Synergistic catalytic oxidation of cinnamaldehydes by poly(vinyl alcohol) functionalized β-cyclodextrin polymer in CaO2/HCO3 ? system

Article abstract of DOI:10.1080/10610278.2017.1371719

Poly (vinyl alcohol) (PVA)–functionalized β-cyclodextrin (β-CD) polymer crosslinked by citric acid (PVA-g-CD) was synthesized, characterized and evaluated for the catalytic oxidation of cinnamaldehydes. The polymer?showed good activity and?selectivity to aldehydes for some structurally diverse cinnamaldehydes. The enhanced catalytic activity may be attributed to the synergistic effect of the intermolecular weak interactions between β-CD and the functional group of PVA. In addition, calcium peroxide?as?a solid oxidant was found to significantly affect the reaction. This catalyst can be recovered and reused for five times without a significant loss in its activity and selectivity.

Full text of DOI:10.1080/10610278.2017.1371719

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Synergistic catalytic oxidation of cinnamaldehydes
by poly(vinyl alcohol) functionalized β-cyclodextrin
−
3
polymer in CaO /HCO system
2
Yanxiong Fang, Zujin Yang, Xia Zhang & Hongbing Ji
To cite this article: Yanxiong Fang, Zujin Yang, Xia Zhang & Hongbing Ji (2017): Synergistic
catalytic oxidation of cinnamaldehydes by poly(vinyl alcohol) functionalized β-cyclodextrin polymer
−
3
in CaO /HCO system, Supramolecular Chemistry, DOI: 10.1080/10610278.2017.1371719
2
To link to this article: http://dx.doi.org/10.1080/10610278.2017.1371719
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Date: 02 October 2017, At: 01:06

Supramolecular chemiStry, 2017
ꢁꢁꢂs://dꢃꢄ.ꢃꢅg/10.1080/10610278.2017.1371719
ꢀ
Synergistic catalytic oxidation of cinnamaldehydes by poly(vinyl alcohol)
−
3
functionalized β-cyclodextrin polymer in CaO /HCO system
2
a
b,d
a
c,d
Yanxiong Fang , Zujin Yang
, Xia Zhang and Hongbing Ji
ꢆ
b
Fꢆꢇꢈꢉꢁꢊ ꢃf cꢀꢋꢌꢄꢇꢆꢉ engꢄnꢋꢋꢅꢄng ꢆnd lꢄgꢀꢁ indꢈsꢁꢅꢊ, Gꢈꢆngdꢃng unꢄvꢋꢅsꢄꢁꢊ ꢃf tꢋꢇꢀnꢃꢉꢃgꢊ, Gꢈꢆngzꢀꢃꢈ, cꢀꢄnꢆ; Fꢄnꢋ cꢀꢋꢌꢄꢇꢆꢉ indꢈsꢁꢅꢊ rꢋsꢋꢆꢅꢇꢀ
ꢇ
insꢁꢄꢁꢈꢁꢋ, Sꢇꢀꢃꢃꢉ ꢃf cꢀꢋꢌꢄꢇꢆꢉ engꢄnꢋꢋꢅꢄng ꢆnd tꢋꢇꢀnꢃꢉꢃgꢊ, Sꢈn yꢆꢁ-sꢋn unꢄvꢋꢅsꢄꢁꢊ, Gꢈꢆngzꢀꢃꢈ, cꢀꢄnꢆ; Fꢄnꢋ cꢀꢋꢌꢄꢇꢆꢉ indꢈsꢁꢅꢊ rꢋsꢋꢆꢅꢇꢀ insꢁꢄꢁꢈꢁꢋ,
Sꢇꢀꢃꢃꢉ ꢃf cꢀꢋꢌꢄsꢁꢅꢊ, Sꢈn yꢆꢁ-sꢋn unꢄvꢋꢅsꢄꢁꢊ, Gꢈꢆngzꢀꢃꢈ, cꢀꢄnꢆ; hꢈꢄzꢀꢃꢈ rꢋsꢋꢆꢅꢇꢀ insꢁꢄꢁꢈꢁꢋ ꢃf Sꢈn yꢆꢁ-sꢋn unꢄvꢋꢅsꢄꢁꢊ, hꢈꢄzꢀꢃꢈ, cꢀꢄnꢆ
d
ABSTRACT
ARTICLE HISTORY
Poly (vinyl alcohol) (PVA)–functionalized β-cyclodextrin (β-CD) polymer crosslinked by citric
acid (PVA-g-CD) was synthesized, characterized and evaluated for the catalytic oxidation of
cinnamaldehydes. The polymer showed good activity and selectivity to aldehydes for some
structurally diverse cinnamaldehydes. The enhanced catalytic activity may be attributed to the
synergistic effect of the intermolecular weak interactions between β-CD and the functional group
of PVA. In addition, calcium peroxide as a solid oxidant was found to significantly affect the reaction.
This catalyst can be recovered and reused for five times without a significant loss in its activity and
selectivity.
rꢋꢇꢋꢄvꢋd 18 Jꢈnꢋ 2017
aꢇꢇꢋꢂꢁꢋd 19 aꢈgꢈsꢁ 2017
KEYWORDS
β-cD; ꢂꢃꢉꢊ (vꢄnꢊꢉ ꢆꢉꢇꢃꢀꢃꢉ);
ꢇꢆꢁꢆꢉꢊꢁꢄꢇ ꢃxꢄdꢆꢁꢄꢃn; nꢆꢁꢈꢅꢆꢉ
bꢋnzꢆꢉdꢋꢀꢊdꢋ; sꢊnꢋꢅgꢄsꢁꢄꢇ
ꢋffꢋꢇꢁ
1
. Introduction
every year, especially in western countries. The conven-
tional industrial process via the alkaline hydrolysis of laetrile
only produces natural BzH that contains toxic hydrogen
cyanide (1). Therefore, hydrolysis of natural cinnamon
oil which contains more than 80% of cinnamaldehyde
The market demand of natural benzaldehyde (BzH) as a
valuable ingredient for the food, beverages, cosmetics,
perfumery, and pharmaceutical industries, is tremendous
CONTACT Zꢈjꢄn yꢆng
yꢆngzj3@ꢌꢆꢄꢉ.sꢊsꢈ.ꢋdꢈ.ꢇn; hꢃngbꢄng Jꢄ
Jꢄꢀb@ꢌꢆꢄꢉ.sꢊsꢈ.ꢋdꢈ.ꢇn
Sꢈꢂꢂꢉꢋꢌꢋnꢁꢆꢉ dꢆꢁꢆ fꢃꢅ ꢁꢀꢄs ꢆꢅꢁꢄꢇꢉꢋ ꢇꢆn bꢋ ꢆꢇꢇꢋssꢋd ꢆꢁ ꢀꢁꢁꢂs://dꢃꢄ.ꢃꢅg/10.1080/10610278.2017.1371719.
©
2017 infꢃꢅꢌꢆ uK lꢄꢌꢄꢁꢋd, ꢁꢅꢆdꢄng ꢆs tꢆꢊꢉꢃꢅ & Fꢅꢆnꢇꢄs Gꢅꢃꢈꢂ

2
Y. FANG ET AL.
CIN) has attracted considerable attention as an alternative
to produce natural BzH (1–3). However, the application of
these methods has been limited because of the poor sol-
ubility of CIN in water and the low selectivity to natural
BzH. Phase transfer catalysis (PTC) is a simple and feasible
method which has been widely investigated to synthesize
some organic chemicals with high yield of products, large
reaction rate and high selectivity of the desired products
with more than one active center and have attracted
much attention in the development of phase-transfer cata-
lyzed systems (17–19). Epichlorohydrin (EPI) is a common
crosslinking reagent for the β-CDP synthesis, but its use
has been restricted in the food industry due to its toxicity
to human health and the environment (22, 23). In compari
-
son to EPI, citric acid has a low toxicity and is friendly to the
environment. As a cross-linker, citric acid has been used to
synthesize β-CDP at temperatures below 200 °C without
any organic solvents or harmful additives (24).
(
4, 5). In recent years, the liquid phase oxidation of CIN to
natural BzH has been carried out with cyclodextrins (CDs)
as reverse phase-transfer catalysts (2, 6–8).
Oxidation is an important class of reaction from
both industrial and academic points of view. In gen-
eral, the choice of oxidants is very important for the
multiphase reaction system. PTC provides many good
opportunities for the oxidation reactions with certain oxi-
dizing agents such as NaOCl, H O , and KMnO (25, 26).
Cyclodextrins (CDs) are cyclic oligosaccharides with
6–8 d-glucose units linked by α-1,4-glucose bonds, which
are called α-, β-, and γ-CD, respectively. They have a trun-
cated cone-shaped molecular structure with a relatively
hydrophobic inner cavity and hydrophilic outer surface,
which can form inclusion complexes with guest mole-
cules in their hydrophobic cavities. By using the specific
microenvironment, they can selectively bind substrates
in the aqueous phase and catalyze chemical reactions by
noncovalent host–guest bonding (9–14). Although the
catalysts show good catalytic activity for the reaction,
the separation of catalysts from the homogeneous sys-
tem is difficult. Therefore, immobilization of CDs is more
appealing because of their many attractive advantages
2
2
4
Among them, H O is attractive for the reaction systems,
2
2
with H O as a by-product. However, since H O is easily
2
2
2
decomposed at high temperature (27), the use of the
excess amount of H O would lead to decrease selectivity
2
2
of natural BzH (15, 17–19). Calcium peroxide (CaO ) is an
2
environmentally friendly solid oxidizing agent. At a large
pH range, CaO can dissolve in water to form H O and
2
2
2
Ca(OH) , releasing a maximum of 0.47 g H O /g CaO (28–
2
2
2
2
30). And the release of H O can be effectively regulated by
2
2
(
15–20). Firstly, these catalysts can be recovered and
the rate of CaO dissolution, thus improving the utilization
2
reused with good catalytic activity; Secondly, synergistic
action between CDs and the functional group of the sup-
ports can significantly improve the selectivity of guests.
Since β-cyclodextrin (β-CD) is the least expensive among
the cyclodextrins, it has been used as the complexing
host. Previous studies have reported that water-insoluble
β-CD-based polymers (β-CDP) are prepared by the reac-
tion of the hydroxyl groups of CDs with bi- or multi-func-
tional crosslinking agents (21, 22). β-CDP, as multi-site
phase-transfer catalysts present good catalytic activity
efficiency of H O . Therefore, CaO has been widely used
2
2
2
for remediation of saturated soil and ground water con-
taminated by the hazards of gasoline contamination (28,
31). However, there has been no study on the application
of CaO as an oxidant in preparing natural BzH so far.
2
In the present work, we synthesized a PVA–function-
alized β-CD polymer crosslinked by citric acid (PVA-g-CD,
Q) as a new multisite phase-transfer catalyst and CaO as
2
the terminal oxidant for the catalytic oxidation of CIN to
natural BzH in aqueous solution. Various physico-chemical
techniques were used to characterize the structure of PVA-
g-CD. Important factors affecting the reaction rate were
investigated systematically and a reasonable mechanism
was proposed for the oxidation of CIN.
1
730
a
1210
b
2. Results and discussion
2
.1. Characterization of PVA-g-CD
c
In order to confirm that PVA was crosslinked with β-CD
by using citric acid as crosslinking agent, FTIR spectra of
PVA (a), β-CD (b), and PVA-g-CD (c) are shown in Figure 1.
1
630
For pure PVA, the characteristic peaks from 2850 to
1
155
1030
500
000 cm− are due to C–H broad alkyl stretching band.
1
3
4
000 3500 3000 2500 2000 1500 1000
−
1
-1
Wavenumber (cm )
The broad absorption peak around 3400 cm could
be assigned to the –OH stretching. The intra- and inter-
molecular hydrogen bonding also exists among the poly-
mer chains due to high hydrophilic forces. A characteristic
Figure 1. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) Ftir sꢂꢋꢇꢁꢅꢆ ꢃf pVa (ꢆ), β-cD (b), ꢆnd
pVa-g-cD (ꢇ).

SUPRAMOLECULAR CHEMISTRY
3
peak at 1140 cm−1 is attributed to the crystallization of
PVA, which relates to alcoholic C–O stretching vibration
(
32) (Figure 1(a)). From Figure 1(b), the absorption peaks
c
−1
at 3300, 2920, 1646, 1470, and 1030 cm correspond
to the structure of β-CD (33). After preparation of PVA-
g-CD, the absorption bands can also be seen in Figure
b
1(c), implying that the β-CD was grafted on the surface of
PVA and the formation of PVA-g-CD well maintained its
native structure of β-CD. In addition, an intensive absorp-
tion band appears at 1730 cm− (Figure 1(c)) is assigned
to the C=O of carboxyl groups in citric acid. The peak at
a
1
0
6
12
18
24
30
36
42
2
Theta (degree)
−
1
1210 cm which is attributed to the C–O–C stretching
vibration of ester groups is also observed in Figure 1(c).
The result indicates that the hydroxyl groups of β-CD have
reacted with the carboxyl groups of citric acid and thereby
a three-dimensional network can be formed. PVA-g-CD is
stable and insoluble because of the cross-linked network.
Therefore, FTIR results indicate that the experimental pro-
cedure developed in this work is successful in obtaining a
water-insoluble β-cyclodextrin grafted poly (vinyl alcohol)
cross-linked by citric acid.
Figure 2. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) XrD ꢃf β-cD (ꢆ), pVa (b), ꢆnd pVa-g-cD (ꢇ).
The XRD patterns of β-CD (a), PVA (b), and PVA-g-CD (c)
are presented in Figure 2. β-CD in its crystalline form dis-
plays diffraction peaks at 2θ values of 6.2°, 8.0°, 10.7°, 12.9°,
19.8°, 20.9°, 22.8°, 24.3°, and 36.0° (33). PVA has shown a
characteristic intense peak at 2θ = 20° corresponding to
its crystalline structure (34). For the PVA-g-CD, the some
characteristic 2θ peaks of β-CD disappeared, and the char-
acteristic peak of PVA at 2θ = 21.3° decreased, shifted, and
obviously broadened. The results imply that the chemical
modification of PVA with β-CD using citric acid as a cross-
linker destroys the original crystallinity of PVA to some
extent and β-CD was grafted on the surface of polymer
matrix at the molecular level, and no crystals could be
observed in the PVA-g-CD.
Figure 3. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) tG ꢆnd DtG ꢃf pVa ꢆnd pVa-g-cD.
that chemical modification has destroyed intra-molecu-
lar hydrogen bonding of PVA, resulting in lower stability.
1
3
The C NMR can provide some important structural
information of the insoluble polymers (37). Figure 4 shows
1
3
the solid-state C CP/MAS NMR spectra of PVA (a), β-CD
(b), and PVA-g-CD (c).
Figure 3 exhibits the three major weight stages for PVA
is in the range of 25–450 °C. For the first stage, mass loss
of 7% can be observed from room temperature to 150 °C,
which caused by dehydration from PVA. The second stage
begins at 200 °C with a major degradation peak at 270 °C
with mass loss of 66% due to heat decomposition of PVA.
The third stage, which starts at 400 °C, involves the car-
bonization process of the PVA residue (35). PVA-g-CD also
shows three weight losses. The first mass loss with the
temperature range of 25–160 °C is mainly attributed to
the loss of water. The second weight loss observed around
From Figure 4(a), the signals at about 45 ppm is due
to the CH carbon, and the signals at about 65–77 ppm
2
represent the CH carbon. The splitting for the CH carbon
is assigned to intra- or intermolecular hydrogen bond-
ing. The signals at 77, 71, and 65 ppm were due to CH
with two hydrogen bonds, CH with one hydrogen bond,
and CH with no hydrogen bond, respectively. Therefore,
the CH peaks have regarded as indicators of the style of
intra- or intermolecular molecular hydrogen bonding of
-
3
OH groups between two consecutive units of PVA (38,
9). The spectrum of β-CD is similar to that previously
reported data (40) and multiple resonances for each type
200–310 °C with a major degradation peak at 275 °C is due
to the thermal decomposition of PVA in the PVA-g-CD. For
the third stage, mass loss could be observed from 310 to
13
of carbon atom are shown in Figure 4(b). C signals for the
glucopyranose unit of β-CD are due to C-1 (103.4 ppm), C-4
450 °C, which caused by the thermal decomposition of
(
80.6 ppm), C-5 (78.6 ppm), C-3 (74.6 ppm), C-2 (72.4 ppm)
and C-6 (59.6 ppm). The spectrum of PVA-g-CD is quite sim-
ilar to PVA in the solid state, and most of them are observed
β-CD in the PVA-g-CD (36). The second degradation stage
of PVA-g-CD exhibits a lower decomposition temperature
(
180 °C) than that of PVA (220 °C), which demonstrates

4
Y. FANG ET AL.
13
Figure 4. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) cp/maS c Nmr sꢂꢋꢇꢁꢅꢆ ꢃf pVa (ꢆ), β-cD (b), ꢆnd pVa-g-cD (ꢇ).
in Figure 4(c), which could be directly assigned to PVA.
Moreover, some peaks are observed in the 40–80 ppm
region, demonstrating their structure characteristics (39).
dC0
dt
−
= −rCIN = kappCo
(3)
The intensities of the peak, which is assigned to the CH
carbon of PVA significantly decreases with addition of
β-CD, and a new peak appears at about 175 ppm, which
is due to the crosslinking reaction between the OH groups
of PVA and the OH groups of β-CD by using citric acid as a
crosslinking agent. In addition, the resonances from PVA-
g-CD are broad, implying that the crystalline nature of
β-CD disappears. The decrease of the C-1signals of β-CD
and the increase of the signals in the region between 60
and 70 ppm are due to the hydroxylmethyl group at C-6 in
the glucose unit of β-CD. The results clearly show that β-CD
was grafted on the surface of PVA by citric acid.
Equation (3) can be transformed to the following function
ꢀ
ꢁ
Co
−
ln
= − ln(1 − X) = kapp
t
(4)
Ct
kapp can be obtained from the slope of linear plot of ln
(C /C ) against t.
o
t
Under optimized conditions, a high selectivity of
product was observed. In the work, no byproducts
were detected during the reaction by GC-MS analysis.
Only BzH produced from the oxidation of CIN catalyzed
by phase-transfer catalysis and cocatalyst in this work.
Therefore, the consumption of CIN equaled the yield
of BzH. In this section, the effects of the reaction condi-
tions on the conversion of CIN were summarized in the
following.
2
.2. Catalytic activity investigation
In the present work, the two-phase catalytic oxidation of
CIN to natural BzH was successfully synthesized by CaO as
2
the terminal oxidant, PVA-g-CD as the phase-transfer cata-
2.2.1. Effect of the cocatalysts
lyst and NaHCO as the cocatalysts, as shown in Scheme 1.
The conversion (X) of CIN was defines as:
In general, it is difficult to oxidize the organic substance
using the water-soluble oxidant agent. Therefore, it is
necessary to investigate the role of these oxidant agents,
phase-transfer catalysts, or cocatalysts to promote the
3
Ct
X = 1 −
(1)
Co
reaction. In this work, NaHCO was used as the cocatalyst.
3
As shown in Figure 5, 60% conversion of CIN was observed
in the presence of CaO , PVA-g-CD, and NaHCO in aque-
where C is the initial concentration of CIN, C is the con-
o
t
2
3
centration of CIN at time t, respectively.
The rate expression for this reaction can be calculated
from the following equation:
ous solutions. The conversion was significantly decreased
at the absence of any one of the components. In the reac-
tion, QCIN was synthesized, and then CaO would dissolve
2
in water to liberate H O , and the active oxidant-perox-
ymonocarbonate ion (HCO4 ), with structure HOOCO2
2
2
−
r = kappCo
(2)
−1
−1
where kapp is the apparent reaction rate constant. This reac
-
formed by a reaction between bicarbonate ion and H O2
2
tion was performed in a reactor, and the reaction rate of
CIN with time (t) can be expressed as
in the aqueous solutions. Finally, the true oxidant agent
HCO4− was then transferred to the third phase by the
1

SUPRAMOLECULAR CHEMISTRY
5
Scheme 1. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) oxꢄdꢆꢁꢄꢃn ꢃf ꢇꢄnnꢆꢌꢆꢉdꢋꢀꢊdꢋ wꢄꢁꢀ pVa-g-cD ꢆs ꢂꢀꢆsꢋ-ꢁꢅꢆnsfꢋꢅ ꢇꢆꢁꢆꢉꢊsꢁ ꢆnd cꢆo ꢆs ꢁꢀꢋ ꢁꢋꢅꢌꢄnꢆꢉ ꢃxꢄdꢆnꢁ.
2
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5
00 rpm
00 rpm
00 rpm
00 rpm
00 rpm
0
5
10
15
20
25
30
35
t (min)
Figure 5. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) effꢋꢇꢁs ꢃf ꢁꢀꢋ ꢃxꢄdꢆnꢁ ꢆgꢋnꢁ, ꢇꢃꢇꢆꢁꢆꢉꢊsꢁ,
ꢆnd ꢂꢀꢆsꢋ ꢁꢅꢆnsfꢋꢅ ꢇꢆꢁꢆꢉꢊsꢁ ꢃn ꢁꢀꢋ ꢇꢃnvꢋꢅsꢄꢃn ꢃf ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ:
Figure 6. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) effꢋꢇꢁs ꢃf sꢁꢄꢅꢅꢄng sꢂꢋꢋd ꢃn ꢁꢀꢋ ꢇꢃnvꢋꢅsꢄꢃn
ꢃf ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), pVa-g-cD (0.8 g),
cꢆo (1 ꢌꢌꢃꢉ), Nꢆhco (2 ꢌꢌꢃꢉ), 60 °c, 32 ꢌꢄn.
ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), pVa-g-cD (0.8 g), cꢆo (1 ꢌꢌꢃꢉ),
2
2
3
Nꢆhco (2 ꢌꢌꢃꢉ), 400 ꢅꢂꢌ, 60 °c, 32 ꢌꢄn.
3
Table 1. aꢂꢂꢆꢅꢋnꢁ ꢅꢆꢁꢋ ꢇꢃnsꢁꢆnꢁs ꢈndꢋꢅ dꢄffꢋꢅꢋnꢁ ꢇꢆꢁꢆꢉꢊꢁꢄꢇ sꢊs-
ꢁꢋꢌs.
phase-transfer catalyst (Q) for further reaction with CIN. As
a phase-transfer catalyst, PVA-g-CD showed much better
catalytic activity than that of β-CD, implying the synergistic
effects via the various intermolecular weak interactions
between β-CD and the functional group of PVA. The effect
of the different components on the apparent rate constant,
kapp, was shown in Table 1.
CaO +
2
NaHCO3
NaHCO3
+ PVA-
g-CD
Compo-
nents
CaO +
+ CaO +
2
2
PVA-g-CD CaO2 NaHCO3
β-CD
2
Kꢆꢂꢂ × 10
0
0.172
0.873
1.692
3.234
−
1
(ꢌꢄn )
agitation speeds were shown in Table 2. The apparent
rate constant increased linearly when the agitation
speed was increased. The mass transfer rate almost
reached a constant value when the agitation speed was
above 400 rpm. Therefore, the agitation speed was set
at 400 rpm for further experiments.
2
.2.2. The effect of agitation speed
For a liquid–solid–liquid three-phase reaction system,
the conversion of the three-phase reaction is significantly
affected by the mass transfer. The effect of agitation speed
on the conversion of CIN was investigated in the range of
0
–500 rpm in the presence of phase transfer catalyst, PVA-
g-CD, as shown in Figure 6.
2.2.3. The effect of PVA-g-CD amount
As shown in Figure 6, the conversion of CIN increased
with increasing agitation speed from 100 to 500 rpm.
However, the increase of CIN conversion was negli-
gible beyond an agitation speed of 400 rpm. As solid
PTC was added in the aqueous solution, the complex
of QCIN was influenced by the speed of agitation due
to enhancement of mass transfer. With the increase in
the number of QCIN complex, subsequent oxidation of
CIN to natural BzH was observed. The experimental data
for the reaction kinetics obeyed the pseudo-first-order
rate law and passed the point of origin a straight line
for each experimental run. kapp were obtained from the
slope of the straight lines. A plot of kapp and various
In general, the reactivity was increased with increasing
in the amount of PVA-g-CD. In the work, PVA-g-CD as
phase-transfer catalysts was added to the reaction mixture
for enhancing the transfer rate of CIN. Thus, the amount
of PVA-g-CD would affect the reaction rate of CIN, and the
results were shown in Figure 7.
As shown in Figure 7, the conversion of CIN was
increased with increasing the amount of PVA-g-CD. The
rate constants were linearly dependent on the amount of
catalyst from 0 g to 0.8 g in the reaction. A further increase
in the amount of PVA-g-CD did not increase the reaction
rate significantly. It was attributed that more number of
PVA-g-CD molecules provided more number of QCIN

6
Y. FANG ET AL.
1
1
0
0
0
0
0
.2
-
2
0
0
0
0
.2 g
.4 g
.6 g
.0
.8
.6
.4
.2
.0
E = 52.55 kJ/mol
a
-4
0.8 g
1.0 g
-
-
6
8
E = 75.86 kJ/mol
a
-
10
0
5
10
15
20
25
30
35
2
.96
3.04
3.12
000/T(K
3.20
3.28
3.36
t (min)
-
1
1
)
Figure 7. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) effꢋꢇꢁs ꢃf ꢁꢀꢋ ꢆꢌꢃꢈnꢁ ꢃf pVa-g-cD ꢃn
Figure 9. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) aꢅꢅꢀꢋnꢄꢈs ꢂꢉꢃꢁ: dꢋꢂꢋndꢋnꢇꢋ ꢃf kꢆꢂꢂ ꢃn
ꢁꢀꢋ ꢇꢃnvꢋꢅsꢄꢃn ꢃf ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ),
ꢁꢋꢌꢂꢋꢅꢆꢁꢈꢅꢋ.
cꢆo (1 ꢌꢌꢃꢉ), Nꢆhco (2 ꢌꢌꢃꢉ), 400 ꢅꢂꢌ, 60 °c, 32 ꢌꢄn.
2
3
Table 4. effꢋꢇꢁs ꢃf ꢆꢌꢃꢈnꢁ ꢃf cꢆo ꢃn ꢁꢀꢋ ꢇꢃnvꢋꢅsꢄꢃn ꢃf ꢇꢄnnꢆꢌ-
2
ꢆdꢋꢀꢊdꢋ.ꢆ
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
o
3
4
5
6
0 C
Entry
CaO2
Conversion (%)
Selectivity (%)
o
0 C
1
2
3
4
5
0
0.25
0.5
1
1.25
5.4
36.9
48.8
60.0
72.5
74.4
83.6
91.9
100
o
0 C
o
0 C
92.4
ꢆ
rꢋꢆꢇꢁꢄꢃn ꢇꢃndꢄꢁꢄꢃns: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), pVa-g-cD (0.8 g), Nꢆhco3
2 ꢌꢌꢃꢉ), 400 ꢅꢂꢌ, 32 ꢌꢄn.
(
complex which resulted in the formation of CIN available
for the oxidation reaction. However, the further increase
inevitably led to the decrease of BzH selectivity. It was due
to the excess oxidation of BzH to benzoic acid. Therefore,
the conversion was obviously affected by the amount of
PVA-g-CD, so 0.8 g of PVA-g-CD per 25 ml water was used
for the study.
0
5
10
15
t (min)
20
25
30
35
Figure 8. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) effꢋꢇꢁs ꢃf ꢅꢋꢆꢇꢁꢄꢃn ꢁꢋꢌꢂꢋꢅꢆꢁꢈꢅꢋ ꢃn ꢁꢀꢋ
ꢇꢃnvꢋꢅsꢄꢃn ꢃf ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), cꢆo2
(
1 ꢌꢌꢃꢉ), pVa-g-cD (0.8 g), Nꢆhco (2 ꢌꢌꢃꢉ), 400 ꢅꢂꢌ, 32 ꢌꢄn.
3
2.2.4. The effect of temperature
Effect of reaction temperature on the oxidation of CIN was
studied in the temperature range of 30–60 °C as shown
in Figure 8.
As Figure 8 showed the conversion of CIN increased
with increasing the reaction temperature and the product
yields in 32 min of reaction were 16.2% for 30 °C, 30.3% for
Table 2. aꢂꢂꢆꢅꢋnꢁ ꢅꢆꢁꢋ ꢇꢃnsꢁꢆnꢁs ꢈndꢋꢅ vꢆꢅꢄꢃꢈs ꢆgꢄꢁꢆꢁꢄꢃn sꢂꢋꢋds.
Agitation speed
(
rpm)
0
100
200
300
400
500
2
−1
Kꢆꢂꢂ × 10 (ꢌꢄn )
0.478
0.898
1.465
2.314
3.234
3.467
4
0 °C, 48.4% for 50 °C, and 60.2% for 60 °C, respectively.
The apparent rate constant increased with the increasing
temperature from 30 °C to 60 °C and could well follow
the pseudo-first-order kinetic model in the presence and
absence of PVA-g-CD (Table 3). By applying Arrhenius’
equation, plots of ln k and 1/T were drawn in Figure 9. The
plots were of good linearity and the activation energies Ea
in the presence and absence of PVA-g-CD were calculated
Table 3. tꢀꢋ ꢅꢆꢁꢋ ꢃꢅdꢋꢅs ꢆnd ꢅꢆꢁꢋ ꢇꢃnsꢁꢆnꢁs ꢆꢁ dꢄffꢋꢅꢋnꢁ ꢅꢋꢆꢇꢁꢄꢃn
ꢁꢋꢌꢂꢋꢅꢆꢁꢈꢅꢋs ꢄn ꢁꢀꢋ ꢂꢅꢋsꢋnꢇꢋ ꢆnd ꢆbsꢋnꢇꢋ ꢃf pVa-g-cD.
In the presence of
PVA-g-CD
In the absence of PVA-g-CD
Temperature
−
1
k (min−1)
(
°C)
n
k (min )
R
n
R
30
40
50
40
1
1
1
1
0.00521 0.9948
0.01092 0.9956
1
1
1
1
0.0001024 0.9978
0.0004048 0.9951
0.0008187 0.9987
0.0016296 0.9914
−1
to be 75.86 and 52.55 kJ mol , respectively. It is obvious
that the oxidation of CIN was promoted by the PVA-g-CD,
0.0238
0.9947
0.03218 0.9991

SUPRAMOLECULAR CHEMISTRY
7
Table 5. effꢋꢇꢁs ꢃf ꢆꢌꢃꢈnꢁ ꢃf Nꢆhco ꢃn ꢁꢀꢋ ꢇꢃnvꢋꢅsꢄꢃn ꢃf ꢇꢄn-
120
00
3
nꢆꢌꢆdꢋꢀꢊdꢋ.ꢆ
Conversion
Selectivity
1
Entry
NaHCO (mmol)
Conversion (%)
Selectivity (%)
3
1
2
3
4
5
6
7
0
0.5
1
1.25
1.5
2
4.0
4.7
5
40
52.5
60
65.1
68.1
68.0
79.9
89.9
100
8
6
0
0
2.25
70.8
90.9
40
20
0
ꢆ
rꢋꢆꢇꢁꢄꢃn ꢇꢃndꢄꢁꢄꢃns: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), cꢆo (1 ꢌꢌꢃꢉ), pVa-g-cD
2
(
0.8 g), 400 ꢅꢂꢌ, 32 ꢌꢄn.
implying that the PVA-g-CD indeed contributed to the con-
siderable improvement of activity, thus PVA-g-CD was an
efficient phase transfer catalyst for the oxidation of CIN.
1
2
3
4
5
6
Cycles
Figure 10. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) rꢋꢈsꢆbꢄꢉꢄꢁꢊ ꢃf ꢁꢀꢋ ꢇꢆꢁꢆꢉꢊsꢁ. rꢋꢆꢇꢁꢄꢃn
ꢇꢃndꢄꢁꢄꢃns: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), pVa-g-cD (0.8 g), cꢆo2
2
.2.5. The effect of amount of CaO2
(1 ꢌꢌꢃꢉ), Nꢆhco (2 ꢌꢌꢃꢉ), 400 ꢅꢂꢌ, 32 ꢌꢄn.
3
As shown in Table 4, the amount of CaO , which dissolved
2
to form H O had a significant influence on the oxida-
tion of CIN. The conversions of CIN and selectivity to BzH
2
2
Therefore, an appropriate amount of NaHCO is necessary
for the reaction (2 mmol).
3
were 5.4% and 74.4% with the absence of CaO at 60 °C
2
and a reaction time of 32 min, and they were increase to
6
0% and 100%, respectively, when 1 mmol of CaO was
2.3. The oxidation of substituted cinnmaldehydes
2
present. However, further increase the amount of CaO to
2
As shown in Table 6, we further optimized and investi-
gated the oxidation of substituted cinnamaldehydes to
the corresponding benzaldehydes. As shown in Table 6,
the oxidation of substituted cinnamaldehydes to the cor-
responding benzaldehydes was performed smoothly in
good conversion and excellent selectivity. However, the
electronic natures of substituent groups on the cinnamal-
dehydes have some impact on their catalytic oxidation.
The oxygen-containing groups (entries 1–3, 10–12) sub-
stituted cinnamaldehydes produce the corresponding
benzaldehydes in 95–99% selectivity with reaction rates
1.25 mmol leaded to selectivity of BzH decrease to 92.4%.
According to stoichiometry, the molar ratio between H O
2
2
and CIN is 1:1. In the work, the molar ratio of CaO and CIN
2
is 1:1, which was significantly lower that of H O used in
2
2
the reaction (22:1) (17, 20). Therefore, 1 mmol CaO was
2
regarded as the appropriate amount under the conditions
employed in this work.
2
.2.6. The effect of amount of NaHCO3
Hydrogen peroxide is an oxygen-rich, environmentally
friendly oxidant, but it is a rather slow oxidizing agent
in the absence of activators. Richardson et al. (41, 42)
described bicarbonate anion is an efficient activator for
−
1
of 0.0212 to 0.0252 min , which were much higher than
those of the cinnamaldehydes. It was attributed that they
were able to form the inclusion complexes by hydrogen
bonds of the -OCH or -NO groups to secondary hydroxyl
hydrogen peroxide to generate peroxymonocarbonate
−
3
2
(
HCO ), which could effectively oxidize CIN to produce
4
groups on the rim of the β-CD, which could improve the
selectivity and reaction rate of substances. In addition,
the steric hindrance of the substituent groups also sig-
nificantly affected their catalytic activity. Conversion,
selectivity, and reaction rate of the o- (entries 1, 4, 7, and
BzH (17, 18).
As shown in Table 5, in the absence of NaHCO , the
3
conversion of CIN and the selectivity of BzH were only
4.0% and 65.1%, respectively. Increasing the amount of
NaHCO to 1 mmol, the same results were observed due
3
1
1
0), m- (entries 2, 5, 8 and 11) and p-(entries 3, 6, 9 and
2) substituted cinnamaldehydes presented an increased
to the formation of calcium carbonate by the reaction of
sodium hydrogen carbonate and sodium carbonate. When
tendency. The electron-rich methoxyl- (entries 1–3) and
electron-neutral methyl-(entries 4–6) substituted cin-
namaldehydes could give the corresponding benzal-
dehydes in 55–60% conversion and 95–99% selectivity,
respectively. While for the electron-withdrawing chlo-
ride- and nitro-substituted substituted cinnamalde-
hydes, the conversion and selectivity can only achieve
in 50–55% and 90–99% (entries 6–12), respectively. The
the amount of NaHCO was from 1 mmol to 2 mmol, CIN
3
conversion and BzH selectivity were increased to 60% and
1
00%, respectively, which indicated that NaHCO played a
3
crucial role in the oxidation of CIN. Further increasing the
amount of NaHCO to 2.25 mmol increased the CIN con-
3
version to 70.8%, while decreased the selectivity to BzH to
90.9% due to the excess oxidation of BzH to benzoic acid.

8
Y. FANG ET AL.
results in Table 6 clearly showed that the weak interac-
tions between β-CD and substrates could enhance their
reaction activity, which depended on the size, shape and
hydrophobicity of the guest molecules.
ꢆ
Table 6. oxꢄdꢆꢁꢄꢃn ꢃf sꢈbsꢁꢄꢁꢈꢁꢋd ꢇꢄnnꢆꢌꢆꢉdꢋꢀꢊdꢋs ꢁꢃ ꢁꢀꢋ ꢇꢃꢅꢅꢋsꢂꢃndꢄng ꢆꢉdꢋꢀꢊdꢋs ꢃvꢋꢅ pVa-g-cD ꢆnd cꢆo ꢄn wꢆꢁꢋꢅ.
2
−
1
Entry
Reactant
Product
kapp (min )
Conversion (%)
Selectivity (%)
1
0.0212
57
96
2
3
0.0236
0.0241
58
60
98
99
4
5
0.0162
0.0178
54
57
95
97
6
0.0189
60
99
7
8
0.0149
0.0155
50
53
90
92
9
0.0162
0.0228
0.0231
54
52
54
95
96
98
1
1
0
1
1
2
0.0252
55
99
ꢆ
rꢋꢆꢇꢁꢄꢃn ꢇꢃndꢄꢁꢄꢃns: ꢇꢄnnꢆꢌꢆdꢋꢀꢊdꢋ (1 ꢌꢌꢃꢉ), pVa-g-cD (0.8 g), cꢆo (1 ꢌꢌꢃꢉ), Nꢆhco (2 ꢌꢌꢃꢉ), 400 ꢅꢂꢌ, 32 ꢌꢄn.
2
3

SUPRAMOLECULAR CHEMISTRY
9
2
.4. Reusability of the catalyst
2.5. Mechanism
In order to assess the stability of the catalyst, the catalyst
was filtered by centrifugation at 3,000 rpm from the reac-
tion mixture, washed with ethanol and water at 60 °C for
The reaction between CIN and CaO in water using PVA-
2
g-CD as phase transfer catalyst obeyed a solid-liquid-liquid
phase transfer mechanism (Scheme 2). Firstly, CIN would
be adsorbed onto the surface of PVA-g-CD through weak
hydrogen bonding under mechanical stirring. Based on
the lower binding energy (Table s1), β-CD site on the sur-
face of PVA-g-CD captured CIN into its cage structure and
formed a more stable inclusion complex at the interface
between third phase and organic phase. The results are in
good agreement with the previously reported data (15–18,
20, 40). Secondly, with vigorously stirring, a known amount
2
h, respectively. After dried, the catalyst was reused for the
next run under the same conditions. As shown in Figure 10,
the catalyst could be reused at least five times with similar
conversions of CIN and selectivity for natural BzH, which
indicated that the synthesized PVA-g-CD is a stable cata-
lyst. After reaction, the β-CD content of used catalyst was
analyzed with phenolphthalein (43), and the result indi-
cated that the β-CD content changed from 13.5% to 13.0%,
which showed that the structure of these catalysts did not
changed in the catalytic oxidation. Compared with the very
recently reported catalysts, as shown in Table 7, the pres-
ent results exhibit significant advantages in terms of the
selectivity of BzH. Therefore, the study may be helpful for
designing the more efficient catalysts and oxidizers, which
can be conveniently prepared and applied in large scale.
of CaO was added slowly into the mixture, and then they
2
can carry out a complete reaction to release H O . With
2
2
the addition of NaHCO , an active oxidant peroxymonocar-
3
−1
−1
bonate ion, HCO4 , with structure of HOOCO2 formed by
activating hydrogen peroxide with bicarbonate ion. HCO4−1
was adsorbed onto the PVA-g-CD surfaces, went into the
third phase. The generated HCO4− could react with CIN
to yield its epoxide. In situ generated HCO4− can subse-
quently react with the as-prepared epoxide to produce the
BzH. Finally, the catalyst restores its initial state. The data
suggests a solid-liquid-liquid phase transfer mechanism
in accordance with previously published studies (15, 20).
1
1
Table 7. pꢋꢅfꢃꢅꢌꢆnꢇꢋ ꢇꢃꢌꢂꢆꢅꢄsꢃn ꢆꢌꢃng vꢆꢅꢄꢃꢈs β-cD bꢆsꢋd
ꢇꢆꢁꢆꢉꢊsꢁs fꢃꢅ ꢁꢀꢋ ꢃxꢄdꢆꢁꢄꢃn ꢃf ꢇꢄnnꢆꢌꢆꢉdꢋꢀꢊdꢋ ꢁꢃ bꢋnzꢆꢉdꢋꢀꢊdꢋ.
Catalysis
Selectivity (%)
Refs
pVa-g-cD
100
84
71
62
78
85
tꢀꢄs wꢃꢅk
2
-hp-β-cDcp
15
16
17
19
20
β-cDcp
β-cDp
β-cD-ctS
mWcNts-g-cD
3. Conclusions
In conclusion, an efficient and eco-friendly process for the
oxidation of CIN to natural BzH over PVA-g-CD catalyst
Scheme 2. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) oxꢄdꢆꢁꢄꢃn ꢃf ꢇꢄnnꢆꢌꢆꢉdꢋꢀꢊdꢋ ꢁꢃ bꢋnzꢆꢉdꢋꢀꢊdꢋ.

10
Y. FANG ET AL.
Scheme 3. (cꢃꢉꢃꢈꢅ ꢃnꢉꢄnꢋ) Sꢊnꢁꢀꢋꢁꢄꢇ ꢂꢅꢃꢇꢋdꢈꢅꢋ ꢆnd ꢂꢃssꢄbꢉꢋ ꢇꢀꢋꢌꢄꢇꢆꢉ sꢁꢅꢈꢇꢁꢈꢅꢋs ꢃf pVa-g-cD.
combined with CaO as the terminal oxidant was stud-
4.2. Preparation of PVA-g-CD
2
ied in this work. The factors affecting the reaction rate of
CIN, such as agitation speed, amount of PVA-g-CD, tem-
perature, amount of CaO , and amount of NaHCO were
PVA-g-CD was synthesized according to the previous Refs.
with minor modification (44, 45). The detail synthesis of
PVA-g-CD was as following: a mixture of β-CD (2 g), citric
acid monohydrate (1 g), sodium dihydrogen phosphate
2
3
investigated to determine the optimal operating condi-
tions. Under the optimized conditions, 60% conversion
of CIN with 100% selectivity to natural BzH was obtained
with a short reaction time of 32 min. The reaction was
not affected by agitation speed higher than 400 rpm. The
reaction rate increased with increasing temperature, cat-
alyst amount, cocatalyst amount and oxidant amount and
obeyed the pseudo-first order kinetics. The catalyst was
recyclable for up to five runs consecutively without any
appreciable loss of activity and selectivity. Since the PVA-
g-CD catalyst is able to oxidize CIN to natural BzH with high
selectivity, highly recyclable, remarkably stable and above
all, environmentally friendly, they hereby are promising for
the industrial application.
(
0.1 g), PVA-1799 (0.2 g), and deionized water (10 mL)
was stirred to homogeneous at 40 °C in a water bath for
h. It was heated to 140 °C in an electric thermostatic oven
2
and kept the same temperature for 4 h. After the reaction,
the reaction mixture was cooled to room temperature, and
the solids were purified by soaking, washed to neutral
pH, and dried under vacuum at 60 °C to obtain PVA-g-CD,
as showed in Scheme 3. β-CD content of PVA-g-CD was
calculated as 0.119 mmol/g according to the previously
reported method (43).
4.3. Characterization techniques
Fourier transform infrared (FTIR) spectra of β-CD, PVA,
and PVA-g-CD were recorded on a Bruker TENSOR 37 FTIR
4
. Experimental section
−
1
spectrometer as KBr pellets in the 4000–400 cm spectral
range. TG-DTG curves were obtained on a Netzsch STA-
449C thermal analysis system. The samples were put inside
the platinum pans, which were hanging in the heating fur-
nace. The weight percentage of the residue was recorded
while the furnace was heating from 25 to 450 °C. The flow
rate of nitrogen was about 40 mL/min, and a heating
rate of 10 °C/min was employed. X-ray diffraction (XRD)
was carried out on D/max-2200/PC X-ray Diffractometer
with an area detector using a Cu Kα radiation source
(λ = 1.54056 Å) to study the crystal structure of the CaO2.
4
.1. General
PVA-1799 (hydrolysis degree ≥ 99%; DP = 1799) was sup-
pliedfromSichuanVinylonFactory,China.Cinnamaldehyde
(
> 99%) was obtained from Sinopharmacy Chemical
Reagent, China. β-CD (> 99%) was purchased from
Shanghai Boao Biotechnology, China. CaO was synthe-
sized and characterized in the supplementary material
2
(
Figures S1–S3). All other chemicals were purchased in
analytical purity and used without further purification
and all solutions were prepared with distilled water under
ambient conditions.

SUPRAMOLECULAR CHEMISTRY
11
X-ray photoelectron spectroscopy (XPS, ESCALab250) was
used to analyze the elemental sates. Transmission elec-
tron microscopy (TEM, JEOL S-520) was used to examine
the surface morphology and the particle size of the solid
oxidant. The solid-state CP/MAS C NMR data of β-CD,
PVA, and PVA-g-CD were performed on Bruker Avance II
(6) Chen, H.Y.; Yang, Z.J.; Zhou, X.T.; Ji, H.B. Supramol. Chem.
012, 24, 247–254.
7) Nie, Y.M.; An, Y.P.; Peng, C.H.; Yao, X.D. Appl. Mech. Mate.
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2
(
2
(
(
8) Chen, H.Y.; Ji, H.B. Chinese. J. Chem. Eng. 2011, 19, 972–977.
9) Takahashi, K. Chem. Rev. 1998, 98, 2013–2034.
1
3
(10) Surendra, K.; Krishnaveni, N.S.; Reddy, M.A.; Nageswar,
Y.V.D.; Rao, K.R. J. Org. Chem. 2003, 68, 2058–2059.
500 MHz spectrometer to determine the successful graft
(
(
(
(
(
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2
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Disclosure statement
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09, 153–158.
No potential conflict of interest was reported by the authors.
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(
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Funding
(
(
(
(
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28) Northup, A.; Cassidy, D. J. Hazard. Mater. 2008, 152, 1164–
This work was preliminarily supported by the National Natural
Science Foundation of China [grant number 21376279], [grant
number 21425627]; the National Natural Science Foundation of
China-SINOPEC Joint fund [grant number U1663220]; the Natu-
ral Science Foundation of Guangdong Province [grant number
1
170.
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J. Hazard. Mater. 2015, 284, 253–260.
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2017A030313057]; the China and Guangdong Technology Re-
search Center for Synthesis and Separation of Thermosensitive
Chemicals [grant number 2015B090903061].
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ORCID
1
Zujin Yang
http://orcid.org/0000-0003-2319-3055
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