Selective esterification of aliphatic carboxylic acids in the presence of aromatic carboxylic acids over monoammonium salt of 12-tungstophosphoric acid

Article abstract of DOI:10.1080/00397910500328266

Monoammonium salt of 12-tungstophosphoric acid [(NH₄)H ₂PW₁₂O₄₀] was found to be a practical and useful heterogeneous catalyst for an efficient and selective esterification of aliphatic carboxylic acids with alcohols in the presence of aromatic carboxylic acids. The heteropoly acid-based heterogeneous catalyst has the advantages of a simple workup procedure, water insolubility, and good activity. Copyright Taylor & Francis LLC.

Full text of DOI:10.1080/00397910500328266

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Selective Esterification of Aliphatic
Carboxylic Acids in the Presence of Aromatic
Carboxylic Acids Over Monoammonium Salt of
1
2‐Tungstophosphoric Acid
a
a
a
B. Y. Giri , B. L. A. Prabhavathi Devi , K. N. Gangadhar , K. Narasimha
b
b
b
a
Rao , N. Lingaiah , P. S. Sai Prasad & R. B. N. Prasad
a
Lipid Science and Technology Division, Indian Institute of Chemical
Technology (CSIR), Hyderabad, India
b
Inorganic and Physical Chemistry Division, Indian Institute of Chemical
Technology (CSIR), Hyderabad, India
Published online: 21 Aug 2006.
To cite this article: B. Y. Giri , B. L. A. Prabhavathi Devi , K. N. Gangadhar , K. Narasimha Rao , N. Lingaiah ,
P. S. Sai Prasad & R. B. N. Prasad (2006) Selective Esterification of Aliphatic Carboxylic Acids in the
Presence of Aromatic Carboxylic Acids Over Monoammonium Salt of 12‐Tungstophosphoric Acid, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:1,
7-11, DOI: 10.1080/00397910500328266
To link to this article: http://dx.doi.org/10.1080/00397910500328266
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Synthetic Communications , 36: 7–11, 2006
Copyright # Taylor & Francis LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500328266
Selective Esterification of Aliphatic
Carboxylic Acids in the Presence
of Aromatic Carboxylic Acids
Over Monoammonium Salt
of 12-Tungstophosphoric Acid
B. Y. Giri, B. L. A. Prabhavathi Devi, and K. N. Gangadhar
Lipid Science and Technology Division, Indian Institute of Chemical
Technology (CSIR), Hyderabad, India
K. Narasimha Rao, N. Lingaiah, and P. S. Sai Prasad
Inorganic and Physical Chemistry Division, Indian Institute of Chemical
Technology (CSIR), Hyderabad, India
R. B. N. Prasad
Lipid Science and Technology Division, Indian Institute of Chemical
Technology (CSIR), Hyderabad, India
Abstract: Monoammonium salt of 12-tungstophosphoric acid [(NH )H PW O ] was
12 40
4
2
found to be a practical and useful heterogeneous catalyst for an efficient and selective
esterification of aliphatic carboxylic acids with alcohols in the presence of aro-
matic carboxylic acids. The heteropoly acid–based heterogeneous catalyst has the
advantages of a simple workup procedure, water insolubility, and good activity.
Keywords: Alcohol, ammonium salt of 12-tungstophosphoric acid, carboxylic acid,
esterification, heterogeneous catalyst
Received in India July 7, 2005
IICT Communication No. 040417.
Address correspondence to R. B. N. Prasad, Lipid Science and Technology
Division, Indian Institute of Chemical Technology (CSIR), Uppal Road, Hyderabad
500 007, India. Fax: 91-40-27193370; E-mail: rbnprasad@iict.res.in
7

8
B. Y. Giri et al.
INTRODUCTION
The selective esterification of aliphatic carboxylic acid, either alone or in the
presence of aromatic carboxylic acid, is a very useful synthetic reaction.
[
1]
Different methods are reported for the selective esterification of aliphatic
carboxylic acids; however, most of these methods are associated with
several drawbacks such as complex, expensive, and hazardous reagents.
Because there is high demand for environmentally clean processes, the
chemical industry is forced to look for alternative materials that are safer.
In this context, there are a few reports on the usage of nonhazardous
[
2]
[3]
3þ
.
catalytic systems such as NiCl 6H O, NaHSO4 SiO2 and Fe -K10
.
6
2
[
4]
montmorillonite clay, which offer selective esterification of aliphatic car-
boxylic acids.
The acidity of heteropoly acid varies with its structure; however, the acid
strength can be tuned to suit a particular demand by introducing the hetero-
atom. Generally heteropoly acids are very soluble in polar solvents;
however, transformation into their insoluble salts can be achieved, which
can then be used as heterogeneous catalysts. Various 12-tungtophosphoric
[
5]
acids were utilized for the acetylation, esterification, and etherification
reactions without much selectivity. In an attempt to prepare heterogeneous
catalysts, fully and partially proton-exchanged ammonium salt of 12-tungsto-
phosphoric acid catalysts [(NH ) PW O and (NH )H PW O ] were
4
3
12 40
4
2
12 40
[6]
prepared and studied for their esterification activity.
RESULTS AND DISCUSSION
The present study reports the first application of a heteropoly acid catalyst
i.e., monoammonium salt of 12-tungstophosphoric acid) as an efficient
catalyst for the selective esterification of aliphatic carboxylic acids
Scheme 1).
Esterification of hexanoic, heptanoic, nonoic, and palmitic acids with
(
(
methanol, ethanol, and isopropanol gave the corresponding esters in good
yields (92–97%) in a 6-h period. Prolonged reaction time (12 h) could
improve the yields almost quantitatively. The unsaturated (entries 7 and 8,
Table 1) and other functional groups such as Cl and NO (entries 11 and
2
12, Table 1) were tolerated during the esterification. Similarly, esterification
of phenyl acetic acid with methanol, ethanol, and benzyl alcohol afforded cor-
responding esters, whereas no reaction was observed with benzoic acid and
Scheme 1.

a
Table 1. Esterification of aliphatic and aromatic carboxylic acids with alcohols
b
Yield (%)
Entry
Carboxylic acid
Product
Time (h)
Aliphatic carboxylic ester
Aromatic carboxylic esters
c
1
2
3
4
5
6
7
8
9
CH
CH
3
-(CH
-(CH
2
)
)
5
-COOH
-COOH
CH
CH
3
-(CH
-(CH
2
)
)
5
-COOCH
-COOC
3
6
6
96 (99)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0
3
2
5
3
2
5
2
H
5
95 (98)
97 (99)
94 (98)
96 (100)
92 (98)
96 (100)
94 (98)
95 (99)
92 (97)
95 (98)
94 (98)
92 (97)
93 (98)
—
CH -(CH ) -COOH
CH -(CH ) -COOCH
6
3
3
3
2 7
3
3
3
2 7
3
CH
CH
-(CH
-(CH
2
)
)
7
-COOH
14-COOH
CH
CH
-(CH
-(CH
2
)
)
7
-COOC
2
H
5
3
6
2
2
14-COOCH
6
CH -(CH ) -COOH
3 2 14
CH -(CH ) -COOC H
2 5
6
3
2 14
CH
CH
2
55 CH-(CH
55 CH-(CH
-CH
2
)
)
8
-COOH
-COOH
CH
CH
2
55 CH-(CH
55 CH-(CH
-CH
2
)
)
8
-COOCH
-COOC
3
6
2
2
8
2
2
8
2
H
5
6
C
6
H
5
2
-COOH
6
C H
5
2
-COOCH
3
6
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
C H -CH -COOH
6
C H -CH -COOC H
6
6
5
2
5
2
2
5
4-(Cl)-C
4-(Cl)-C
6
6
H
4
-CH
-CH
2
-COOH
-COOH
4-(Cl)-C
4-(Cl)-C
6
H
4
-CH
-CH
2
-COOCH
-COOC
3
6
H
4
2
6
H
4
2
2
H
5
6
CH -(CH ) -COOH
2 14
CH -(CH ) -COOCH -C H
6
6
3
3
2 14
2
5
C
C
6
H
5
-CH
-COOH
2
-COOH
C
C
6
H
5
-CH
2
-COOCH
2
-C
6
H
5
6
6
H
5
6
H
5
-COOCH
3
12
12
12
12
C H -COOH
6
C H -COOC H
6 2 5
—
0
5
5
4-(NO
4-(NO
2
)-C
)-C
6
H
H
4
-COOH
-COOH
4-(NO
4-(NO
2
)-C
)-C
6
H
4
-COOCH
-COOC
3
—
—
0
2
6
4
2
6
H
4
2
H
5
0
a
Reaction conditions: carboxylic acid (5 g), alcohol (10 mL), catalyst (0.25 g, 5 wt.% of the acid), reflux temperature. All the products were charac-
1
terized by H NMR and GC.
b
Isolated yield.
Figures in parenthesis are the yields after 12 h.
c

1
0
B. Y. Giri et al.
4-nitro benzoic acid (entries 15 and 18, Table 1). The unique selectivity of the
present reaction was well demonstrated by a competition experiment (Table 2)
with an equimolar mixture of aliphatic carboxylic acid and benzoic acid with
methanol, ethanol, and isopropanol, which afforded only the aliphatic car-
boxylic esters in 98–99% yield.
In conclusion, aliphatic carboxylic esters can be prepared by a facile and
selective esterification using an efficient and water-insoluble monoammonium
salt of 12-tungstophosphoric acid catalyst.
EXPERIMENTAL
General Procedure for the Preparation of the Catalyst
[6]
Monoammonium salt of 12-tungstophosphoric acid was prepared by simple
ion exchange of 12-tungstophosphoric acid with a required amount of
ammonium carbonate in aqueous medium. Ammonium carbonate solution
(
0.167 g, 0.0017 mol, dissolved in 10 mL of distilled water) was added
dropwise to an aqueous solution of 12-tungstophosphoric acid (10 g,
.0035 mol, dissolved in 50 mL of distilled water) at 808C under stirring.
0
The reaction mixture was stirred at 808C for 3 h, evaporated to dryness, and
kept overnight at 1208C. The catalyst was calcined in air at 3508C for 4 h.
General Procedure for Esterification
A mixture of carboxylic acid (5 g), alcohol (10 mL), and the monoammonium
salt of 12-tungstophosphoric acid catalyst (5 wt.% of the acid, 250 mg) were
Table 2. Esterification of aliphatic carboxylic acids in presence of aromatic car-
boxylic acids
a
Yield (%)
Aliphatic
carboxylic
ester
Aromatic
carboxylic
esters
Entry
1
Carboxylic acid
Alcohol
C H -CH -COOH and
2
CH -OH
99
98
98
0
0
0
6
5
3
3
3
C
6
H
5
-COOH
2
3
4-(Cl)-C
6
H
4
-CH
and C H -COOH
2
-COOH
CH
CH
-OH
-CH
6
5
C
6
H
5
-CH
2
-COOH and
2
-OH
4
-(NO
2 6 4
)-C H -COOH
a
Isolated yield after 12 h.

Selective Esterification of Aliphatic Carboxylic Acids
11
refluxed, filtered, and concentrated. The residue was purified over silica gel to
get pure ester. All the products were known compounds and were easily
identified by comparison of their spectral data with those of authentic samples.
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