Acid Catalysts Based on Mesoporous Aromatic Frameworks in Aldol Condensation of Furfural with Some Carbonyl Compounds

Article abstract of DOI:10.1134/S107042721906017X

Aldol condensation of furfural with acetone and a series of aldehydes in the presence of PAF-SO₃H acid catalyst based on mesoporous aromatic frameworks was investigated. The reaction course depending on the process temperature, catalyst amount, and reactant ratio was considered for the furfural condensation with acetone as an example. The catalyst can be reused in several cycles without appreciable activity loss.

Full text of DOI:10.1134/S107042721906017X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2019, Vol. 92, No. 6, pp. 857−864. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Prikladnoi Khimii, 2019, Vol. 92, No. 6, pp. 800−807.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Acid Catalysts Based on Mesoporous Aromatic
Frameworks in Aldol Condensation of Furfural
with Some Carbonyl Compounds
M. Yu. Talanovaa,*, V. A. Yarchaka, and E. A. Karakhanova
a Moscow State University, Moscow, 119991 Russia
* e-mail: marta_tal@mail.ru
Received November 26, 2018; revised March 14, 2019; accepted March 20, 2019
Abstract—Aldol condensation of furfural with acetone and a series of aldehydes in the presence of PAF–SO3H
acid catalyst based on mesoporous aromatic frameworks was studied. The reaction course depending on the
process temperature, catalyst amount, and reactant ratio was studied for the furfural condensation with acetone
as an example. The catalyst can be reused in several cycles without appreciable activity loss.
Keywords: aldol condensation, furfural, acetone, aldehydes, mesoporous aromatic frameworks
DOI: 10.1134/S107042721906017X
Much attention is paid today to the development of
methods for using renewable resources of vegetable
origin for preparing valuable chemical products. Syn-
theses based on furfural, which can be readily obtained
from such bioresources as cellulose, hemicellulose, and
lignin [1, 2], show promise in this respect. The devel-
opment of new catalytic systems for condensations in-
volving furfural derivatives and carbonyl compounds
attracts attention in connection with the possible use of
the condensation products as, e.g., monomers for pre-
paring polyesters and epoxy resins, diesel fuel compo-
nents, etc. [3, 4].
Porous aromatic frameworks (PAFs), a subclass of
porous organic polymers, form a relatively new class of
carbon materials. They fully consist of aromatic rings,
have high specific surface area, are extremely stable
in water, acids, and alkalis, and are heat-resistant. In
addition, their structure and surface can be modified,
which allows using them as supports of heterogeneous
catalysts for various petrochemical processes:
hydrogenation, reductive amination, cross coupling, and
alkylation [13–20]. However, aldol condensations in the
presence of such catalysts were not studied previously.
In this study, we prepared mesoporous aromatic
frameworks (PAFs) based on tetraphenylmethane and
modified them with sulfonic acid groups SO3H to obtain
the catalyst. The catalytic activity of the materials
obtained was studied in aldol condensation of furfural
with acetone and various aldehydes.
Metal oxides MgO, CaO, and ZnO and mixed oxides
MgO–ZrO2 and MgO–TiO2 are widely used today as
effective heterogeneous catalysts for aldol condensations
[5–8]. Some authors [9–12] also evaluated the possibility
of using layered double hydroxides (LDHs), also known
as anionic clays, and hydrotalcite-like materials (HTC).
EXPERIMENTAL
The development of cheap, environmentally safe,
and, at the same time, highly active heterogeneous cata-
lysts for aldol condensations still remains a topical prob-
lem.
The following substances were used for preparing
the catalyst: trityl chloride (Aldrich), aniline (Ruskh-
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TALANOVA et al.
im), isoamyl nitrite (Aldrich), hypophosphorous acid
(Aldrich, 50% aqueous solution), bromine (Russia),
1,4-benzenediboronic acid (Aldrich), triphenylphos-
phine (Aldrich), palladium(II) acetate (Aldrich), and
chlorosulfonic acid (Fluka). The condensations were
performed using as substrates furfural, 5-(hydroxym-
ethyl)furfural, 5-nitrofurfural (Sigma–Aldrich), acetone
(Sigma–Aldrich), hexanal, heptanal, nonanal, decanal,
and undecanal (Aldrich). The solvents were pretreated
by standard procedures.
helium; DB-5MS column, 12 m × 0.1 mm × 0.25 μm;
column temperature schedule: initial temperature 70°С,
then heating to 300°С at a rate of 40 deg min–1 with
keeping at the final temperature for 20 min; ionization
energy 70 eV; scanning in the range 40–500 amu. The
products were identified by comparing their mass spectra
with those of the compounds present in the NIST/EPA/
NIH database.
Catalytic experiments. A steel autoclave equipped
with a magnetic stirrer was charged with the calculated
amounts of the catalyst, furfural, and carbonyl com-
pound, a solvent was added if necessary, and undecane
was added as an internal reference. The autoclave was
sealed, filled with argon to a pressure of 1 MPa (in the
case of condensation with acetone), and placed in a ther-
mostat. The mixture was stirred at a certain temperature
for the required time. Then, the reactor was cooled, and
the catalyst was separated by centrifugation. The mix-
ture was analyzed by GLC. The product identification
was confirmed by GC–MS.
Low-temperature nitrogen adsorption–desorp-
tion. The sample porosity characteristics were deter-
mined with a Gemini VII 2390 analyzer. Prior to meas-
urements, the samples were degassed at 120°С for 6 h.
The nitrogen adsorption–desorption isotherms were
recorded at 77 K. The specific surface area was deter-
mined by the Brunauer–Emmett–Teller (BET) method
at the relative partial pressure p/p0 = 0.2. The total pore
volume and pore-size distribution were determined us-
ing the Barrett–Joyner–Halenda (BJH) method at the
relative partial pressure p/p0 = 0.95.
Analysis by transmission electron microscopy
(TEM) was performed with a LEO912 AB OMEGA
microscope (magnification from 80 to 500 000, image
resolution 0.2–0.34 nm). The electron beam potential
was 100 eV. ImageJ program was used for processing
the electron micrographs and calculating the mean
particle size.
Analysis by solid-state 13C NMR spectroscopy was
performed with a Varian NMR Systems device operating
at 125 MHz in the pulse mode at a spinning frequency
of 10 kHz.
RESULTS AND DISCUSSION
Porous aromatic framework (PAF) samples were
synthesized by Suzuki cross coupling from tetrakis(4-
bromophenyl)methane and 1,4-benzenediboronic acid,
following the procedures described previously [21, 22].
The surfaces were functionalized with sulfo groups by
treatment with chlorosulfonic acid (Scheme 1) [23].
The PAF obtained was characterized by solid-state
13С NMR spectroscopy, low-temperature nitrogen
adsorption–desorption, and transmission electron
microscopy (TEM).
The 13С NMR spectrum contains signals at 120–
150 ppm, characteristic of the sp2 carbon atoms of the
benzene rings, and in the region of 65 ppm, characteris-
tic of the sp3 carbon atoms in the nodes of the tetraphe-
nylmethane fragments.
Analysis by Fourier IR spectroscopy was performed
with a Nicolet IR2000 device.
Analysis by gas–liquid chromatography (GLC)
was performed with a Khromos GKh-1000 chro-
matograph equipped with a flame ionization detec-
tor using a RESTEK MXT-2887 capillary column
(10 m × 0.53 mm × 2.65 μm) at programmed heating
from 60 to 230°C; the carrier gas was helium.
The PAF porosity characteristics are given in Table 1.
The low-temperature nitrogen adsorption–desorption
measurements reveal sharp nitrogen uptake at low
pressures (p/p0 = 0–0.05), indicative of the presence of
micropores in the structure. The hysteresis loop confirms
the mesoporous nature of the framework. The PAF has
high specific surface area (SBET = 556 m2 g–1) with the
mean pore diameter of 6.9 nm. The data obtained agree
with those reported previously [24, 25].
Elemental analysis was performed with a LECO
CHNS-932 analyzer.
Analysis by gas chromatography–mass spectrometry
(GC–MS) was performed using a system consisting of a
Finnigan Focus gas chromatograph and a Finnigan DSQ
mass spectrometer under the following conditions: flow
split ratio 1 : 20; injector temperature 250°С; carrier gas
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ACID CATALYSTS BASED ON MESOPOROUS AROMATIC FRAMEWORKS
859
Scheme 1. Synthesis of sulfonated aromatic framework PAF–SO3H.
The PAF morphology was examined by TEM
(Fig. 2a). The electron micrographs show that the PAF
material has an amorphous structure with globules 150–
200 nm in diameter with small inclusions 2–5 nm in
diameter.
desorption, transmission electron microscopy, and IR
spectroscopy.
According to the low-temperature nitrogen
adsorption–desorption data, sulfonated PAF–SO3H is
characterized by the mean specific surface area SBET
=
The sulfonated material PAF–SO3H was
characterized by low-temperature nitrogen adsorption–
192 m2 g–1 and smaller pore volume and mean pore
radius compared to the initial PAF, which may be due
Table 1. Physicochemical characteristics of mesoporous surfaces
Sample
Ssp, m2 g–1
Pore volume, cm3 g–1
Mean pore size, nm
Acidity [H+], mmol g–1
PAF
PAF–SO3H
556
192
0.52
0.18
7.3
5.5
—
1.45
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TALANOVA et al.
(b)
(a)
Adsorption
Desorption
Relative pressure p/p0
Relative pressure p/p0
Fig. 1. Isotherm of the low-temperature nitrogen adsorption–desorption for (a) PAF and (b) PAF–SO3H.
(a)
(b)
200 nm
100 nm
Fig. 2. Electron micrographs of (a) PAF and (b) PAF–SO3H.
to partial break of the structure of the material in the
course of sulfonation. However, PAF–SO3H preserved
the mesoporous structure, as indicated by the shape of
the nitrogen adsorption–desorption isotherm (Table 1,
Fig. 1b).
The catalytic activity of the functionalized material
obtained, PAF–SO3H, was studied for the aldol–
crotonic condensation of furfural with acetone as an
example (Scheme 2). The cross condensation yields
furfurylideneacetone (FAc) and difurfurylideneacetone
(F2Ac); acetone self-condensation products such as
mesityl oxide and phorone are also present.
According to the TEM data (Fig. 2b), the sulfonated
material preserved the morphology of the initial
framework. The presence of sulfo groups in the structure
of PAF–SO3H is confirmed by the appearance of strong
IR bands characteristic of stretching vibrations of SO3H
groups at 1033–1224 cm–1 [25].
The condensation was performed in a tenfold excess
of acetone at an argon pressure of 1 MPa (to ensure
liquid-phase conditions). We studied the influence of
temperature on the furfural conversion. As seen from
Fig. 3a, the furfural conversion regularly increases as
the temperature is increased from 90 to 110°С, reaching
24%. Further increase in the temperature leads to an
only insignificant increase in the conversion. It is not
The sulfur content of the PAF–SO3H sample,
according to the elemental analysis data, is 4.61%,
i.e., 1.45 mmol g–1 (0.8 sulfo group per framework
fragment).
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ACID CATALYSTS BASED ON MESOPOROUS AROMATIC FRAMEWORKS
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Scheme 2. Aldol–crotonic condensation of furfural with acetone.
appropriate to perform the reaction at 140°С and higher
temperatures because of the formation of polymeric
compounds of various structures.
or 2.5 mol % relative to the furfural amount taken into
the reaction. A further increase in the catalyst amount
does not lead to an increase in the conversion.
We have studied the influence of the substrate
(furfural) : catalyst ratio at 130°С (Fig. 3b). As we
found, the optimum catalyst amount is 20 mg, which
corresponds to the amount of sulfo groups of 0.03 mmol,
The kinetic curve and product distribution are
shown in Fig. 4. In the initial period, furfural undergoes
rapid condensation, with the conversion reaching 24%
in approximately 4 h; but a further increase in the
(b)
(a)
Catalyst amount, mg
Temperature, °C
Fig. 3. Furfural conversion in condensation with acetone. Reaction conditions: (a) 1.2 mmol of furfural, furfural : acetone = 1 : 10,
20 mg of PAF–SO3H (2.5 mol %), 4 h, 1 MPa of Ar; (b) 1.2 mmol of furfural, furfural : acetone = 1 : 10, 130°С, 4 h, 1 MPa of Ar.
Time, h
Fig. 4. Furfural conversion and selectivity with respect to reaction products in condensation of furfural with acetone using PAF–SO3H.
Reaction conditions: 1.2 mmol of furfural, furfural : acetone = 1 : 10, 20 mg of PAF–SO3H (2.5 mol %), 130°С, 1 MPa of Ar.
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TALANOVA et al.
Table 2. Condensation of 5-substituted furfurals with acetone.
Reaction conditions: 1.2 mmol of substrate, substrate :
acetone = 1 : 10, 20 mg of PAF–SO3H, 130°С, 4 h, 1 MPa
of Ar
Furfural
Substituent in 5-position of furfural
conversion, %
Н
24
32
12
NO2
CH2OH
2 : 1
1 : 2
1 : 5
Furfural : acetone
1 : 10
the second furfural molecule with furfurylideneacetone
does not occur to a significant extent.
Fig. 5. Product distribution in condensation of furfural with
acetone in the presence of PAF–SO3H catalyst. Reaction
conditions: 1.2 mmol of furfural, 20 mg of PAF–SO3H
(2.5 mol %), 130°С, 4 h, 1 MPa of Ar.
We performed experiments at different initial reactant
ratios. The distribution of the condensation products is
shown in Fig. 5. With excess acetone, the major product
is FAc; as the furfural : acetone ratio is increased, the
amount of F2Ac slightly increases. The selectivity with
respect to difurfurylideneacetone reaches a maximum
(34%) at the furfural :acetone molar ratio of 2 : 1 (Fig. 5).
The catalyst was separated from the products after
the reaction by centrifugation followed by decantation.
The repeated cycles were performed without additional
loading of the catalyst. As seen from Fig. 6, the catalyst
does not lose activity in several cycles.
We evaluated the dependence of the conversion on
the substituents in the furfural ring (Table 2). We chose as
substrates 5-hydroxymethylfurfural and 5-nitrofurfural.
As expected, the strongly electron-withdrawing nitro
group enhances the carbonyl activity of the С=О group,
and the conversion increases to 32%. The presence of
the donor hydroxymethyl group decreases the yield of
the condensation products to 12%.
Cycle no.
Fig. 6. Repeated use of PAF–SO3H in condensation of furfural
with acetone. Reaction conditions: 1.2 mmol of furfural,
furfural : acetone = 1 : 10, 20 mg of PAF–SO3H (2.5 mol %),
130°С, 4 h, 1 MPa of Ar.
It was interesting to use a series of linear aldehydes:
hexanal, heptanal, nonanal, decanal, and undecanal, as
substrates (Scheme 3). Products of cross condensation,
FCn, and n-aldehyde self-condensation, (Сn)2, were
obtained. The aldol formation was not observed. In
addition, carboxylic acids formed by oxidation of the
starting compounds were detected.
condensation time to 8 h does not lead to a noticeable
increase in the conversion. The major reaction product
is furfurylideneacetone FAc. The difurfurylideneacetone
content increases with time, but in 8 h the selectivity
with respect to F2Ac does not exceed 20%; i.e., under
the conditions of our experiments the condensation of
Scheme 3. Aldol–crotonic condensation of furfural with n-aldehydes.
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ACID CATALYSTS BASED ON MESOPOROUS AROMATIC FRAMEWORKS
863
FCn
Other
products
F conversion
Fig. 7. Condensation of furfural with n-aldehyde in the presence of PAF–SO3H catalyst and distribution of reaction products. Reaction
conditions: 1.2 mmol of furfural, 1.2 mmol of n-aldehyde, 1 mL of DMF, 20 mg of PAF–SO3H (2.5 mol %), 130°C, 4 h.
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The reaction was performed in toluene and DMF at
equimolar ratios of the substrates. Irrespective of the
solvent, the maximal conversion, 23–24%, was reached
for hexanal and heptanal. As the carbon chain length
in the aldehyde molecule is increased, the furfural
conversion decreases, which may be associated with an
increase in the molecule size. The major products are
substituted α-alkyl-β-furanylacroleins, or FCn (Fig. 7).
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The catalyst based on mesoporous aromatic frame-
works modified with sulfonic acid group, PAF–SO3H,
was prepared. Its catalytic activity in aldol condensation
of furfural with carbonyl compounds (acetone and a se-
ries of aldehydes) was studied. The use of PAF–SO3H
in an amount of 2.5 mol % allows preparation of the
condensation products in a total yield of up to 25%. The
catalyst practically preserves its activity in several cy-
cles.
9. Hora, L., Kelbichová, V., Kikhtyanin, O., Bortnovskiy, O.,
and Kubička, D., Catal. Today., 2014, vol. 223, pp. 138–
147.
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CONFLICT OF INTEREST
12. Hora, L., Kikhtyanin, O., Čapek, L., Bortnovskiy, O., and
Kubička, D., Catal. Today., 2015, vol. 241, pp. 221–230.
The authors declare that they have no conflict of
interest.
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