Convenient method for the transformation of epoxide to aldehyde and acetonide mediated by Cr-PLM

Article abstract of DOI:10.1080/00397911.2016.1254799

Chromium-pillared montmorillonite (Cr-PLM) could be synthesized and efficiently utilized for styrene oxide transformations. The target aldehyde product could be quantitatively achieved from the isomerization of styrene oxide by using 10 wt% of Cr-PLM under reflux temperature for 15 min. The acetonide product could be achieved in excellent yield from the reaction of styrene oxide and acetone by using 10 wt% of Cr-PLM under room temperature for 20 min. The catalyst could be recovered and reused at least five times without loss of activity.

Full text of DOI:10.1080/00397911.2016.1254799

A convenient method for the transformation of epoxide to aldehyde and acetonide
mediated by Cr-PLM
Laddawan Chareonsiriwat1, Warinthorn Chavasiri2
1Program in Petrochemistry, Faculty of Science, Chulalongkorn University, Bangkok,
Thailand 2Department of Chemistry, Faculty of Science, Chulalongkorn University,
Bangkok, Thailand
Corresponding author Warinthorn Chavasiri E-mail: warinthorn.c@chula.ac.th
Abstract
Chromium-pillared montmorillonite (Cr-PLM) could be synthesized and efficiently
utilized for styrene oxide transformations. The target aldehyde product could be
quantitatively achieved from the isomerization of styrene oxide by using 10 wt% of Cr-
PLM under reflux temperature for 15 min. The acetonide product could be achieved in
excellent yield from the reaction of styrene oxide and acetone by using 10 wt% of Cr-
PLM under room temperature for 20 min. The catalyst could be recovered and reused at
least five times without loss of activity.
Graphical Abstract
KEYWORDS: clay catalyst; chromium pillared clay; epoxide; isomerization; acetonide
1

INTRODUCTION
Epoxides are versatile intermediates in synthetic organic chemistry since they can be
easily transformed into valuable chemicals with a wide range of functional groups [1,2]
.
The isomerization of epoxides to carbonyl compounds is one of the most useful synthetic
transformation. The products from epoxide isomerization are widely used in
pharmaceutical, perfume, agrochemical industries and others. Various Lewis acid
reagents have been addressed for epoxide isomerization such as InCl3 [3], BF3 Et2O [4],
lithium salts [5], MgBr2 [6] and Pd(OAc)2 in the presence of a phosphine ligand with
frequently used in stoichiometric amounts [7]. Since some of these reagents are toxic,
corrosive and air- or moisture-sensitive. Heterogeneous catalysts have been developed to
overcome these drawbacks due to their easiness in separation and reusability with low
toxicity. Solid acid catalysts, such as zeolites [8,9], Nafion-H [10] and heteropoly acids [11]
have been applied for this isomerization reaction. However, the aldehyde products could
be undergone the competitive aldol condensation or polymerization makes some process
suffers from the rapid catalyst deactivation by coke formation [9,12]. The development of
catalytic processes for the isomerization of styrene oxide still attracted much attention in
the fine chemical industry.
Pillared clays are micro-mesoporous materials synthesized by exchanged cations with
polyoxocations into the interlayer of clay. After calcination, the intercalated
polyoxocations are transformed into inorganic oxide-pillared between the silicate layers
contribute high surface area and acidic property. Pillared clays have been shown to
contain both Brønsted and Lewis acid sites. Several modifications of pillared clays
2

produce a wide range of catalytic activities for utilizing in numerous applications such as
adsorbents and efficient catalysts [13–17]. The investigation on the catalytic performance of
the pillared clay materials has increased considerably, mostly in acid catalysis. Acid
catalyzed reactions and selective oxidation can be occurred efficiently by using
chromium pillared clay catalysts such as benzylic oxidation [18], oxidation of chlorinated
hydrocarbons [19], propene oxidation [20] and synthesis of octahydroxanthenes [21]. Due to
the variety of chromium oxidation states made it is an interesting metal for catalytic
applications [22]
.
In this work, we report the utilization of chromium pillared montmorillonite as a solid
acid catalyst for the transformation of styrene oxide. The corresponding aldehyde derived
from styrene oxide isomerization, phenylacetaldehyde, is an important intermediate for
the production of floral fragrances (a narcissus-like smell), pharmaceuticals, pesticides
and herbicides [12]. As for the transformation to acetonide products that used in the
pharmaceutical and fragrance production were also revealed. To our best knowledge,
there is no report on the utilization of chromium pillared clays as a catalyst for these
reactions.
RESULTS AND DISCUSSION
Characterization Of Catalysts
The XRD patterns of Cr-pillared clay and parent montmorillonite are shown in Fig. 1.
The d001 basal spacing of Cr-PLM was found as a broad peak and larger basal spacing,
compared with the parent clay. The reflection angle (2θ) of Cr-PLM and parent clay at
3

the 001 plane are determined as 6.30° and 6.90°, corresponding to a basal spacing (d001)
value of 14.0 and 12.8 Å which revealed that the Cr2O3 clusters were intercalated into the
interlayer of montmorillonite [23]
.
The BET specific surface area and acidity of synthesized clay catalyst and
montmorillonite clay are displayed in Table 1.
The nitrogen adsorption–desorption isotherms of Cr-PLM suggested the type IV isotherm
according to the IUPAC classification with H4 type of hysteresis loop, indicating that the
Cr pillaring precursor converted to mesoporous pillared structure between the clay layer
[24]. The higher BET specific surface area of the synthesized Cr-pillared clay was
obtained as expected. The pillaring process resulting in the improvement of acidity to
2.039 mmol/g. This total acidity (both weak and strong acid sites) of pillared clay was
derived from Brønsted and Lewis acid sites [23–25]. The amount of weak Brønsted acidic
sites was detected at the lower temperature NH3 desorption whereas the strong Lewis
acidic sites were detected at the high temperature desorption of NH3. Brønsted acid site is
related to the coordination of water molecule with chromium in pillars, while Lewis acid
site is ascribed to the Cr2O3 in pillars [23,25]
.
Catalytic Activity Of Cr-Pillared Clay In Styrene Oxide Transformation
The Isomerization Of Styrene Oxide
4

The isomerization of styrene oxide was selected for the catalytic activity testing of
synthesized clay catalysts. Various factors were carefully investigated to optimize the
conditions for the isomerization of styrene oxide to produce phenylacetaldehyde.
Firstly, various solvents were screened for styrene oxide isomerization at room
temperature (Table 2).
The use of 1,4-dioxane provided the desired product in 22% yield, whereas using CH2Cl2,
1,2-DCE, EtOAc, CH3CN or toluene, the products were obtained in low yields. Using
THF as solvent gave the best yield of phenylacetaldehyde.
The catalytic activity of the acidity improved Cr-pillared montmorillonite for
styrene oxide isomerization to selectively furnish corresponding aldehyde was
investigated (Table 3).
No isomerization activity was observed when the reactions were performed in the
absence of clay catalyst or in the presence of montmorillonite under refluxing THF. The
quantitative yield of phenylacetaldehyde was obtained when refluxing styrene oxide in
THF with 10 wt% of Cr-PLM for 4 h. It should be mentioned that Cr-PLM was a highly
effective catalyst for isomerization. To obtain optimal conditions for this catalytic
system, reaction time and temperature were investigated. The reaction could be carried
out at room temperature to afford the product of 35% within 15 min and continued for 6 h
to complete the reaction. Therefore, the shorten reaction time could be achieved by
5

raising temperature. Under refluxing within 15 min, the quantitative yield could be
furnished. The proposed mechanism of styrene oxide isomerization catalyzed by Cr-PLM
is presented in Fig. 2. The aldehyde formation proceeds via coordination of metal cation
of clay catalyst to the epoxide oxygen atom followed by C–O bond cleavage to form a
more stable benzylic cation. Then 1,2-shift of a hydrogen atom and regenerated the active
catalyst to give phenylacetaldehyde.
The isomerization of trans-stilbene oxide was used to demonstrate regioselectivity since
the isomerization can take place with either phenyl migration to produce
diphenylacetaldehyde or with hydrogen migration to furnish 2-phenylacetophenone. The
reaction time and the amount of Cr-PLM for the isomerization of trans-stilbene oxide
were examined to optimize the reaction conditions (Table 4).
The isomerization of trans-stilbene oxide could be carried out utilizing Cr-PLM at reflux
temperature. The yield of product was increased when prolonged the reaction time.
Nevertheless, a relatively long reaction time as 6 h led to the formation of undesired 2-
phenylacetophenone. Increasing amount of Cr-PLM, only desired product was obtained
in excellent yield. Prolonged the reaction time to 4 h could not enhance the yield. Under
these conditions trans-stilbene oxide underwent regioselective isomerization to produce
diphenylacetaldehyde as the major product in excellent yield. Interestingly, the catalyst
could be reused at least five times without loss of activity.
The Synthesis Of Acetonide
6

1,3-Dioxolanes are widely used protecting group for the synthetic carbohydrate and
steroid chemistry [26–29]. In the pharmaceutical and fragrance industries, acetonides (2,2-
dimethyl-1,3-dioxolanes) are used both as intermediates and as final products [30–34]
.
Epoxides can be transformed to acetonides straightforwardly with carbonyl compounds,
generally with ketones, in the presence of Brønsted or Lewis acid catalysts [35–40]. In
recent years, the development and application of effective heterogeneous catalysts has
increased greatly [41–45]. Pillared clays have been shown to be effective catalysts for the
transformation of epoxides to acetonides.
Hence, the catalytic activity of synthesized clay catalysts was examined for the synthesis
of acetonide from styrene oxide and acetone (Table 5).
When the reactions were carried out in the absence of clay catalyst or in the presence of
montmorillonite, no desired product was obtained. Cr-pillared clay gave 96% yield of
acetonide much higher than unmodified montmorillonite with 8% of the isomerized
aldehyde according to the high acidity and the suitable interlayer spacing of Cr-PLM.
Shortened the reaction time to 20 min, the catalytic efficiency was still great.
Furthermore, the high yield of acetonide product was obtained, when 2 mL of acetone
was used. Thus, it was revealed that Cr-PLM could be used as an efficient catalyst for the
synthesis of acetonide from styrene oxide.
The proposed mechanism of the synthesis of acetonide from styrene oxide and acetone
catalyzed by Cr-PLM is presented in Fig. 3. The acetonide formation proceeds via the
7

coordination of a metal cation of the catalyst with the epoxide oxygen atom. Followed by
nucleophilic epoxide ring-opening through the carbonyl oxygen and then regenerated the
active catalyst led to dioxolane ring formation.
The Synthesis Of Acetonides From Other Epoxides With Acetone
Various epoxides were reacted with acetone using a catalytic amount of Cr-PLM. The
excellent yields of the corresponding acetonides were obtained in all cases with different
reaction conditions (Table 6).
The transformation of styrene oxide to the corresponding acetonide was much faster than
the reaction of terminal aliphatic epoxide such as 1-dodecene oxide. Because of the stable
benzylic cation was formed while epoxide has undergone ring-opening. Epoxides with
ethereal linkage need more strongly reaction condition to obtain their corresponding
acetonides in high yields. Owing to the steric effect of bulky phenyloxy, butyloxy, and t-
butyloxy groups on the epoxide ring decreased the rate of reaction. The catalyst could be
reused at least five times without loss of catalytic activity.
CONCLUSION
A convenient catalytic method for styrene oxide transformation have been developed by
utilizing Cr-PLM. Excellent yields of the corresponding products from both of the
styrene oxide isomerization and the acetonide synthesis were obtained. Cr-PLM was
found to be highly effective, easily separable and could be reused at least five times
without loss of catalytic activity.
8

EXPERIMENTAL
Materials
Bentonite clay (Cernic International Co. Ltd.) with the typical chemical analysis of
(wt%): SiO2 63.60, Al2O3 17.60, Fe2O3 3.10, CaO 3.00, Na2O 3.40, K2O 0.50, was used
as raw material for catalyst preparation. Raw clay material was firstly purified by
fractionated centrifugation to remove quartz and other impurities.
The synthesized clay catalyst was characterized by XRD, surface area analyzer and NH3-
TPD. The XRD patterns of parent clay and synthesized Cr-pillared clay were obtained by
a Rigaku, D/MAX-2200 Utima-plus X-ray powder diffractometer with a monochromator
for Cu K radiation (40 kV, 30 mA). The 2 was ranged from 2-30º at a scanning rate of
3º/min and a step size of 0.02º. The BET specific surface areas of parent clay and
synthesized Cr-pillared clay were obtained from surface area analysis using the Microtrac
BELSORP mini-II adsorption instrument. Acidity of all clay materials was measured by
temperature-programmed desorption (TPD) method. The TPD spectra of ammonia were
recorded by the BELCAT equipped with thermal conductivity detector.
For the catalytic study, products from epoxide transformation were determined by Varian
CP-3800 GC (FID, BP1 column, 30 m). The 1H NMR spectra were obtained in CDCl3
and determined by Varian Mercury plus 400 NMR spectrometer which operated at
399.84 MHz.
9

Preparation And Characterization Of Cr-Pillared Clay Catalyst
Bentonite was purified by fractionated sedimentation. Raw bentonite was suspended in
deionized water under vigorous stirring at room temperature. The colloid clay was
centrifuged, after that quartz sediments and other impurities could be separated. The
colloid bentonite was collected and dried at 100 ºC. The purified bentonite as
montmorillonite was characterized by XRD, BET and TPD method.
Cr-pillared montmorillonite was synthesized according to the method reported by
Yurdakoç et al. with some modifications [25]. CrCl3 6H2O (2.67 g) was dissolved in 100
mL of deionized water. Na2CO3 (0.02 g) was added to the CrCl3 solution at room
temperature. This solution mixture was then aged at 95 ºC for 40 h. At the same time, 2 g
of montmorillonite was suspended in 100 mL of deionized water under stirring at room
temperature. Afterwards, the warm hydrolyzed chromium solution was slowly added to
the montmorillonite suspension and stirred for 24 h. The Cr-pillared montmorillonite
suspension was collected by centrifugation, washed with deionized water until chloride
ions were eliminated, dried at 100 ºC and calcined at 300 ºC for 5 h. The calcinated
products were designated as Cr-PLM. The obtained Cr-PLM was characterized using
XRD, BET and TPD method.
GENERAL CATALYTIC PROCEDURE
For The Isomerization Of Styrene Oxide
Cr-PLM (10 wt%) was added to the mixture of styrene oxide (1 mmol) and THF (5 mL)
and the reaction was then continuously stirred for desired time and temperature
10

(monitored by TLC). After the appropriate time or the reaction was completed, the
catalyst was easily filtered out, and thoroughly washed with Et2O. The solvent was partly
evaporated under reduced pressure. The obtained mixture was taken and analyzed by GC
with the addition of an exact amount of an appropriate internal standard.
For The Synthesis Of Acetonide
Cr-PLM (10 wt%) was added to the mixture of styrene oxide (1 mmol) and acetone (3
mL) and the reaction was then continuously stirred for desired time and temperature
(monitored by TLC). After the appropriate time or the reaction was completed, the
catalyst was easily filtered out, and thoroughly washed with acetone. The solvent was
partly evaporated under reduced pressure. The obtained mixture was taken and analyzed
by GC with the addition of an exact amount of an appropriate internal standard.
Recovery And Reuse Of Cr-Pillared Clay
Cr-PLM could be easily recovered from the reaction mixture by filtration or
centrifugation. After washing with Et2O, dried at 120 ºC in oven for 2 h, the regenerated
Cr-PLM was used in the next run.
ACKNOWLEDGEMENTS
We gratefully thank the 90th Anniversary of Chulalongkorn University, Rachadapisek
Sompote Fund (GCUGR1125582022D21) for the financial support and the Natural
Products Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn
University, Thailand for the provision of chemicals and laboratory facilities.
11

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17

Table 1 The amount of acidity and surface area of catalysts
Entry Catalyst
Surface area
(m2/g)
Acidity (m mol/g
Total acidity
(mmol/g)
Weak acid Strong acid
sites
sites
1
2
Cr-PLM
91.2
0.126
0.000
1.913
1.188
2.039
1.188
Montmorillonite 58.4
18

Table 2 The solvent effect on isomerization of styrene oxide catalyzed by Cr-PLM
Recovery (%)a Yield (%)a
Entry Solvent
1
2
3
4
5
6
7
CH2Cl2
88
81
6
1,2-DCE
12
22
14
35
3
1,4-dioxane 72
EtOAc
THF
84
70
CH3CN
toluene
95
100
10
Reaction conditions: styrene oxide (1 mmol), Cr-PLM (10 wt%), solvent (5 mL) at room
temperature (30oC) for 15 min.
a determined by GC using an internal standard technique
19

Table 3 Catalytic activity of clay catalysts in the isomerization of styrene oxide
Entry Catalyst
Temp.
reflux
Time (h) Recovery (%)a Yield (%)a
1
2
3
4
5
6
7
-
4
4
4
quant.
0
Montmorillonite reflux
quant.
0
Cr-PLM
Cr-PLM
Cr-PLM
Cr-PLM
Cr-PLM
reflux
0
quant.
35
RT (30 oC) 0.25
RT (30 oC) 6
70
0
quant.
89
reflux
reflux
0.08
0.25
14
0
quant.
Reaction conditions: styrene oxide (1 mmol), clay catalyst (10 wt%), THF (5 mL)
a Determined by GC using an internal standard technique
20

Table 4 The isomerization of trans-stilbene oxide catalyzed by Cr-PLM
Entry Catalyst amount (wt%) Time (h) Recovery (%)a Yield (%)a,b
1
2
3
4
5
10
10
10
30
30
0.25
60
44
11
5
35
1
6
1
4
51
73 (12)c
91
6
92
Reaction conditions: trans-stilbene oxide (1 mmol), Cr-PLM (vary), THF (5 mL) at reflux
temperature
a determined by GC using an internal standard technique
b diphenylacetaldehyde
c The yield of 2-phenylacetophenone is shown in the parenthesis
21

Table 5 Catalytic activity of clay catalysts in the synthesis of acetonide
Time (h) Recovery (%)a Yield (%)a,b
Entry Catalyst
1
2
3
4
5
-
2
96
93
0
0
2
Montmorillonite 2
0
3
Cr=PLM
Cr=PLM
Cr=PLM
2
96
93
98
8
0.33
0.33
0
11
9
0
Reaction conditions: styrene oxide (1 mmol), acetone (3 mL), clay catalyst (10 wt%) at
room temperature (30oC)
a determined by GC using an internal standard technique
b 2,2-dimethlyl-4-phenyl-1,3-dioxolane
c phenylacetaldehyde
d acetone (2 mL)
22

Table 6 The synthesis of acetonides catalyzed by Cr-PLM
Entry Epoxides
1b
Acetonides
Yield (%)a
98
2c
97
3
102
97
4d
5
99
Reaction conditions: epoxide (1 mmol), acetone (2 mL and Cr-PLM (10 wt%) at reflux
temperature for 2 h
a determined by GC using an internal standard technique
b Cr-PLM (10 wt%) at room temperature (30 oC) for 20 min
c Cr-PLM (20 wt%) at reflux temperature for 4 h
d Cr-PLM (10 wt%) at reflux temperature for 4 h
23

Fig. 1. X-ray diffraction patterns of (a) montmorillonite and (b) Cr-pillared
montmorillonite.
24

Fig. 2. Proposed mechanism for styrene oxide isomerization catalyzed by Cr-PLM.
25

Fig. 3. Proposed mechanism for the synthesis of acetonide catalyzed by Cr-PLM.
26