 Hz),
4.70 (m, 1H), 3.66 (s, 3H), 2.34–2.31 (m, 1H), 2.22–2.20
(m, 1H),2.10 (s, 3H), 2.03 (s, 3H), 1.88–1.10 (m, 24H), 0.90
(s, 3H), 0.81 (s, 3H), 0.79 (s, 3H): 13C NMR (100 MHz,
CDCl3): 174.6, 170.5, 170.4, 75.9, 74.2, 51.5, 49.4, 47.6,
45.0, 41.8, 35.7, 34.7, 3.4.4, 34.0, 32.2, 31.0, 30.8, 27.3,
26.9, 26.6, 25.8, 25.6, 23.4, 23.0, 21.4, 21.3, 17.5.
3α-Acetoxy-5β-cholan-24-oic acid methyl ester (13)
1H NMR (400 MHz, CDCl3): 4.71 (d, 1H, J = 4.8 Hz),
2.40–2.36 (m, 1H), 2.30–2.26 (m, 1H), 2.17 (s, 3H), 2.02 (s,
3H), 1.98–0.90 (m, 32H), 0.64 (s, 3H): 13C NMR (100 MHz,
CDCl3): 178.0, 76.7, 74.4, 56.5, 56.0, 42.7, 41.9, 40.4, 40.1,
35.8, 35.3, 35.0, 34.6, 32.2, 30.8, 30.6, 28.1, 27.0, 26.6,
26.3, 24.2, 23.3, 21.4, 20.8, 18.2.
Acetic acid benzhydryl ester (entry 4) FTIR (ATR,
νcm−1): 3033, 2360, 1737, 1495, 1370, 1227, 1020, 743,
697, 549; 1H NMR (400 MHz, CDCl3): δ=7.34–7.25 (m,
10H), 6.82 (s, 2H), 2.15 (s, 3H); 13C NMR (100 MHz,
CDCl3) 170.0, 140.2, 127.8, 77.3, 30.0, 22.0, 14.1
Acetic acid 1-phenyl-propyl ester (entry 5) FTIR (ATR,
νcm−1): 3385, 3152, 2975, 2365, 1701, 1518, 1370, 1247,
1
1164, 1011, 849, 755; H NMR (400 MHz, CDCl3):
δ = 7.34–7.30 (m, 2H), 7.39–7.25 (m, 2H), 5.66 (t, 1H),
2.08 (s, 3H), 1.97–1.77 (q, 2H), 0.87 (t, 3H); 13C NMR
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Chemical Papers
Acetic acid 3-fuoro-5-nitro-phenyl ester (entry 14) FTIR
(ATR, νcm−1): 3092, 2349, 1775, 1597, 1529, 1345, 1274,
1149, 1085, 1011, 891, 826, 689, 620; 1H NMR (400 MHz,
CDCl3): δ 10.79 (s, 1H), 8.19–7.47 (m, 2H), 7.46- 7.21 (m,
1H), 3.99 (s, 3H) 2.08 (s, 3H); 13C NMR (100 MHz, CDCl3):
193.8, 170.5, 134.7, 133.6, 128.9, 29.5, 21.7, 14.2.
place rapidly under solvent free systems. It is also important
to point out that the ionic liquid could easily be recycled and
reused up to four cycles without the loss of activities. These
results may ofer a wide opportunity to use Boc-NH-EMIM.
OAc catalysts within the area of organic transformations.
Further study on the application of this kind of catalyst is
under progress in our laboratory.
Acetic acid 4-formyl-2-methoxy-phenyl ester (entry 15)
FTIR (ATR, νcm−1): 3028, 3028, 2626, 2359, 1706, 1506,
1
1384, 1278, 1193, 1147, 1014, 897, 735, 603 cm−1; H
Acknowledgements RM is also thankful to IISC-SAIF Bangalore for
the 1H and 13 C NMR spectral analysis and Gujarat Forensic University
for the mass and IR analysis.
NMR (400 MHz, CDCl3): δ 9.94 (s, 1H), 7.50–7.47 (m,
2H), 7.46–7.21 (m, 1H), 3.99 (s, 3H) 2.08 (s, 3H); 13CNMR
(100 MHz,CDCl3): 191.3, 177.2, 168.5, 166.5, 152.0, 145.0,
138.5, 137.9, 135.3,134.3, 131.2, 124.7, 123.0, 118.9, 111.4,
89.4, 60.5, 56.1, 49.5, 40.1, 36.8, 29.3, 21.2, 14.2.
Funding This work has been supported by the Department of Science
and Technology, India, (SERB/F/8435/2015-16) to RM.
N-(4-Acetyl-phenyl)-acetamide (entry 16) FTIR (ATR,
Compliance with ethical standards
νcm−1): 3119, 2359, 1674, 1592, 1407, 1318, 1259, 1013,
1
Conflict of interest The authors declare no confict of interest.
838, 759, 592; H NMR (400 MHz, CDCl3): δ 7.95 (d,
J=5.6 Hz, 2H), 7.92 (d, J =2.4 Hz, 2H), 7.62 (br, s, 1H),
2.57 (s, 3H), 2.21 (s, 3H); 13C NMR (100 MHz, CDCl3):
196.9, 168.5, 142.2, 132.9, 129.7, 118.8, 26.4, 24.7.
1
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