Selective Acetalization of ethylene glycol with methyl 2-napthyl ketone over solid acids: Efficacy of acidic clay supported Cs2.5H0.5PW12O40

Article abstract of DOI:10.1016/j.cattod.2014.03.079

Catalytic conversion of biomass to value added products is relevant with regard to several industries. Biomass derived ethylene glycol has many applications. Acetalization is used to synthesize valuable chemicals and also occasionally to protect carbonyl

Full text of DOI:10.1016/j.cattod.2014.03.079

Catalysis Today 237 (2014) 125–135
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Selective acetalization of ethylene glycol with methyl 2-napthyl
ketone over solid acids: Efficacy of acidic clay supported
Cs2.5H0.5PW12O40
Ganapati D. Yadav∗, Suraj O. Katole
Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai 400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Catalytic conversion of biomass to value added products is relevant with regard to several industries.
Biomass derived ethylene glycol has many applications. Acetalization is used to synthesize valuable
chemicals and also occasionally to protect carbonyl groups of aromatic molecules in organic trans-
formations. Acetalization of ethylene glycol to cyclic dioxolane has many applications in fragrance,
cosmetics, food and beverage additives, pharmaceuticals, detergents, and lacquer industries. The cur-
rent work reports synthesis of 2-methyl-2-napthyl-1,3-dioxolane by acetalization of ethylene glycol
with methyl 2-napthyl ketone using several heterogeneous solid acid catalysts including 20% (w/w)
Cs2.5H0.5PW12O40/K-10 (Cs-DTP/K-10), UDCaT-4, UDCaT-5 and K-10 clay. Among them, 20% (w/w) Cs-
DTP/K-10 catalyst was found to be the most efficient catalyst giving 87% conversion of methyl 2-napthyl
ketone with 100% selectivity toward 2-methyl-2-napthyl-1,3-dioxolane. Effects of several reaction
parameters were studied and optimized. The optimum reaction conditions were: 110 ◦C, molar ratio of
methyl 2-naphthyl ketone to ethylene glycol 1:2, catalyst loading 0.02 g/cm3, speed of agitation 800 rpm,
and time 3 h. Reaction mechanism and kinetic model were developed. The methodology was extended
to different substrates, and catalyst reusability was also studied. The catalyst was well characterized by
various techniques such as XRD, BET, FTIR, TPD and SEM. It is robust and recyclable.
Received 19 November 2013
Received in revised form 17 March 2014
Accepted 28 March 2014
Available online 15 July 2014
Keywords:
Heteropolyacids
Clay
Acetalization
Ethylene glycol
Methyl 2-napthyl ketone
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
ketalization which are acid catalyzed reactions. Common method
for the synthesis of acetals and ketals of glycerol or other glycols is
The defuctionalization of biomass and subsequent conversion to
various platform molecules is highly desirable to develop sustain-
able chemical industry. Such feedstock could be generated through
syngas (Fischer Tropsch) synthesis, fermentation and extraction
of biomass. Among these routes sugars, HMF, glycerol, ethanol,
butanol, ethylene glycol, etc. are promising feedstocks to make a
variety of value added chemicals. Acetalization is a general process
that is usually used as a protecting method for carbonyl com-
pounds such as aldehydes and ketones in the presence of other
functional groups in reactions of multifunctional organic molecules
[1,2]. However, in fragrance and flavor industries, acetals and
ketals are very widely used in formulations because of the type
of ‘notes’ they create, whereas some of these compounds are used
as oxygenated fuel additives having tremendous scope. Glycerol
and other glycols can be thus valorized through acetalization and
through reaction with aldehyde or ketone in the presence of an acid
catalyst [3,4]. The most commonly used acids catalysts are homo-
geneous such as sulfuric acid, phosphoric acid, hydrochloric acid,
and p-toluenesulfonic acid (PTSA) [5–7], and also heterogeneous
ion-exchange resins [8–11] and zeolites [12]. Acetals and ketals
of glycerol comprise valuable constituents for the formulation of
gasoline, diesel and biodiesel fuels. These oxygenated compounds,
when included into standard diesel fuel, lead to emissions with
substantial decrease in particulate matter, hydrocarbons, carbon
monoxide and unregulated aldehydes [5,9]. Similarly, these prod-
ucts can act as cold flow improvers for use in biodiesel and also
reducing its viscosity [5]. This issue is of significant importance
due to the growing demand for new additives specifically for
biodiesel that are biodegradable, non-toxic and renewable. Addi-
tion of acetals and ketals to biodiesel improves its viscosity and also
meets the conventional requirements of flash point and oxidation
stability [7].
The propylene glycol acetal of methyl naphthyl ketone is
a flavoring material with blossom orange note, which involves
the acetalization of the methyl naphthyl ketone with propylene
∗
Corresponding author. Tel.: +91 22 3361 1001; fax: +91 22 3361 1002/1020.
E-mail addresses: gdyadav@yahoo.com, gd.yadav@ictmumbai.edu.in
(G.D. Yadav).
http://dx.doi.org/10.1016/j.cattod.2014.03.079
0920-5861/© 2014 Elsevier B.V. All rights reserved.

126
G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
Sigma Aldrich, Mumbai, India); dodecyl amine, chlorosulfonic acid
(Spectrochem Ltd., Mumbai, India).
Nomenclature
A
AS
B
BS
E
ES
W
CA, CB
reactant species A–ethylene glycol
chemisorbed A
reactant species B–methyl 2-naphthyl ketone
chemisorbed B
product, 2-methyl-2-naphthyl-1, 3-dioxolane
chemisorbed product
2.2. Catalyst synthesis
20% (w/w) Cs2.5H0.5PW12O40/K-10 (designated as Cs-DTP/K-10)
was prepared by incipient wetness technique developed in our lab
[19–21] including UDCaT-4 [23–25] and UDCaT-5 [25,26].
water
concentration of A and B (mol/cm3)
CA0, CB0 initial concentration of A and B (mol/cm3)
CAS, CBS concentration of A and B on solid catalyst surface
(mol/g-cat)
2.3. Catalyst characterization
X-ray powder diffraction (XRD) was performed using a Bruker
AXS powder diffractometer D8 instrument, with Cu-K␣ (1.54 A)
CES, CWS concentration of E and W at solid catalyst surface
(mol/g-cat)
˚
radiation, to analyze the crystallinity, textural patterns of the
catalyst and the phase purity of synthesized catalysts. The XRD
patterns were recorded by scanning the catalyst sample within
the 2ꢀ range of 10–80◦. The specific surface area, pore volume
and pore diameter of each sample were obtained from nitrogen
adsorption–desorption isotherms measured in Micromeritics ASAP
2010 automated instrument and specific surface area, pore vol-
ume and pore diameter of all prepared catalysts were calculated
by using the BET model. Fourier transform infrared (FTIR) spectra
in the range of 400–4000 cm−1 were collected on a Perkin Elmer
Spectrophotometer using a sample disk of 5% catalyst weight in
KBr powder. Surface morphology of the catalyst was captured by
SEM (SU 30 microscope, JEOL, Japan). The sample was dried and
mounted on specimen studs and sputter coated with a thin film
of platinum to make the surface conducting. Temperature pro-
grammed desorption (TPD) was performed by using ammonia as
a probe molecule in Micromeritics AutoChem 2920 instrument. It
was carried out by heating 0.2 g of the catalyst at 573 K in dry air for
1 h and then purging it 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 sample until no more uptake of NH3
was observed. NH3 was then desorbed in helium 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.
CS
Ct
concentration of vacant sites (mol/g-cat)
total concentration of sites (mol/g-cat)
rate of disappearance of A (mol/cm3 s)
equilibrium constant for adsorption of A on catalyst
surface (cm3/mol)
−rA
KA
KB
k
equilibrium constant for adsorption of B on catalyst
surface (cm3/mol)
surface reaction rate constant for forward reaction
(cm6 mol−1 min−1 g-cat−1
)
KP
KW
equilibrium constant for adsorption of P on catalyst
surface (cm3/mol)
equilibrium constant for adsorption of W on catalyst
surface (cm3/mol)
vacant site
S
t
w
XA
time
catalyst loading (g/cm3 of liquid phase)
fractional conversion of A
glycol [3]. The commercial process for acetals is catalyzed by strong
acids such as p-toluenesulfonic acid. The acetalization of ethylene
glycol with methyl 2-napthyl ketone to synthesize 2-methyl-2-
napthyl-1,3-dioxolane is industrially important and has blossom
orange fragrance. However, the process is normally carried out
using homogeneous acid catalysts which need to be replaced. The
use of heteropolyacids [13–17] and their modified forms with
in situ generation of nano-catalysts [18–21] including different
supports such clays [13–21] and hexagonal mesoporous silica [22],
their characterization and applications have been deliberated in
some of our publications.
The current investigation deals with efficacy of different solid
acid catalysts for acetalization of ethylene glycol with methyl 2-
napthyl ketone to synthesize 2-methyl-2-napthyl-1,3-dioxolane. A
variety of catalysts were evaluated for their activity and selectiv-
ity. Use of modified heteropolyacid supported on acid treated K-10
clay as the most active and selective catalyst is discussed. Reaction
mechanism and kinetics are established.
2.4. Reaction procedure and analytical methods
A typical acetalization reaction of methyl napthyl ketone with
ethylene glycol was carried out in a 100-ml glass reactor (5 cm
diam.) fitted with a Dean-Stark apparatus for continuous removal
of water during reaction with overhead stirring and water con-
denser (Fig. 1). The reactor was charged with methyl napthyl ketone
(0.10 mol), ethylene glycol (0.20 mol), toluene as solvent, and n-
decane as internal standard. A known catalyst loading was used
(0.02 g/cm3) in control experiments. The reaction mixture was
vigorously stirred at different reaction temperatures. The reac-
tion was continued until maximum conversion was obtained. The
analysis of reaction products was carried out using GC (Chemito
1000) equipped with a BPX-50 capillary column (length: 30 m, ID:
0.25 mm) and with FID detector. Confirmation of reaction products
was achieved by GC–MS (Perkin Elmer, Clarus 500) using the same
capillary column.
2. Experimental
2.1. Chemicals and catalysts
The sources of various chemicals were as follows: dodeca-
tungstophosphoric acid (DTP), cesium chloride, methanol, n-
decane, zirconium oxychloride, aluminum nitrate, ammonium
persulfate, ethanol (M/s s.d. Fine Chem. Ltd., Mumbai, India);
montmorillonite K-10 clay, tetraethyl orthosilicate (M/s. Fluka
Chemicals, Germany);ethylene glycol, methyl 2-napthyl ketone,
benzophenone, acetophenone, propylene glycol, toluene (M/s.
3. Results and discussion
Preliminary experiments suggested that the best catalyst was
20% (w/w) Cs-DTP/K-10 and its characterization is briefly presented
here including the used catalyst.

G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
127
DTP on K-10, some of its crystallinity was lost. XRD patterns of 20%
(w/w) Cs-DTP/K-10 showed that there was no change in textural
pattern and crystallinity thereby confirming the stability of the
catalyst (Fig. 2).
3.1.2. BET surface area analysis (nitrogen adsorption)
The specific surface area of K-10 clay (240 m2/g) was found to
decrease with 20% Cs-DTP loading on K-10 clay (193 m2/g) (Table 1).
This may be due to the blockages of pores by particles Cs-DTP gen-
erated in situ on K-10 clay. The pore size distribution suggested that
the average pore size for catalysts was in the range of 5.0–6.5 nm
(mesoporous region). The adsorption–desorption isotherms for K-
10 and 20% Cs-DTP/K-10 showed that they have form of Type IV
isotherm with the hysteresis loop of type H3, which is a character-
istic of mesoporous solid (Fig. 3a and b).
3.1.3. Fourier transform infrared (FTIR) spectroscopy
Primary structures of supported DTP and Cs-DTP were identi-
fied by comparing their FTIR absorbance bands to those of bulk
DTP, Cs-DTP salt alone and 20% Cs-DTP/K-10 which showed char-
acteristic IR bands at approximately 1080 cm−1 (P O in central
tetrahedral), 984 cm−1 (terminal W O), 897 cm−1 and 812 cm−1
(W
polyanion. However, Cs-DTP is characterized by the split in the
O band, suggesting the direct interaction between the poly
O W) associated with the asymmetric vibrations in the Keggin
W
anion and Cs+. FTIR spectra of 20% (w/w) DTP/K-10 and 20% (w/w)
Cs-DTP/K-10 indicated that the primary Keggin structure was pre-
served in both the cases on K-10 support. When the characteristic
peaks of unsupported HPA and K-10 were superimposed, the peaks
for the supported catalysts appeared without any shift in the peak
position. Sharp peak at 1631 cm−1 indicated the presence of H3O+
(Bronsted acidity). In DTP, water was present as water of crystal-
lization while in the case of Cs-DTP/K-10 it indicated the presence
of partial H+ ion directly attached to the polyanion (· · ·O H) and
was present in K-10 and possibly as H3O+ (Fig. 4).
Fig. 1. Schematic diagram of the glass reactor assembly with modified Dean Stark
apparatus. 1. water condenser, 2. Dean Stark apparatus, 3. overhead stirrer, 4. sample
port, 5. oil bath, 6. thermostatic oil bath.
3.1. Catalyst characterization
3.1.1. X-ray powder diffraction (XRD)
From the background XRD reflection for K-10, it was found that
K-10 was amorphous in nature. The XRD patterns for K-10 reveal
one peak at 2ꢀ = 28.1◦, which is due to quartz, and there is no effect
on the 2␪ value of quartz even after supporting K-10 clay either
with dodeca-tungstophosphoric acid (DTP) or with Cs-DTP. Bulk
DTP is crystalline in nature, but it was observed that while loading
3.1.4. Scanning electron microscope (SEM)
SEM images of K-10 clay and 20% (w/w) Cs-DTP/K-10 show
almost similar morphological properties and no change in catalyst
surface morphology was observed (Fig. 5a and b).
Fig. 2. XRD of catalysts.

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G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
Table 1
Textural properties and acidities of catalysts.
Catalyst
BET surface area (m2/g)
Pore volume (cm3/g)
Pore diameter (nm)
Total acidity (mmol/g)
(Acidity/area) × 104 mmol/m2
K-10 clay
20% Cs-DTP/K-10
UDCaT-4
240
193
232
84
0.38
0.29
0.20
0.21
6.36
6.21
3.10
3.00
0.139
0.405
0.560
0.582
5.8
21.0
24.1
69.2
UDCaT-5
Fig. 3. (a) BET of K-10 clay. (b) BET of 20%Cs-DTP/K-10.

G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
129
Fig. 4. FTIR spectra of catalyst. (a) Fresh 20% Cs-DTP/K-10, (b) reused 20% Cs-DTP/K-
10, (c) Cs-DTP salt, (d) pure DTP.
3.1.5. Temperature programmed desorption (TPD)
TPD using ammonia as a probe was employed for the measure-
ment of the total acidity and acid strength and details regarding
total acidity of the catalysts are given in Table 1. These catalysts are
superacids having high site density.
3.2. Acetalization of ethylene glycol with methyl 2-naphthyl
ketone
3.2.1. Catalyst screening
For acetalization of ethylene glycol with methyl 2-naphthyl
ketone, solid acid catalysts including, 20% (w/w) Cs-DTP/K-10,
UDCaT-4, UDCaT-5, and K-10 clay were screened. The reaction
without catalyst (blank) was also studied by using identical
reaction parameters: temperature 110 ◦C, methyl 2-naphthyl
ketone:ethylene glycol mole ratio of 1:2, speed of agitation
800 rpm, catalyst loading 0.02 g cm−3, 3 h reaction time. Toluene
was used as solvent and n-decane as internal standard. Efficacy
of these catalysts was found as follows: 20% (w/w) Cs-DTP/K-
10 > UDCaT-4 > UDCaT-5 > clay K-10 > blank (Fig. 6). Out of them
20% (w/w) Cs-DTP/K-10 catalyst gave the highest methyl 2-
naphthyl ketone conversion of 86.8%, followed by UDCaT-4,
UDCaT-5 and K-10 clay gives 79.5, 74.9, 30.2%, respectively with
100% product selectivity (Table 2). Since water was removed con-
tinuously, the reaction was irreversible. Without catalyst (blank)
reaction gives conversion of 10% (Fig. 6). This is not surprising
since in acetalization reactions at high temperature, self-catalysis
due to protons from glycol can also take place. The surface areas
and acidity of catalysts are given in (Table 1). In all studied cata-
lysts 100% selectivity toward 2-methyl-2-naphthyl-1,3-dioxolane
Fig. 5. (a) SEM of K-10 clay. (b) SEM of 20% Cs-DTP/K-10.
was observed (Table 2). 20% (w/w) Cs-DTP/K-10 catalyst shows the
highest conversion of methyl 2-naphthyl ketone, the limiting reac-
tant due to its Bronsted acidic sites having acidity of 0.405 mmol/g
and high surface area of 193 m2/g as compared to clay K-10. Even
though the surface area of clay K-10 is high 240 m2/g, its acidity
of 0.139 mmol/g is less. The complete characterization of UDCaT-4
and UDCaT-5 has been reported earlier [23–26]. These catalysts are
superacids with distribution of Bronsted and Lewis acidity which
has been discussed in detail. Their activity can be explained in
terms of Bronsted acid and acidity per unit surface area and average
pore sizes which are responsible for activity (Tables 1 and 2). The
pore sizes of UDCaT-4, UDCaT-5 and Cs-DTP/K-10 are 3.10, 3.0 and
6.21 nm with corresponding conversions of 79.5, 74.9 and 86.8%,
respectively. The accessibility of active sites by the reactants ethyl-
ene glycol with methyl 2-napthyl ketone in all three catalysts would
not pose any problem but the product 2-methyl-2-napthyl-1,3-
dioxolane being bulky would have intraparticle diffusion limitation
Table 2
Product selectivity in acetalization of methyl 2-naphthyl ketone with ethylene glycol
using different catalysts.
Catalyst
Conversion (%)
Selectivity (%)
2-methyl-2-naphthyl-1,3-
dioxolane
20% Cs-DTP/K-10
UDCaT-4
UDCaT-5
K-10 clay
Blank
86.8
79.5
74.9
30.2
10.4
100
100
100
100
100

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G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
O
O
HO
O
110° C
CH3
H2O
CH3
+
+
Solid acid, Modified dean-Stark
OH
2-methyl-2-naphthyl-1,3-dioxolane
Ethylene glycol
Methyl 2-naphthyl ketone
Scheme 1. Acetalization of ethylene glycol with methyl 2-naphthyl ketone.
100
80
60
40
20
0
100
80
60
40
20
0
20% Cs-DTP- UDCaT-4
K10
UDCaT-5
Clay-K10
Blank
0
50
100
150
200
Time (min)
Catalyst Screening
Fig. 7. Effect of speed of agitation of acetalization of ethylene glycol. Reaction con-
Fig. 6. Catalyst screening of acetalization of ethylene glycol. Methyl 2-naphthyl
ditions: temperature 110 ◦C, molar ratio of methyl 2-naphthyl ketone to ethylene
ketone conversion ( ). Reaction conditions: temperature 110 ◦C, molar ratio of
glycol is 1:2, catalyst loading 0.02 g cm−3, reaction time of 3 h. ( ) 600 rpm; (
800 rpm; ( ) 1000 rpm.
)
methyl 2-naphthyl ketone to ethylene glycol is 1:2, catalyst loading 0.02 g cm−3
speed of agitation 800 rpm, reaction time of 3 h.
,
transfer effects did not influence the rate of reaction. Theoretical
calculations were also done as delineated earlier [23] to find that
a speed of 800 rpm was indeed sufficient to ensure absence of
external mass transfer resistance. That confirms the absence of
resistance to external mass transfer of methyl 2-naphthyl ketone
to the external surface of the solid acid catalyst.
to some extent in UDCaT-4 and UDCaT-5 and thus the conversion is
less in these two catalysts. UDCaT-4 (persulfated alumina and zirco-
nia on hexagonal mesoporous silica (HMS) catalyst had Lewis acidic
sites of 0.582 mmol/g, and the support used is hexagonal meso-
porous silica (HMS). It is reported in the literature that K-10 clay is
the better support for acetalization, esterification and etherification
reactions [27]. K-10 clay is better support because it adsorbs the
water molecules generated in the reaction and shifts the reaction
equilibrium toward the product. UDCaT-4 (persulfated alumina
and zirconia on hexagonal mesoporous silica (HMS) and UDCaT-
5 (super acidic modified sulfated zirconia based catalysts) showed
slightly less conversion 79.5 and 74.9%, respectively as compared
to 20% (w/w) Cs-DTP/K-10. This is because of these catalysts having
Lewis acidic sites of 0.582 and 0.560 mmol/g respectively and lower
surface area (84 m2/g) in case of UDCaT-5. Hence catalyst plays a
significant role in this study and 20% (w/w) Cs-DTP/K-10 catalyst
was found robust catalyst and used for further study (Scheme 1).
3.2.3. Effect of mole ratio
Effect of methyl 2-naphthyl ketone to ethylene glycol mole ratio
was studied at 1:1, 1:2, and 1:3, on methyl 2-naphthyl ketone con-
version was studied over 20% (w/w) Cs-DTP/K-10 catalyst (Fig. 8). It
was observed that methyl 2-naphthyl ketone conversion increased
with increasing mole ratio from 1:1 to 1:2 with final conversions
of 71 to 87%, respectively. At 1:2 mole ratio the conversion was
87% but with further increasing molar ratio at 1:3, the final conver-
sion was slightly lower (84%). Further, it is also likely because there
is competitive adsorption between methyl 2-naphthyl ketone and
ethylene glycol molecules on the catalytic sites and more of eth-
ylene glycol was adsorbed. Hence 1:2 molar ratio was found to be
the optimum and therefore further reactions were carried out using
1:2 molar ratio.
3.2.2. Effect of speed of agitation
The effect of speed of agitation was studied in the range
of 600–1000 rpm with 20% (w/w) Cs-DTP/K-10 (Fig. 7). It was
observed that there was very marginal increase in conversion of
methyl 2-naphthyl ketone when speed of agitation was increased
from 600 to 1000 rpm. At 600 rpm the initial rate of reaction was
almost the same as that at 800 and 1000 rpm. Hence, further
reactions were carried out at 800 rpm to ensure that external mass
3.2.4. Effect of catalyst loading
The effect of 20% (w/w) Cs-DTP/K-10 loading on the conversion
of methyl 2-naphthyl ketone was studied by varying the amount
from 0.01 to 0.03 g cm−3 of total reaction mixture at 110 ◦C for 3 h.

G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
131
100
80
60
40
20
0
100
80
60
40
20
0
0
50
100
150
200
0
50
100
150
200
Time (min)
Time (min)
Fig. 8. Effect of mole ratio of acetalization of ethylene glycol. Reaction conditions:
Fig. 10. Effect of reaction temperature of acetalization of ethylene glycol. Reaction
conditions: molar ratio of methyl 2-naphthyl ketone to ethylene glycol is 1:2, cata-
lyst loading 0.02 g cm−3, speed of agitation 800 rpm, reaction time of 3 h. ( ) 90 ◦C;
temperature 110 ◦C, speed of agitation 800 rpm, catalyst loading 0.02 g cm−3, reac-
tion time of 3 h. ( ) 1:1; (
) 1:2; ( ) 1:3.
(
) 100 ◦C; ( ) 110 ◦C.
3.2.5. Effect of reaction temperature
It was observed that with increase in catalyst loading the conver-
sion of methyl 2-naphthyl ketone was increased; it was due to the
increase in number of active sites and availability of large surface
area and pore dimension of the catalyst. And in the absence of
external mass transfer resistance, the rate of reaction was directly
proportional to the amount of catalyst loading. Hence with increase
in catalyst loading from 0.01 to 0.03 g cm−3, the conversion of
methyl 2-naphthyl ketone was increased from 71 to 92%. The ini-
tial rate of reaction, given as change in fractional conversion with
respect to time (dXA/dt) was directly proportional to catalyst load-
ing (Fig. 9).
Methyl 2-naphthyl ketone conversion as a function of temper-
ature was studied in the range of 90–110 ◦C; conversion of methyl
2-naphthyl ketone increased with increasing temperature from 90
to 110 ◦C (Fig. 10). At 90 ◦C the conversion was 61% which increased
up to 87% at 110 ◦C. Initial rates of reaction were calculated and
it was found that the rate increased substantially with increasing
temperature.
3.2.6. Reaction mechanism and kinetics
Scheme 2 depicts the mechanism. 20% (w/w) Cs-DTP/K-10 is
a strong solid acid catalyst which can donate a proton to the
hydroxyl group of the ethylene glycol which leads to the for-
mation of an oxonium ion. These are Bronsted acid sites. The
carbonyl of the methyl 2-naphthyl ketone could attack the car-
bon bearing the oxonium ion on the ethylene glycol to form an
intermediate which then releases water to form the five-member
ring product. The initial rate data could be analyzed on the basis of
Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism.
Weak adsorption of ethylene glycol (A) on a vacant site S is given
by
K
A
A + SꢀAS
(1)
Similarly, adsorption of methyl 2-naphthyl ketone (B) on the
vacant site is represented as
K
B
B + SꢀBS
(2)
Surface reaction of AS with BS on the adjacent sites leads to
formation of 2-methyl-2-naphthyl-1, 3-dioxolane (ES) and water
(WS) on the catalytic sites
K
2
AS + BSꢀES + WS
(3)
Desorption of 2-methyl-2-naphthyl-1, 3-dioxolane and water is
shown as
ES1ꢀ/KEE + S
(4)
Fig. 9. Plot of initial rate of reaction vs. catalyst loading.

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G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
Scheme 2. Possible reaction mechanism of acetalization of ethylene glycol with methyl 2-naphthyl ketone forming 2-methyl-2-naphthyl-1,3-dioxolane.
WS1/ꢀKWW + S
(5)
(6)
(7)
Upon integration this leads to:
ꢃ
ꢄ
M − XA
Now the total concentration of the sites, Ct is expressed as
ln
= k1(M − 1)t
(15)
M(1 − XA)
Ct = CS + CAS + CBS + CES + CWS
where k1 = kwCA0(M − 1)
This can also be expressed as:
Thus, in consonance with Eq. (15)
a
plot of
ln((M − XA)/(M(1 − XA))) vs. t at different catalyst loading (w)
to get straight lines passing through origin, the slopes of each
line divided by CA0(M − 1) gives the average k values and gave an
excellent fit (Fig. 11). The rate of reaction is proportional to the
number of active sites present on the surface. It would therefore
Ct = KACACS + KBCBCS + KECECS + KWCWCS
Or, the concentration of vacant sites as
Ct
CS
=
(8)
1 + KACA + KBCB + KECE + KWCW
If the surface reaction (C) is controlling the rate of reaction, then
the rate of reaction of A is given by the equation
dCA
−rA = −
= k2CASCBS − k2ꢀ CESCWS
(9)
dt
k2{KAKBCACB − (KEKWCECW)/K2}Ct2
dCA
−
=
(10)
2
dt
(1 + KAKC + KBCB + KECE + KWCW
)
When the reaction is far away from the equilibrium
k2Ct2KAKBCACB
dCA
−
=
=
(11)
(12)
ꢀ
ꢂ
ꢁ
2
dt
1 +
KiCi
kwCACB
(1 + KiCi)2
where kw = k2Ct2KAKB and w is catalyst loading. If the adsorption
constants are very small, then above equation reduces to
dCA
−
= kwCACB
(13)
dt
Let CB0/CA0 = M, the molar ratio of methyl-2-naphthyl ketone to
ethylene glycol at time t = 0. Then, Eq. (13) can be written in terms
of fractional conversion as
dXA
= kwCA0(1 − XA)(M − XA)
(14)
Fig. 11. Slope k1 vs. catalyst loading (w) (g/cm3).
dt

G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
133
Fig. 12. Second order plot of −ln{(M − XA)/[M(1 − XA)]}.
Fig. 14. Reusability study of acetalization of ethylene glycol. Methyl 2-naphthyl
ketone conversion ( ). Reaction conditions: temperature 110 ◦C, molar ratio of
mean that the reaction mechanism is LHHW type with very weak
adsorption of both the reactants in the absence of any diffusional
resistance. The values of k1 were also found at the different
temperatures at the same w and M (Fig. 12). The Arrhenius plot of
ln k1 vs. 1/T is shown in (Fig. 13), from which the activation energy
was calculated and found to be 11.66 kcal/mol. The high value of
activation energy also supported the fact that the overall rate of
reaction is not influenced by external mass transfer or intraparticle
diffusion resistance and it is intrinsically kinetically controlled
reaction on active sites.
methyl 2-naphthyl ketone to ethylene glycol is 1:2, catalyst loading 0.02 g cm−3
speed of agitation 800 rpm, reaction time of 3 h.
,
reaction time of 3 h (Fig. 14). After completion of the reaction, the
catalyst was recovered by filtration and washed with methanol
several times to remove the adsorbed materials from the surface
of the catalyst. There was some loss of catalyst during filtration
and handling (∼4–5%). Further there was no loss or leaching of
the active component Cs-DTP in the liquid phase which was con-
firmed by the ascorbic acid test [17]. Since the product is bulkier,
it was thought desirable to activate the catalyst. The catalyst was
calcined at 300 ◦C for 3 h, in the flowing air for re-activation. It was
characterized again. BET surface area of the used catalyst was very
marginally reduced from 193 to 189 m2/g which is within exper-
imental error. The XRD and FTIR studies of the used catalysts are
given in Figs. 2 and 4 which show that the catalyst has retained
its fidelity during reuse. This catalyst showed practically the same
activity and selectivity of desired products even after three catalytic
cycles. The nano-particles of Cs-DTP on K-10 surface are robust as
has been found out in other studies [28].
3.2.7. Catalyst reusability study
Catalyst reusability study was carried out by performing the
reaction under the optimized reaction conditions: temperature
110 ◦C, molar ratio of methyl 2-naphthyl ketone to ethylene gly-
col 1:2, catalyst loading 0.02 g cm−3, speed of agitation 800 rpm,
3.2.8. Substrate study
1,2-Propylene glycol and ethylene glycol were used along with
other substrates over 20% Cs-DTP/K-10 catalyst as given (Table 3) at
identical reaction parameters. In all substrates 100% selectivity of
1,3-dioxolane of glycols was obtained. The conversion and selectiv-
ity to the 1,3-dioxolane were influenced by the size of ketones used.
In the case of ethylene glycol, other ketones were tested under simi-
lar reaction conditions, including acetophenone and benzophenone
and conversion of acetophenone and benzophenone obtained was
72 and 69% respectively. Benzophenone is a bulky ketone and
leads to lower conversion. In the case of 1,2-propylene glycol,
acetalization with ketones including acetophenone and methyl 2-
naphthyl ketone were studied. The conversion of acetophenone and
methyl 2-naphthyl ketone was obtained of 60 and 56%, respec-
tively. Methyl 2-naphthyl ketone gave lower conversion with
1,2-propylene glycol as compared to ethylene glycol because of the
bulkiness of the product and its steric hindrance. In any of these
substrates, no by-product was formed.
Fig. 13. Arrhenius plot.

134
G.D. Yadav, S.O. Katole / Catalysis Today 237 (2014) 125–135
Table 3
Substrate study for acetalization of glycols with different ketone using 20% (w/w) Cs-DTP/K-10 catalyst.
Limiting reactant
Execs reactant
Product
Conversion (%)
O
O
HO
O
87
CH3
CH3
OH
HO
O
O
O
72
CH3
CH3
OH
HO
O
O
O
69
OH
HO
O
O
O
CH3
O
60
CH3
H3C
CH3
OH
O
HO
CH3
O
56
H3C
CH3
OH
Reaction conditions: temperature 110 ◦C, molar ratio of ketone to glycol is 1:2, catalyst loading 0.02 g cm−3, speed of agitation 800 rpm, reaction time of 3 h. Selectivity 100%
in each case.
Sharp peak at 1631 cm−1 indicated the presence of Bronsted acid-
ity. SEM images of K-10 clay and 20% (w/w) Cs-DTP/K-10 show
almost similar morphological properties and no change in catalyst
surface morphology was observed. NH3-TPD showed the catalyst
was superacidic in nature having high site density.
4. Conclusions
Acetalization of ethylene glycol with methyl 2-naphthyl ketone
was studied using a number of catalysts to synthesize 2-methyl-2-
naphthyl-1,3-dioxolane, amongst which 20% (w/w) Cs-DTP/K-10
was the best catalyst. The process gives 87% methyl 2-naphthyl
ketone conversion with 100% selectivity of 2-methyl-2-naphthyl-
1,3-dioxolane at 110 ◦C. Various reaction parameters were studied
to fix the optimized reaction conditions. Various substrates like
as 1,2 propylene glycol, and different ketones were studied at
identical reaction conditions to get 100% selectively toward 1,3-
dioxolane of different glycols. Reaction mechanism and kinetic
model were well fitted and the apparent activation energy was
calculated. The catalyst was regenerated after the reaction and
showed very good reusability. The catalyst 20% (w/w) Cs-DTP/K-10
was fully characterized both before and after use to understand its
superior properties and reusability. The XRD patterns showed that
there was no change in textural pattern and crystallinity thereby
confirming the stability of the catalyst. The pore size distribu-
tion suggested that the average pore size for catalysts was in the
range of 5.0–6.5 nm (mesoporous region). FTIR spectra indicated
that the primary Keggin structure was preserved on K-10 support.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
GDY received support from the R.T. Mody Distinguished Profes-
sor endowment and J.C. Bose National Fellowship of Department of
Science and Technology, Govt. of India. SOK received financial sup-
port as JRF/SRF of the UGC-SAP meritorious fellowship programme
under Center for Green Technology.
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