8 Synthesis of Chloromethyl -1,3-dioxolanes from epichlorohydrin...
Transcript of 8 Synthesis of Chloromethyl -1,3-dioxolanes from epichlorohydrin...
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8 Synthesis of Chloromethyl -1,3-dioxolanes from
epichlorohydrin using supported heteropolyacids
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8.1 INTRODUCTION
Chloromethyl-1,3-dioxolane and derivatives are important pharmaceutical
intermediates, which are obtained by cycloaddition reaction of epichlorohydrin with
ketones. Chloromethyl-1,3-dioxolane derivatives are used as tranquilizers,
plasticizers, potential monomers for polymerization and ploy condensation and also as
important intermediates in synthesis of a new class of adrenoceptor antagonists
(Abdel-Rahman et al., 2008; Brasili et al., 2003; Okaoda and Mita, 1975; Povedai et
al., 2011). They are often used as protecting groups for aldehyde, ketones and 1,2-
diols in natural product synthesis. Several types of Bronsted as well as Lewis acid
catalysts such as SnCl4, TiCl4, BF3–OEt2, RuCl3, anhydrous CuSO4, TiO(TFA)2,
TiCl3(OTf), and methyl rhenium trioxide have been used in synthesis of 1,3-
diooxolane derivatives (Torok et al., 1993; Iranpoor and Kazeim, 1998; Hanzlik and
Leinwetter, 1978; Iranpoor and Zeynizadeh, 1998; Zhu and Espenson, 1997).
Although the above catalysts give very good catalytic activity and higher yields, they
are being replaced due to their corrosive nature, separation problems, economical and
environmental issues. Hence there is a need to develop processes that reduce and
eliminate the use and generation of hazardous substances. Green Chemistry has
emerged as a means to shift the focus of environmental impact to the prevent adverse
impact through the design of chemical processes to be more compatible with positive
environmental outcomes, such as decreasing the amounts of harmful chemicals used
in processes, use of heterogeneous solid acid catalysts, and implementation of
strategies to achieve zero-discharge of pollutants and emissions (Zatorsky and
Wierzchowski, 1991).
Synthesis of 1,3-dioxolanes from epoxides and carbonyl compounds has been
successfully demonstrated by a numerous research groups, with a variety of solid acid
catalysts like zeolites (ZSM-5, Y and ultra stabilized HUSY), Bentonite clay, K10
montmorillonite and were found to give satisfactory results (Cabrera et al., 1992;
Cabrera et al., 1995; Busci et al., 2001). These catalytic systems are fraught with
polymerization and oligomerization. Amrute et al., have overcome these problems by
using 10% MoO3 supported on SiO2 as a reusable catalyst, but the reaction requires
high catalyst loading and longer reaction times (Amrute et al., 2009).
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Catalysis by heteropolyacid (HPA) has been most successful in fundamental and
applied areas in the last two decades. HPAs show higher catalytic activities in acid
catalyzed reactions than conventional acids due to their strong acidic character
(Okuhara et al., 1996; Kozhevnikov, 1998; Kozhevnikov, 2002; Okuhara, 2002). It
has been also used in 1,3-dioxolane synthesis and found to be more effective (Li et al.,
2005). Extremely low surface area, poor stability and rapid deactivation are the major
problems associated with heteropoly acids. Our group has overcome this problem by
supporting these heteropolyacids on high surface area inorganic supports such as K10,
hexagonal mesoporous silica, etc. (Li et al., 2005) and also achieved thermal stability
by partial substitution of protons of dodecatungstophosphoric acid with Cs+ ions
(Bachiller-Baeza and Anderson, 2004; Cardoso et al., 2004; Misono et al., 1982).
Supporting Cs+ substituted dodecatungstophosphoric acid on montmorillonite K10
results in enhancement of catalytic activity, which have been reported by Yadav and
coworkers.(Yadav and Kirtivasan, 1995; Yadav and Kirtivasan, 1997; Yadav and
Bokade, 1996) for the first time and it was found to be highly active in many
industrially important reactions. Our group has successfully incorporated
Cs2.5H0.5PW12O40 on to K-10 clay by in situ generation of this salt in K-10 clay
(Yadav et al., 2003(a); Yadav et al., 2004; Yadav and Asthana, 2002; Yadav and
Bhagat, 2004). In the present study, catalytic activity of cesium substituted
dodecatungstophosporic acid (Cs2.5H0.5PW12O40, Cs-DTP) supported on K-10 clay
and hexagonal mesoporous silica has been brought out for the synthesis of
chloromethyl-1,3-dioxolane including the characterization and kinetic modeling.
8.2 EXPERIMENTAL
8.2.1 Chemicals
The following chemicals were procured from firms of repute and used without further
purification: epichlorohydrin, acetone, n-dodecane, cesium chloride,
dodecatungstophosphoric acid, methanol (M/s. S.D. Fine Chem. Ltd., Mumbai, India),
montmorillonite K10 (Sigma Aldrich, U.S.A.)
8.2.2 Catalyst synthesis
8.2.2.1 Preparation of Cs2.5H0.5PW12O40/K-10
Approximately 10 g of K-10 was dried in an oven at 120 ºC for 1 h of which 8 g was
weighed accurately. Approximately, 0.2808 g (1.671×10-3 mol) of CsCl was weighed
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accurately and dissolved in 10 ml of methanol. This volume of solvent used was
approximately equal to the pore volume of the catalyst. The solution was added to the
previously dried and accurately weighed 8 g of K-10 clay to form slurry. The slurry
was stirred vigorously and air-dried. The resulted material was then dried in an oven
at 120 ºC for 2 h. This was then further subjected to impregnation by an alcoholic
solution of 2 g (6.688×10-4 mol) of DTP in 10 ml of methanol. The solution was
added to the previously treated K-10 clay with CsCl again to form slurry. The slurry
was stirred vigorously and air-dried. The preformed catalyst was dried in an oven at
120 ºC for 2 h and then calcined at 300 ºC for 3h.
8.2.2.2 Preparation of Cs2.5H0.5PW12O40/hexagonal mesoporous silica (HMS)
Approximately 10 g of precalcined HMS was dried in oven at 120 ºC for 3 h of which
8 g was weighed accurately. CsCl (1.671×10-3 mol) was dissolved in 10 ml of
methanol. This volume of solvent used was approximately equal to the pore volume
of the catalyst. The solution was added in small aliquots of 1ml each time to the silica
molecular sieve with constant stirring with a glass rod or kneading it properly. The
solution was added at time intervals of 2 min. Initially on addition of the CsCl
solution to HMS was in powdery form but on complete addition it formed a paste.
The paste on further kneading for 10 min resulted in a free flowing powder. The
resulted material was dried at 120 ºC for 3 h for the removal of solvents. This then
was further subjected to impregnation by an alcoholic solution of 2 g (6.688×10-4
mol) of DTP in 10 ml of methanol. The solution was added to the treated HMS by
above procedure. The preformed material was dried in an oven at 120 ºC for 3 h and
then calcined at 300 ºC for 3 h. The catalyst was found to possess highest activity
when calcined at above-mentioned temperature.
8.2.3 Catalyst characterization
Surface area measurements and pore size distributions analysis were done by nitrogen
adsorption on Micromeritics ASAP 2010 instrument at an adsorption temperature 77
K, after pretreating the sample under high vacuum at 300 ºC for 4 h. Infrared spectra
of the samples pressed in KBr pellets were obtained at a resolution of 2 cm-1 between
4000 and 400 cm-1. Spectra were collected with a Perkin-Elmer instrument and in
each case the sample was referenced against a blank KBr pellet. Powder X-ray
diffraction (XRD) patterns were obtained using (Bruker AXS, D8 Discover, USA) Cu
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Ka radiation (l = 1.540562). Samples were step scanned from 5 to 45 in 0.045 steps
with a stepping time of 0.5 s. The elemental composition of 20% (w/w)
Cs2.5H0.5PW12O40/K10 and 20% (w/w) Cs2.5H0.5PW12O40/HMS were obtained by
Energy Dispersive X-ray Spectroscopy (EDXS) on KEVEX X-ray spectrometer.
Scanning electron micrographs of 20% (w/w) Cs2.5H0.5PW12O40/K-10 and 20% (w/w)
Cs2.5H0.5PW12O40/HMS were taken on Cameca SU 30 microscope. The dried samples
were mounted on specimen studs and sputter coated with a thin film of platinum to
prevent charging. The platinum-coated surface was then scanned at various
magnifications using scanning electron microscope. The ammonia-TPD data were
recorded for K10 clay, Cs-DTP salt, 20% (w/w) Cs2.5H0.5PW12O40/K-10 and 20%
(w/w) Cs2.5H0.5PW12O40/HMS by using AutoChem II 2920 TPD/TPR instrument
(Micromeritics, USA) by using 10% NH3 in helium.
8.2.4 Reaction procedure
Reactions were carried out in an autoclave having 100 cm3 capacity (M/s. Amar
Equipments, Mumbai, India), equipped with a four-bladed pitched-turbine impeller
along with temperature controller, speed controller, and pressure indicator. In the
control experiment, the autoclave was charged with the reaction mixture consisting of
0.06 mol epichlorohydrin, 0.48 mol of acetone, internal standard (n-decane) and a
catalyst loading of 0.04 g/cm3 of total volume of reaction mixture. The temperature
was raised and maintained at (1 °C of the set value with the help of an in-built
proportional integral derivative (PID) controller. Once the temperature reached the
desired value, agitation was started. Then, an initial sample was withdrawn. Further
samples were drawn at periodic intervals up to 1 h. The temperature was maintained
at 70 °C and the speed of agitation at 1000 rpm. The reaction was carried out without
solvent. The total volume of liquid phase was 40 cm3. Scheme 8.1 depicts the
reaction.
8.2.5 Analysis of reaction mixture
The samples were analyzed using a gas chromatograph (Chemito 1000 model)
equipped with a 30 m×0.32 mm i.d. BPX-50 capillary column and a flame ionization
detector (FID). n-Decane was used as an internal standard in the reaction. The
reaction products were confirmed by GC-MS (PerkinElmer clarus 500).
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Scheme 8.1: Cycloaddition of epichlorohydrin with acetone
8.3 RESULT AND DISCUSSION
8.3.1 Catalyst characterization
A brief characterization is presented here.
8.3.1.1 FT-IR studies
FT-IR studies have been done to confirm preservation of Keggin structure. Bulk DTP
(H3PW12O40) and Cs2.5H0.5PW12O40 show the characteristic IR bands at ca 1080cm-1
(P–O in central tetrahedral), 984 cm-1 (terminal W=O) 897 cm-1 and 812 cm-1 (W–O–
W) associated with the asymmetric vibrations in the Keggin polyanion. However,
Cs2.5H0.5PW12O40 is characterized by a split in the W=O band, suggesting the
existence of direct interaction between the polyanion and Cs+. FT-IR of 20% (w/w)
DTP/K-10 and 20% (w/w) Cs2.5H0.5PW12O40/K-10 indicate that the primary Keggin
structure is preserved in both the cases on K-10 support (Figure 8.1). The bands in the
region of 1600–1700 cm−1 (at 1631–1642 cm−1) are attributed to –OH bending
frequency of water molecules present in catalysts. In case of DTP, it is present as
water of crystallization, while in case of Cs2.5H0.5PW12O40, it indicates the presence of
partial H+ ion directly attached to the polyanion (–O–H) and is present in K-10 as M–
OH and possibly as H3O+ (Yadav and Kirthivasan, 1995; Yadav and Kirthivasan,
1997; Yadav and Bokade, 1996; Yadav et al., 2005; Yadav and Kumar, 2005).
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Figure 8.1: FTIR spectra (a) Fresh 20% Cs-DTP/K10, (b) reused 20% Cs-DTP/K10,
(c) Cs-DTP salt, (d) Pure DTP
8.3.1.2 XRD studies
Crystallinity and textural patterns of the catalysts obtained from X-ray diffractograph
of Cs2.5H0.5PW12O40/K-10 showed that DTP is crystalline while K-10 is amorphous.
Although the Cs2.5H0.5PW12O40 salt had lost some of its crystallinity when supported
on K-10, the Keggin structure of DTP remained intact. XRD pattern of fresh and
reused catalyst show no change in crystallinity (Figure 8.2).
8.3.1.3 SEM studies
The scanning electron micrographs reveal that both K-10 and 20% (w/w) DTP/K-10
samples possess rough and rugged surfaces. On the contrary 20% (w/w)
Cs2.5H0.5PW12O40/K-10 shows a smoother surface because of a layer of
Cs2.5H0.5PW12O40 over the external surface of K-10 (Figure 8.3).
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Figure 8.2: XRD of 20% w/w Cs-DTP/K-10 catalyst
Figure 8.3: SEM of 20% w/w Cs-DTP/K-10 catalyst (a) Fresh (b) Reused
8.3.1.4 Surface area analysis
The textural characterization of K10, 20% (w/w) DTP/K-10 and 20% (w/w)
Cs2.5H0.5PW12O40/K-10 was determined by nitrogen BJH surface area and pore size
analysis. BET surface area of 20% (w/w) Cs2.5H0.5PW12O40/K-10 is higher than that of
20% (w/w) DTP/K-10 and Cs2.5H0.5PW12O40 and slightly lower than that of K-10
(Table 8.1). The pore size distribution of K-10 clay and K-10 clay supported catalysts
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were in the range of 5–7.5 nm suggesting that pore sizes of the catalysts lie in the
mesoporous region, i.e. >2.0 nm (Figure 8.4). The adsorption–desorption isotherms
for K-10, 20% Cs2.5H0.5PW12O40/K-10 showed that they possess the form of Type IV
isotherm with the hysteresis loop of type H3, which is a characteristic of mesoporous
solid (Figure 8.4).
Table 8.1: Surface area, pore volume and pore diameter analysis
Catalyst Surface area
(m2/g)
Pore volume
(cm2/g)
Pore
diameter(nm)
K-10 230 0.36 6.4
20% DTP/K-10 107 0.32 7.1
20% Cs2.5H0.5PW12O40/K-10 207 0.29 5.8
20% Cs2.5H0.5PW12O40/HMS 598 0.52 3.5
Figure 8.4: Pore size distribution of catalysts
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8.3.1.5 Temperature programmed desorption TPD studies
TPD using ammonia as a probe was employed for the measurement of the total acidity
and acid strength distribution using a Micromeritics AutoChem 2910 instrument. It
was carried out by dehydrating 0.2 g of the catalyst sample at 573 K in dry air for 1 h
and then purging with helium for 0.5 h. The temperature was decreased to 398 K
under the flow of helium and then 0.5 ml NH3 pulses were supplied to the samples
until no more uptake of NH3 was observed. NH3 was desorbed in He flow by
increasing the temperature to 573 K, with a heating rate of 10 K/min, and NH3
desorption was measured using a TCD detector. Details regarding the amount of
desorbed ammonia (total acidity) and the increase in the concentration of acid sites
after heteropoly acid loading are summarized in Table 8.2. The loading of different
heteropolyacid on plain clay (K-10) catalyst led to an increase in the concentration of
acidic sites (Figure 8.5).
Table 8.2: Acidity of different catalysts
Sr.No. Catalyst Total acidity (mmol/g)
1 K-10 0.139
2 20% DTP/K-10 0.328
3 20% Cs2.5H0.5PW12O40/K-10 0.405
4 20% Cs2.5H0.5PW12O40/HMS 0.135
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Figure 8.5: NH3 TPD; (a) Cs-DTP salt, (b) K10 clay, (c) fresh Cs-DTP/K10, (d)
reused Cs-DTP/K10
8.3.2 Catalytic activity
It has been observed that Bronsted acid catalyzed reactions of oxiranes lead to
isomerization, oligomerization and polymerization which lower the overall yield
(Bartok, 1993). As acid strength of different hetropolyacids increases, polymerization
decreases. Although H3 [PW12O40] has highest acid strength and hence lower degree
of polymerization products its Cs+ salt gives higher degree of polymerization
products. It has been also reported that montmorillonite K10 itself was found to give
higher yield with lower degree of polymerization products (Amrute et al., 2009).
Various solid acid catalysts such as K-10, 20% DTP/K-10, 20% Cs2.5H0.5PW12O40/K-
10, 20% Cs2.5H0.5PW12O40/HMS were examined to find out their activity in
cycloaddition reaction of epichlorohydrin. The standard experiment consisting
0.04g/cm3 loading of catalyst based on the total volume of reaction mixture was
employed at 70°C at a speed of agitation of 1000 rpm (Table 8.3). The
Cs2.5H0.5PW12O40/K-10 was found to give complete conversion without any
polymerization or oligomerization products. K-10 and 20% DTP/K-10 are also found
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to give good conversion but selectivity is much less. Due to solubility of DTP in
acetone 20% DTP/K-10 leaches out and hence is not reusable. The reason behind
increase in 1,3- dioxolane selectivity without any polymerization product is may be
due to incorporation of Cs+ ion in to dodecatungstphosphoric acid supported on
montmorillonite K10 which results in enhancement of catalytic activity and also
change in surface structural properties such as pore volume, pore diameter and surface
area.
Table 8.3: Efficacy of different catalysts
Sr.No. Catalyst Reaction
Time (h)
Conversion
(%)
Selectivity
(%)
1 K-10 1 98 95
2 20% DTP/K-10 1 100 97
3 20% Cs2.5H0.5PW12O40/K-10 1 100 98
4 20% Cs2.5H0.5PW12O40/HMS 1 20 100
8.3.3 Effect of speed of agitation
To understand the role of external mass transfer on the rate of reaction, the effect of
the speed of agitation was studied (Figure 8.6). The speed of agitation was varied
from 600 to 1200 rpm. It was observed that the conversion of epichlorohydrin was
practically the same beyond 1000 rpm with the same selectivity. Thus, it was ensured
that external mass-transfer effects did not influence the reaction. Hence, all further
reactions were carried out at 1000 rpm.
8.3.4 Effect of catalyst loading
The effect of catalyst loading was studied over range of 0.02–0.05 g/cm3 (Figure 8.7).
In the absence of external mass transfer resistance, the rate of reaction was directly
proportional to catalyst loading based on the entire liquid phase volume. This
indicates that as the catalyst loading increased the conversion of epichlorohydrin
increases, which is due to proportional increase in the number of active sites.
However, beyond a catalyst loading of 0.04 g/cm3, there was no significant increase in
the conversion and hence all further experiments were carried out at this catalyst
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loading. This was due to the fact that more number of acidic sites are available than
required beyond 0.04 g/cm3.
Figure 8.6: Effect of speed of agitation
Epichlorohydrin, 5.5 g (0.06 mol), acetone, 27.87 g (0.48 mol), reaction temperature,
70 °C, catalyst loading, 0.04 g/ cm3, speed of agitation , 600 rpm, 800 rpm,
1000 rpm, 1200 rpm
0
20
40
60
80
100
0 10 20 30 40 50 60
Con
vers
ion
(%)
Time (min)
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Figure 8.7: Effect of catalyst loading
Epichlorohydrin, 5.5 g (0.06 mol), acetone, 27.87 g (0.48 mol), reaction temperature,
70 °C, speed of agitation, 1000 rpm, catalyst loading, 0.02 g/ cm3 , 0.03 g/ cm3,
0.04 g/ cm3, 0.05 g/ cm3
8.3.5 Effect of mole ratio
The mole ratio of epichlorohydrin to acetone was varied from 1:4 to 1:10 (Figure 8.8)
under otherwise similar conditions. As the concentration of acetone is increased with
respect to the concentration of epichlorohydrin, an increase in the conversion of
epichlorohydrin was observed. Selectivity towards 1,3- dioxolane was also found to
increase with an increase in concentration of acetone. Bucsi et al. have reported that
enhancement of ketone concentration increases selectivity in dioxolane synthesis by
depressing excessive polymerization (Bucsi et al., 2001). Therefore, all further
experiments were studied by keeping a high epichlorohydrin: acetone mole ratio of
1:8.
0
20
40
60
80
100
0 10 20 30 40 50 60
conv
ersi
on(%
)
Time (min)
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Figure 8.8: Effect of mole ratio
reaction temperature, 70 ºC, speed of agitation, 1000 rpm, catalyst loading, 0.04 g/
cm3, mole ratio(epichlorohydrin:acetone), 1:4, 1:6, 1:8, 1:10
8.3.6 Effect of temperature
The effect of temperature on the reaction between epichlorohydrin and acetone was
studied under otherwise similar conditions. The temperature was varied from 50 to 80
ºC. It was observed that at 50 ºC, the reaction rate was slow. With increase in the
temperature the reaction rate intensified as expected (Figure 8.9).
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Con
vers
ion
(%)
Time (min)
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Figure 8.9: Effect of temperature
Epichlorohydrin, 5.5 g (0.06 mol), acetone, 27.87 g (0.48 mol), speed of agitation,
1000 rpm, catalyst loading, 0.04 g/cc , temperature, 50 ºC, 60 ºC, 70 ºC,
80 ºC.
8.3.7 Reusability of catalyst
The reusability of the catalyst was studied by filtering the catalyst obtained after fresh
use. Filtered catalyst was washed and refluxed with ethylene dichloride (3×50 ml) in
order to remove any adsorbed material from the catalyst surface and pores. Washed
catalyst was dried at 120 °C for 3 h before every reuse. The catalyst was reused thrice.
There was no loss in activity. Textural properties for fresh and spent catalyst were
determined to understand any change in surface area and pore volume (Table 8.4).
BET surface area decreases from 217 m2/g to 205 m2/g for third reuse cycle indicating
weak adsorption of reaction components on catalyst surface. FTIR analysis of fresh
and spent catalyst reveals that basic structural aspects was maintained with essentially
similar bands in FTIR spectra as shown in Figure 8.1.
8.3.8 Reaction mechanism and kinetic model
Cycloaddition reaction of epichlorohydrin with acetone occurs by adsorption of
epichlorohydrin on Bronsted acidic site leading to formation of carbocation which
0
20
40
60
80
100
0 10 20 30 40 50 60
Con
vers
ion(
%)
Time (min)
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attacked by carbonyl oxygen of acetone adsorbed on adjacent site and intermolecular
rearrangement leading to formation of product as demonstrated in Scheme 8.2.
Scheme 8.2: Reaction mechanism
1. Adsorption of Epichlorohydrin (A) on the vacant site S is given by:
AKA S AS���� ��� (a)
Similarly adsorption of Acetone (B) on the vacant site is presented by:
BKB S BS���� ��� (b)
2. Surface reaction of AS with BS (acetone), in the vicinity of the site, leading to
formation of Chloromethyl 1,3-dioxolane (DS) on the site. 2KAS BS DS S���� ���� (c)
Desorption of chloromethyl dioxolane(DS)
1/ EKDS D S���� ����� (d)
The total concentration of the sites, Ct expressed as,
t S AS BS DSC C C C C� � � � (1)
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Or,
t S A A S B B S D D SC C K C C K C C K C C� � � � (2)
or, the concentration of vacant sites,
1
tS
A A B B D D
CCK C K C K C
�� � �
(3)
If surface reaction controls the rate of reaction, then the rate of reaction of A is given
by
'2 2
AA AS BS DS S
dCr k C C k C Cdt
�� � � � (4)
2 ' 22 2
AA B A B S D D S
dC k K K C C C k K C Cdt
� � � �� �
2 2 '2 2
AS A B A B S D D
dC C k K K C C C k K Cdt
� � � �� �
From eq.3
� �� �
2 '2 2
21t A B A B D DA
A A B B D D
C k K K C C k K CdCdt K C K C K C
���
� � � (5)
Considering initial rate of reaction,
� �22
2(1 )t A B A BA
A A B B
C k K K C CdCdt K C K C
��
� � (6)
As adsorption constant are very low,
= � �22
At A B A B
dC C k K K C Cdt
�� (7)
'AA B
dC k wC Cdt
� �
Where, ' 2
2t A Bk w C k K K�
And w is catalyst loading in g/cm3
Let,
0
0
B
A
C MC
� (8)
The molar ratio of acetone to epichlorohydrin at t = 0. Then the equation (8) can be
written in terms of fractional conversion as
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'0 (1 )( )A
A A AdX k wC X M Xdt
�� � � (9)
This upon integration leads to: '
0ln{( ) / (1 )}A A AM X M X k wC t� � � (10)
1ln{( ) / (1 )}A AM X M X k t� � � (11)
Where k’wCA0 = k1 is a pseudo constant
To validate the above mechanism, plots were made in consonance with Eq. (11)
(Figure 8.10). It shows four straight lines passing through the origin at catalyst
loading of 0.02, 0.03 and 0.004 g/cc respectively. The slopes of these lines are k1=
k’wCA0 which are functions of w. Thus, plots of k1 were made against w to show that
it is linear relationship (Figure 8.11).This linear relationship also indicates that the
rate is proportional to the number of active sites present on the surface. It would
therefore mean that the reaction mechanism is LHHW type with very weak adsorption
of both the reactants in the absence of any diffusional resistance.
Figure 8.10: Plot of ln [M-XA/ (M(1-XA)] Vs Catalyst loading (w) (g/cm3);
0.02 g/ cm3, 0.03 g/ cm3, 0.04 g/ cm3
y = 0.0123x R² = 0.9873
y = 0.0195x R² = 0.9933
y = 0.0262x R² = 0.9993
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50
ln[M
-XA/(M
(1-X
A))
]
Catalyst loading w (g/cc)
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Figure 8.11: Slope k1 vs Catalyst loading (w) (g/ cm3)
Figure 8.12: Plot of ln [M-XA/ (M (1-XA)] vs temperature
50 ºC, 60 ºC, 70 ºC, 80 ºC
y = 0.6379x R² = 0.9916
0
0.005
0.01
0.015
0.02
0.025
0.03
0 0.01 0.02 0.03 0.04 0.05
Slop
e (k
1)
Catalyst Loading ,W (g/cc)
y = 0.0061x R² = 0.9373
y = 0.0154x R² = 0.9918
y = 0.0271x R² = 0.9993
y = 0.0508x R² = 0.9977
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50
ln[M
-XA/(M
(1-X
A))
]
Time(min)
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Figure 8.13: Arrhenius plot
The values of k1 were also found at the different temperatures at the same w and M
(Figure 8.12). The Arrhenius plot of ln k1 vs. T-1 is shown in Figure 8.13, from which
the activation energy was calculated as 15.77 kcal mol-1. The high value of activation
energy also supported the fact that the overall rate if reaction is not influenced by
either external mass transfer or intra-particle diffusion resistance and it is intrinsically
kinetically controlled reaction on active sites.
8.4 CONCLUSION
Cycloaddition reaction of epichlorohydrin with acetone using different catalysts such
as K10 clay, Dodecatungstophosphoric acid/K10, 20 wt% Cs2.5H0.5PW12O40 / K-10
clay and 20 wt% Cs2.5H0.5PW12O40 / HMS. Cs2.5H0.5PW12O40 (Cs-DTP)/ K-10 clay
was found to be highly active. Increase in molar ratio of epichlorohydrin to acetone at
1:8 was found to give no oligomerization or polymerization products and hence the
catalyst could be reused several times. Incorporation of Cs-DTP salt on K10 clay
changes structural properties such as surface area, pore size, pore volume and it gives
99% selectivity towards desired product. The effects of various parameters were
studied using this catalyst. The experimental data so generated were used to develop a
model. The model fits the experimental data very well. The studies were used to
y = -7.939x + 19.533 R² = 0.9926
-6
-5
-4
-3
-2
2.8 2.9 3 3.1 3.2
ln K
(1/T) *103 (1/K)
185
achieve at optimum parameters to suppress deactivation and thus a temperature of 70
ºC and mole ratio of epichlorohydrin to acetone of 1:8 should be used.
186
9 Regioselective ring opening of epichlorohydrin with
acetic acid to 3-chloro-2-hydroxypropyl acetate
187
9.1 INTRODUCTION
Catalysis by heteropolyacids (HPA), and their modified and/or supported forms has
gained considerable importance in synthesis of a variety of chemicals in the last two
decades. They offer higher catalytic activities in acid catalyzed reactions in
comparison with conventional acid catalyst due to their strong/super acidic character
(Okuhara et al., 2002 and 1996; Kozhevnikov et al., 1998; Yadav et al., 2005).
Considerable catalytic activity has been observed in ring opening reactions of
epoxides and tetrahydrofuran with carboxylic acids/anhydrides (Izumi et at., 1983).
Extremely low surface area, poor stability and rapid deactivation are the major
problems associated with HPAs. Several attempts have been made to overcome these
limitations; our group has overcome them by supporting HPAs on high surface area
inorganic supports such as K10 (Izumi and Matsuo et al., 1983; Yadav et al., 2003(a);
Yadav et al., 2003(b)), hexagonal mesoporous silica (Yadav and Asthana, 2002 and
Yadav et al., 2004; Yadav and Bhagat, 2004; Yadav and Manyar, 2003; Cardoso et
al., 2004;Bachiller-Baeza et al., 2004). The thermal stability was achieved by partial
substitution of protons of dodecatungstphosphoric acid with Cs+ ions (Misonoet al.,
1982) whereas, supporting Cs+ substituted dodecatungstphosphoric acid on
montmorillonite K10 resulted in enhancement of catalytic activity, which was
reported by Yadav et al. for the first time and the catalyst was found to be highly
active in many industrially relevant reactions. Our group has successfully
incorporated nano Cs2.5H0.5PW12O40 on K-10 clay (Yadav and Kirthivasan, 1995;
Yadav and Kirthivasan, 1997; Yadav and Asthana, 2003; Yadav and Kumar, 2005).
The current work deals with a very important application of this catalyst.
Regioselective ring opening product of epichlorohydrin with acetic acid affords 3-
chloro-2-hydroxypropyl acetate. It has wide applications in production of various
epoxy resins, reactive polymers used for coating metal, leather, paper and woods
(Gelbard et al., 2000; Kotha et al., 1996; Korshunov et al., 1979; Nurbas et al., 2005;
Ellis et al., 1993). It is prepared conventionally by using highly corrosive
homogeneous acid catalysts like sulfuric acid and p-toulenesulphonic acid which lead
to lower selectivity, and separation and disposal problems (Izumi et al., 1980). Several
other homogeneous catalysts have been used such as FeCl3(Baum et al., 1983),
Fe(O2CCF3)3(Iranpoor et al., 2000), SnCl4(Moberg et al., 1992), BF3OEt2(Jaramillo et
al., 1994), (NH4)2Ce(NO3)3(Iranpoor et al., 1991). These problem has overcome by
188
number of researcher’s finding’s coming out with heterogeneous catalyst
FeCl3.6H2O/SiO2 (Iranpoor et al., 1996),Fe(III)/Montmorillonite (Choudary et al.,
1996), Ce(OTf)4(Iranpoor et al., 1998), Ce[(PVP)2(NO3)3] (Tamami et al., 1993),
(NH4)8[CeW10O36] 20H2O (Mirkhani et al., 2003), Cp2ZrCl2(Kantam et al., 2003),
AlPW12O40(Habib et al., 2006), K5Co(III)W12O40(Tangestaninejad et al., 2006),
Acid treated clay (Selvin et al., 2009), DTP/K10, ZnCl2/K10 (Selvin et al., 2011),
tin(IV)tetraphenylporphyrinatotetrafluoroborate (Moghadam et al., 2007),
salenCo(III)OAc complexes (Bukowska et al., 2008). The lacunae in the current state
of the art was indentified and addressed in the current work.
The present study aimed at development of ecofriendly, recyclable, efficient catalyst
in the ring opening reaction of epichlorohydrin with acetic acid to 3-chloro-2-
hydroxypropyl acetate. A mechanistic model is developed and the kinetics of the
reaction is deduced. The catalyst was fully characterized by various techniques such
as FTIR, SEM, NH3-TPD, Surface area (ASAP), XRD.
9.2 EXPERIMENTAL
9.2.1 Chemicals
The following chemicals were procured from firms of repute and used without further
purification: epichlorohydrin, acetic acid, n-dodecane, cesium chloride,
dodecatungstophosphoric acid, methanol (S.D. Fine Chem. Ltd., Mumbai, India),
montmorillonite K10 clay (Sigma Aldrich, U.S.A.).
9.2.2 Catalyst synthesis
All the known catalysts were prepared by well established methods developed in our
laboratory; 20%Cs2.5H0.5PW12O40/K-10 (Yadav and Asthana, 2003), sulfated zirconia
(Reddy et al., 2006), tungstated zirconia (Shiju et al., 2009), 20% w/w
dodecatungstophosphoric acid (DTP)/K10 clay (Yadav et al., 2004 (c)).
9.2.3 Reaction procedure
The reaction was carried out in a 100 cm3 capacity glass reactor of 5 cm internal
diameter which was equipped with four equally spaced baffles and a standard six-
blade pitched turbine impeller, and a reflux condenser. The reaction temperature was
189
maintained by means of a thermostatic oil bath in which the reaction assembly was
immersed. In the standard experiment reactor was charged with the reaction mixture
consisted of 0.02 mol of epichlorohydrin, 0.3 mol of acetic acid, internal standard (n-
decane) and a catalyst loading of 0.06 g/cm3 of total volume of reaction mixture,. The
temperature was raised and maintained at the desired value, and then agitation was
tarted. An initial sample was withdrawn. Further samples were drawn at periodic
intervals up to 1 h. The temperature was maintained at 90 °C and the speed of
agitation at 1000 rpm. The reaction was carried out without using any solvent. The
total volume of liquid phase was 18 cm3. The reaction products were confirmed by
GC-MS. The reaction scheme is as shown in scheme 9.1.
Scheme 9.1: Acetolysis of epichlorohydrin
9.2.4 Analysis of reaction mixture
The samples were analyzed using a gas chromatograph (Chemitoceres 800 model)
equipped with a 30 m × 0.32 mm i.d. BPX-5 capillary column and a flame ionization
detector (FID). n-Decane was used as internal standard in the reaction. The reaction
products were confirmed by GC-MS.
9.3 RESULT AND DISCUSSION
9.3.1 Catalyst characterization
The catalyst was well characterized, and details are elaborated in our recent reports
elsewhere (Yadav et al., 2003(a)). Some of important aspects are explained here. FT-
IR studies were done to confirm preservation of the Keggin structure of HPA.
However, Cs2.5H0.5PW12O40 is characterized by a split in the W=O band, suggesting
the existence of direct interaction between the polyanion and Cs+. Crystallinity and
textural patterns of the catalysts obtained from X-ray diffractograph of
Cs2.5H0.5PW12O40/K-10 show that DTP is crystalline while K-10 is amorphous.
Although Cs2.5H0.5PW12O40 salt had lost some of its crystallinity when supported on
K-10, the Keggin structure of DTP remained intact. XRD pattern of fresh and reused
190
catalyst shows no change in crystallinity (Figure 9.1). The scanning electron
micrographs reveal that both K-10 and 20% (w/w) DTP/K-10 samples possess rough
and rugged surfaces. On the contrary 20% (w/w) Cs2.5H0.5PW12O40/K-10 shows a
smoother surface because of a layer of Cs2.5H0.5PW12O40 over the external surface of
K-10 (Figure 9.2).The Brunauer-Emmett-Teller (BET) surface area of 20% (w/w)
Cs2.5H0.5PW12O40/K-10 was measured to be 207 m2g-1, and the pore volume and pore
diameter were 0.29 cm3/g and 5.8nm, respectively. The adsorption–desorption
isotherms for fresh and reused 20% Cs2.5H0.5PW12O40/K-10 show that they have the
form of Type IV isotherm with the hysteresis loop of type H3, which is a
characteristic of mesoporous solid (Figure 9.3).
Figure 9.1: XRD (a) Fresh catalyst (b) Reused catalyst
10 20 30 40 50 2 Theta
Lin (counts) arb. units
(a) H
(b)
191
Figure 9.2: SEM (a) Fresh catalyst (b) Reused catalyst
Figure 9.3: Surface area analysis (a) Fresh catalyst (b) Reused catalyst
9.3.2 Catalytic activity
Various solid acid catalysts such as 20% w/w DTP/K-10, 20% Cs2.5H0.5PW12O40/K-
10, sulphated zirconia (SO4/ZrO2) and tungstated zirconia (WO3/ZrO2) were
examined to find out their activity in cycloaddition reaction of epichlorohydrin
(a)
(b)
(a) (b)
192
(ECH). The standard experiment consisting 0.06g/cm3 loading of catalyst based on
the total volume of reaction mixture was employed at 90°C and speed of agitation of
1000 rpm (Table 9.1). High mole ratio of 1:15 (ECH: acetic acid) was taken to
suppress unwanted polymerization.
Among all screened catalysts 20% w/w Cs-DTP/K10 catalyst was found to be highly
active and selective. Although other catalyst gave good conversion values, attributes
such as stability, selectivity and reusability were of principal importance. Selectivity
towards 3-chloro-2-hydroxypropyl acetate was less in the case of sulphated and
tungstate zirconia. Another byproduct formed in the reaction is the β regio-isomer. It
has been observed that heteropolyacids (HPA) were most efficient catalyst in
acetolysis of cyclic ethers (Izumi et at., 1983). Solubility of HPAs in reaction mixture
leads to separation problems. This can be overcome by partial substitution of DTP
with cesium to give heterogeneous insoluble salt of DTP. Supporting Cs-DTP on K10
by in-situ impregnation increases its surface area and thereby its catalytic activity
(Yadav 2005; Okhura et al.,1996). Hence, further experiments were carried out using
20%Cs-DTP/K-10.
Table 9.1: Catalytic activity
Catalyst Time (h) Conversion Selectivity
WO3/ZrO2 5 30 87
SO4/ZrO2 2 100 88
20% DTP/K10 1 100 92
20% Cs-DTP/K10 1 100 98
(temperature, 90°C, catalyst loading, 0.06g/cm3, Epichlorohydrin, 0.02 mol, acetic acid, 0.3 mol, speed
of agitation, 1000rpm)
9.3.3 Effect of speed of agitation
In order to understand the role of external mass transfer on the rate of reaction, the
effect of the speed of agitation was studied (Figure 9.4). The speed of agitation was
varied from 800 to 1200 rpm under otherwise similar reaction conditions. It was
observed that the conversion of epichlorohydrin was slightly less at 800 rpm but it
was practically the same beyond 1000 rpm without any change in selectivity. Thus, it
193
was ensured that external mass-transfer effects did not influence the reaction beyond
1000 rpm. Hence, all further reactions were carried out at 1000 rpm.
7.3.4 Effect of catalyst loading
In the absence of external mass transfer resistance, the rate of reaction was directly
proportional to catalyst loading based on the entire liquid phase volume. The catalyst
loading was varied over the range of 0.06–0.08 g/cm3 on the basis of the total volume
of reaction mixture (Figure 9.5). This indicates that as the catalyst loading increased
the conversion of epichlorohydrin increased, which is due to proportional increase in
the number of active sites. It is further confirmed by plot of initial rate versus catalyst
loading (Figure 9.6).
Figure 9.4: Effect of speed of agitation on conversion of (Epichlorohydrin).
Temperature, 90°C, catalyst loading, 0.06g/cm3, Epichlorohydrin, 0.02 mol, acetic
acid, 0.3 mol, speed of agitation, 800rpm, 1000 rpm, 1200 rpm.
9.3.4 Effect of mole ratio
The mole ratio of epichlorohydrin to acetic acid was varied from 1:9 to 1:15 (Figure
9.7) under otherwise similar operating conditions with constant catalyst loading per
unit volume. As the concentration of acetic acid was increased with respect to the
concentration of epichlorohydrin, an increase in the conversion of epichlorohydrinwas
observed. Epichlorohydrin in the presence of acidic catalyst undergoes polymerization
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40
Con
vers
ion
(%)
Time (min)
194
or oligomerization on catalyst surface and hence deactivates active catalyst sites. To
avoid oligomerization or polymerization of epichlorohydrin on catalyst surface high
molar ratio of 1:15 (epichlorohydrin: acetic acid) was taken for further study. At this
molar ratio no polymerization or oligomerization products were observed. This can be
explained. Excessive adsorption of acetic acid on catalyst site does not allow
epichlorohydrin molecules to react with each other and hence suppress polymerization
/ oligomerization products.
Figure 9.5: Effect of catalyst loading (in g/cm3) on conversion of Epichlorohydrin
speed of agitation, 1000 rpm, Epichlorohydrin, 0.02 mol, acetic acid, 0.3 mol,
temperature, 90ºC, 0.06 g/cm3, 0.07 g/cm3, 0.08 g/cm3
0102030405060708090
100
0 10 20 30 40
Con
vers
ion
(%)
Time (min)
195
Figure 9.6: Plot of initial rate vs catalyst loading
Figure 9.7: Effect of mole ratio of Epichlorohydrin to acetic acid
speed of agitation, 1000 rpm, catalyst loading, 0.06 g/cm3, temperature, 90ºC, mole
ratio (Epichlorohydrin : acetic acid); 1:9, 1:12, 1:15.
y = 1.0362x R² = 0.9854
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0 0.02 0.04 0.06 0.08 0.1
Initi
al ra
te r i
ni
Catalyst loading (g/cm3)
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40
Con
vers
ion
(%)
Time (min)
196
9.3.5 Effect of temperature
The effect of temperature on the reaction between epichlorohydrin and acetic acid was
studied under otherwise similar conditions. The temperature was varied from 70 to
90ºC. It was observed that conversion of epichlorohydrin increased with temperature
(Figure9.8). This would suggest a kinetically controlled mechanism. This will be
discussed later.
Figure 9.8: Effect of temperature on conversion of Epichlorohydrin
speed of agitation, 1000 rpm, Epichlorohydrin, 0.02 mol, acetic acid, 0.3 mol, catalyst
loading, 0.06 g/cm3, temperature, 70 °C, 80 °C, 90 °C
9.3.6 Reusability of catalyst
The reusability of the catalyst was studied by filtering the catalyst at the end of the
reaction and conducting three runs after fresh use (Figure 9.9). After each reaction the
catalyst was filtered and then refluxed with (3×50 ml) of methanol for 2 h in order to
remove any adsorbed material from the catalyst surface and pores and dried at 120°C
for 2 h after every use. There was no loss in activity. Textural properties for fresh and
spent catalyst were determined to understand any change in surface area and pore
volume (Table 9.2). BET surface area decreases from 217 m2/g to 210 m2/g for third
reuse cycle, which is reasonable since there was no make-up catalyst was added.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40
Con
vers
ion
(%)
Time (min)
197
FTIR analysis of fresh and spent catalyst revealed that basic structural aspects was
maintained with essentially similar bands in FTIR spectra (Figure 9.10).
Figure 9.9: Reusability study
Table 9.2: Surface area analysis
No. 20% Cs-DTP/K-10 BET surface area (m2/g)
1. Fresh 217.6
2. 1st Reuse 215
3. 2nd Reuse 212
4. 3rd Reuse 210
Conversionselectivity97
98
99
100
Fresh 1st reuse 2nd reuse 3rd reuse
198
Figure 9.10: FTIR spectra (a) Fresh catalyst (b) Reused catalyst
9.3.7 Reaction mechanism and kinetic model
From the observed initial rate, it is evident that the rate is independent of the external
mass transfer effects. It was also seen from the values of activation energy, that the
intra-particles diffusion resistance is absent. Thus, the reaction could be controlled by
one of the following steps, namely: (a) adsorption, (b) surface reaction or (c)
desorption. Therefore, actual reaction mechanism was under taken for the further
development of model.
The initial rate data can be analysed on the basis of Langmuir-Hinshelwood-Hougen-
Watson (LHHW) or Eley-Rideal mechanism. From the initial rate, the following
analysis was found to be the most appropriate. The mechanism shown in Scheme 9.2
can be used to arrive at the LHHW type of mechanism.
500 3500 3000 2500 2000 1500 1000 Wavenumber cm
-1
Transmittance (%) arb. units
(b)
(a)
199
Scheme 9.2: Plausible reaction mechanism
1. Adsorption of epichlorohydrin(A) on the vacant site S is given by:
AKA S AS���� ��� (a)
Similarly adsorption of acetic acid (B) on the vacant site is presented by:
BKB S BS���� ��� (b)
2. Surface reaction of AS with BS, in the vicinity of the site, leading to formation of
3-chloro-2-hydroxypropyl acetate (DS) on the site.
2KAS BS DS S���� ���� (c)
Desorption of 3-chloro-2-hydroxypropyl acetate (DS) and vacant site S
1/ DKDS D S���� ����� (d)
The total concentration of the sites, Ct expressed as,
t S AS BS DSC C C C C� � � �
or,
t S A A S B B S D D SC C K C C K C C K C C� � � � (2)
or, the concentration of vacant sites,
200
1
tS
A A B B D D
CCK C K C K C
�� � �
(3)
If surface reaction controls the rate of reaction, then the rate of reaction of A is given
by
'2 2
AA AS BS DS
dCr k C C k Cdt
�� � � � (4)
2 '2 2
AS A B A B D D
dC C k K K C C k K Cdt
� � � �� �
By substituting value of Cs from equation 3
� �
2 '2 2
21t A B A B D DA
A A B B D D
C k K K C C k K CdCdt K C K C K C
� �� � ��� � �
(5)
When the reaction is far away from the equilibrium 2
22(1 )
t A B A BA
i i
k C K K C CdCdt K C
��
� (6)
= 22(1 )
A R A B
i i
dC k wC Cdt K C
��
� (7)
Where, 2
2 2R t A Bk w k C K K�
And w is catalyst loading.
If the adsorption constants are very small, then the above equation reduces to
2A
R A BdC k C C wdt
� � (8)
Since, acetic acid was taken in far molar excess over epichlorohydrin ([B0] >> [A0]),
it becomes a pseudo 1st order equation which can be integrated.
2A
R AdC k wCdt
�� �
(1 )AP A
dC K Xdt
�� � �
ln(1 )A PX K t� � �
Thus, plots of –ln (1-XA) versus time were made to show a linear relation, where XA is
the fractional conversion of epichlorohydrin. Thus plots were made, for instance, for
different temperatures for conversion up to 20 min to minimize the errors (Figure
201
9.11). The slopes of these lines are equal to kp from which Arrhenius plots were made
to determine the apparent energy of activation (Figure 9.12). It was found to be 8.3
kcal/mol, which indicates that the reaction rate is intrinsically kinetically controlled.
Figure 9.11: Plot of –ln(1-XA) vs Time at different temperatures
( 70 °C, 80 °C, 90 °C)
y = 0.0458x R² = 0.989
y = 0.0623x R² = 0.9958
y = 0.0881x R² = 0.999
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 5 10 15 20 25
-Ln
(1-X
A)
Time (min)
y = -4.1893x + 9.1031 R² = 0.9984
-3.2
-3.1
-3
-2.9
-2.8
-2.7
-2.6
-2.5
-2.4
-2.3
-2.2
2.7 2.75 2.8 2.85 2.9 2.95
Ln k
(1/T) *10-3
202
Figure 9.12: Arrhenius plot
9.4 CONCLUSION
In this work regioselective ring opening reaction of epichlorohydrin with acetic acid
using heterogeneous catalyst was studied. Different catalysts such as DTP supported
on K10 clay, 20 wt % Cs2.5H0.5PW12O40 supported on K-10 clay, sulphated zirconia
and tungstated zirconia were synthesized and their efficacies were studied.
Cs2.5H0.5PW12O40 (Cs-DTP) supported on K-10 clay was found to be highly active.
Incorporation of Cs-DTP salt on K10 clay enhances the acidity and change in
structural properties and e gives 98% selectivity towards 3-chloro-2-hydroxypropyl
acetate. The effects of various parameters were studied using this catalyst.The
experimental data so generated were used to develop a model. The model fits the
experimental data very well. The studies were used to achieve at optimum parameters
to suppress deactivation and thus a temperature of 90ºC and mole ratio of 1:15 should
be used. The catalyst gave complete conversion of epichlorohydrin and can be used
several times.