Potassium Natural Asphalt Sulfonate (K-NAS): Synthesis and characterization as a new recyclable solid basic nanocatalyst and its application in the formation of carbon–carbon bonds

Article abstract of DOI:10.1002/aoc.5840

In this research, we synthesized and characterized a new heterogeneous basic nanocatalyst and its catalytic application was studied in the Claisen-Schmidt and Knoevenagel condensations. In order to prepare this nanocatalyst, first, the Iranian natural asphalt was sulfonated with the concentrated sulfuric acid and then, converted to the potassium natural asphalt sulfonate (K-NAS). In order to characterization of the nanocatalyst, used of FT-IR spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), inductively coupled plasma (ICP) and thermogravimetric analysis (TGA) techniques. This new basic heterogeneous nanocatalyst have advantages such as being eco-friendly, huge specific surface area, high reactivity and recyclability.

Full text of DOI:10.1002/aoc.5840

Received: 24 March 2020
DOI: 10.1002/aoc.5840
Revised: 6 May 2020
Accepted: 9 May 2020
F U L L P A P E R
Potassium Natural Asphalt Sulfonate (K-NAS): Synthesis
and characterization as a new recyclable solid basic
nanocatalyst and its application in the formation of carbon–
carbon bonds
Saeid Falah | Mohammad Soleiman-Beigi
| Homa Kohzadi
Department of Chemistry, Faculty of
In this research, we synthesized and characterized a new heterogeneous basic
nanocatalyst and its catalytic application was studied in the Claisen-Schmidt
and Knoevenagel condensations. In order to prepare this nanocatalyst, first,
the Iranian natural asphalt was sulfonated with the concentrated sulfuric acid
and then, converted to the potassium natural asphalt sulfonate (K-NAS). In
order to characterization of the nanocatalyst, used of FT-IR spectroscopy,
scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),
X-ray diffraction (XRD), inductively coupled plasma (ICP) and thermogravimetric
analysis (TGA) techniques. This new basic heterogeneous nanocatalyst have
advantages such as being eco-friendly, huge specific surface area, high reactivity
and recyclability.
Basic Sciences, Ilam University, P.O. Box
69315-516, Ilam, Iran
Correspondence
Mohammad Soleiman-Beigi, Department
of Chemistry, Faculty of Basic Sciences,
Ilam University, P.O. Box 69315-516,
Ilam, Iran.
Email: soleimanbeigi@yahoo.com
K E Y W O R D S
basic nanocatalyst, Claisen- Schmidt condensation, Knoevenagel condensation, potassium
naturassl asphalt sulfonate
1 | INTRODUCTION
an interesting challenge to find new solid basic catalysts
that have high activities in reactions for the synthesis
Nowadays, a wide variety of researches were focused on
the development of nanocatalyst in the various reac-
tions due to the size of these catalysts that reduced to
nano scale and gives them unique properties. Many
researchers were focused on synthesizing new
nanocatalysts. Among these catalysts, heterogeneous
nanocatalysts have attracted more attention rather than
the others.[1–5] These types of catalysts have many
advantages in compare to hemogeneous catalysts,
including high activity and easier separation.[6–8] In
nanocatalysts, carbon materials can be utilized as cata-
lysts or catalyst supports in the place of traditional cata-
lyst materials.[9–12] It is so due to the fact that carbon
materials have specific benefits: carbon can be man-
ufactured in different shapes and sizes and also, are sta-
ble and inert in both acidic and basic conditions. It is
of pharmaceutical and chemicals. In this sense, numer-
ous and varied materials have been used as solid basic
catalysts[13–17] but these types of bases have numerous
disadvantages i.e. being expensive, low stability, waste
products, corrosion and difficult separation. Some of
the most important reactions in chemistry and industry
are catalyzed by the bases.
Natural asphalt is a solid hydrocarbon that often
found in underground mines as a hard and black mate-
rial with a relatively high melting temperature. Natural
asphalt is generally characterized by aromatic fused rings
and functional groups containing polar heteroatoms
(Figure 1). Due to the fragility of this material, its appli-
cation is often in powder form. Although this material
has various applications, especially in the industrial but
its use as a catalyst has not been reported. Because of the
Appl Organomet Chem. 2020;e5840.
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https://doi.org/10.1002/aoc.5840

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FALAH ET AL.
2 | EXPERIMENTAL
2.1 | Materials and apparatus
All reagents and solvents were purchased from Sigma-
Aldrich, Merck and Fluka Companies and natural
asphalt from the Kimia bitumen Zagros Cooperative,
Iran. All the known compounds were identified by com-
paring their melting points and/or spectral data to those
reported in the literature. The reactions were monitored
using TLC on silica-gel Polygram SILG/UV254 plates.
Proton nuclear magnetic resonance (1H NMR) spectros-
copy was also performed on Bruker AVANCE DPX-400
and DPX-500 spectrometers. Chemical shifts were
reported in ppm relative to TMS as the internal standard.
Fourier-transform infrared spectroscopy (FTIR) was per-
formed using FTIR-8300 spectrometer made by
Shimadzu. The morphology of the catalyst was examined
by performing scanning electron microscopy (SEM) using
Mira 3-XMU. The elemental composition was determined
using EDS and Mira 3-XMU. The exacted amount of K in
the catalyst was determined by Inductively Coupled
Plasma (ICP) using VISTA-PRO, Australia. X-ray diffrac-
tion (XRD) was investigated using a Holland Philips X
and the thermogravimetric analysis (TGA) curve was
recorded using a PL-STA 1500 device manufactured by
Thermal Sciences.
FIGURE 1 A part of natural asphalt molecular structure
unique properties of natural asphalt such as availability,
high activity, thermal stability, capable recovery and
reusability, we were encouraged to use it in the prepara-
tion of nanocatalyst.
The carbon–carbon bond formation is one of the most
significant reactions in organic chemistry. For example,
Claisen-Schmidt and knoevenagel condensations are the
most powerful, versatile and important tools for the for-
mation of carbon–carbon bonds. Claisen-Schmidt and
Knoevenagel condensations are useful tools for the syn-
thesis of α,β-unsaturated compounds[18,19] which are
important pharmaceutical intermediates.[20–22]
2.2 | Synthesis of potassium natural
In this regard, the aim of the present study was the
synthesize, introduce and characterize potassium natural
asphalt sulfonate (K-NAS) as a novel heterogeneous basic
nanocatalyst and application of it in the Claisen-Schmidt
and Knoevenagel condensations (Scheme 1).
asphalt sulfonate (K-NAS)
2.2.1 | Preparation of sulfonated natural
asphalt
In order to prepare this nanocatalyst, we used natural
asphalt as a natural, green, inexpensive and available
material. The potassium natural asphalt sulfonate have
advantages such as high stability, being eco-friendly, low
toxicity, easy extraction from the mixture, recovery and
reusability without significant loss of catalytic activity.
At first, in order to synthesize the Sulfonated natural
asphalt, a mixture of the Iranian natural asphalt (1.0 g)
and the concentrated sulfuric acid (5 ml) was stirred for
15 min at room temperature. Then, the resulting reaction
mixture was heated at 220 C for 2 hr and finally, it was
added to water and ice slowly. The product (Sulfonated
ꢀ
SCHEME 1 Synthesis of α,β-unsaturated
derivatives

FALAH ET AL.
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natural asphalt) (1.4 gr) was obtained using simple filtra-
tion, washed twice with distilled water (2 × 20 ml) and
dried at 100 ꢀC in the oven. In this step, the C=C bounds
in aromatic and vinyl moieties and also OH groups in
asphalten (harden part of natural asphalt) are most possi-
ble to sulfonation.[23]
the reaction mixture to yield the products. Finally, the
pure products were obtained through recrystallization
with ethanol and water.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of K-NAS
2.2.2 | Conversion of natural asphalt
sulfonic acid (NASA) to potassium natural
asphalt sulfonate (K-NAS)
The synthesized nanocatalyst (K-NAS) has been charac-
terized by the FT-IR, SEM, XRD, EDS, ICP and TGA
techniques.
Finally, NASA (1 g) and 20 ml of a potassium hydroxide
solution 10% were stirred for 1 h at room temperature.
Then, the solvent was evaporated and potassium Natural
Asphalꢀt Sulfonate (K-NAS) was obtained by being dried
at 100 C in oven (Scheme 2). K-NAS was characterized
by FT-IR, SEM, EDS, XRD, TGA and ICP techniques.
Thisꢀnanocatalyst is black with a melting point of over
300 C. Although K-NAS is not soluble in organic sol-
vents, it can be easily dissolved in water.
3.1.1 | FT-IR studies
Figure 2 shows the FTIR spectra of natural asphalt,
NASA, K-NAS and recovered K-NAS. In all these spectra,
the stretching vibrations of O-H and N-H groups on
the surface of natural asphalt were observed at
approximately 3,440 cm−1. The absorbing bands at about
1,450–1,640 cm−1 corresponded to the aromatic rings in
all the samples. According to Figure 2 (spectrum b), a
stretching vibration at about 616 cm−1 was related to the
sulfur vibration which confirmed the sulfonation of natu-
ral asphalt by H2SO4. Moreover, a major broad sharp
peak at 800–1200 cm-1 that overlapped with several sig-
nals, including asymmetric and symmetric stretching
modes of O-S-O. In addition, in Figure 2 (Spectrum c),
the broad peak of the O-H group was observed at
3441 cm−1. The spectrum of the recycled K-NAS is shown
in Figure 2 (Spectrum d) that confirmed the stability of
the nanocatalyst during the reactions.
2.3 | Procedure for Claisen- Schmidt
condensation catalyzed by K-NAS
A mixture of benzaldehyde derivatives (1 mmol), ketones
(1 mmol) and K-NAS (15 mg) in ethanol (2 ml) was
stirred at room temperature until the reaction was com-
pleted. After completion of the reaction, the catalyst was
separated by filtration and cold water (1 ml) was added
to the reaction mixture. Finally, the products were
obtained through simple filtration and recrystallization
with ethanol and water.
3.1.2 | SEM studies
2.4 | General procedure for Knoevenagel
condensation catalyzed by K-NAS
In order to characterize the morphology and size of the
nanocatalyst, SEM technique was used. (Figure 3a-b)
respectively shows the SEM images of natural asphalt
(NA) (a) and K-NAS (b). The SEM image showed that the
nanoparticles are approximately spherical in shape and
the average diameter of the K-NAS nanoparticles is about
16 nm.
(1 mmol) of benzaldehyde derivatives, (1 mmol) of com-
pounds with active methylene group and (10 mg) ofꢀK-
NAS in ethanol (2.0 ml) as solvent were stirred at 80 C.
When the reaction was completed, the catalyst was sepa-
rated using filtration and cold water (1 ml) was added to
SCHEME 2 General route
for the synthesis of K-NAS
nanocatalyst

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FALAH ET AL.
FIGURE 2 FT-IR spectra
of natural asphalt (a), NASA
(b), K-NAS (c) and recovered
K-NAS (d)
FIGURE 3 SEM images of NA (a) and
K-NAS (b)

FALAH ET AL.
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3.1.3 | XRD analysis
associated with the successful sulfonation of natural
asphalt. Moreover, the exact amount of potassium in the
catalyst which was obtained by ICP technique was found
The XRD pattern of K-NAS is shown in Figure 4.
According to it, seven peaks observed in XRD spectrum
of K-NAS at 2Ɵ = 30.32ꢀ, 32.87ꢀ, 33.02ꢀ, 39.37ꢀ, 41.87ꢀ,
41.92ꢀ and 49.47ꢀ were related to the k in the catalyst.[24]
to be 5.01 × 10−3 mol g−1
.
3.1.5 | TGA analysis
3.1.4 | EDX analysis and ICP
The thermal stability of the K-NAS was investigated by
thermal analysis DSC-TGA. As shown in Figure 6, the
nanocatalyst is stable up to 300 C which can be used
in high temperature reactions. Weight loss between
300–600 ꢀC is due to the decomposition of organic groups
of the nanocatalyst. K-NAS has high tolerance at high
temperatures, therefore can be considered as an effective
and stable nanocatalyst to perform the reaction at high
temperatures.
ꢀ
In order to determine the elemental composition of K-
NAS nanocatalyst, the components of the nanocatalyst
were analyzed using EDS (Figure 5). As depicted, the
EDS spectrum of K-NAS: S, O, C, N and K species were
observed in the catalyst composition. The high percent-
age of sulfur and potassium in K-NAS confirmed the
presence of SO3K group in this catalyst, which is
FIGURE 4 XRD pattern of K-NAS
FIGURE 5 EDX pattern of K-NAS

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FALAH ET AL.
3.2 | Catalytic studies
Accordingly, we selected the reaction of benzaldehyde
and acetone as the model reaction and studied this reac-
tion in different conditions of solvent, temperature and
the amount of catalyst whose results are presented in
Table 1. According to Table 1, Entry 1, the reaction was
initially performed in the absence of the catalyst in EtOH
at room temperature and no product formed in this case.
Catalytic activity of K-NAS was investigated in the
Claisen-Schmidt and Knoevenagel condensations. At
first, we examined the activity of K-NAS for the synthesis
of α,β-unsaturated carbonyl compounds via Claisen-
Schmidt condensation.
FIGURE 6 DSC-TGA diagram of K-NAS
TABLE 1 Optimization conditions of reaction benzaldehyde with acetonea
Entry
Solvent
EtOH
Temp (o C)
Catalyst (mg)
Time (hr)
Yield (%)
1
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
r.t
30
40
60
-
5
3
3
3
3
3
3
3
3
3
3
3
3
3
3
0
70
87
97
97
86
47
68
15
10
97
95
95
91
2
EtOH
3
EtOH
10
15
20
15
15
15
15
15
15
15
15
15
4
EtOH
5
EtOH
6
PEG
7
Toluene
Dioxane
n-hexan
Solvent-free
EtOH
8
9
10
11
12
13
14
EtOH
EtOH
EtOH
aReaction conditions: benzaldehyde (1 mmol). acetone (2 mmol), solvent (2 ml), rt, 3 hr.

FALAH ET AL.
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TABLE 2 Synthesis of α,β-unsaturated derivatives from Claisen- Schmidt condensation in the presence of K-NASa
Entry
Aldehyde
Ketone
Product
Time (hr)
Yield (%)b
MP (ꢀC) (Ref.)
1
3
97
41–43[25]
2
3
4
5
4
24
12
16
94
84
87
75
27–28[25]
199–200[25]
115–117[25]
169–171[25]
6
7
2
5
89
86
150–154[26]
129–131[27]
(Continues)

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FALAH ET AL.
TABLE 2 (Continued)
Entry
Aldehyde
Ketone
Product
Time (hr)
Yield (%)b
MP (ꢀC) (Ref.)
8
3
98
110–112[26]
9
5
91
143–144[28]
10
11
3.5
95
89
54–56[26]
6
120–122[26]
12
2.5
94
100–102[26]
13
14
4
5
91
92
102–105[27]
98–99[28]

FALAH ET AL.
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TABLE 2 (Continued)
Entry
Aldehyde
Ketone
Product
Time (hr)
Yield (%)b
MP (ꢀC) (Ref.)
140–144[26]
15
2.5
96
aReaction conditions: aldehyde (1 mmol). acetone (2 mmol) and other Ketones (1 mmol), K-NAS(15 mg), r.t, EtOH (2 ml).
bIsolated yield.
TABLE 3 Optimization conditions of reaction benzaldehyde with malononitrilea
Entry
Solvent
EtOH
Temp (o C)
Catalyst (mg)
Time (min)
Yield (%)
1
80
80
80
80
80
80
80
80
80
RT
30
40
60
80
-
45
45
45
45
45
45
45
45
45
45
45
45
45
45
0
2
EtOH
5
75
95
95
76
25
45
20
0
3
EtOH
10
15
10
10
10
10
10
10
10
10
10
10
4
EtOH
6
PEG
7
Toluene
DMF
8
9
Dioxane
Solvent-free
EtOH
10
11
12
13
14
15
10
40
65
80
95
EtOH
EtOH
EtOH
EtOH
aReaction conditions: malononitrile (1 mmol), benzaldehyde (1 mmol), solvent (2 ml), 45 min.
Then, the reaction was repeated using different amounts
of K-NAS in the same reaction condition which resulted
in a significant increase of up to 97% in the yield using
(15 mg) of the catalyst (Table 1, Entries 2–5). Afterwards,
the reaction was investigated in different solvents at
different temperature. Consequently, the best conditions
were obtained in ethanol at room temperature (Entry 11).
Results are shown in Table 1.
According to Table 2, after optimizing the reaction
conditions, a variety of benzaldehyde derivatives with

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FALAH ET AL.
TABLE 4 Synthesis of α,β-unsaturated carbonyl compounds and arylidene malononitriles derivatives from Knoevenagel condensation
in the presence of K-NASa
Compounds with
active methylene
Entry
Aldehyde
Product
Time (min)
Yield (%)b
MP (ꢀC)(Ref)
1
45
95
80–82[29]
2
3
63
55
92
94
106–108[29]
98–100[30]
4
5
6
7
50
40
89
91
94
88
162–164[29]
130–133[31]
181–183 [30]
114–116[30]
65
190

FALAH ET AL.
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TABLE 4 (Continued)
Compounds with
active methylene
Entry
Aldehyde
Product
Time (min)
Yield (%)b
MP (ꢀC)(Ref)
8
70
90
193–195[32]
9
60
82
89
88
125–128[33]
10
132–135[33]
11
12
82
65
93
94
44–45[34]
125–127[34]
13
14
56
61
92
89
92–94[34]
160–163[34]
aReaction conditions: aldehyde (1 mmol), compounds with active methylene group (1 mmol), cat (10 mg), 80 ꢀC, EtOH (2 ml).
bIsolated yield.

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FALAH ET AL.
electron-donor and electron-withdrawing functional
groups and wide range of ketones (aliphatic and
aromatic) were successfully examined to prepare the
4 | CONCLUSIONS
In this research, we synthesized and characterized a new
carbon form nanocatalyst and used it as a heterogeneous
basic nanocatalyst with a high catalytic activity for
Claisen-Schmidt and Knoevenagel condensations. This
nanocatalyst have advantages such as easy produce and
separation from the reaction mixture, low toxicity, high
stability, high reactivity and recyclability. Also, this
research has high yields and low time of the condensa-
tions in comparison to the prior research.
I
corresponding α,β-unsaturated derivatives; R, 1H and
13C NMR of some of products are presented in the
supporting information (Figures S1-S20).
In the second part of the research, we studied the
activity of K-NAS nanocatalyst in the Knoevenagel con-
densation for the synthesis of α,β-unsaturated carbonyl
compounds and arylidene malononitriles derivatives.
Therefore, we selected the reaction between benzal-
dehyde and malononitrile as the model reaction. In
the Table 3, summarized the results of investigating
the effects of different parameters including solvent,
the amount of the catalyst (K-NAS) and temperature of
the model reaction.
ACKNOWLEDGMENTS
Authors thank of Ilam University, Ilam, Iran, for finan-
cial support of this research project.
After optimizing the reaction conditions, various
aromatic aldehydes and compounds with active
methylene group were used for condensation. The
results are summarized in Table 4; IR, 1H and 13C
NMR of some of products are presented in the
supporting information (Figures S21-S29).
ORCID
Mohammad Soleiman-Beigi https://orcid.org/0000-
0002-7805-5066
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How to cite this article: Falah S, Soleiman-
Beigi M, Kohzadi H. Potassium Natural Asphalt
Sulfonate (K-NAS): Synthesis and characterization
as a new recyclable solid basic nanocatalyst and its
application in the formation of carbon–carbon
bonds. Appl Organomet Chem. 2020;e5840. https://
doi.org/10.1002/aoc.5840