164

8 Synthesis of Chloromethyl -1,3-dioxolanes from

epichlorohydrin using supported heteropolyacids

165

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).

166

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

167

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

168

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).

169

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).

170

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).

171

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

172

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

173

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

174

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

175

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

176

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)

177

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)

178

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)

179

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)

180

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)

181

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

182

'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)

183

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)

184

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.