Silica Chloride: A Versatile Heterogeneous Catalyst for Esterification and Transesterification

Article abstract of DOI:10.1055/s-2003-42406

Silica chloride has been found to be an efficient catalyst for esterification of carboxylic acids (aliphatic, aromatic and conjugated) with alcohols (primary, secondary and tertiary) as well as for transesterification of esters (by both alcoholysis and acidolysis).

Full text of DOI:10.1055/s-2003-42406

PAPER
2479
Silica Chloride: A Versatile Heterogeneous Catalyst for Esterification and
Transesterification1
Silica Chloride as
.Catalyst for
Esterificationand
T
ransesterific
N
ation . S. Srinivas, I. Mahender, Biswanath Das*
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Fax +91(40)27160512; E-mail: biswanathdas@yahoo.com
Received 10 July 2003; revised 8 August 2003
Abstract: Silica chloride has been found to be an efficient catalyst
for esterification of carboxylic acids (aliphatic, aromatic and conju-
gated) with alcohols (primary, secondary and tertiary) as well as for
transesterification of esters (by both alcoholysis and acidolysis).
Key words: esterification, transesterfication, silica chloride, alco-
holysis, acidolysis
Scheme 1
Esterification of carboxylic acids with various alcohols is
one of the most important and widely applicable transfor-
mations in organic synthesis.2 A large number of methods
for esterification catalyzed by various protic and Lewis
acids including solid acids, ion exchange resins, zeolite
and clay are now well-known.2,3 However, some of the re-
ported methods are associated with certain drawbacks
such as harsh reaction conditions, tedious experimental
procedures, long reaction times, poor yields, complex side
reactions and narrow range of applicability. Moreover, the
number of suitable methods for one-step esterification of
carboxylic acids with tertiary alcohols are also limited.3c
The reagents (such as phosgene, isobutene etc.) which are
generally utilized for this purpose are incompatable with
harsh reaction conditions and tedious experimental proce-
dures.
Scheme 2
Various carboxylic acids were treated with different alco-
hols in the presence of silica chloride to produce the cor-
responding esters (Table 1). Both the aliphatic and
aromatic acids can be applied for esterification and all the
three types of alcohols (primary, secondary and tertiary)
can be used. Different other catalysts reported2,3 earlier
were found to be active for esterification with primary and
Transesterification of an ester with an alcohol (alcoholy- secondary alcohols but it was difficult to prepare the es-
sis) or with an acid (acidolysis) can also be applied for the ters with tertiary alcohols. Even, some of the catalysts
preparation of another ester.4a A variety of protic and which have been reported to work for esterification with
Lewis acids, organic and inorganic bases, enzymes, and tertiary alcohols, have been studied with a very limited
antibodies are known3f,4 to catalyze this reaction. Recently number of reactions.3e,5b Silica chloride has presently been
some of the catalysts, like diphenylammonium triflate, io- found to be an efficient catalyst for esterification of ali-
dine etc., have been employed for both esterification and phatic, aromatic and conjugated acids with tertiary alco-
transesterification.5 However, the number of such cata- hols (Table 1).
lysts are limited. Additionally, the transesterification of an
Transesterification of esters has also effectively been car-
ester applying both alcoholysis and acidolysis by utilizing
ried out using silica chloride as catalyst. Aliphatic as well
the same catalyst is also not frequently observed. Here we
as aromatic esters were equally applied (Table 2). Both
report a simple and general method for esterification and
the alcoholysis and acidolysis of esters could be carried
transesterification using silica chloride as a heterogeneous
out under mild reaction conditions. Thus the acid part and
catalyst.
also the alcohol part of an ester can easily be exchanged
During our recent work on the development of novel syn- with other acids or alcohols to generate new esters.
thetic methodologies we have observed that silica chlo-
Trimethylsilyl chloride was also previously applied8 for
ride is an efficient catalyst for esterification of carboxylic
esterification of carboxylic acids but the reaction was re-
acids and transesterification of esters (Schemes 1 and 2)
ported with only primary alcohols. The reaction times
were generally very high and the reagent was used in ex-
cess. Transesterification was also not studied with this re-
agent.
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DOI: 10.1055/s-2003-42406; Art ID: P06203SS
© Georg Thieme Verlag Stuttgart · New York

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K. V. N. S. Srinivas et al.
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Table 1 Esterification of Carboxylic Acids with Alcohols
Entry
Acid
Alcohol
Time (h)
Isolated
Ref.
Yielda (%)
6
6
6
7
6
6
6
6
6
6
6
6
6
6
6
7
5b
6
6
1
2
PhCH2CO2H
MeOH
EtOH
5
5
6
8
5
6
5
5
5
6
7
5
7
7
6
7
7
6
7
10
9
8
9
96
94
95
86
94
96
95
93
97
95
93
94
93
94
93
92
93
92
93
79
82
85
83
PhCH2CO2H
3
4-OHC6H4CH2CO2H
PhCH2CO2H
EtOH
4
PhCH2OH
MeOH
EtOH
5
CH3(CH2)16CO2H
CH3(CH2)16CO2H
PhCO2H
6
7
MeOH
MeOH
MeOH
EtOH
8
4-OHC6H4CO2H
3-ClC6H4CO2H
3-ClC6H4CO2H
2-CO2HC6H4CH2CO2H
PhCH=CHCO2H
PhCH=CHCO2H
CH3(CH2)7CH=CH(CH2)7CO2H
C6H4CH2CO2H
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
MeOH
MeOH
BuOH
MeOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
t-BuOH
t-BuOH
t-BuOH
t-BuOH
4-OHC6H4CH2CO2H
CH3(CH2)16CO2H
4-OHC6H4CO2H
PhCH=CHCO2H
PhCH2CO2H
-
6
4-OHC6H4CO2H
3-ClC6H4CO2H
PhCH=CHCO2H
-
6
a The structures of all the esters were settled from their spectral (1H NMR and MS) data.
The present catalyst, silica chloride can easily be In summary, silica chloride can be applied as a versatile
prepared9 from silica gel (finer than 200 mesh) and thio- catalyst for esterification of carboxylic acids (aliphatic,
nyl chloride, and should be properly activated. Both the aromatic and conjugated) with primary, secondary and
ingredients are inexpensive and readily available. The cat- tertiary alcohols as well as for transesterfication of esters
alyst is heterogeneous and can easily be handled and re- by both alcoholysis and acidolysis. The catalyst is hetero-
moved from the reaction mixture by simple filtration. The geneous, inexpensive, non-hazardous and convenient to
recovered catalyst, however, when applied again under handle. We feel the present procedure of esterification and
the present experimental conditions has been found to de- transesterification can be applied for both academic and
crease the yields of esters (isolated yields: 26–38% only). industrial purposes.
With different acids, alcohols and esters silica chloride
was verified to be effective for both esterification and
transesterification. Only a few catalysts like diphenylam-
monium triflate,5a iodine,5b silica supported sodium hy-
drogen sulfate7 and distannoxanes10 are known to possess
the capacity to catalyze both these reactions.
The spectra were run on the following instruments: 1H NMR: Vari-
an Gemini 200 MHz and EIMS: VG Micromass 7070 H (70 eV).
The carboxylic acids and alcohols were obtained commercially.
Synthesis 2003, No. 16, 2479–2482 © Thieme Stuttgart · New York

PAPER
Silica Chloride as Catalyst for Esterification and Transesterification
2481
Table 2 Transesterification of Carboxylic Esters with Alcohols or Acids
Entry
Ester
Alcohol/Acid
Time (h)
Isolated
Ref.
Yielda (%)
6
6
7
6
6
5b
6
6
6
6
6
6
6
6
6
6
6
6
6
6
1
2
PhCH2CO2Me
PhCH2CO2Me
4-OHC6H4CH2CO2Et
CH3(CH2)16CO2Me
CH3(CH2)16CO2Pr
CH3(CH2)16CO2Me
PhCO2Me
EtOH
8
9
91
90
83
89
86
82
76
82
85
86
88
86
85
94
92
93
79
83
82
80
i-PrOH
3
i-PrOH
12
11
10
9
4
BuOH
5
MeOH
6
i-PrOH
7
BuOH
10
12
9
8
4-OHC6H4CO2Me
3-ClC6H4CO2Me
PhCH=CHCO2Me
PhCH=CHCO2Et
PhCH=CHCO2Pr
CH3(CH2)7CH=CH(CH2)7CO2Me
EtOAc
i-PrOH
9
EtOH
10
11
12
13
14
15
16
17
18
19
20
BuOH
10
12
11
9
BuOH
MeOH
EtOH
PhCH2CO2H
4-OHC6H4CH2CO2H
CH3(CH2)16CO2H
4-OHC6H4CO2H
3-ClC6H4CO2H
CH3(CH2)7CH=CH(CH2)7CO2H
PhCH=CHCO2H
7
EtOAc
7
EtOAc
6
EtOAc
11
10
9
EtOAc
EtOAc
EtOAc
11
a The structures of all the products were settled from their spectral (1H NMR and MS) data.
Esterification of Acids; Ethyl 2-Phenylacetate; Typical Proce-
dure
refluxed for 12 h and filtered. The filtrate was concentrated and the
residue was purified by column chromatography over silica gel us-
ing hexane–EtOAc (8:2) as eluent to give ethyl 4-hydroxybenzoate
(131 mg, 79%).
The spectral (1H NMR and MS) and analytical data of the unknown
esters are given below.
To a solution of phenyl acetic acid (136 mg, 1 mmol) in EtOH (10
mL) was added silica chloride (150 mg). The mixture was refluxed
and the progress of the reaction was monitored by TLC. After 5 h,
the mixture was filtered and the concentrated filtrate was subjected
to column chromatography over silica gel using hexane–EtOAc
(9:1) as eluent to yield ethyl 2-phenylacetate (154 mg, 94%).
tert-Butyl 2-Phenylacetate (entry 20, Table 1)
1H NMR (CDCl3): = 7.36–7.17 (m, 5 H), 3.43 (s, 2 H), 1.42 (s, 9
H).
Transesterification of Esters (Alcoholysis); Isopropyl 2-Phenyl-
acetate; Typical Procedure
EI-MS: m/z = 192 (M+), 119, 91.
To a solution of methyl 2-phenylacetate (150 mg, 1 mmol) in i-
PrOH (10 mL) was added silica chloride (150 mg). The mixture was
refluxed for 10 h and filtered. The filtrate was concentrated and the
residue was purified by column chromatography over silica gel us-
ing hexane–EtOAc (8:2) as eluent to obtain pure isopropyl 2-
phenylacetate (178 mg, 90%).
Anal. Calcd for C12H16O2: C, 75.00; H, 8.33. Found: C, 74.96; H,
8.27.
tert-Butyl 3-Chlorobenzoate (entry 22, Table 1)
1H NMR (CDCl3): = 7.94 (t, 1 H, J = 2.4 Hz), 7.83 (dd, 1 H,
J = 8.0, 2.4 Hz), 7.48 (dd, 1 H, J = 8.0, 2.4 Hz), 7.35 (1 H, t, J = 8.0
Hz), 1.58 (s, 9 H).
Transesterification of Esters (Acidolysis); Ethyl 4-Hydroxybenz-
oate; Typical Procedure
4-Hydroxybenzoic acid (138 mg, 1 mmol) was dissolved in EtOAc
(10 mL). Silica chloride (150 mg) was added, and the mixture was
EI-MS: m/z = 212 (M+), 157, 139.
Anal. Calcd for C11H13ClO2: C, 62.26; H, 6.13. Found: C, 62.35; H,
6.19.
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K. V. N. S. Srinivas et al.
PAPER
(4) (a) Finar, I. L. Organic Chemistry: The Fundamental
Acknowledgment
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London, 1973, 253. (b) Fujira, T.; Tanaka, M.; Narimine,
Y.; Marzi, M. H. J. Org. Chem. 1997, 62, 3824. (c) Ranu,
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(d) Ponde, V.; Deshponde, V. H.; Bulbule, V. J.; Sudalai, A.;
Gajare, A. S. J. Org. Chem. 1998, 63, 1058.
The authors thank CSIR, New Delhi and IICT for financial assi-
stance.
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Synthesis 2003, No. 16, 2479–2482 © Thieme Stuttgart · New York