Cyclization of pseudoionone into α-Ionone over heteropolyacid supported on mesoporous silica SBA-15

Article abstract of DOI:10.1007/s10562-011-0631-1

Cyclization of pseudoionone into α-ionone was performed over the series heteropolyacid supported on SBA-15 in liquid-phase at 363 and 373 K using a batch reactor. It has been demonstrated that the liquid-phase synthesis of α-ionone by pseudoionone cyclization can be efficiently achieved on heteropolyacid/SBA-15 materials. The high catalytic performance of PW ₁₂/SBA-15 materials is due to their strong Bronsted acidity, high dispersion of active phase and also to absence of steric constraints for pseudoionone cyclization. PW₁₂/SBA-15 catalysts are specially active and selective for this reaction giving predominantly α-ionone, as the main product, with high yield (about 60% at 373 K after 2 h) close to that obtained via the homogeneous synthesis. This catalytic system is more active and efficient in comparison with heteropolyacid supported on commercial silica. In order to achieve comparable amount of α-ionone, as is got for PW ₁₂/SBA-15, belongs to apply five times more of the catalyst based on classical SiO₂.

Full text of DOI:10.1007/s10562-011-0631-1

Catal Lett (2011) 141:1384–1390
DOI 10.1007/s10562-011-0631-1
Cyclization of Pseudoionone into a-Ionone Over Heteropolyacid
Supported on Mesoporous Silica SBA-15
•
R. Rachwalik P. Michorczyk J. Ogonowski
•
Received: 4 May 2011 / Accepted: 16 May 2011 / Published online: 2 June 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Cyclization of pseudoionone into a-ionone was
performed over the series heteropolyacid supported on
SBA-15 in liquid-phase at 363 and 373 K using a batch
reactor. It has been demonstrated that the liquid-phase
synthesis of a-ionone by pseudoionone cyclization can be
efficiently achieved on heteropolyacid/SBA-15 materials.
The high catalytic performance of PW12/SBA-15 materials
is due to their strong Brønsted acidity, high dispersion of
active phase and also to absence of steric constraints for
pseudoionone cyclization. PW12/SBA-15 catalysts are
specially active and selective for this reaction giving pre-
dominantly a-ionone, as the main product, with high yield
(about 60% at 373 K after 2 h) close to that obtained via
the homogeneous synthesis. This catalytic system is more
active and efficient in comparison with heteropolyacid
supported on commercial silica. In order to achieve com-
parable amount of a-ionone, as is got for PW12/SBA-15,
belongs to apply five times more of the catalyst based on
classical SiO2.
widely found in various quantities, in essentials oils, veg-
etables, fruits, tea and tobacco. a-Ionone is often used in
flavours (e.g., berry flavours such as raspberry) and fra-
grances industry (violet and rose note) [4–6]. The main
industrial method for synthesis of a-ionone is based on the
cyclization of pseudoionone, carried out in a homogenous
system, in the presence of mineral acid [phosphoric (85%)
or dilute sulphuric acid (60%)] (Fig. 1). As was mentioned,
in the commercial production processes homogeneous
acids are used, resulting in considerable waste streams and
corrosion problems. Therefore, all works concern to design
highly active and selective heterogeneous acidic catalysts
suitable for the replacement of currently applied mineral
acids in homogeneous liquid-phase reactions.
Only several studies for the cyclization reaction of
pseudoionone into a-ionone in heterogeneous system have
appeared in the literature. Various catalysts are applied
for this process, particularly, Ca–Y zeolite [7], sulphated
mesoporous silica MCM-41 [8], sulphated TiO2 grafted
MCM-41 [9, 10], ZrO2 [11], polymer resins with both
sulfonic and perfluoroalkilosulfonic groups [12] and silica
supported heteropolyacids [13–15]. At presented work, the
cyclization of pseudoionone into a-ionone has been
investigated over heteropolyacid supported on mesoporous
silica SBA-15. Activity of the catalysts prepared in this
manner was compared with catalytic behaviour of hetero-
polyacid supported on commercial silica.
Keywords a-Ionone ꢀ Cyclization ꢀ Tungstophosphoric
acid ꢀ SBA-15 ꢀ UV DRS
1 Introduction
a-Ionone has been one the oldest classic perfume ingredi-
ent known since XIX century when it was first time syn-
thesized by Tiemann and Kru¨ger [1–3]. It is nor-isoprenoid
2 Experimental
R. Rachwalik (&) ꢀ P. Michorczyk ꢀ J. Ogonowski
Faculty of Engineering and Chemical Technology, Institute
of Organic Chemistry and Technology, Cracow University
´
of Technology, Warszawska 24, 31-155 Krakow, Poland
e-mail: rachwalik@chemia.pk.edu.pl
2.1 Samples Preparation
Pure siliceous SBA-15 was prepared as follows: in a
solution containing 80 ml of distilled water and 120 g of
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Cyclization of Pseudoionone into a-Ionone Over Heteropolyacid
1385
Diffusion reflectance UV (UV DR) spectra were taken on
an Ocean Optics HR2000 ? instrument (integration time
50 ms, 100 scans) equipped with an Ocean Optics DH-2000
BAL halogen-deuterium light source at room temperature.
The spectra were recorded at room temperature in the
wavelength range from 200 to 400 nm with BaSO4 as a
standard. The spectra are shown in a Kubelka–Munk func-
tion (F(R) = (1-R)2/2 R; where R is reflectance).
2.3 Catalytic Tests
All catalysts were tested in the pseudoionone cyclization.
Reaction was carried out at atmospheric pressure in a glass
reactor with a reflux condenser, an efficient stirrer and a
temperature controller. In a typical run, 300 mg of pseu-
doionone (Fluka) and 4 ml of toluene (POCh) were heated to
363 or 373 K. Afterwards, 200 mg of dried catalyst was
added to the reaction mixture. The test reaction was carried
out under isothermal (363 or 373 K) conditions for 1 and 2 h.
After this time, the reaction slurry was cooling down and
filtered. All catalysts after reaction were washed out with
toluene and dried. The reaction products were analyzed by
Agilent 6890 gas chromatograph equipped with a MS
detector, and a capillary column HP-5 ms.
Fig. 1 Cyclization reaction of pseudoionone to a-, b- and c-ionone
hydrochloric acid (2 M aqueous solution) placed in a
polypropylene bottle 8 g of Pluronic P123 (Aldrich) was
dissolved at 308 K. Subsequently, 17 g of tetraethyl
orthosilicate (TEOS 98%, Aldrich) was added dropwise to
the acidic solution and the reaction mixture was left stirring
(400 rpm) at 308 K for 20 h. After stirring the mixture was
aged for 24 h at 363 K. The resultant white precipitate was
filtered off and dried overnight at 333 K. Finally, the
material was calcined by increasing the temperature by
1 K/min to 823 K and maintained at this temperature for
12 h under flowing air to decompose the template and to
obtain siliceous SBA-15.
Conversion and others parameters were calculated as
shown below.
ꢀ
ꢁ
100 mol% ꢁ cpseudoionone
100 mol%
ꢀ 100 %
Conversion of pseudoionone ¼
The hybrid samples were prepared by impregnation of
SBA-15 with ethanolic solutions of tungstophosphoric acid
(Aldrich). Impregnation of mesoporous materials was car-
ried out at room temperature by applying incipient wetness
method. The resultant samples were dried at 393 K for 6 h
and labelled as PW12/SBA-15(x), where x represents the
loading of heteropolyacid in wt%. In the same manner was
prepared a catalyst with 20 wt% modifying agent sup-
ported on commercial silica (POCh—Polish Chemical
Reagents). The sample was denoted as PW12/SiO2(20).
ꢀ
ꢁ
caꢁionone
100 mol%
yield of a ꢁ ionone ¼
ꢀ 100 %
where cpseudoionone and ca-ionone, is the concentration
(mol%) of pseudoionone, and a-ionone in products,
respectively. Concentration of pseudoionone in feed was
taken as 100 mol% (without a solvent).
3 Results and Discussion
2.2 Samples Characterization
3.1 Physicochemical Properties
Powder X-ray diffraction (XRD) patterns in the range of
2h = 0.5–70° were recorded on a PANanlytical X’Pert
PRO diffractometer with Bragg–Brentano geometry with
CuKa radiation.
The XRD diffraction patterns for studied materials in low
angle region display one sharp line at 2h = 0.96° and two
weak peaks at 1.65 and 1.9 which can be assigned to (100),
(110) and (200) reflections which demonstrates the well
ordered nature of phases of two-dimensional hexagonal
(P6 mm) mesostructure (Fig. 2a). With increasing of PW12
loadings, the intensities of these diffraction lines gradually
decrease. Additionally, no shifting of mentioned diffraction
lines was observed. It is an evidence of absence destructive
influence of Keggin units on structure of mesoporous silica.
Sorption properties were studied using Micromeritics
ASAP 2020 instrument. Prior to the measurements, the
samples were outgassed at 523 K for 12 h. The specific
surface area (SSA) was measured in a relative pressure
range from 0.04 to 0.2. The total pore volume (VT) was
taken at the p/p° = 0.98 single point. Values of the mes-
opore volume (Vm) and micropore volume (Vl) were esti-
mated by applying the t-plot method.
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R. Rachwalik et al.
Fig. 2 XRD patterns for the
hybrid materials
Whereas, in the case of long angles range no characteristic
peaks of bulk heteropolyacid crystals are observed in
PW12/SBA-15 materials even for higher loadings of mod-
ifying agent. It is consistent with former observation made
by Liu et.al. for similar catalytic system [16], and also by
Kozhevnikov et al. [17] and Q.-H. Xia et al. [18] for het-
eropolyacid supported on MCM-41. These typical for
PW12 XRD reflections can be noticeable after enlargement
(50 times!) of ‘‘heteropolyacid region’’ (Fig. 2b). Then for
the samples with the higher amount of PW12 (above
30 wt%) on the support weak diffraction lines attributed to
heteropolyacid are observed. Additionally those lines are
broadened what clearly indicates that the particles of
modifying agent are highly dispersed on the surface of
amorphous pore walls of SBA-15. It evidences also prin-
ciple of the method applied for preparation of the studied
materials PW12/SBA-15.
Fig. 3 UV-vis DRS spectra for all studied samples
Sorption properties of the mentioned materials
PW12/SBA-15 derived from nitrogen adsorption–desorp-
tion isotherms at 77 K are summarized in Table 1. The
SSA, mesopore volumes (Vm) and the total pore volumes of
the samples decreased with increasing PW12 loadings. The
stepwise reduction of the surface area and also in the pore
volume of the PW12/SBA-15 materials can be attributed to
increasing of heteropolyacid percentage in the studied
materials. Moreover, even for PW12/SBA-15(50) the high
surface area above 450 m2/g could be retained. It can be
evidence that even for highest loading (50 wt%) hetero-
polyacid molecules did not block the access into meso-
porous channels. Microporous volume can be practically
neglected and in the case of the samples is PW12 loading
independent (cf. Table 1, last column). These pores, pres-
ent in studied materials originally come from SBA-15.
Micropores can be also, as was shown in literature, formed
after heteropolyacid adsorption on silica [20]. However, as
is presented in Table 1 volume of micropores remains
practically unchangeable even for highest PW12 loading
In order to confirm integrity of the heteropolyacid
structure UV DR spectroscopic measurements were
made. Figure 3 shows the spectra of the studied materials
PW12/SBA-15 [presented in a Kubelka–Munk function
(F(R))]. As can be seen all of them possess one band at ca.
265 nm which can be assigned to charge transfer O2-?W6
in the Keggin unit [19]. Moreover, the position of the band
is not shifted, while its intensity proportionally increases to
the amount of modifying agent applied for impregnation
(inset to Fig. 3). Above results clearly confirm high sta-
bility of heteropolyacid on the mesoporous silica SBA-15
without any depolymerization or degradation.
The nitrogen adsorption–desorption isotherms for het-
eropolyacid supported on mesoporous silica SBA-15
materials are shown in Fig. 4. As can be seen all isotherms
are type IV with H1 type hysteresis loop at high relative
pressure range of 0.6–0.8, attributed to the capillary con-
densation in the mesopores. It suggests that studied mate-
rials possess very regular mesoporous channels. The size of
hysteresis loop decreases with increasing of PW12 loading.
123

Cyclization of Pseudoionone into a-Ionone Over Heteropolyacid
1387
Fig. 4 N2 adsorption–
desorption isotherms
of PW12/SBA-15 hybrid
materials
(50 wt%). So the packing of the Keggin PW12 units is not
an additional source of microporosity.
PW12 after 1 h and it remains constant for higher loading.
Further increasing of the reaction temperature causes a
rise of the conversion value in comparison with reaction
carried out for 1 h (see Fig. 5a). Whereas, for the reaction
carried out at 373 K rapid increase of activity is notice-
able. Total conversion of pseudoionone is reached after
2 h for the catalysts with loading as high as 30 wt%
(Fig. 5b).
3.2 Cyclization of Pseudoionone Reaction
3.2.1 Conversion of Pseudoionone
In Fig. 5a the course of pseudoionone cyclization as a
function of PW12 loading is plotted, when the reaction is
carried out at 363 K for 1 and 2 h. The pseudoionone
conversion increases at the beginning up to 30 wt% of
The principal product obtained was a-ionone. Moreover
other chemical compounds were observed as the reac-
tion product. Namely, b-ionone, c-ionone in negligible
123

1388
R. Rachwalik et al.
Table 1 Characteristics of porosity of the hybrid materials PW12/SBA-15
Sample
SSA (m2/g)
Vl (cm3/g)
Vm (cm3/g)
VT (cm3/g)
SBA-15
748
656
595
518
483
451
0.04
0.05
0.04
0.04
0.05
0.05
0.85
0.72
0.68
0.59
0.53
0.49
0.89
0.77
0.72
0.63
0.58
0.54
PW12/SBA-15(10)
PW12/SBA-15(20)
PW12/SBA-15(30)
PW12/SBA-15(40)
PW12/SBA-15(50)
SSA specific surface area
Vl micropore volume
Vm mesopore volume
VT total pore volume
Fig. 5 Conversion of
pseudoionone versus PW12
loading at 363 (a) and 373 K (b)
quantities and also compounds from degradation both
substrate and ionone isomers were detected (a- and b- as
well as c-ionone). Absence of c-ionone in noticeable
quantities can be explained by high reactivity and low
stability of that isomer in the reaction mixture. It is easily
transformed to more stable a-ionone [17]. As was shown
by sorption of nitrogen measurements the tungstophos-
phoric acid deposited on the surface of SBA-15 did not
cause of blocking an access of pseudoionone into the
channel system.
ionone for PW12/SBA-15(50) catalyst is near 60%
(Fig. 6b) at 373 K after 2 h, this value was very similar to
the ones published by other authors for this reaction [16,
17] using solid catalytic system.
Ionone isomers distribution remains almost at the same
levels with PW12 loading (a:b = 4:1). This observation is
´
inconsistent with results presented in literature before. Dıez
at al. [13] showed that this phenomenon is observed only
for the catalyst with 58.5 wt%. of PW12 on silica for the
reaction carried out at 383 K for 6 h when total conversion
of pseudoionone is reached. In that case a product which
contains about 80% a-ionone and 20% b-ionone was
obtained. Whereas, for lower amount of heteropolyacid or
shorter reaction time all three ionone isomers were
observed with typical distribution a:b:c = 54:20:26.
Therefore, there are no steric limitations for the cycli-
zation reaction. This led us to conclusion that for kind of
ionone isomer decisive role play rate of corresponding
reactions. PW12/SBA-15 catalysts produced predominantly
a-ionone with yield comparable to that obtained via the
homogeneous synthesis.
3.2.2 Yield of a-Ionone
As was mentioned above a-ionone was main product of
this reaction. Total selectivity of this compound was close
to 60% for all catalysts.
The yield a-ionone formation in liquid-phase cyclization
of pseudoionone was subsequently explored as a function
of PW12 loading in order to test the effect of samples
acidity. Figure 6 shows the resulting yield for a-ionone
obtained after 1 and 2 h at 363 and 373 K. The yield of a-
123

Cyclization of Pseudoionone into a-Ionone Over Heteropolyacid
1389
Fig. 6 Yield of a-ionone at
363 (a) and 373 K (b)
3.2.3 Heteropolyacid Supported on Commercial
and Mesoporous Silica—Comparison of Catalytic
Behaviour
In order to present the advantage of tungstophosphoric acid
supported on mesoporous silica in the cyclization of
pseudoionone reaction, transformation of this ketone was
done over heteropolyacid on commercial silica. 20 wt% of
PW12 loading was chosen for comparison (conversion of
pseudoionone is below 100% at 373 K for the catalyst with
SBA-15 and in this manner clearly for weighing).
As can be seen in Fig. 7a generally, the catalytic system
with heteropolyacid supported on mesoporous SBA-15 is
more active in comparison with tungstophosphoric acid on
commercial silica. It is observed especially at higher tem-
perature and for longer reaction time (2 h). Further
increasing of reaction time for PW12/SiO2(20), even to 6 h
(not shown), results in little change in conversion of
pseudoionone (additional 5%) while, the distribution of
main reaction products is not changed. Our observations
concerning the activity of PW12 supported on commercial
silica were consistent with those presented by Diez and co-
workers for similar catalytic system [14].
The catalytic system based on commercial silica
undergoes deactivation faster than heteropolyacid sup-
ported on mesoporous silica (first after reaction is com-
pletely black whereas second only light-brown). It is
caused by deposition of different polymeric species on the
surface of catalyst. This process proceeds faster at the
beginning of the reaction. The kind of support is respon-
sible for this behaviour. Namely, SBA-15 possesses higher
SSA (c.a. 3 times) in comparison to commercial silica.
Additionally, mesoporous material is characterised by
regular channels system (8 nm in diameter) in mesoporous
region while commercial silica by irregular (in wide range,
from micropores to mesopores) pores size. When the size
Fig. 7 Comparison of catalytic behaviour heteropolyacid supported
on commercial and mesoporous silica
of pore entrances is smaller or not much bigger than
diameter of tungstophoshoric acid molecules (1 nm),
access to the channels for modifying reagent can be diffi-
cult. Then, heteropolyacid acid is mainly deposited on the
external surface and/or in the entrances to the pores
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1390
R. Rachwalik et al.
(blocking them). It results in formation of either bigger
crystals or more than one monolayer of modifying agent
predominantly at the external surface. In this manner het-
eropolyacid particles supported on commercial SiO2 also
can block access into the part of channels system for both
pseudoionone and reagent molecules.
comparison to material with heteropolyacid supported on
mesoporous SBA-15.
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Likewise as for heteropolyacid on mesoporous material
when commercial silica was applied as a support a-ionone
was a main reaction product (Fig. 7b). However selectivity
to this compound, as can be calculated from Fig. 7a and b,
is lower over PW12/SiO2(20) in comparison to PW12/SBA-
15(20) (&48% instead 60%). Simultaneously, the selec-
tivity of b-ionone formation reaches higher value and more
secondary products were observed. It is an evidence
that PW12/SiO2(20) possesses little higher acidity than
PW12/SBA-15(20) which slightly favours formation of b
isomer and other minor reaction compounds.
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The liquid-phase synthesis of ionones by pseudoionone
cyclization can be efficiently achieved on heteropolyacid/
SBA-15 hybrid materials. As was shown the catalytic
system PW12/SBA-15 is more active in comparison to
PW12/SiO2 material. The performance of PW12/SBA-15
materials is mainly due to their high dispersion of active
phase and also to absence of steric constraints for pseu-
doionone cyclization. PW12/SBA-15 catalysts are specially
active and selective for this reaction giving predominantly
a-ionone with yield comparable to that obtained via the
homogeneous synthesis. Moreover, in order to get com-
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