Green synthesis of natural benzaldehyde from cinnamon oil catalyzed by hydroxypropyl-β-cyclodextrin

Article abstract of DOI:10.1016/j.tet.2010.10.063

The efficient synthesis of natural benzaldehyde from natural cinnamon oil catalyzed by 2-hydroxypropyl-β-cyclodextrin (2-HPβ-CD) in water under rather mild conditions has been developed. Various analysis methods, e.g., DSC, UV-vis, ¹H NMR, ROES

Full text of DOI:10.1016/j.tet.2010.10.063

Tetrahedron 66 (2010) 9888e9893
Contents lists available at ScienceDirect
Tetrahedron
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Green synthesis of natural benzaldehyde from cinnamon oil catalyzed
by hydroxypropyl-
b-cyclodextrin
,
,
a
c
Hongyan Chen a b, Hongbing Ji a , Xiantai Zhou , Lefu Wang
*
a School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China
b Department of Chemical Engineering, Huizhou University, Huizhou 516007, China
c School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 June 2010
Received in revised form 10 October 2010
Accepted 22 October 2010
Available online 28 October 2010
The efficient synthesis of natural benzaldehyde from natural cinnamon oil catalyzed by 2-hydroxypropyl-
b
-cyclodextrin (2-HP
b-CD) in water under rather mild conditions has been developed. Various analysis
methods, e.g., DSC, UVevis, 1H NMR, ROESY, and fluorescence measurements had been utilized to
demonstrate formation of the 1:1 (molar ratio) complexes between 2-HPb-CD and cinnamaldehyde. The
inclusion equilibrium constant Ka was 928 Mꢀ1 at 298 K. The inclusion complex activated the substrate
and promoted the reaction selectivity. The yield for benzaldehyde could reach 70% under the optimized
Keywords:
2-Hydroxypropyl-
Cinnamaldehyde
Natural benzaldehyde
Inclusion complex
conditions (323 K, 5 h, 2% NaOH (w/v), cinnamaldehyde: 2-HP
investigation on kinetics and solubilization revealed that the binding ability between 2-HP
cinnamaldehyde is primarily responsible for the catalytic effects.
b
-CD¼1:1 (molar ratio)). Further
b-cyclodextrin
b-CD and
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
those methods did not give a high yield for benzaldehyde. Besides,
the severe reaction conditions or strong oxidant would unavoidably
decrease the natural essence of benzaldehyde. It is significant to
develop a new and clean process under mild reaction conditions
with high selectivity for natural benzaldehyde and the natural
essence of benzaldehyde is well preserved.
Supramolecular reactivity has attracted much attention over the
past decade.11e13 As one of the important and nontoxic supramo-
lecular hosts, cyclodextrin (CD) has been widely introduced into
various aqueous-phase organic reactions including oxidation,
reduction, ring opening and hydrolysis etc.14e20 It is able to catalyze
chemical reactions because of its particular inclusion and kinetic
properties. Specifically speaking the CDs can selectively form
hosteguest inclusion complex with guest molecule, which has
appropriate size and polarity in aqueous solution under mild con-
ditions, for they own a hollow truncated cylinder-shaped structure
with one hydrophobic internal cavity and two hydrophilic external
faces.21,22
Natural benzaldehyde, the second largest perfume in the world,
has captivated many researchers’ interest both in organic synthesis
and industry, as benzaldehyde plays important roles in food, bev-
erages, cosmetics, and pharmaceutical industries etc.1,2 Moreover,
compared to chemically synthetic benzaldehyde, natural benzal-
dehyde is more popular and represents a strong market advantage.3
Generally natural benzaldehyde is from alkaline hydrolysis of Lae-
trile catalyzed by enzyme, however, the process need thoroughly
dispose of the toxic hydrocyanic acid, which results in high cost for
production.
In recent years, natural benzaldehyde can also be produced from
natural cinnamon oil through various clean processes. Yi and her
group reported ozonization of natural cinnamon oils,4 the reaction
conditions were rather harsh (273 K, anhydrous conditions) and
the yield of benzaldehyde was 62%. Gao and Lv used near-critical
water (553 K, 15 MPa) as solvent for the conversion of cinna-
maldehyde, and the yield of benzaldehyde was 57%.5 As
manufacturing method, alkaline hydrolysis of cinnamaldehyde or
natural cinnamon oil is desirable,6e10 but the reaction requires high
temperature (373 e393 K), toxic phase transfer or surfactants cat-
alysts, and the yield of benzaldehyde was about 50%. Therefore,
In this paper, a practical challenge is to explore a water-soluble
and robust catalyst, that is, able to increase reaction selectivity for
the hydrolysis of cinnamaldehyde to benzaldehyde under mild
reaction conditions efficiently. For this purpose, 2-hydroxypropyl-
b
-CD (2-HP
maldehyde (Scheme 1). HP
of natural -CD, and is usually produced via a condensation reac-
tion between -CD and propylene oxide in alkaline solution, which
can extend the physicochemical and inclusion properties and
b
-CD) was used to catalyze the hydrolysis of cinna-
b
-CD is a highly water-soluble derivative
b
b
* Corresponding author. Tel.: þ86 20 84113658; fax: þ86 20 84113654; e-mail
address: jihb@mail.sysu.edu.cn (H. Ji).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.10.063

H. Chen et al. / Tetrahedron 66 (2010) 9888e9893
9889
catalytic activities of natural
b
-CD. 2-HP
b
-CD means hydroxypropyl
and 290 nm, the former is attributed to aldehyde group and the
other one is from its aromatic ring; besides, the absorption maxi-
mum gradually increased at 220 nm and decreased at 290 nm along
substitution only is at the O2 positions. It has been applied more
frequently than CD in food and pharmaceutical industry because of
its relatively more flexible cavity sizes, greater water solubility and
with increasing concentration of 2-HP
be considered as the proof of cinnamaldehyde incorporating into
the HP -CD cavity, that is, both phenyl ring and aldehyde group of
cinnamaldehyde were entrapped into the 2-HP -CD cavity, because
the non-polar cavity of HP -CD provided a smaller polar micro-
environment, which enhanced dissolution of guest molecule,
increased n/ electron transition of aldehyde group and reduced
electron transition of phenyl ring.25e28
b-CD. These behaviors may
lower toxicity than the natural b
-CD.23,24
b
OH-/H2O
b
O
O
+
O
b
2-HPβ-CD
Scheme 1. Alkaline hydrolysis of cinnamaldehyde to benzaldehyde promoted by
2-HP -CD.
p
*
b
p/p
*
In contrast to transition-metal catalysts and organocatalysts,
supramolecular catalysts employ non-covalent intermolecular
interactions between host and guest molecule. The inclusion
behavior of 2-HPb-CD with cinnamaldehyde was investigated by
Differential Scanning Calorimetry (DSC), UVevis, 1H NMR, Rotat-
ing-frame Overhauser Effect Spectroscopy (ROESY), and Fluores-
cence measurement. These characteristic methods served as an aid
for better understanding of how weak interactions affect reactivity.
In order to get further insight into the catalytic effects of 2-HPb-CD
for the alkaline hydrolysis, the solubilization of the CDs for cinna-
maldehyde solubility in water was investigated and the reaction
activation energy was calculated using the initial concentrations
method. It has been found that the reactivity is driven by the
binding ability between the host and the guest for the supramo-
lecular catalytic system. The reported hydrolysis process in the
present paper used green catalyst (2-HPb-CD) and green solvent
(water) to realize the clean synthesis of natural benzaldehyde.
2. Results and discussion
Fig. 2. The absorption spectra of cinnamaldehyde (7.5ꢁ10ꢀ5 mol/L) in the presence of
2-HP
b
-CD with different concentrations (ꢁ10ꢀ3 mol/L) at 298 K: (1) 0, (2)0.5, (3) 1.0,
2.1. Characterization of inclusion complex
(4) 2.0, (5) 3.0, (6) 4.0, and (7) 5.0.
2.1.1. DSC results. DSC reveals some evidence about complex for-
mation between cinnamaldehyde and cyclodextrins. The DSC curves
of pure components, physical mixture, and the inclusion complex of
cinnamaldehyde/2-HPb-CD were presented in Fig. 1. A typical ther-
mal curve for pure cinnamaldehyde (curve b) was a broad endo-
thermic peak at 409 K corresponding to its boiling point. For the
2.1.3. NMR results. In order to provide a definitive proof of the for-
mation of the inclusion complex, 1H NMR spectroscopy was carried
out using D2O as solvent, since the chemical and electronic envi-
ronments of protons changed during the inclusion complexation
process, which is reflected by changes of chemical shifts (Dd din-
¼
clusionꢀdfree).29 The comparison of the spectra for the individual
physical mixture of cinnamaldehyde/2-HPb-CD, the characteristic
components and the cinnamaldehyde/2-HPb-CD inclusion complex
thermal profile of cinnamaldehyde (curve c) was distinguishable
and shifted to lower temperature of 395 K. The formation of the
inclusion complex can be strongly evidenced by the disappearance
of the cinnamaldehyde endothermic peak (curve d).
was shown in Fig. 3. The 1H chemical shift values for free cinna-
maldehyde and the complex were reported in Table 1. The spectrum
of the complex is significantly different from cinnamaldehyde and
2-HPb-CD. Cinnamaldehyde has six types of protons: aldehyde
hydrogen (1-H), olefinic hydrogens (2-H and 3-H), and aromatic
protons (4-H, 40-H, 5-H, 50-H, and 6-H). From Fig. 3, all protons of
cinnamaldehyde had clear chemical shifts. Remarkable shift was
observed for 1-H, 3-H, 4-H, and 40-H protons in Table 1. It demon-
strates that inclusion complex was formed, and the highly hydro-
phobic phenyl ring and unsaturated double bond entered into the
c
b
d
a
cavity of 2-HPb-CD.
2D NMR studies revealed some useful information on the nature
of the inter- and intra-actions between guest and cyclodextrin in
the inclusion complexes.30 The contour map expansion for the
inclusion complex with 1:1 cinnamaldehyde/2-HPb-CD (molar
ratio) was presented in Fig. 4. The 2D ROESY spectra show corre-
lations between the protons of 2-H (olefinic hydrogen) and 1-H
(aldehyde hydrogen) in cinnamaldehyde and the protons of the
0
50
100
150
200
250
300
Temperature (oC)
internal hydrogen (H-3) and methyl hydrogen (CH3) in 2-HP
respectively, which suggest the benzene ring and eC]Ce were
included into the 2-HP -CD cavity, moreover the aldehyde group of
cinnamaldehyde was near the secondary face of 2-HP -CD, and
might form hydrogen bond with the hydroxypropyl group of
2-HP
-CD. The results were consistent with those obtained by 1H
NMR and UVevis experiments.
b-CD,
Fig. 1. DSC thermograms of 2-HP
b-CD (a), cinnamaldehyde (b), the physical mixture of
2-HP -CD and cinnamaldehyde (c), and the inclusion complex (d).
b
b
2.1.2. UVevis results. The UV absorption spectra of the aqueous
solution of the inclusion complex with different concentration of
b
2-HP
b
-CD were shown in Fig. 2. It can be seen clearly from Fig. 2
b
that the dual absorption peaks of cinnamaldehyde appear at 220

9890
H. Chen et al. / Tetrahedron 66 (2010) 9888e9893
5 '
4
2.1.4. Fluorescence results. Fig. 5(a) shows the changes of fluores-
6
4'
cence intensity of cinnamaldehyde with various CDs concentration at
room temperature. The maximum excitation and emission wave-
lengths were 248 and 322 nm, respectively. It is clear that the fluo-
rescence intensity of cinnamaldehyde was enhanced with increasing
CDs concentration, which is attributed to CD hydrophobic cavity
providing an apolar environment for cinnamaldehyde molecule and
thus increasing the quantum yield for the fluorescence of cinna-
maldehyde. It is notable that considerable enhancement was
2
5
O
3
1
cinnam aldehyde
(b)
(a)
observed for the 2-HP
lengths had a small red shift from 322 nm to 329 nm with increasing
concentration of 2-HP -CD. A reasonable explanation is that the
substitution group of hydroxypropyl in 2-HP -CD provided a large
b-CD system. Moreover the emission wave-
b
(c)
b
and deep cavity as well as strong hydrogen bond between the host
and the guest,31 thus included the guest much tightly.
The association constant (Ka) and the stoichiometry of the cin-
10
8
6
4
2
0
namaldehyde/2-HP
b-CD complex can be calculated based on the
ppm
BenesieHildebrand plots32 from the fluorescence data.
Fig. 3. 1H NMR spectra of (a) cinnamaldehyde, (b) 2-HP-
b-CD and (c) cinnamaldehyde
complexed with 2-HPb-CD.
1
1
1
½Gꢂo
¼
þ
a
F ꢀ Fo
a
Ka½Gꢂo½CDꢂo
Table 1
1H NMR chemical shift of cinnamaldehyde, and the inclusion complex of 2-HP
with cinnamaldehyde
b-CD
Here F and Fo represent the fluorescence intensity of cinna-
maldehyde in the presence and absence of CD, respectively; Ka is the
association constant; [G]o is the concentration of guest; [CD]o is the
1H
9.702
9.556
2H
3H
4H and 40H 5H and 50H 6H
concentration of CD;
a is the fluorescence measurement coefficient,
Cinnamaldehyde
Inclusion
6.731 7.568 7.486
6.737 7.715 7.586
7.440
7.475
7.428
7.460
which is a constant. The double reciprocal plots of 1/(FꢀFo) versus
1/[CD]o was shown in Fig. 5(b). The BenesieHildebrand plot exhibits
good linearity, which suggests the stoichiometry of the inclusion
complex is 1:1. The association constant Ka for the complexes was
928 Mꢀ1, and the corresponding standard free energy change DgGmӨ
Dd (ppm)
ꢀ0.146 ꢀ0.006 0.147 0.100
0.035
0.032
(298 K) was ꢀ16.93 kJ molꢀ1. The negative values of
DG indicated the
formation of hosteguest inclusion complexes in aqueous solution at
298 K was spontaneous.
7.00
7.50
8.00
8.50
9.00
9.50
2.2. Reaction studies
The reaction in the presence of 2-HPb-CD was carried out under
the condition (the concentration of NaOH was 2% (w/v), cinna-
maldehyde: CD (molar ratio)¼1:1), and the results were illustrated
in Table 2.
Benzaldehyde (70%) was obtained at 323 K, the optimum reaction
temperature. Comparing with other reports of producing benzalde-
hyde from cinnamaldehyde,4e10 this method provided the highest
yield for benzaldehyde under much milder conditions, which is very
important to preserve natural essence of benzaldehyde.
In order to further verify the efficiency of the present catalytic
system, a large-scale experiment was carried out as shown in
10.00
ppm (t1
5.0
4.0
3.0
2.0
1.0
ppm (t2)
Fig. 4. The 2D ROESY spectrum of the inclusion complex.
(a)
(b)
140
0.035
6
1
120
100
80
60
40
20
0
0.030
0.025
0.020
0.015
0.010
260
280
300
320
340
360
380
400
1000
2000
3000
4000
5000
Wavelength (nm)
1/[2-HPβ -CD] (L/mol)
Fig. 5. (a) Fluorescence spectra of 1ꢁ10ꢀ4 mol/L cinnamaldehyde in the presence of CD with different concentrations (ꢁ10ꢀ4 mol/L) at 298 K: (1) 0, (2) 2, (3) 4, (4) 6, (5) 8 and (6)10;
(b) the corresponding BenesieHildebrand plot of 1/(FꢀF0) versus 1/[CD] for the cinnamaldehyde complexed with 2-HP
b-CD.

H. Chen et al. / Tetrahedron 66 (2010) 9888e9893
9891
Table 2
Influence of 2-HP
temperature
b-CD on the hydrolysis of cinnamaldehyde under different reaction
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
Temperature
(K)
Reaction
time (h)
Conversation of
cinnamaldehyde (%)
Yield of
benzaldehyde (%)
313
323
333
6
5
4
86
95
90
52
70
68
Reaction condition: 2-HP
(1 mmol), NaOH (0.5 g), H2O (25 mL).
b-CD/cinnamaldehyde (mol/mol）¼1:1, cinnamaldehyde
Scheme 2. The isolated yield of benzaldehyde was 61% based on the
natural cinnamon oil used. This is because of the effective activation
of cinnamaldehyde via complexation with 2-HP
b
-CD.
O
0.00290 0.00295 0.00300 0.00305 0.00310 0.00315 0.00320
1/T (1/K)
2-HPβ-CD (15mmol)
O
+
O
NaOH (7.5 g), H O, 323K, 6h
2
15mmol
Fig. 6. Arrhenius plots of the rate constants for the alkaline hydrolysis.
Scheme 2. Large-scale alkaline hydrolysis of natural cinnamal oil to benzaldehyde
catalyzed by 2-HP -CD.
b
2.4. Solubilization studies
2.3. Kinetic studies
In order to further characterize how the weak interactions
between host and guest affected reactivity, the influence of 2-HPb-
CD on the apparent solubility of cinnamaldehyde in water had been
investigated, as listed in Table 4. Not surprisingly, the hydrophilic
CD derivate was much effective for increasing the apparent solu-
bility (increased 18.8-folds at 40% w/w). The phase diagram (Fig. 7)
In order to investigate the catalytic nature of the present system,
the reaction kinetics in the presence or absence of 2-HPb-CD were
studied using the initial concentration method. The obtained rate
orders and rate constants were listed in Table 3.
showed a linear increase of guest solubility as a function of 2-HPb-
Table 3
The rate orders (n) and rate constants (k) of the alkaline hydrolysis of cinnamalde-
hyde at different reaction temperatures
CD concentration though a slightly negative deviation at higher
concentrations and was classified as AL type, indicating formation
of a 1:1 stoichiometry complex. Great increase of cinnamaldehyde
solubility in water enlarges the contact area of the two phases,
resulting in acceleration of reaction and increase the yield for the
target production.
T (K)
na
nb
ka (minꢀ1
)
kb (minꢀ1
)
313
323
333
343
0.87
1.06
0.97
1.02
1.01
1.11
1.08
1.16
0.0178
0.0428
0.0722
0.1260
0.0532
0.0888
0.1410
0.2170
Table 4
a
In the absence of 2-HP
In the presence of 2-HP
b
-CD.
Apparent solubility of cinnamaldehyde in cyclodextrin solutions with different
concentration at 298 K
b
b-CD.
CD
CD concentration Cinnamaldehyde
Solubility
(w/w) %
solubility (mg/mL) enhancement
factor
From Table 3, it was concluded that the rate orders were nearly
equal to 1 for all cases, which indicated that the hydrolysis of cin-
namaldehyde or its inclusion complex with 2-HP -CD was first-
order reaction. The rate constants apparently increased with raising
reaction temperature. Furthermore, the rate constants for the
None
0.0
1.5
10.0
20.0
40.0
4.33
5.85
25.40
49.95
81.43
1.00
1.35
5.87
11.54
18.81
2-HP
b
-CD (DS¼3.9)
b
2-HP
suggested the hydrolysis rate for the 2-HP
higher than that without 2-HP -CD. Fig. 6 shows an Arrhenius
analysis for Table 3. The plots were linear and the calculated acti-
vation energy Ea from the slopes was 41.72 kJ/mol for the 2-HP -CD
system and 57.11 kJ/mol for the blank experiment, respectively.
Obviously, 2-HP -CD decreased the activation energy of the hy-
drolysis reaction, and it enhanced the selectivity for benzaldehyde.
As a result, 2-HP -CD was an efficient catalyst for the hydrolysis of
b
-CD system were higher than that without 2-HP
b-CD, which
b
-CD system was much
These results suggested that the intensity and the pattern of
molecular interactions between guest and the CDs had a direct
consequence on their solubilization efficiency. The intramolecular
hydrogen bonding formed between the hydroxyl groups at the
C3 of the glucose units and the hydroxyl alcohol enhances the
2-hydroxypropyl groups at the O2 positions to adopt a more
spread-out configuration, that is, the O2 hydroxypropyl sub-
b
b
b
b
stitution increases the size of cavity for the natural
b
-CD (diameters
-CD cavity: 6.0e6.5 A). This feature was man-
ifested as the remarkable enhancement of binding and solubility of
the cinnamaldehyde/2-HP -CD inclusion complex.
31
ꢀ
cinnamaldehyde to natural benzaldehyde.
of the natural
b
The catalytic proficiency ((kcat/KM)/kuncat) provides a measure
for the catalytic effect of the supramolecular catalysts, that is,
a measure of how affinity affects the reaction compared with the
b
uncatalyzed reaction under similar conditions.33,34 For 2-HP
b-CD,
the catalytic proficiencies was 3.48ꢁ103 Mꢀ1 at 298 K. The data
suggested that the catalytic hydrolysis effects primarily depended
on the KM values for the CDs, in other words, CDs can activate
cinnamaldehyde by forming hosteguest include complex and
promote the hydrolysis reaction.
2.5. Proposed reaction mechanism
In fact, the mechanism of alkaline hydrolysis of cinnamaldehyde
to benzaldehyde was considered as retro-Aldol condensation and
base acted as nucleophile. It was well known that the mechanism of

9892
H. Chen et al. / Tetrahedron 66 (2010) 9888e9893
3. Conclusion
90
80
70
60
50
40
30
20
10
0
The combination of DSC, UVevis, 1H NMR, ROESY, and fluores-
cence measurements was used to investigate interactions between
cinnamaldehyde and 2-HP -CD. Because of its expanding entrance
size, 2-HP
b
b
-CD was suitable for including cinnamaldehyde. Its
association constant was 928 Mꢀ1 at 298 K. Moreover, the aldehyde
group of cinnamaldehyde formed strong hydrogen bond with the
hydroxypropyl group of 2-HP
of cinnamaldehyde to benzaldehyde. As expected, it was demon-
strated 2-HP -CD conferred high activity and selectivity for the
b-CD, which promoted the conversion
b
alkaline hydrolysis of cinnamaldehyde. Further investigation on
kinetics and solubilization indicated that weak molecular in-
teractions between guest and CDs had a direct relevance on their
solubilization efficiency, and the binding abilities among CDs and
substrate mainly affected the hydrolysis reactivity. The benign, mild
and straightforward methodology for the conversion of cinna-
maldehyde to benzaldehyde may find its application in industry
and provide a general method for production of other similar
aldehyde or ketone fragrant compounds.
0
5
10
15
20
25
30
35
40
45
[cyclodextrin] (w/w,%)
Fig. 7. Experimental phase solubility diagrams of cinnamaldehyde for 2-HP
298 K.
b
-CD at
4. Experimental
CD-mediated hydrolysis was related with the formation of
CD/guest inclusion complex. As a result, owing to intermolecular
interactions among the inclusion complex of cinnamaldehyde with
4.1. General
GCeMS analysis was performed on a Shimadzu GC-MS-QP2010
2-HP
b
-CD, the hydrolysis mechanism in the present paper was
-CD. Based on the above exper-
plus with capillary column (Shimadzu Rtx-5MS, 30 m, 250
0.25 m).
2-HP
-CD (average substitution degrees DS¼3.9) was purchased
mm,
different from that without 2-HP
b
m
imental results, a possible reaction mechanism has been proposed
for the alkaline hydrolysis of cinnamaldehyde in the presence of
b
from Wuhan Yuancheng Technology Development Co. Ltd. Cinna-
maldehyde was obtained from Sinopharm Chemical Reagent. Nat-
ural cinnamal oil containing of 93% cinnamaldehyde, was bought
from Fulong Spice Co. Sodium hydroxide, petroleum ether and
ethyl acetate were obtained from Guangzhou Chemical Reagent
Factory, China. All chemicals were of analytical grade and were used
without further purification. Deionized water was applied for all
the experiments.
2-HPb-CD (Fig. 8).
4.2. Preparation of the inclusion complex of cinnamaldehyde
with 2-HP
b-CD
2-HP -CD (1 mmol) and 1 mmol cinnamaldehyde were mixed
b
in 25 mL deionized water. After stirred at 323 K for 2 h the mixture
was utterly clear. It was frozen for 24 h in refrigerator and then
lyophilized by freeze dryer (ALPHA 1-2LD, Christ, Germany). The
white amorphous powder, which is the inclusion complex of cin-
namaldehyde with 2-HPb-CD was obtained.
4.3. Characterization of the inclusion complex
Differential Scanning Calorimetry (DSC) data were obtained on
€
an STA 409 PC/PG (NETZSCH Geratebau GmbH). Each sample
Fig. 8. The possible mechanism of the alkaline hydrolysis of cinnamaldehyde catalyzed
by 2-HP -CD.
(2e6 mg) was exactly weighed in an aluminum crucible and was
heated from 313 to 673 K at the rate of 20 ꢃC/min in nitrogen gas.
UVevis spectra were measured on a UV-2450 UVevis spec-
trophotometer (Shimadzu, Japan). The absorption spectra of cin-
namaldehyde (7.5ꢁ10ꢀ5 mol/L) were measured with different
b
As shown in Fig. 8, first of all, 2-HPb-CD and cinnamaldehyde
can form the inclusion complex with the intermolecular hydrogen
bond OeH/O at the secondary rim. It is the hydrogen bond be-
tween aldehyde group in cinnamaldehyde and hydroxypropyl
concentrations of 2-HPb-CD (0.0, 0.5, 1.0, 2.0, 3.0, 4.0, and
5.0ꢁ10ꢀ3 mol/L).
groups in 2-HP
b
-CD, that is, able to facilitate formation of the ox-
1H NMR and 2D ROESY spectra were carried out at room tem-
perature in D2O on a Bruker Advance DRX-400 spectrometer
(Bruker BioSpin, Rheinstetten, Germany) equipped with a 5 mm
inverse probe with z-gradient coil. 1H NMR experiment was ach-
ieved with a spectral width 8012 Hz, acquisition time 2.04 s and
a relaxation delay 2 s with 32 scans. ROESY was conducted by using
the roesyetgp pulse sequence in the phase sensitive mode with
ygen anion (Oꢀ) and the nucleophilic addition of external hydrox-
ide ion (OHꢀ) to cinnamaldehyde, which results in the acceleration
of 2-HP
b-CD over alkaline hydrolysis of cinnamaldehyde. Through
the retro-Aldol condensation of cinnamaldehyde in the 2-HP
b
-CD-
mediated alkaline solution, the target product, benzaldehyde was
produced.

H. Chen et al. / Tetrahedron 66 (2010) 9888e9893
9893
a spin-lock mixing time of 200 ms and other parameters equal to
those of 1H NMR spectra.
diluted with deionized water, and the cinnamaldehyde concen-
tration was analyzed by UV-2450 UVevis spectrophotometry at
290 nm.
Fluorescence measurements were performed on F-4500 Fluo-
rescence spectrophotometer (Hitachi, Japan) to calculate the
inclusion equilibrium constant and thermodynamic parameters.
Quartz cell (1 cm) was used. The excitation wavelength was set at
248 nm and the emission at 322 nm with both the slits at 10 nm.
Acknowledgements
The authors thank the National Natural Science Foundation of
China (Nos 21036009 and 20776053), higher-level talent project
for Guangdong provincial universities, the Fundamental Re-
search Funds for the Central Universities and the Combination of
Industry, Schools and Research Institutions Project in Zhongshan
City (2009CXY011) for providing financial supports for this
project.
4.4. General procedure for the alkaline hydrolysis of
cinnamaldehyde to benzaldehyde
All reactions were performed in a 100 mL glass reaction flask
equipped with a condenser. In a typical experiment, cinnamaldehyde
(1 mmol) was mixed with deionized water (25 mL), NaOH (0.5 g), and
Supplementary data
2-HPb-CD (1 mmol) at 323 K while stirring. The reaction mixture was
extracted byethyl acetate and subsequentlyanalyzed by GCeMS with
naphthalene as an internal standard. The reproducibility for all the
data was within 5%.
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2010.10.063.
Large-scale alkaline hydrolysis of natural cinnamal oil catalyzed
by 2-HPb-CD was carried out as follows: the mixture of NaOH
References and notes
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the samples were filtered through a 0.45
mm membrane filter,