Novel and efficient method for esterification catalyzed by 1-glycyl-3-methyl imidazolium chloride-iron (III) complex

Article abstract of DOI:10.1007/s13738-012-0116-1

1-Glycyl-3-methyl imidazolium chloride-iron (III) complex [[Gmim]Cl-Fe(III)] was found to be a heterogeneous catalyst for an efficient and greener solvent free synthesis of esters by the condensation of carboxylic acids and alcohols with excellent yield at ambient temperature. This operation formulates very interesting, ecological perspective due to simple reaction condition, isolation, and purification of products. In addition, this method features reusability of catalyst, reduced waste, thus making new protocol more environmentally suitable whilst no catalyst leaching was observed. Iranian Chemical Society 2012.

Full text of DOI:10.1007/s13738-012-0116-1

J IRAN CHEM SOC (2012) 9:983–990
DOI 10.1007/s13738-012-0116-1
ORIGINAL PAPER
Novel and efficient method for esterification catalyzed
by 1-glycyl-3-methyl imidazolium chloride-iron (III) complex
•
Parasuraman Karthikeyan Pundlik Rambhau Bhagat
•
•
•
Sellappan Senthil Kumar Prashant Narayan Muskawar
Sachin Arunrao Aswar
Received: 27 January 2012 / Accepted: 31 May 2012 / Published online: 19 June 2012
Ó Iranian Chemical Society 2012
Abstract 1-Glycyl-3-methyl imidazolium chloride-iron
(III) complex [[Gmim]Cl–Fe(III)] was found to be a het-
erogeneous catalyst for an efficient and greener solvent free
synthesis of esters by the condensation of carboxylic acids
and alcohols with excellent yield at ambient temperature.
This operation formulates very interesting, ecological
perspective due to simple reaction condition, isolation, and
purification of products. In addition, this method features
reusability of catalyst, reduced waste, thus making new
protocol more environmentally suitable whilst no catalyst
leaching was observed.
esterification of salicylic acid using Bronsted acidic ionic
liquids under Microwave acceleration. Recently, Zhen
et al. [4] reported the synthesis of alkyl sulfonate func-
tionalized Ionic liquids and its application in esterification.
Nowrouzi and co-workers [5] have reported a simple and
convenient method for the preparation of carboxylic acid
alkyl esters, phenolic and thio-esters using chloro diphenyl
phosphine/I2 and imidazole reagent system. However,
Prasad et al. [6] descried the liquid–liquid biphasic syn-
thesis of long chain wax esters using the Lewis acidic ionic
liquid choline chlorideÁ2ZnCl2. Yoon and co-workers [7]
have reported the effective esterification of carboxylic
acids using (6-oxo-6H-pyridazin-1-yl) phosphoric acid
diethyl ester as novel coupling agents. These methods
provide good yields, but have drawbacks such as lengthy
workup procedure, harsh reaction conditions and require
absolutely dry and inert media. Thus, there is a need to
develop an operationally simple, safe and widely usable
eco-friendly method.
Keywords Iron (III) complex Á Esters Á Ionic liquid Á
Amino acid Á Room temperature
Introduction
Esterification is among the oldest and vital transformation
in organic chemistry [1] and numerous methods have been
advanced for this, assuring that most esters can be prepared
[2]. Nonetheless, a simpler, general method would facili-
tate future synthetic studies. We sought a readily available
esterification reagent that could convert carboxylic acids to
their alkyl esters. However, Li et al. [3] described the
Amino acids (glycine) metal compound is a kind of
catalyst that has wide applications in both laboratory and
industry [8]. However, recovery and leaching can occur in
the extractive workup, leading to a loss of the catalyst in
the reaction mixture on the one hand and requests addi-
tional effort to purify the extracted product. To overcome
such problems, novel complex was developed [9] by the
covalent linking of organocatalytic unit with an ionic liquid
moiety (often chloroglycine). This imparts a low solubility
of catalyst in the solvents used for the extraction of the
product on the one hand and high solubility in the reaction
medium on the other hand [10–14]. This strategy was also
applied to the esterification reaction providing high yield
and good recyclability of the organocatalyst.
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-012-0116-1) contains supplementary
material, which is available to authorized users.
P. Karthikeyan Á P. R. Bhagat (&) Á S. S. Kumar Á
P. N. Muskawar Á S. A. Aswar
Organic Chemistry Division, School of Advanced Sciences,
VIT University, Vellore 632 014, India
e-mail: drprbhagat111@gmail.com
Recently, iron complex has been used for several
organic transformations such as the epoxidation of
123

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J IRAN CHEM SOC (2012) 9:983–990
Experimental
Apparatus and analysis
All solvents and chemicals were commercially available
and used without further purification unless otherwise
stated. [Gmim]Cl–Fe(III) complex was characterized by
powder X-ray diffraction (P-XRD) diffractometer, a Bru-
ker D8 (advance model); Germany and lynx eye detector
operating with nickel filtered Cu-K radiation. The 1H-NMR
spectra was recorded on a Bruker 500 MHz using CDCl3/
DMSO-d6 as the solvent and mass spectra were recorded
on JEOL GC MATE II HRMS (EI) spectrometer. FT-IR
was recorded on AVATRA 330 spectrometer with DTGS
detector. Column chromatography was performed on silica
gel (200–300 mesh). Analytical thin-layer chromatography
(TLC) was carried out on precoated silica gel GF-254
plates. AFM and SEM were analyzed by Nano Surf Easy
Scan-2 Switzerland and Carl Zeiss EVO MA 15 (model),
respectively.
Fig. 1 1-Glycyl-3-methyl imidazolium chloride-iron (III) complex
[[Gmim]Cl–Fe(III)]
[Gmim]Cl-Fe (III)
R-COOR'
R'-OH
R-COOH
+
25°C
R= Aryl, alkyl
Preparation of [Gmim]Cl–Fe(III) complex
Scheme 1 Synthesis of various esters using [Gmim]Cl–Fe(III)
complex as a catalyst
The catalyst [Gmim]Cl–Fe(III) was synthesized according
to the literature [28].
styrene [15], oxidation of alcohol [16, 17], asymmetric
synthesis [18–20], amination [21] and also for the
Michael addition [22, 23] reactions. Modifying the cat-
alyst by ionic compounds is a dynamic field [24–27].
Most of the earlier papers aimed at making reusable
catalyst by ionic compound modification. The properties
of the catalysts modified by ionic compound can be
tuned by the variation of cations and anions. Hence, we
believe that these catalysts modified by ionic compounds
should be potentially excellent catalysts with high reac-
tivity. Herewith, we have reported the design of
[[Gmim]Cl–Fe(III)] complex (Fig. 1) for the cost-effec-
tive and eco-friendly synthesis of ester under solvent free
condition as shown in Scheme 1.
General procedure
A mixture of benzoic acid (1.2 mmol), benzyl alcohol
(1 mmol) and [Gmim]Cl–Fe(III) complex (0.01 mmol)
was added to a 50 mL round-bottomed flask and stirred at
ambient temperature for a period as indicated in Table 5.
The product was extracted with diethyl ether (3 9 5 mL)
and dried over MgSO4 and evaporated under reduced
pressure. The crude product was purified by column
chromatography over silica gel using n-hexane/ethyl acetate
(4:1) as eluent to give the desired product.
Results and discussion
Interestingly, many works have been performed on the
esterification reaction in the presence of iron and other
co-catalysts with the range of organic solvent [28–30].
However, to the best of our knowledge, no reports are
available on the esterification reaction catalyzed by iron
functionalised ionic liquid in absence of organic solvent.
From the above literature, the development of benign, cost-
effective and eco-friendly for the catalytic esterification
reaction, based on iron functionalized ionic liquid, is a major
challenge. Typically, the [Gmim]Cl–Fe(III) was prepared by
simple coupling between the 3-(amino(carboxy)methyl)-1-
methyl-1H-imidazol-3-ium chloride and ferric chloride
[31–33].
The iron complex catalyzed esterification reaction was
carried out using benzoic acid and benzyl alcohol as a
model reaction to investigate different parameters, such as
the effects of solvent, diverse bases, catalysts and con-
centration of the catalyst. Initially, the influence of differ-
ent bases to the model reaction was studied; these results
are summarized in Table 1. It was observed that the base
free condition was the most effective and thus chosen as
the one preferred for the reaction, although organic and
inorganic bases can be used. This may be due to the
blocking of free coordination sites on the iron center. The
effect of the base in the esterification reaction is still
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J IRAN CHEM SOC (2012) 9:983–990
985
solvents tend to give the best results for the ester reaction,
while Prasad [6] obtained high-activity catalysts in Lewis
acidic ionic liquid. We employed several solvents in the
model reaction. Among the previous reports, the reaction
under solvent free condition was the most productive, as
compared with the polar and non-polar solvents. The cat-
alyst easily coordinated with organic co-solvents. It has
also been reported that H2O molecule sometimes is
required to activate the Fe(III) catalyst. In our case, car-
rying out the reaction in H2O (5 mL) 90 °C gave a negative
effect on the product yield in comparison with solvent free
condition. This lower yield could be due to the complex
delocalization under aqueous condition.
Table 1 Effect of the base on esterification reaction
Entry
Base
Time (h)
Yielda (%)
1
K2CO3
24
24
24
24
24
24
24
18
12
6
Trace
50
2
KOH
3
NaOH
47
4
Py
51
5
Imidazole
68
6
Et3N
70
7
–
–
–
–
–
–
94
8
95
9
95
10
11
12
96
Next, to optimize the reaction conditions for a particular
catalyst, the condensation reaction was executed using
different catalysts and the results are given in Table 3.
When the reaction was carried out using various catalysts
such as L-glycine, Chloroglycine, 1-carboxy ethyl-3-methyl
imidazolium bromide [Cemim]Br, 1-aminoethyl-3-methyl
imidazolium bromide [Aemim] Br, FeCl3/[Cemim] Br,
FeCl3/[Aemim] Br and FeCl3/[Gmim]Cl in the absence of
solvent, it gave trace to 75 % of described product. How-
ever, when the same reaction was conducted with
[Gmim]Cl–Fe(III) as a catalyst, it gave remarkable yield of
product in short duration. Almost similar yield was
obtained when increasing the duration.
3
90
1
88
Reaction condition: benzoic acid (1.2 mmol), benzyl alcohol
(1 mmol) and [Gmim]Cl–Fe(III) complex (0.01 mmol) at 25 °C for
6 h
a
Isolated yield by flash chromatography
imperfectly understood and many recent works are based
on this subject. Recently, Nowrouzi have studied the role
of the base in the esterification reaction using chloro
diphenyl phosphine/I2 and imidazole as catalytic precursors
and concluded that the oxidative addition step (when per-
formed from aromatic acid/alcohol) becomes slower and
the carbanion step becomes faster in the absence of the
base [5].
The catalytic reaction which can be carried out with a
small amount of expensive complexes is the most useful
feature of synthetic reaction involving iron complex.
According to the literature, Jai Prakasha and co-workers
obtained good yield in the direct condensation of carbox-
ylic acids with alcohols using 250 mg of Fe3?-montmo-
rillonite in the presence of toluene [28]. Using FeCl3/Al2O3
in the range between 1 and 1.2 mmol, Niasari et al. [29]
observed acceptable rate in the ester reaction of alcohols.
Among the previous reports, increasing the quantity of the
Furthermore, we have screened several solvents for the
reaction between benzoic acid and benzyl alcohol
(Table 2). According to the publications from Yong-Jin
Yoon and co-workers [7] and Nowrouzi [5], polar aprotic
Table 2 Effect of the solvent on esterification reaction
Entry
Solvent
Temp (°C)
Time (h)
Yielda (%)
1
DCM
35
50
50
50
65
60
130
90
25
20
35
90
24
24
24
24
24
24
24
24
6
38
43
40
50
53
50
60
63
96
95
93
40
2
CHCl3
Table 3 Effect of the various catalysts on esterification reaction
3
THF
Entry
Catalyst
Time (h)
Yielda
4
Methanol
Ethanol
1
2
3
4
5
6
7
8
9
L-Glycine
24
24
24
24
24
24
24
6
Trace
35
5
Chloroglycine [Cl-gly]
[Cemim] Br
6
CH3CN
42
7
DMF
[Aemim] Br
44
8
PhMe
FeCl3/[Cemim] Br
FeCl3/[Aemim] Br
FeCl3/[Gmim]Cl
[Gmim]Cl-Fe(III)
[Gmim]Cl-Fe(III)
60
9
Solvent free
Solvent free
Solvent free
Water (5 mL)
71
10
11
12
6
75
6
96
24
7
97
Reaction condition: benzoic acid (1.2 mmol), benzyl alcohol
(1 mmol) and [Gmim]Cl–Fe(III) complex (0.01 mmol) at 25 °C for
6 h
Reaction condition: benzoic acid (1.2 mmol), benzyl alcohol
(1 mmol) and different catalyst (0.01 mmol) at 25 °C for 6 h
a
a
Isolated yield by flash chromatography
Isolated yield by flash chromatography
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J IRAN CHEM SOC (2012) 9:983–990
[Gmim]Cl–Fe(III) do not undergo any chemical and
structural changes, thus proving its surface catalytic
activity towards the condensation reaction between benzoic
acid and benzyl alcohol. On the other hand, the presence of
peaks due to metallic iron is noted in the powder XRD
pattern of the complex in the case of ‘Fe(III)’ (Fig. 2a, b).
Moreover, surface and size of that reused catalyst was
captured by AFM. The surface of recycled iron complex is
shown in the rough topography evidence and reduced size
of the particle of 657 nm (Fig. 3a, b). The precise mech-
anism of the catalytic reaction needs to be elucidated, but it
is noticeable that the mechanism is strongly modified
depending on the substituted aromatic acid/alcohol-
employed, obtaining ester as the main product (Scheme 2).
The spectroscopic data were consistent with those
reported in the literature [5].
Table 4 Effect of the catalyst loading on esterification reaction
Entry
[Gmim]Cl–Fe(III) mmol
Time (h)
Yielda
1
2
3
4
5
6
7
8
–
24
6
Trace
96
0.1
0.075
0.050
0.025
0.01
0.0075
0.005
6
96
6
96
6
96
6
96
6
94
6
93
Reaction condition: benzoic acid (1.2 mmol), benzyl alcohol
(1 mmol) at 25 °C for 6 h
a
Isolated yield by flash chromatography
catalyst can improve the reaction yield and shorten the
reaction time (Table 4). First, ester reaction was carried out
in the absence of catalyst at ambient temperature; it was
found that no product formed even after 24 h. Even though
the amount of catalyst decreased from 0.1 to 0.025 mmol,
there was no change in the yields, whereas using
0.01 mmol [Gmim]Cl–Fe(III), in the model reaction gen-
erated 96 % product. Almost dissimilar yield was obtained
when decreasing the catalyst amount from 0.01 to
0.005 mmol. Therefore, the esterification reaction was
carried out at the molar ratio of benzoic acid, benzyl
alcohol and [Gmim]Cl–Fe(III), 1.2:1:0.01 mmol under
solvent free condition at ambient temperature.
Benzyl-4-methylbenzoate
1H-NMR (500 MHz, CDCl3): d 7.95 (d, 2H, J 8.0 Hz),
7.45–7.29 (m, 5H, m), 7.21 (d, 2H, J 7.8 Hz), 5.35 (s, 2H),
2.38 (s, 3H); 13C-NMR: 163.0, 143.7, 136.2, 133.3, 133.0,
129.8, 129.1, 128.6, 128.2, 128.1, 127.6, 127.4, 127.0, 66.5
and 21.7.
4-Chlorobenzyl benzoate
1H-NMR (500 MHz, CDCl3): d 7.94 (d, 2H, J 8.4 Hz),
7.43–7.40 (m, 1H), 7.36–7.23 (m, 6H), 5.23 (s, 2H,); 13C-
NMR: 163.3, 134.6, 133.1, 132.2, 128.9, 127.7, 126.6,
128.8, 128.4 and 65.9.
To test the substrate generality of [Gmim]Cl–Fe(III)
complex catalyzed direct ester reaction, the condensation
of various aromatic/aliphatic acids and alcohol was studied
under the optimized conditions. The results are summa-
rized in Table 5. It can be noticed that a wide range of
aromatic acid can contribute efficiently in the ester reac-
tions. However, the reaction condition was compatible with
various functional groups, ranging from the electron-
withdrawing nitro groups to the halide. Indeed, it was
observed that the oxidation prone groups (–OMe) were
tolerated in this reaction. In general, the yield was high,
regardless of the structural variations.
Benzyl-4-nitrobenzoate
1H-NMR (500 MHz, CDCl3): d 8.30–8.25 (m, 4H),
7.45–7.37 (m, 5H), 5.44 (s, 2H); 13C-NMR: 164.5, 150.6,
135.5, 135.3, 130.8, 130.0, 128.7, 128.6, 128.4, 123.5 and
67.6.
4-Methoxybenzyl benzoate
Subsequently, the recyclability of the used complex was
confirmed for the synthesis of ester. The catalytic system
could be reused directly for the next cycle, after full
extraction of the product three times with 5 mL diethyl
ether per extraction and drying in vacuo. The results shown
in Table 6 demonstrate that this catalytic system was
readily recyclable for six runs without any significant loss
of catalytic activity.
1H-NMR (500 MHz, CDCl3): d 8.03 (d, 2H, J 8.1 Hz),
7.50–7.48 (m, 1H), 7.40–7.35 (m, 4H), 6.88 (d, 2H,
J 6.5 Hz), 5.28 (s, 2H), 3.78 (s, 3H); 13C-NMR: 166.5,
159.7, 147.6, 133.4, 130.5, 130.1, 129.7, 128.7, 114.0, 66.5
and 55.3
4-Methoxyphenyl benzoate
Furthermore, The [Gmim]Cl–Fe(III) catalyst was col-
lected after the completion of the reaction and analyzed by
powder X-ray diffraction method and the diffraction pat-
terns are given in Fig. 2. The analysis specifies that the
1H-NMR (500 MHz, CDCl3): d 8.09 (dd, 2H, J 8.3,
1.2 Hz), 7.50–7.48 (m, 1H), 7.39 (t, 2H, J 8.0 Hz), 7.04
(dd, 2H, J 8.7 Hz), 6.84 (dd, 2H, J 8.9, 1.7 Hz), 3.73 (s,
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J IRAN CHEM SOC (2012) 9:983–990
987
Table 5 The synthesis of substituted esters at ambient temperature
Entry
1
Acid
Alcohol
Timea (h)
6
Yieldb (%)
96
2
6.5
86
3
4
6
5
90
92
5
6
5
91
87
4.5
7
8
5
7
91
90
9
6
6
5
94
92
85
10
11
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J IRAN CHEM SOC (2012) 9:983–990
Table 5 continued
Entry
Acid
Alcohol
Timea (h)
6.5
Yieldb (%)
85
12
13
5
5
91
88
14
Reaction condition: substituted acid (1.2 mmol), substituted alcohol (1 mmol) and [Gmim]Cl–Fe(III) complex (0.01 mmol) at 25 °C
a
Time required
b
Isolated yield by flash chromatography
1
All the compounds were characterized by spectroscopy method H-NMR, Mass and IR from authentic sample [5]
c
Table 6 Successive recycling of [Gmim]Cl–Fe(III) complex for the
model reaction
Cycles
1
2
3
4
5
6
Yields (%)a
94
94
92
92
91
90
Reaction condition: benzoic acid (1.2 mmol), benzyl alcohol
(1 mmol) and [Gmim]Cl–Fe(III) complex (0.01 mmol) at 25 °C for
6 h
a
Isolated yield by flash chromatography
b
a
0
30
60
90
2θ
Fig. 3 AFM image of 3-(amino (carboxy) methyl)-1-methyl-1H-
imidazol-3-ium chloride supported iron complex (zero cycle) (a) and
after 6th run (b)
Fig. 2 Powder X-ray diffraction patterns of the [Gmim]Cl–
Fe(III)complex a before reaction b after reaction (6th run)
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J IRAN CHEM SOC (2012) 9:983–990
989
Conclusions
N
In summary, we have developed an expedient, elegant and
clean protocol for the synthesis of esters using 1-glycyl-3-
methyl imidazolium chloride-iron (III) complex as a cata-
lyst under solvent free condition. The procedure is easy and
does not require special precautions. All the reactions were
conducted in the air without the use of an organic co-
solvent. The remarkable features of this procedure are atom
efficiency, high conversions, operational simplicity and
ready availability of reagents at low cost. The reaction was
tolerant of varying substitution patterns on the benzoic
acid/alcohol component. It is noteworthy to mention that
the complex could easily be recycled and reused without
the loss of activity.
N
Cl
O
H2N
O
O
O
Fe
NH2
Cl
N
N
O
N
Cl
H2
N
N
O
O
R'
R
O
R-COOH
Acknowledgments We greatfully acknowledge the management of
VIT University for providing required facilities and SAIF (IITM) for
providing the spectral data.
[Gmim]Cl-Fe (III)
O
R
O
R
R' Heterogeous catalyst
O
O
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