Zirconium based ion exchangers as catalysts in esterification reactions of benzoic acid

Article abstract of DOI:10.14233/ajchem.2015.18822

Zirconium based double salts were used as catalysts in esterification reactions of benzoic acid with some primary and secondary alcohols. Ester products were characterized with ¹H NMR and FT-IR techniques. Product yields from different set of combinations of benzoic acid and alcohols were monitored using gas chromatography. Double salt based ion exchangers selectively catalyzed esterification reactions based on steric considerations. Electronic factor did not seem to play any role in efficiency of the inorganic ion exchangers as heterogeneous catalysts.

Full text of DOI:10.14233/ajchem.2015.18822

Asian Journal of Chemistry; Vol. 27, No. 8 (2015), 3035-3038
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.18822
Zirconium Based Ion Exchangers as Catalysts in Esterification Reactions of Benzoic Acid
1
2
CHARANJIT SINGH , SUSHEEL K. MITTAL1,* and NAVNEET KAUR
1School of Chemistry & Biochemistry, Thapar University, Patiala-147 004, India
2Centre for Nanoscience and Nanotechnology, Panjab University, Chandigarh-160 014, India
*Corresponding author: Fax: +91 175 2364498; E-mail: smittal@thapar.edu
Received: 25 October 2014;
Accepted: 30 January 2015;
Published online: 27 April 2015;
AJC-17187
Zirconium based double salts were used as catalysts in esterification reactions of benzoic acid with some primary and secondary alcohols.
Ester products were characterized with 1H NMR and FT-IR techniques. Product yields from different set of combinations of benzoic acid
and alcohols were monitored using gas chromatography. Double salt based ion exchangers selectively catalyzed esterification reactions
based on steric considerations. Electronic factor did not seem to play any role in efficiency of the inorganic ion exchangers as heterogeneous
catalysts.
Keywords: Heterogeneous catalysis, Zirconium based ion-exchangers, Esterification, Steric orientation, Closed reactor synthesis.
resin catalysts such asAmberlyst-15 to determine the intrinsic
reaction kinetics. Esterification by solid acid catalysts
(Amberlyst-36, Bayer K2441, Amberlyst-15, Dowex 50Wx8,
Indion-130, Deloxane ASP, Filtrol- 24 clay, K-10 montmorri-
lonite clay and sulphated zirconia) gave the desired level of
activity which could be easily removed from the reaction
mixture with no residual inorganic contamination of the
organic products.Another review intended to give a wide scope
on the uses of ion-exchange resins as catalysts or catalyst
precursors in organic synthesis. The acylation of diphenyl
ethers with acetic anhydride was performedusing various solid
acid catalysts3 such as tungstophosphoric acid, sulfonated
zirconia, K10 clay and Indion and Amberlyst resins.
INTRODUCTION
Esters are common in organic chemistry and biological
materials and often have a characteristic pleasant, fruity odor.
This leads to their extensive use in the fragrance and flavour
industry. Ester bonds are also found in many polymers. As a
result of the reversibility, many esterification reactions are
equilibrium reactions and, therefore, need to be driven to comp-
letion, according to Le Chatelier’s principle.
The present research showed that the hybrid catalysts with
2D hexagonal p6mm mesostructure exhibited the highest
catalytic activity towards both esterification and transesteri-
fication reactions among the above hybrid catalysts with various
pore morphologies. This enhanced catalytic activity is due to
the fact that the ordered mesostructure can decrease the mass-
transport limitation of the reactants and products significantly.
Recent studies have proven the technical feasibility and the
environmental and economic benefits of biodiesel production
via heterogeneous acid-catalyzed esterification and trans-
esterification1.
Inorganic ion exchanger as a catalyst support is capable
of creating precisely controlled catalytically active species
responsible for targeted organic reactions. A major advantage
of ion-exchangers as catalysts is that heterogeneously catalyzed
reactions allow easy and efficient separation of high value
products from the catalyst. Clearfield et al.2 in an important
review mentioned the structure of inorganic ion exchanger and
their ion exchange capacity. The esterification of acetic acid
with n-butanol was studied in the presence of ion-exchange
Mercaptoacetates4 were prepared by esterification of
mercaptoacetic acid with several alcohols with yields in the
range 84.1-91.7 % cyclohexane as solvents, in the presence of
D61 or D72 cation ion-exchange resins. A similar reaction is
the inter-esterification4, where the alcohol parts of two esters
are exchanged. These equilibrated reactions are driven to full
completion by the use of an excess of reagent. Dimethyl carbonate
was synthesized by transesterification of methanol with
propylene carbonate, using CHS-1 or CHS-2 strong acid resins
as catalysts and reaction times of 40-60 min with a methanol/
propylene carbonate weight ratio of 8-10. The contribution5
of the catalysts led to the synthesis of some commercially
valuable products such as p-methoxy acetophenone, dimethyl
phthalate, diethyl phthalate, methyl anthranilate, methyl
salicylate and methyl p-hydroxybenzoate (methyl paraben).
Zirconium sulphate6 showed very good catalytic performance,

3036 Singh et al.
Asian J. Chem.
due to its high acidity together with low surface area. These
combined features allow the sterically hindered FFA molecules
to easily reach the active sites on the catalyst’s surface. The
other inorganic catalysts did not give satisfactory FFA con-
version, probably due to the low acidity related to a quite high
surface area. Platinum group metals7-10 are reported as highly
selective catalysts and are widely used in organic synthesis,
chemical industry and other areas like dehalogenation,
hydrodechlorination, carbonylation or oxidation.
Esterification of benzoic acid has been studied with some
primary and secondary alcohols like n-propanol, iso-propanol,
n-butanol and iso-butanol using synthetic inorganic ion
exchangers like zirconium antimonophosphate11 (ZrSbP),
zirconium antimonoarsnate12 (ZrSbAs), zirconium tungsto-
phosphate13 (ZrWP) and zirconium phosphoborate14 (ZrPB).
The idea is to understand if electronic environments of different
ion-exchangers have any role to play in catalyzing the organic
synthesis reactions. Esterification of alcohols were adopted
as model reactions for the study.Alcohols were used as solvents
as well as reagents in reactions with carboxylic acid in presence
of catalytic amounts of zirconium based inorganic ion
exchangers. These catalysts offered remarkably simple workup
procedure and were reusable without loss in its activity.
TLC of the reaction mixtures were spotted on freshly
coated silica plates with co-spotting of starting benzoic acid.
For all the samples TLC was run in 9:1 pet. ether: chloroform
solvent system. For all the reactions, the spot of the product
was observed to be non- polar as compared to benzoic acid.
Preparation of crystalline zirconium antimonophosphate
catalyst: Crystalline zirconium antimonophsphate11 was
prepared by adding zirconium oxychloride 0.1 M to a continuous
stirred mixture of potassium pyroantimonate (0.1 M) and
phosphoric acid solution (0.1 M) at 60 °C in 2:1:1 (v/v) ratio.
This gel was stirred for 2.5 h at 60 °C, washed till free from
halides tested with silver nitrate solution, filtered and the
product was dried at 40 °C. The dried product broke down
into particles when immersed in water and was converted into
H+ form by treating with HCl (0.1 M) for 24 h. The product
was washed with demineralized water to remove the excess
acid and dried at 40 °C.
Activity of catalyst
Ion-exchange capacity: Ion-exchange capacity (IEC) of
different lots of zirconium antimonophosphate was determined
by column method and the average of five such measurements
had a value 0.98( 0.03) meq/g, which is almost similar to the
reported value5. Hence, the material was taken as an active
catalyst.
EXPERIMENTAL
Esterification of benzoic acid with n-propanol, n-butanol,
iso-butanol using Zirconium based inorganic ion-
exchanger catalysts: ZrSbAs, ZrSbP, ZrPB & ZrWP
Zirconium oxychloride, potassium pyroantimonate and
phosphoric acid were obtained from SD Fine Chemicals
(India), n-propanol, iso-propanol, n-butanol, iso-butanol,
cyclohexanol and benzoic acid were obtained from Loba
Chemie (India). All the chemicals were used as received
without any further purification.
Methods used for analysis: Physico-chemical properties
of ZrSbP, ZrPB, ZrWP and ZrSbAs catalysts were studied by
various techniques i.e., FT-IR, Powder XRD and TGA. Ion
exchange capacity of the catalysts was measured to charac-
terize the materials as ion exchangers. Formation of various
esters (n-propyl benzoate, iso-propyl benzoate, n-butyl
benzoate and iso-butyl benzoate) was determined by FT-IR,
GC and 1H NMR Spectra.
Instrumental analysis: IR spectrum was recorded in the
range 4000-500 cm-1 on Perkin Elmer FTIR spectrometer.
Powder XRD patterns of the prepared catalysts were recorded
on PanAnalytic X’pertpro MPD Netherland, using Ni-filtered
Cu-Kα radiations. Thermo gravimetrical analyses (TGA) of
the samples were performed on Perkin Elmer Pyris Diamond
TG/DTA instrument with inert atmosphere of argon at the
heating rate of 10 °C/min up to 1000 °C.
General procedure: The 15 mL capacity glass vials
containing benzoic acid (100 mg, 0.8 mM), and corresponding
alcohol (5 mL), taken in excess to use it as a solvent and catalyst
(100 mg) were capped tightly and heated for 3 h at 150 °C.
The vials were removed, brought to room temperature and
opened to check the formation of product with the help of
TLC and GC. Excess alcohol was removed by evaporation
and excess benzoic acid was washed off by using 10 %
NaHCO3 solution. The product was extracted in organic phase
using chloroform. Ester so formed was analyzed by FT-IR
and 1H NMR.
(a) n-Propyl benzoate: 1H NMR (400 MHz, CDCl3): 8.07
(2H, d, ArH), 7.57 (1H, tt, ArH), 7.48 (2H, t, ArH), 4.30 (2H,
t, OCH2), 1.82 (2H, m, CH2), 1.05 (3H, t, CH3); IR (cm-1):
1724; GC (retention time): 9 min 14 sec;
(b) n-Butyl benzoate: 1H NMR (400 MHz, CDCl3): 8.06
(2H, d, ArH), 7.56 (1H, tt, ArH), 7.45 (2H, t, ArH), 4.34 (2H,
t, OCH2), 1.78 (2H, q, CH2), 1.52 (2H, m, CH2), 0.99 (3H, t,
CH3); IR (cm-1): 1716; GC (retention time): 10 min 38 sec.
(c) iso-Butyl benzoate: 1H NMR (400 MHz, CDCl3): 8.07
(2H, d, ArH), 7.57 (1H, tt, ArH), 7.48 (2H, t, ArH), 4.11 (2H,
d, OCH2), 2.11 (1H, m, CH), 1.03 (2 × 3H, d, CH3); IR (cm-1):
1716; GC (retention time): 10 min.
1H NMR Spectra were recorded on 400 MHz FT-NMR
Cryo Spectrometer (Bruker). Chromatograms were recorded
on Nucon-5765 (India) gas chromatograph.A sample of 0.5 µL
was injected with a nitrogen gas at a flow rate of 2.5 mL/min.
Oven was set at a temperature of 80 °C hold for 1 min then
continued up to 220 °C at a heating rate10 °C/min. At 220 °C,
temperature was on hold for 5 min then continued up to 310
°C at heating rate 20 °C/min. Temperature was kept on hold
for 6 min at 310 °C. Supelco 28098-U (30 m × 0.25 mm)
column was used. Flow rates of the gases in GC were: H2 flow:
30 mL/min;Air flow: 300 mL/min; Make up (N2): 30 mL/min.
RESULTS AND DISCUSSION
Hetropoly acid salts of zirconium11-14 have been used as
catalysts in simple esterification reactions of benzoic acid with
some primary and secondary alcohols like n-propyl alcohol,
iso-propyl alcohol, n-butyl alcohol and iso-butyl alcohol as
shown in Fig. 1.

Vol. 27, No. 8 (2015)
Zirconium Based Ion Exchangers as Catalysts in Esterification Reactions of Benzoic Acid 3037
O
O
acid to its corresponding ester was distinctly higher with anti-
monate based salts of zirconium as compared with phosphorus
catalyst
H2O
+
OH
OR
ROH
+
based salts. This is due to more acidic character of the protons
bound electrostatically to phosphate groups in phosphate based
catalysts than those of antimonate groups of antimonite based
ion exchangers (P is more basic in character than that of Sb
due to its smaller size).
2
1
3
R = 2a = n-propyl
2b = n-butyl
2c = iso-propyl
2d = iso-butyl
Fig. 1. Esterification of benzoic acid
Average yields of esters are observed in the following
order:
Initial attempts to synthesize the corresponding esters at
iso-Butylbenzoate > n-Propylbenzoate > n-Butylbenzoate
atmospheric pressure were not successful. There was hardly
any conversion of benzoic acid in any of the esters, which
were tried with different alcohols. Even changing the amount
of catalysts from 10 mol % to stoichiometric amounts (1:1,
1:2) did not produce any result. Change in temperature condi-
tions also did not show improvement in results (Fig. 2). There
was no conversion of the acid into ester even with ZrPB, ZrWP
and ZrSbAs, under these conditions.
This trend indicates that the selected group of ion exchan-
gers have preferred catalytic activity for 2° alcohols over 1°
alcohols, notwithstanding the length of carbon chain. This
probably is due to the similar interlayer spacing of these
exchangers which is more suitable to accommodate 2°
substrate. Alcohols smaller in size and orientation would be
too loosely held in the inter layer spacings, to be catalyzed at
the protonated sites of the exchanger. The benzoic acid gets
protonated after abstracting proton that is elecrostatically
bound to the fixed anionic moiety of phosphate/antimonate/
aresenate/borate groups of their corresponding catalysts. The
protonated benzoic acid is then held electrostatically to a fixed
anionic group of the catalyst.
Oxygen of alcohol behaves as a nucleophile and attaches
to the protonated acid. At this stage, attack of nucleophilic
oxygen of alcohol is facilitated by suitable geometry and
environment around the protonated acid at the exchanger site,
hence, introducing a selective character to the mechanism. This
hypothesis is well supported by the results shown in Table-1,
where the order of yields of catalyzed conversion of alcohol
is:
O
O
catalyst
H2O
OH
O
+
+
OH
2a
Fig. 2. A model reaction using ZrSbAs as a catalyst
1
3
The scheme of synthesis was re-strategized, wherein
reactions were carried out in a closed vial of 15 mL capacity.
It was anticipated that under closed system, rate of the forward
reaction would increase due to application of solvent pressure.
A model reaction was studied wherein benzoic acid was treated
with n-propanol in the presence of stoichiometric quantities
of ZrSbAs at 100 °C. TLC and GC did not indicate any conver-
sion. Further, the reaction temperature was varied by increasing
it from 100 to 120 °C and then finally to 150 °C. At 150 °C, it
was found that reaction proceeds efficiently in closed reaction
medium. The same reaction was studied by decreasing the
quantity of catalyst from 100 to 50 mol % at 150 °C in a closed
system which worked well without loss of catalytic efficiency.
Same procedure was used for the synthesis of esters with diffe-
rent catalysts. Results of the amounts of n-propyl benzoate
formed using different catalysts are given in Table-1. This
strategy was extrapolated to alcohols like n-butanol, iso-
propanol, iso-butanol with all the four catalysts, respectively.
The results are shown in Table-1.
iso-Butanol > n-Propanol > n-Butanol
Table-2 indicates that greater amount (97 %) of product
is formed in case of sterically hindered alcohol (like iso-
butanol) indicating that steric factor prominently controls the
efficiency as compared to electronic factor, because, for a given
alcohol, zirconium based catalysts with different anionic
moieties do not affect the yields significantly. As expected,
the yields of product are nearly similar with exchangers like
ZrSbP and ZrSbAs, used as catalysts. In this pair of catalysts,
antimonate moiety is common and the phosphate and arsenate
moieties do not have different electronic effects on the acidic
character of the catalyst, as they belong to same group 15 of
the periodic table. Interestingly, the iso-propanol based ester
is not obtained at all, probably due to restricted orientation of
the OH group of the 2° alcohol and also mismatching with
anionic site of the catalyst.
For all catalysts, the amounts of products formed were
more with secondary alcohols than with the primary alcohols.
However, esterification of benzoic acid with iso-propyl alcohol
did not yield any product. The yield of conversion of benzoic
TABLE-1
PERFORMANCE OF DIFFERENT ZIRCONIUM BASED ION EXCHANGE CATALYSTS IN
ESTERIFICATION REACTIONS OF BENZOIC ACID WITH DIFFERENT ALCOHOLS
n-Butyl benzoate
iso-Butyl benzoate
n-Propyl benzoate
iso-Propyl benzoate
S. No.
Catalyst
GC yield (%)
(Rt = 10 min 38 s)
GC yield (%)
(Rt = 10 min)
97.2
GC yield (%)
(Rt = 9 min 14 s)
GC/isolated yield (%)
1
2
3
4
ZrSbAs
ZrSbP
ZrPW
ZrPB
43.2
47.1
51.8
55.5
81.1
76.7
40.4
78.3
No product
No product
No product
No product
98.7
89.1
82.0

3038 Singh et al.
Asian J. Chem.
TABLE-2
• Different ion exchangers of zirconium behave almost
similarly as catalysts and there is hardly any influence of elec-
tronic state of the anionic component of the double salt, e.g.,
same amounts of zirconium antimonoarsenate and zirconium
antimonophosphate yield the same amount of ester from
reaction of benzoic acid with iso-butanol.
EFFECT OF SUBSTRATE AMOUNT (BENZOIC ACID) ON
THE YIELD OF PRODUCT USING SAME AMOUNT
OF ION EXCHANGE CATALYST
Amount of
ZrSbAs
Catalyst (mg)
Benzoic
acid mM
(mg)
GC Yield of
butyl benzoate
(%)
n-Butanol
(mL)
S.
No.
1
2
3
4
5
6
0.8 (100)
1.2 (150)
1.6 (200)
4.0 (500)
4.8 (600)
8.0 (1000)
100
100
100
100
100
100
5.0
5.0
5.0
5.0
5.0
5.0
43.2
65.2
69.7
88.4
90.0
93.8
ACKNOWLEDGEMENTS
The authors are thankful to Director, Thapar University
for providing research facilities. Thanks are also due to Dr.
Ashok Kumar SK,VIT University, Vellore, India for the useful
discussions and suggestions provided by Dr. Manmohan
Chhibber during the preparation of the manuscript.
Esterification using different amounts of benzoic acid:
Experiments were conducted using different amount of benzoic
acid for its conversion into n-butyl benzoate (retention time
10.44 min) with a fixed amount of n-butanol. It was found
that product yield increased in almost hyperbolic fashion with
the increase in the amount of substrate. The conversion effi-
ciency almost stabilises with 8 mM of benzoic acid for 100
mg of the catalyst.
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A number of researchers15-17 have reported esterification
reactions using heteropolyacids and their salts but relative
selectivity of the catalyst have not been claimed.
Conclusions
Following conclusions can be drawn from the esterification
reactions of aliphatic carboxylic acids with some alcohols.
• Zirconium based inorganic ion exchangers i.e., ZrSbP,
ZrSbAs, ZrWP and ZrPB can be used as Brønsted acids in
thermal reactions of carboxylic acids with some primary and
secondary alcohols.
• Esterification reactions can be held more efficiently in a
closed reactor than an open conventional refluxing method
using Dean-Stark apparatus.
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• The amount of catalyst is optimized as: 100 mg of each
exchanger having ion exchange capacity nearly 1.0 meq/g is
sufficient to catalyze 8.0 mM of benzoic acid.
• 2° alcohol is catalyzed more efficiently than 1° alcohol
indicating that efficiency of a given exchanger is controlled
by steric orientation of the alcohol.