4-Chloro-2,6-Pyridinedicarboxylic Acid Functionalized Mesoporous Silica Nanocomposites for the Synthesis of Sinapaldehyde

Article abstract of DOI:10.1134/S0023158420010103

Abstract: 4-Chloro-2,6-pyridinedicarboxylic acid (CPDA) functionalized mesoporous silica SBA-15 nanocomposites (SBA/5CPDA) were synthesized and characterized for the Knoevenagel condensation of syringaldehyde and acetaldehyde to synthesize sinapaldehyde i

Full text of DOI:10.1134/S0023158420010103

ISSN 0023-1584, Kinetics and Catalysis, 2020, Vol. 61, No. 1, pp. 112–118. © Pleiades Publishing, Ltd., 2020.
4
-Chloro-2,6-Pyridinedicarboxylic Acid Functionalized Mesoporous
Silica Nanocomposites for the Synthesis of Sinapaldehyde
a
a,
,
S. Verma and A. Dubey * **
a
Department of Chemistry Maulana Azad National Institute of Technology (MANIT), Bhopal (M.P.), India
*
e-mail: dramit.dubey@gmail.com
*e-mail: amitdubeydr@manit.ac.in
Received June 17, 2019; revised July 12, 2019; accepted September 13, 2019
*
Abstract—4-Chloro-2,6-pyridinedicarboxylic acid (CPDA) functionalized mesoporous silica SBA-15 nano-
composites (SBA/5CPDA) were synthesized and characterized for the Knoevenagel condensation of syrin-
galdehyde and acetaldehyde to synthesize sinapaldehyde in the liquid phase. The physicochemical character-
ization of the SBA/CPDA nanocomposites showed the decrease in the surface properties (surface area, pore
size, pore volume) compared to SBA-15 confirming the complete functionalization of CPDA inside the mes-
opores of SBA-15 materials. The catalytic activity results displayed high activity (~90%) and selectivity (90–
9
5%) of the desired product (sinapaldehyde) under environmental friendly conditions. All the reaction
parameters were optimized to accomplish the maximum conversion of the selective products. Finally, the
mechanism of the formation of the products was proposed and discussed.
Keywords: 4-chloro-2,6-pyridinedicarboxylic acid, SBA-15, catalytic activity, syringaldehyde
DOI: 10.1134/S0023158420010103
INTRODUCTION
The growing risk of incurable diseases and strin-
strengthening the necessary reproductive proteins
forming the prime units of dispersal in fungi [9]. Pyri-
dinedicarboxylic acids have emerged as potential
organic ligands for the fabrication of hydro-
philic/hydrophobic hybrid materials for industrial
applications [9, 10]. Substituted 2,6-pyridinedicar-
boxylic acid may exhibit additional prospective for the
formation of bridging coordination complexes by pro-
viding multiple combination of these ligands for self-
assembled structures [11]. Moreover, pyridine-2,6-
dicarboxylic acid (PDA) also finds applications for
binding lead as a complexing reagent. PDA promptly
concentrates considerably high percentage of the
adsorbed lead over broad range of pH from a spiked
soil [12–14].
gent environmental legislation are forcing the
researchers to develop new biochemical methods to
control the impact of these syndromes for human
health. Nowadays, nanoscale porous materials are
achieving tremendous attention for the advancement
of new biocatalytic system for smoother product sepa-
ration and cost effective methods. In this regard, hex-
agonal mesoporous SBA-15 silica materials may be a
lucrative alternative to achieve these objectives due to
their fascinating surface peculiarity such as larger sur-
face areas, adjustable pore diameter and pore volume
[
1]. Additionally, the surface of these materials can be
functionalized with different ligands to generate more
facile and active functional sites for catalysis, ion
Cinnamaldehyde derivatives, an important class of
exchange, antibacterial activity and the adsorption of organic compounds, are immensely used in photosen-
toxic substrates [2–5]. One such ligand may be chloro sitive compositions, as an intermediate for a plant
derivative of pyridine-2,6-dicarboxylic acid (dipi- growth regulator, wood-products, paper, dyes, fibers,
colinic acid, DPA or PDA) which can be effectively plastics, etc. [15–20]. Usually, the cinnaminaldehyde
explored for biological activity, adsorption studies, derivatives are synthesized by well-known Knoevena-
antibody formulation and catalysis [6–8]. To date, the gel condensation reaction [21, 22]. Many homoge-
explicit role of DPA in spores could not be identified neous and heterogeneous reagents have already been
but it has definite functionality in maintaining and employed for this well known conversion but exploring
essential product selectivity can be a thought provok-
Abbreviations: PDA, pyridine-2,6-dicarboxylic acid; CPDA,
ing aspect in the liquid phase conditions [20, 23]. One
4
-chloro-2,6-pyridinedicarboxylic acid; SBA/CPDA, CPDA
of the cinnamaldehyde derivatives, sinapaldehyde –
functionalized mesoprous silica SBA-15 nanocomposites;
PXRD, powder X-ray diffraction; SEM, scanning electron
microscopy.
(
E)-3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enal –
a flavoring organic compound, is an intermediate
112

4-CHLORO-2,6-PYRIDINEDICARBOXYLIC ACID
113
in lignin biosynthetic pathway and its integration into solution at 318 K. Desired amount of TEOS was added
metabolism [23]. It is also used for the production of in the solution and the resultant mixture was kept for
+
sinapyl alcohol and NADP with the enzyme dihydro- 24 h under stirring conditions followed by hydrother-
flavonol [24]. Moreover, it is potentially used as anti- mal treatment at 373 K. The solid product, obtained
fungal agent and plant metabolite [25]. Reports are after filtration, was calcined at 823 K to remove the
scanty, especially, for the synthesis of sinapaldehyde surfactant. To functionalize mesoporous silica with
under environmental friendly conditions in the liquid CPDA, 1 g of SBA-15 in the presence of toluene with
phase [26] and according to the best of literature, no APTS was stirred for 24 h in an inert atmosphere. Thus
systematic detailed studies for the synthesis of sina- synthesized SBA/APTS product was filtered and
palaldehyde via Knoevenagel condensation reaction washed by ethanol. EDCl and HOBt were used
of syringaldehyde with acetaldehyde (Scheme 1) is respectively as carboxyl activating agent of CPDA (to
available over 4-chloro-2,6-pyridinedicarboxylic acid bond with primary amine of APTS) and to suppress
(
CPDA) functionalized mesoporous silica nanocom- racemization of peptide bond at 273 K. Different
posites. Therefore, the present paper deals with the amount of activated CPDA was mixed with
synthesis and characterization of CPDA functional- SBA/APTS and kept for stirring for 24 h. The product
ized mesoprous silica nanocomposites (SBA/CPDA) was filtered, washed properly by solvent and water to
for the synthesis of sinapaladehyde in the liquid phase. remove the impurities [28]. The nanocomposites thus
synthesized were as named as SBA/xCPDA, where ‘x’
represents percentage of CPDA in SBA-15. The per-
MATERIALS AND METHODS
centage of C, H, N and O by CHN analysis was in
agreement with the calculated values. The number of
acidic sites (2.9 mmol/L) in SBA/5CPDA was calcu-
lated by titration method [29].
Materials
The extra pure chemicals were used for the synthe-
sis and catalysis: pluronic P123 copolymer (EO20-
PO70EO20, MW = 5800), TEOS (tetraethyl orthosil-
icate), hydrochloric acid (35%), aminopropyl triethoxysi-
lane (APTS), 1-hydroxybenzotriazole (HOBt), 1-ethyl-
Catalysis
3
-(3-dimethylaminopropyl) carbodiimide (EDCl),
The liquid phase condensation reaction of syrin-
4
-chloro-2,6-pyridinedicarboxylic acid (CPDA), eth- galdehyde and acetaldehyde was carried out in spe-
anol, acetaldehyde, syringaldehyde and etc.
cially designed stainless steel reactors (Scheme 1).
Typically, 1 mol of each reactant was mixed with the
required amount of SBA/xCPDA catalysts in different
solvents at a reflux temperature. The analysis of the
Synthesis of SBA-15 and SBA/CPDA Nanocomposites
SBA-15 was synthesized in acidic medium using products was determined by gas chromatography using
non-ionic surfactant (pluronic P123) and tetraethyl their standard samples and the concentration of prod-
orthosilicate (TEOS) as silica source respectively by ucts was analyzed using n-decane as an internal stan-
keeping the reactant molar ratio P123 : 5562.9 H O : dard via withdrawing samples at different intervals of
2
8
6.29 HCl : 42.5 TEOS [27]. Typically, 5.8 g of surfac- time. The yield of the product is calculated based on
tant was mixed in 100 mL of distilled water and hydro- weights calculated by an internal standard method
lyzed with 11.3 g of concentrated HCl in the stirring after the reaction.
O
O
H
OCH3
O
H+
H
H
H C
3
O
+
H
+
OH
CH3
H
H C O
3
O CH3
H C O
3
OH
Sinapaldehyde (A)
Syringaldehyde
Acetaldehyde
Crotonal (B)
Scheme 1. Condensation reaction of syringaldehyde and acetaldehyde in acidic medium.
Physicochemical Characterizations
ray diffractometer with CuK radiation. N adsorp-
2
α
The powder X-ray diffraction (PXRD) measure- tion-desorption isotherm measurements were done at
ments of samples were taken on Rigaku D/Max-II X- 77 K using a Micromeritics ASAP 2000 analyzer.
KINETICS AND CATALYSIS Vol. 61 No. 1 2020

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VERMA, DUBEY
Intensity, a.u.
800
600
400
200
000
3
Volume adsorbed, cm /g
50
1
1
1
1
3
300
1
2
50
00
1
8
00
00
00
00
0
2
6
4
2
2
150
00
1
1
2
3
–200
50
1
2
3
4
5
0
0.2
0.4
0.6
0.8
1.0
2
θ, deg
Relative pressure, p/p0
Fig. 1. PXRD patterns of SBA-15 (1), SBA/5CPDA cata-
lyst (2) and SBA/5CPDA catalyst after first cycle of the
condensation reaction between syringaldehyde and acetal-
dehyde (3).
Fig. 2. N adsorption-desorption isotherms of SBA-15 (1)
2
and SBA/5CPDA (2) catalysts.
RESULTS AND DISCUSSION
PXRD
Catalytic Activity Studies
Effect of different catalysts. The catalytic activity
results for the condensation of syringaldehyde with
acetaldehyde showed very high conversion and the
yield of the selective product (A) over all the
PXRD patterns (Fig. 1) of the SBA-15 and
SBA/5CPDA nanocomposites at low angles showed
two-diensional hexagonal p6mm symmetry due to the
reflections corresponding to (100), (110) and (200) SBA/CPDA catalysts compared to homogeneous
planes typical of mesoporous nature of the samples CPDA (Table 2). No conversion with pure SBA-15
[
30]. The reduction in the base peak intensity with catalyst further reveals the requirement of active func-
increasing concentration of CPDA in SBA/xCPDA tional groups. The conversion and the yield increased
nanocomposite was observed as compared to SBA-15. with increasing concentration of CPDA in
The mesoporous structure of the samples could be SBA/CPDA catalysts and maximum yield could be
retained up to 5% CPDA concentration and thereafter achieved with SBA/5CPDA catalyst, which was cho-
completely lost with further concentration of CPDA.
sen for further studies. To check the effect of different
catalysts, SiO /5CPDA and Al O /5CPDA catalysts
2
2
3
were also synthesized via impregnation method with
equivalent CPDA concentration (Table 2). No appre-
ciable divergence in the total conversion was noted for
these catalysts. However, the selectivity of the product
N Adsorption–Desorption Studies
2
N adsorption–desorption isotherms (Fig. 2) of
2
SBA-15 and SBA/5CPDA showed Type IV adsorption
isotherm having hysteresis loop (IUPAC classifica-
tion) confirming the nature of mesoporous materials
(
A) was reduced in both the catalysts compared to
SBA/CPDA catalysts substantiating the role of
ordered mesoporous support. These results (high con-
version, yield and the selectivity) of the product are
due to very high surface area and the easier proximity
of the substrates with the acidic sites in the ordered
structure of SBA/5CPDA catalysts. These results
demonstrate advantages over some of the reported
microwave assisted synthesis of cinamaldehyde and
[
31]. A closer look at the adsorption isotherm of
SBA/5CPDA showed a tilted shape, which is due to
the excess load of CPDA that is generated during func-
tionalization. Decrease in the surface properties
(
Table 1 and Fig. 3) of the SBA/5CPDA materials fur-
ther substantiates the successful functionalization with
retention of mesoporous nature of the materials.
Table 1. Structural parameters of the samples
Scanning Electron Microscopic (SEM) Studies
Surface area, Pore volume, Pore diameter,
SEM images (Fig. 4) showed the rod-like structure
of the SBA-15 materials [32] and retention of this rod-
like geometry in SBA/5CPDA clearly depicts that the
functionalization of CPDA took place inside the mes-
oporous walls of SBA-15.
Sample
2
m /g
cc/g
nm
SBA-15
SBA/5CPDA
471
362
0.56
0.38
4.9
3.8
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4-CHLORO-2,6-PYRIDINEDICARBOXYLIC ACID
115
coumarin derivatives using different reagents in terms favorable orientation of the adsorption sites at respec-
of better selectivity and yield [33, 34]. Mechanistically, tive temperature and solvent (Scheme 2) under our
it can be concluded that in the transition state, the experimental conditions. To verify this, the effect of
ordered mesoporous structure helps to suppress (con- temperature and solvent was separately studied for
trol) the self-condensation of acetaldehyde due to the self-condensation of acetaldehyde.
APTS
Cl
HO
O
N
O
OH
Functionalized
SBA-15
SBA-15
Cl
O
O
H
O
O
HO
N
NH
Si
O
H C O
3
H
H
O
O
HO
H C O
O CH3
OH
3
O
CH3
OH
Sinapaldehyde
H C
2
H
Scheme 2. Possible reaction mechanism for the condensation of acetaldehyde and syringaldehyde
in heterogeneous condition (SBA/5CPDA).
Effect of the temperature and solvent over self-con- see the effect, self-condensation of acetaldehyde was
carried out with SBA/5CPDA catalyst with different
solvents at different temperatures. It was observed that
the self-condensation of acetaldehyde increased
slowly up to 323 K and beyond this conversion of acet-
aldehyde was completed very fast. Screening of various
solvents (ethanol, propanol, dichloromethane, etc.)
suggested that polar solvents enhance the self-conden-
sation of acetaldehyde compared to solvent less condi-
tion. These results are similar and beneficial to the
previously reported results on LDH materials [35].
Moreover, self-condensation of acetaldehyde can be
better controlled by acidic reagents compared to the
basic ones [36, 37]. Therefore, after considering all the
parameters, it was assumed that the optimum tem-
perature of 298–343 K without solvent could have
been the ideal experimental conditions with
SBA/5CPDA catalysts and hence these parameters
were selected for further catalytic studies.
densation of acetaldehyde. One of the major complica-
tions to achieve the sinapaldehyde selectivity is to con-
trol the self-condensation of acetaldehyde. In order to
Pore volume, cm g nm–1
3
–1
0.35
0.30
0.25
0.20
1
0
0
.15
2
.10
0.05
Effect of syringaldehyde to acetaldehyde ratio. The
catalytic results showed (Fig. 5) that the yield and the
product selectivity increased up to a certain ratio (1 : 1.5)
and thereafter decreased with further enhancement of
acetaldehyde concentration. This is because the excess
of acetaldehyde, after the completion of the reaction,
undergoes self-condensation to product (B) thereby
reducing the selectivity of the desired product (A).
0
2
4
6
8
10
Pore diameter, nm
Fig. 3. Pore size distribution of SBA-15 (1) and
SBA/5CPDA (2) catalysts.
KINETICS AND CATALYSIS Vol. 61 No. 1 2020

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VERMA, DUBEY
(a)
50 μm
(b)
50 μm
Fig. 4. SEM images of SBA-15 (a) and SBA/5CPDA (b) catalysts.
Yield, %, selectivity, %
Effect of the reaction temperature with time. Varia-
tion of the reaction temperature revealed that the con-
version and yield of the product increased with
increasing reaction temperature initially and became
constant after 3 h at 343 K (Fig. 6). In order to see the
self-condensation of acetaldehyde or any interconver-
sion of the products, the reaction was allowed to pro-
ceed for 48 h. No difference in the yield and selectivity
of the product could be noticed under our experimen-
tal conditions. This result showed significance of con-
trolling the self-condensation of acetaldehyde in the
presence of SBA/5CPDA catalyst to achieve the prod-
uct (A). Interestingly, some induction period in the
total conversion was observed at lower temperature
without formation of self-condensed acetaldehyde
products. This may be due to the lower reactivity of
syringaldehyde with acetaldehyde at lower tempera-
ture. Therefore, the use of ordered solid support is
advantageous in controlling the overall reactivity of
self-condensation of acetaldehyde and enhancing the
selectivity of the product.
95
90
85
80
2
1
75
70
1
: 0.5 1 : 1.0 1 : 1.2 1 : 1.5 1 : 1.7 1 : 2.0
Syringaldehyde : acetaldehyde
Fig. 5. Effects of ratio of reactants on the yield (1) and
selectivity (2) of product sinapaldehyde over SBA/5CPDA
catalyst (conditions as given in Table 2).
Table 2. Effect of different catalysts on the total conversion
and selectivity of products in condensation reaction of
syringaldehyde and acetaldehyde
Reusability of the catalysts. In order to check the
reusability of the SBA/5CPDA, the catalyst after first
cycle of the reaction, was filtered, washed with sol-
vent, dried at 343 K and subjected to fresh reaction.
This procedure was repeated for three cycles. Slight
loss in the yield (10–12%) of the product was noticed
after third cycles (Fig. 7).
Product
Conversion,
%
Yield *,
selectivity, %
A
Catalyst
%
A
B
SBA-15
0
0
0
0
CPDA
90
70
85
90
80
60
65
95
92
96
60
55
35
05
08
04
40
45
60
90
82
95
50
35
SBA/2CPDA
SBA/3CPDA
SBA/5CPDA
CONCLUSIONS
SBA/CPDA functionalized mesoporous silica
nanocomposites were synthesized and characterized
for the synthesis of sinapaldehyde. Physicochemical
characterization of these materials showed that CPDA
was functionalized inside the pores of SBA-15 materi-
als. Catalytic activity studies showed very high yield
and selectivity of the sinapaldehyde over SBA/CPDA
SiO /CPDA
2
Al O /CPDA
2
3
Reaction conditions: syringaldehyde—1 mmol, acetaldehyde—
1
*
mmol, catalyst—100 mg, without solvent, 353 K.
Yield of product A (based on an internal standard method).
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4-CHLORO-2,6-PYRIDINEDICARBOXYLIC ACID
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