Mixed crystalline phases and catalytic performance of OMS-2 based nanocomposites for one-pot synthesis of quinazolines with O2 as an oxidant

Article abstract of DOI:10.1016/j.mcat.2021.111499

In this work, a series of sodium phosphotungstate modified manganese oxide octahedral molecular sieve (OMS-2) catalysts ([PW]-OMS-2) were developed, and their catalytic activities were investigated by one-pot synthesis of quinazolines from benzyl alcohol and 2-aminobenzylamine with O₂ as green oxidant in dimethyl carbonate (DMC). TEM, XRD and EDS confirmed that sodium phosphotungstate decomposed into phosphotungstic acid and sodium tungstate in the doping process. Meanwhile, phosphotungstic acid attached and located at the surface of OMS-2 and W ions were successfully doped into the OMS-2 framework. For comparison, phosphotungstic acid/OMS-2 was prepared by simple wet impregnation method. The [PW]-OMS-2 is the most highly selective and effective over than phosphotungstic acid/OMS-2 and OMS-2 itself in the one-pot synthesis of quinazolines. It may be due to the synergetic effect of phosphotungstic acid and OMS-2, and successfully doping W into OMS-2 frameworks. Hence, this work provides a new environmentally-friendly and heterogeneous OMS-2 based nanocomposites and it may be put into practice to synthesize heterocyclic compounds.

Full text of DOI:10.1016/j.mcat.2021.111499

Molecular Catalysis 504 (2021) 111499
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Mixed crystalline phases and catalytic performance of OMS-2 based
nanocomposites for one-pot synthesis of quinazolines with O2 as an oxidant
,
,
,
,
,
Nan Yaoa, Xiuru Bia b, Liping Zhanga b, Luyao Taoa b, Peiqing Zhaoa *, Xu Menga *,
,
Xiang Liuc *
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of
Sciences, Lanzhou, 730000, China
b University of Chinese Academy of Sciences, Beijing, 100049, China
c College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, China Three Gorges University,
Yichang, Hubei, 443002, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this work, a series of sodium phosphotungstate modified manganese oxide octahedral molecular sieve (OMS-2)
catalysts ([PW]-OMS-2) were developed, and their catalytic activities were investigated by one-pot synthesis of
quinazolines from benzyl alcohol and 2-aminobenzylamine with O2 as green oxidant in dimethyl carbonate
(DMC). TEM, XRD and EDS confirmed that sodium phosphotungstate decomposed into phosphotungstic acid and
sodium tungstate in the doping process. Meanwhile, phosphotungstic acid attached and located at the surface of
OMS-2 and W ions were successfully doped into the OMS-2 framework. For comparison, phosphotungstic acid/
OMS-2 was prepared by simple wet impregnation method. The [PW]-OMS-2 is the most highly selective and
effective over than phosphotungstic acid/OMS-2 and OMS-2 itself in the one-pot synthesis of quinazolines. It may
be due to the synergetic effect of phosphotungstic acid and OMS-2, and successfully doping W into OMS-2
frameworks. Hence, this work provides a new environmentally-friendly and heterogeneous OMS-2 based
nanocomposites and it may be put into practice to synthesize heterocyclic compounds.
OMS-2 based nanocomposites
Heterogeneous catalysis
One-pot synthesis
Quinazolines
Oxidation
1. Introduction
adsorption properties of OMS-2 could be changed and modified by
doping transition metal ions due to their newly-formed active sites,
Manganese oxide octahedral molecular sieve (OMS-2) composed of
MnO6 octahedral units is known to be 2 × 2 tunnel nanostructural
catalyst applied in wide areas of catalytic transformation [1–4]. Since
OMS-2 was first synthesized by Suib and coworkers in 1994 [5], a series
of application of OMS-2-based catalysts in catalytic oxidation for
organic synthesis and environmental catalysis sprung up in succession
due to its attractive nature, such as mixed valence state of Mn4+, Mn3+
and Mn2+, average oxidation state of ~ 3.8, abundant surface defect
vacancies, active lattice oxygen, mild acidity and alkalinity, and its
easiness to be modified [2,6–12]. Meanwhile, many synthesis and
modification methods were developed in order to enhance its catalytic
performance, such as hydrothermal method [13], reflux method [14],
ultrasonic method [15], solid phase method [16], microwave assisted
method [17], which could substantially influence the particle size,
crystallinity, morphology, surface area and surface defect concentration
of OMS-2. In addition, the acidity, porosity, lattice oxygen mobility and
crystalline phases or defect vacancies [16–24].
As the certain kinds of well-known nitrogen-containing heterocyclic
compounds, quinazoline derivatives pose a broad-spectrum of biological
activities and have widely been used in dyes, pharmaceutical, agricul-
tural and chemical industries [25,26]. Some representative examples of
drugs and natural products containing quinazoline motifs are displayed
in Fig. 1. Despite these significant advances, the synthetic route of
quinazolines generally required homogeneous transition metal com-
plexes as catalysts, such as [Cp*RhCl2], [27–29] Ni(II) [30], Pa [31], Cu
[32], AgSbF6 [33], Ir complex [34], Cu(OAc)2 [35,36], Co [35], etc. The
usage of these catalysts mentioned above severely violated the concep-
tion of green chemistry, apart from the hardship to separate catalysts
from the reaction system for the further circulation, especially for in-
dustrial synthesis. Therefore, the development of efficient, stable and
cost-effective heterogeneous non-precious metal catalysts for accessing
quinazolines is highly desirable. Recently, several heterogeneous
* Corresponding authors.
E-mail addresses: zhaopq@licp.cas.cn (P. Zhao), xumeng@licp.cas.cn (X. Meng), xiang.liu@ctgu.edu.cn (X. Liu).
https://doi.org/10.1016/j.mcat.2021.111499
Received 8 January 2021; Received in revised form 7 February 2021; Accepted 9 February 2021
Available online 2 March 2021
2468-8231/© 2021 Elsevier B.V. All rights reserved.

N. Yao et al.
Molecular Catalysis 504 (2021) 111499
non-precious metal catalysts, such as
α
-MnO2 [37], Fe3O4@SiO2@-
were reported in ppm and spin-spin coupling constants (J) were given in
Hz.
TiO2-OSO3H, [38] Fe-Fe3C@MNC-800 [39] have been reported for the
synthesis of quinazolines. These catalysts dramatically boosted the cat-
alytic efficiency of reaction, but some drawbacks still existed, such as the
use of toxic solvents and peroxides as oxidants, difficulties on catalyst
preparation, and the requirement of costly and unstable aldehydes as
starting substrate. Therefore, a more economical, environment friendly
synthetic strategy and simplified route for these bioactive molecules are
urgently needed.
2.2. Preparation of different catalysts
A set of nanorod OMS-2 composites (x[PW]-OMS-2) were synthe-
sized by reflux method according to our previous work [42]. Take the
preparation of 5[PW]-OMS-2 as example (5 mol% sodium phospho-
tungstate to the amount of KMnO4). Firstly, 0.037 mol (5.89 g) KMnO4
was was dissolved in 100 mL deionized water to form KMnO4 solution.
Meanwhile, 0.052 mol (8.8 g) MnSO4⋅H2O was dissolved in 30 mL
deionized water, followed by the addition of 3 mL HNO3 as well as
0.00185 mol (5.45 g) sodium phosphotungstate to form mixed solution.
Afterwards, KMnO4 solution was instilled into the above mixture under
magnetic stirring at room temperature for about 2 h (Adding one drop
every two seconds). Finally, the reaction solution was refluxed at 100 ◦C
for 24 h. Cooled down to the room temperature, the formative solid was
collected by filtration, washed with deionized water and dried at 100 ◦C
for 8 h to afford 5[PW]-OMS-2. The rest of catalysts with different molar
ratio of sodium phosphotungstate and KMnO4 were respectively nomi-
nated as 0.1[PW]-OMS-2, 1[PW]-OMS-2, 2[PW]-OMS-2, 3[PW]-OMS-2,
4[PW]-OMS-2 and 10[PW]-OMS-2.
In recent years, our group successfully synthesized Cu- and Na-
modified OMS-2 for the oxidative synthesis of N-containing heterocy-
cles [7], homocoupling of alkynes, click reaction, reduction of nitro-
phenol compounds [40] and biomass catalytic transformation [41]. It is
especially noticeable that we reported a OMS-2 composite doped by
sodium phosphotungstate (designated as [PW]-OMS-2) for the first time
and it showed much better catalytic performance in oxidative dehy-
drogenation of N-heterocycles than original OMS-2, concluding that
newly-formed mixed crystalline phases could enhance its surface area,
redox ability and lattice oxygen lability [42]. This previous work might
provide a pathway to enhance catalytic efficiency of OMS-2 by the
generation of mixed crystalline phases other than the maintenance of
single cryptomelane phase. Herein, a range of nanorod OMS-2 based
nanocomposites, named as x[PW]-OMS-2 (“x” means x mol% sodium
phosphotungstate to the amount of KMnO4), were synthesized via reflux
method for the synthesis of quinazoline compounds directly using
benzyl alcohols and o-aminobenzylamine as substrates. Among the
synthesized catalysts, 5[PW]-OMS-2 was certified to be the best one,
presenting an excellent synergistic catalytic activity resulted from mixed
crystalline phases of cryptomelane phase and phosphotungstic acid
phase. Additionally, on the basis of the fully characterization methods,
we speculated a possible formation mechanism of the mixed crystal
catalyst and activation mechanism towards the oxidative cyclization
reaction. Kinetic study revealed that the existence of mixed crystal phase
could significantly increase the initial reaction rate, reduce the apparent
activation energy of the oxidation reaction, compared to original OMS-2
with pure cryptomelane phase.
The catalyst, named as H3PW12O40/OMS-2, was prepared by wet
impregnation method. 1.304 g H3PW12O40⋅xH2O (The amount of
phosphotungstic acid is based on its theoretical proportion in 5[PW]-
OMS-2) was absolutely dissolved in 13 mL deionized water, then 2 g
OMS-2 was added, and the mixture was vigorously stirred at room
temperature for 24 h. After water removal by rotary evaporation, the
solid was collected and calcined under 300 ◦C for 3 h to get H3PW12O40
OMS-2.
/
The details in preparing for other manganese oxides, including
α-MnO2, β-MnO2, δ-MnO2, λ-MnO2 was described in the previous liter-
ature [43,44].
2.3. Synthesis of various quinazolines
Typically, a mixture of 0.25 mmol benzyl alcohol, x[PW]-OMS-2 (25
mg) and 1.0 mL DMC were stirred at 80 ◦C for 6 h with O2 as oxidant.
Then, 0.2 mmol 2-aminobenzylamine solution (dissolved in 1 mL DMC)
was injected into the reaction system for another 18 h. The reaction was
monitored and analyzed through 1HNMR to obtain conversion and yield
data.
2. Experimental section
2.1. General information
All reagents derived from commercial suppliers. DMC (CAS NO. 616-
38-6, ReagentPlus®, 99 %) was purchased from Sigma-Aldrich. Silica
gel columns were selected to purify various products with Merck silica
gel 60 (200–300 mesh). The generation of products relied on UV light
detection using analytical TLC. Solvents CDCl3 and TMS were employed
as NMR reagent and internal standard, respectively. Chemical shifts (δ)
A mixture of benzyl alcohols (0.25 mmol), 5[PW]-OMS-2 (25 mg)
and 1.0 mL DMC were stirred at 80 ◦C for 6 h with O2 as oxidant. Then,
0.2 mmol 2-aminobenzylamine solution (dissolved in 1 mL DMC) was
injected into the reaction system for another 18 h. The purification of the
products relied on silica gel chromatography with petroleum ether/
Fig. 1. Selected examples of market available quinazolines drugs.
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N. Yao et al.
Molecular Catalysis 504 (2021) 111499
ethyl acetate as eluent.
2.4. Characterization
Nitrogen adsorption-desorption experiments were conducted at 76
K, and the specific surface areas of a set of x[PW]-OMS-2 were calculated
through BET model. The morphology images derived from high-
resolution transmission electron microscope and scanning electron mi-
croscope, respectively. The powder X-ray diffraction provided crystal
phase structure of catalysts in the 2θ range of 10ꢀ 90◦. The surface
chemical states of catalysts were examined by X-ray photoelectron
spectroscopy (XPS), among which, binding energies were calibrated by
contaminant carbon (C1s =284.8 eV). EDS images displayed the distri-
bution location of main elements. Map sum spectrum offered data of
elemental analysis.
Fig. 3. BET data of x[PW]-OMS-2.
inferior to 204.5 m2 gꢀ 1 of 2[PW]-OMS-2, far greater than 67.1 m2 gꢀ 1
of pure OMS-2. Besides, the pore size of 5[PW]-OMS-2 was 7.7 nm, and
the pore volume of it was 0.3 cm3 gꢀ 1, in comparison with that of OMS-2
(12.7 nm and 0.2 cm3 gꢀ 1). Generally speaking, the surface area is
closely related to catalytic activity and the higher the surface area of the
material is, the more catalytic active sites could be provided. Thus, 5
[PW]-OMS-2 could be speculated to have a good or even outstanding
catalytic activity towards oxidative reaction.
3. Results and discussion
3.1. Formation mechanism of x[PW]-OMS-2
The XRD patterns of x[PW]-OMS-2 obtained from reflux method
with different doping amount of sodium phosphotungstate, and
H3PW12O40/OMS-2 obtained from wet impregnation method were given
in Fig. 2. It could be found that when the content of sodium phospho-
tungstate was in the range of 0.1 mol%ꢀ 2 mol%, no obvious extra
diffraction peaks generated, all of these materials were generally in line
with pure cryptomelane phase (JCPDS No.029-1020), which showed
broad peaks and could be well indexed to (110), (200), (220), (310),
(211), (301), (411), (600) and (521) planes respectively [45]. With the
increase of dopant loading (3 mol%-10 mol%), several extra diffraction
peaks emerged on the basis of OMS-2 cryptomelane phase, getting
stronger and sharper, which fully demonstrated the formation of mixed
crystal phases of the materials (Fig. 2a). These new peaks could be
ascribed to the crystal phase of phosphotungstic acid (JCPDS
No.38-178). Thus, it was considered that in the preparation of x
[PW]-OMS-2, phosphotungstic acid in-situ generated from decomposi-
tion of sodium phosphotungstate dispersed on the OMS-2 nanorods,
drastically improved catalytic activities because of the rich acid sites
provided by phosphotungstic acid in comparison with pure OMS-2. In
addition, the crystal structure of sample H3PW12O40/OMS-2 was also
displayed for comparison. As shown in Fig. 2b, several extra weak peaks
generated on the basis of pure OMS-2. These peaks could be ascribed to
the phase of H3PW12O40. Thus, simple wet-impregnation method could
also give composite that contained crystalline phases of cryptomelane
and phosphotungstic acid.
To investigate the formation mechanism of x[PW]-OMS-2 nano-
structures, representative SEM images of the catalysts were shown in
Fig. 4. Firstly, the catalyst 0.1[PW]-OMS-2 was presented in the form of
slender fibers, which was identified with that of OMS-2 (Figs. 4a and
S1). However, as the doping content increased, there was a distinct
change in morphological structure. As we could see, the morphology of x
[PW]-OMS-2 (x = 1, 2, 3, 4, 5) took on a shorter, thicker nanorod-like
and even granular structure (Fig. 4b–g), it could be inferred that with
higher concentration of sodium phosphotungstate in the precursor so-
lution, the steric hindrance formed and hampered the further growth of
OMS-2, resulting in the formation of short nanorod. Moreover, the
appearance of H3PW12O40/OMS-2 was also displayed. According to
Fig. 4h–i, we could find clear, bright clusters were uniformly dispersed
on the surface of support material. Hence, a conclusion could be drawn
that the phosphotungstic acid was successfully loaded on the surface of
pure OMS-2, consisting with the XRD result (Fig. 2b). However, the
typical morphology of OMS-2 was destroyed and nanofibers or nanorods
disappeared. H3PW12O40/OMS-2 and 5[PW]-OMS-2 obtained from the
different preparation methods showed totally different morphologies on
SEM images.
The TEM images of x[PW]-OMS-2 (x = 3, 4, 5) as given showed clear,
similar nanorods (Fig. 5a, c, e) and all of the materials had clear lattice
fringes (Fig. 5b, d, f). There were also non rod like clusters in these three
materials, and the cluster density is higher in 5[PW]-OMS-2 than the
other two, which can be ascribed to the generated phosphotungstic acid.
The result further demonstrated the existence of coordinated
BET data of x[PW]-OMS-2 were obtained through N2 adsorption-
desorption and the results were summarized in Fig. 3. Surface areas of
doped materials were all enhanced more or less. It was noteworthy that
the surface area of 5[PW]-OMS-2 was 169.1 m2 gꢀ 1, which was only
Fig. 2. XRD patterns of different catalysts.
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N. Yao et al.
Molecular Catalysis 504 (2021) 111499
Fig. 4. SEM images of the x[PW]-OMS-2. (a) 0.1[PW]-OMS-2, (b) 1[PW]-OMS-2, (c) 2[PW]-OMS-2, (d) 3[PW]-OMS-2, (e) 4[PW]-OMS-2, (f) 5[PW]-OMS-2, (g) 10
[PW]-OMS-2, (h-i) H3PW12O40 /OMS-2.
Fig. 5. TEM images of x[PW]-OMS-2. (a-b) 3[PW]-OMS-2 (c-d) 4[PW]-OMS-2, (e-f) 5[PW]-OMS-2.
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N. Yao et al.
Molecular Catalysis 504 (2021) 111499
phosphotungstic acid on 5[PW]-OMS-2. In addition, other TEM images
of x[PW]-OMS-2 (x = 0, 0.1, 1, 2, 10) were presented in Fig. S2.
EDS images (Fig. 6) presented the distribution location of main ele-
ments. For 5[PW]-OMS-2, it was found that the densities of elements O,
K and Mn in the catalyst were quite high and evenly dispersed in the
catalyst. By contrast, the densities of W and K were slightly lower, and
the content of P was the least, but they were also well scattered in the
material. In addition, no Na+ was found in the analysis, because Na+ was
completely eliminated when the catalyst was washed during the prep-
aration. In conclusion, it was convinced that sodium phosphotungstate
decomposed into phosphotungstic acid and sodium tungstate in the
doping process. Meanwhile, W ions were successfully doped into the
framework of OMS-2 to further influence the physicochemical proper-
ties. The uniform distribution of elements in the picture was identified
with the elemental analysis result: Mn(50.75 %) > O(37.03 %) > W(8.05
%) > K(4.02 %) > P(0.14 %) (Table S2, Fig. S3).
O1s was fitted into two peaks, one was surface adsorbed unsaturated
oxygen species with high binding energy, and the other was saturated
lattice oxygen with low binding energy (Fig. 7b). The O1s results of as-
synthesized materials were displayed in Table 2. In our previous work,
sodium phosphotungstate modificaiton was able enhance the concen-
tration of lattice oxygen of [PW]-OMS-2 and its mobility, which
contributed to the superior catalytic ability in oxidative dehydrogena-
tion [42]. As we could observe that 5[PW]-OMS-2 showed the second
highest content of lattice oxygen species (79.8 %) compared to others. It
is concluded that appropriate amount of dopant could efficiently in-
crease the amount of lattice oxygen for modified OMS-2 materials.
3.2. Catalytic activity comparison of x[PW]-OMS-2 for synthesis of 2-
phenylquinazoline
To testify the catalytic activities of a series of x[PW]-OMS-2, we
chose oxidative cyclization of benzyl alcohol (1a) with 2-aminobenzyl-
amine (2a) as the probe reaction.
The surface chemical states of a set of x[PW]-OMS-2 were examined
by XPS. Among these materials, the pure OMS-2 and x[PW]-OMS-2 (x =
0.1, 1, 2) had been characterized in our previous work [42]. The spectra
of the rest of x[PW]-OMS-2 (x = 3, 4, 5, 10) were severally exhibited
(Figs. 7 and S4). For x[PW]-OMS-2, the Mn 2p3/2 bands were selected to
fit the curve, the ratios of Mn3+ and Mn4+ were calculated depending on
their peak areas [42,44]. Additionally, the quantitative analysis on the
XPS spectra was conducted and the results were given in Table 1. The
concentrations of Mn3+ of x[PW]-OMS-2 were all significantly increased
by doping. The proportion of total content of high valence manganese
(Mn3+ and Mn4+) in 5[PW]-OMS-2 was almost same to that in 2
[PW]-OMS-2, which was much higher than other catalysts, implying
that 5[PW]-OMS-2 comparatively possessed more superb oxidation
performance than others. The average oxidation state (AOS) of Mn in a
range of x[PW]-OMS-2, (Fig. S5), was calculated according to the
binding energy difference (ΔE) of Mn 3 s in XPS based on the empirical
formula, i.e. AOS = 8.956ꢀ 1.126×ΔE [42,46]. The result also
confirmed our speculation that 5[PW]-OMS-2 could offer the highest
AOS of 3.82. Moreover, the occurrence of Mn3+ enabled the oxygen
vacancies to form by reason of the electrostatic balance [42,44], while
abundant oxygen vacancies the catalyst filled with tended to play
important roles as active sites for oxidation reactions. The 5[PW]-OMS-2
owned the highest content of Mn3+, indicating that it had a great deal of
oxygen vacancies to maintain electrostatic balance.
Several typical manganese oxides with diverse crystal structures,
including α-MnO2, β-MnO2, δ-MnO2, λ-MnO2 and OMS-2 exhibited much
less performance or even were inactive for the reaction (Table 3, entries
1-5). The catalytic effectiveness of H3PW12O40/OMS-2 prepared by
simple wet impregnation method failed to meet our expectations
possibly because the morphology of OMS-2 was destroyed and sup-
ported H3PW12O40 clusters could not play a synergistic role with OMS-2.
(Table 3, entry 6). For x[PW]-OMS-2, in a certain range of doping
amount, the activities of them gradually strengthened, and the selec-
tivity of 2-phenylquinazoline also improved from 39 % to 60 % with the
increase of sodium phosphotungstate content (Table 3, entries7ꢀ 9).
With the further increase of the amount of sodium phosphotungstate,
activities of the catalysts did not dramatically improved, displaying a
similar catalytic efficiency level, and the product yields retained be-
tween 50 % ~60 % (Table 3, entries 10-11). Unexpectedly, when 0.25
mmol 1a, 0.2 mmol 2a were stirred in 2 mL DMC at 80 ◦C with 5[PW]-
OMS-2 as catalyst, an extremely high yield of 3a (93 %) and 100 %
conversion of 2a were obtained within 24 h under O2 protection
(Table 3, entry 12). The experimental results were in good agreement
with the characterization results of a series of catalysts. It was precisely
due to its retained nanorod morphology, the high specific surface area
(169.09 m2 gꢀ 1) and high average oxidation state (AOS = 3.82) of 5
Fig. 6. EDS images of 5[PW]-OMS-2.
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N. Yao et al.
Molecular Catalysis 504 (2021) 111499
Fig. 7. The XPS spectra of 5[PW]-OMS-2.
3.3. Synthesis of quinazolines
Table 1
The Mn 2p3/2 results of x[PW]-OMS-2.
By identifying the optimal reaction conditions and the catalytically
active sites, we subsequently explored the generality of this protocol for
the synthesis of 2-substituted quinazolines. As shown in Table 4, in
general, various benzyl alcohols could be efficiently converted into
benzaldehydes for further oxidative cyclization reaction, where benz-
aldehydes could bear both electron-donating groups (3b, 3 h) and
-withdrawing groups (3d-3 g) with similar effects, with exception of 3c,
3i and 3 j, efficiently coupling with 2-aminobenzylamine (2a) to give
their corresponding quinazolines in high yields (88 % - 95 %). Hetero-
cyclic benzyl alcohols, 3-pyridine methanol as well as 2-thiophene
methanol were also suitable as the coupling partners to deliver their
corresponding quinazolines (3k, 3 l), in several giving yields of 71 % and
75 %. All of the structures of quinazolines mentioned above have been
Binding energy of Mn 2p3/2 (e.V)
Manganese species (%)
Catalyst
Mn4+
Mn3+
Mn2+
Mn4+
Mn3+
Mn2+
OMS-2
643.36
643.76
643.97
643.71
644.04
643.85
643.93
643.98
642.44
642.34
642.51
642.17
642.32
642.24
642.43
642.27
641.04
640.79
642.20
640.66
641.01
640.93
642.82
641.00
60.0
38.9
28.3
34.4
31.5
34.8
34.4
26.5
35.6
57.3
57.8
63.9
51.5
45.9
63.8
43.7
4.4
0.1[PW]-OMS-2
1[PW]-OMS-2
2[PW]-OMS-2
3[PW]-OMS-2
4[PW]-OMS-2
5[PW]-OMS-2
10[PW]-OMS-2
3.7
13.9
1.7
17.0
19.3
1.8
29.8
Table 2
1
examined by HNMR as well as 13CNMR and proved to be correct. In
The O1s results of as-synthesized materials.
addition, aliphatic alcohols, such as methanol and cyclohexyl methanol
along with the other two alcohols were also tried as the reaction sub-
strates. However, only low yield target products were gained or even no
reaction occurred (3m-3p).
Binding energy of O1s (e.V)
Oxygen species (%)
Catalyst
Surface O
Lattice O
Surface O
Lattice O
OMS-2
531.12
531.43
531.07
531.43
531.49
531.01
531.44
530.97
530.03
529.85
529.71
529.94
529.77
529.75
529.93
529.79
33.6
21.9
32.1
19.6
20.7
35.9
20.2
41.9
66.4
78.1
67.9
80.4
79.3
64.1
79.8
59.1
0.1[PW]-OMS-2
1[PW]-OMS-2
2[PW]-OMS-2
3[PW]-OMS-2
4[PW]-OMS-2
5[PW]-OMS-2
10[PW]-OMS-2
3.4. The kinetic study for synthesis of 2-phenylquinazoline
To gain the reaction rate constants of the two catalysts to further
examine the excellent catalytic activity of the target catalyst in details
with the original OMS-2 as criterion, we monitored the probe reaction in
real time and linear functions were obtained separately. The experi-
mental results showed that the reaction rate of the probe reaction in the
presence of 5[PW]-OMS-2(k5[PW]-OMS-2 = 0.1635 minꢀ 1) was much
higher than that in OMS-2(kOMS-2 = 0.0482 minꢀ 1), Thus, the effec-
tiveness of the catalyst was further confirmed (Fig. 8a, b).
[PW]-OMS-2, as well as the synergistic effect of the mixed crystal phase
formed by its unique reflux preparation method that made the yield and
selectivity of the probe reaction be considerably improved. When the
doping amount reached up to 10 mol%, the poor catalytic effect, by
contrast, occurred mainly because of the small surface area of 10[PW]-
OMS-2 (Table 3, entry 13). The various oxidants were also tested in this
reaction (Table 3, entries 14, 15), the results certified that O2 had the
best oxidation performance under same reaction conditions. Although
air and H2O2 could both lead to a high conversion of 2a, selectivity of
desired product was quite poor. Moreover, the moderate yield and
selectivity gained in N2 further certified this reaction is an aerobic re-
action. More blank experiments showed that precursors for the prepa-
ration of catalysts, such as MnSO4⋅H2O and KMnO4 presented inert
effects toward the reaction (Table 3, entries 17 and 18).
As was shown in Fig. 8c, in the probe reaction system, with the in-
crease of catalyst amount (Fig. S6), the initial reaction rate accelerated
progressively, and there was a good linear relationship between catalyst
concentration and reaction rate. For the catalyst, it was a first-order
reaction. This indicated that the initial reaction rate was related to the
catalyst amount.
The kinetic study of the one-pot synthesis of 2-phenylquinazoline
was also conducted by time-dependent experiments at different tem-
peratures and the calculation of apparent activation energy (Ea) was
based on Arrhenius formula (Figs. S7 and S8). As shown in Fig. 8d, In
this linear regression equation, LnK and 1/T had an outstanding linear
relationship (R2 = 0.9911), and the final activation energy was deter-
H3PW12O40⋅xH2O used as the catalyst also failed the reaction, which
further indicated that the importance of cooperation of phosphotungstic
acid and cryptomelane in the composite (Table 3, entry19). For com-
parison, some similar work in catalytic synthesis of 2-phenylquinazoline
by other groups were also listed (Table 3, entries 20-26). In addition, we
studied several other influential factors producing on the reaction, such
as temperature (Table S3, entries 2-4), the molar ratio of substrates
(Table S3, entries 5-6), the amount of catalyst (Table S3, entries 7ꢀ 9)
and different kinds of solvents (Table S3, entries 10-15). These results
showed that all of them had great effects on the reaction. After screening
the conditions, we obtained the best reaction conditions and applied
them to the substrate expansion.
mined to be 87.73 kJ. molꢀ 1
.
The whole process monitoring experiment and hot filtration test, the
two groups of experiments, were carried out at the same time. According
to Fig. 9, almost instantaneous formation of intermediate 2-phenyl-
1,2,3,4-tetrahydroquinazoline(m) (Fig. 9, line B), the yield of which
was close to 100 % within 30 min, and extremely slow formation rate of
product 3a (Fig. 9, line C), with only 26 % yield after 240 min could be
observed. This result implied that the formation rate of product 3a was
the rate-limiting step. As for hot filtration test, the reaction stopped at
the time of 30 min after the removal of 5[PW]-OMS-2 from the reaction
6

N. Yao et al.
Molecular Catalysis 504 (2021) 111499
Table 3
Catalytic synthesis of 2-phenylquinazoline[a]
.
Entry
Catalyst
Oxidant
Conv.(2a)
Yield(m)
/% [b]
Yield (3a)
Sel.(3a)
/% [b]
/% [b]
/% [b]
1
α
-MnO2
O2
trace
trace
trace
\
trace
trace
trace
\
\
\
2
β-MnO2
O2
trace
trace
\
\
3
γ-MnO2
O2
\
4
λ-MnO2
O2
\
5
OMS-2
O2
100
trace
100
100
100
100
100
100
trace
100
75
50
39
\
39
\
6
H3PW12O40/OMS-2
0.1[PW]-OMS-2
1[PW]-OMS-2
2[PW]-OMS-2
3[PW]-OMS-2
4[PW]-OMS-2
5[PW]-OMS-2
10[PW]-OMS-2
5[PW]-OMS-2
5[PW]-OMS-2
5[PW]-OMS-2
MnSO4 ⋅ H2O
KMnO4
O2
trace
46
7
O2
48
56
60
56
53
93
trace
37
17
35
\
48
56
60
56
53
93
\
8
O2
31
9
O2
35
10
O2
38
11
O2
40
12
O2
trace
trace
51
13
O2
14
air
37
26
35
\
15
H2O2
N2
21
16
100
trace
trace
trace
100
100
\
46
17c
O2
trace
trace
trace
\
18d
O2
\
19e
H3PW12
O40 ⋅ xH2O
O2
\
\
20 [37]
21 [39]
22 [47]
23 [48]
24 [49]
25 [50]
26 [51]
α-MnO2-150
TBHP
H2O2
KOtBu
Air
91
96
66
95
87
80
85
\
Fe-Fe3C@NC-800
[Ni(MeTAA)]
3-nitropyridine
PhI(OAc)2/I2
CsOH⋅H2O
4
96
\
\
\
\
\
PIDA
Dioxane/air
air
\
\
\
\
CuI/K2CO3
\
\
[a]Reaction conditions: 1a (0.25 mmol), 2a (0.2 mmol), catalyst (25 mg), O2 protection, 80 ◦C, 24 h. DMC (2 mL). [b] The yield and conversion were determined by
1HNMR using quinoline as internal standard. [c–e] Catalyst mass were 3.4 mg, 3.2 mg, 16 mg, respectively.
Table 4
Substrate scope for the synthesis of quinazolines [a, b]
.
[a] Reaction conditions: 2-aminobenzylamine (2a) (0.2 mmol), benzyl alcohols (0.25 mmol), 5[PW] -OMS-2(25 mg), DMC (2 mL), 25 ◦C, O2 protection, 80 ◦C, 24 h.
Yields of isolated product were determined by silica gel chromatography. [b] Turn over number, TON = moles of 2-aminobenzylamine converted/moles of catalyst.
Formula weight of OMS-2(KMn8O16⋅nH2O) is 734.6 g molꢀ 1 (excluding the water) [39].
7

N. Yao et al.
Molecular Catalysis 504 (2021) 111499
Fig. 8. Calculation of rate constant with respect to (a) 5[PW]-OMS-2, (b)OMS-2 under standard conditions. (c) Initial rate with respect to catalyst amount. (d)
Calculation of reaction activation energy.
Fig. 9. Whole process monitoring experiment and hot filtration test. Reaction conditions: benzyl alcohol (0.25 mmol), 2-aminobenzylamine (0.2 mmol), 5 [PW]-
OMS-2 (25 mg), DMC (2 mL), O2 balloon, 80 ◦C.
solution (Fig. 9, line A and line D), indicating no dissolved species
contributed to the catalysis and the heterogeneous nature of the 5[PW]-
OMS-2 catalyst. According the recycling test, 5[PW]-OMS-2 could not
reuse and the catalytic ability lost after once run.
form 2-phenylquinazoline. As a result of the real-time monitoring of the
reaction, we found that generation rate of intermediate (m) was
extremely fast, 76 % yield of m could be obtained in 5 min (Figs. 9 and
S10), while step 3 was the rate-determining step since this step had the
lowest reaction rate. All of the catalytic reactions might take place on
surface defect sites of 5[PW]-OMS-2, in which phosphotungstic acid
played an important role to catalyze the reaction cooperatively.
The reaction mechanism was investigated (Table 5). In the presence
of 5[PW] -OMS-2 and O2, 80 % yield of benzaldehyde generated in 5 h
with 100 % conversion of benzyl alcohol, which was detected by GC
(Fig. S9). Subsequently, benzaldehyde coupled with 2-aminobenzyl-
amine (2a) to give intermediate (m), followed by dehydrogenation to
8

N. Yao et al.
Molecular Catalysis 504 (2021) 111499
Foundation for Young Scholars (HZJJ20-10). the 111 Project (D20015)
and the Engineering Research Center of Eco-environment in Three
Gorges Reservoir Region, Ministry of Education, China Three Gorges
University (KF2019-05), the outstanding young and middle-aged sci-
ence and technology innovation teams, Ministry of Education, Hubei
province, China (T2020004).
Table 5
Control experiments [a]
.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2021.111499.
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CRediT authorship contribution statement
Nan Yao: Investigation, Methodology, Software, Data curation,
Writing - original draft. Xiuru Bi: Visualization, Investigation. Liping
Zhang: Visualization, Investigation. Luyao Tao: Visualization, Investi-
gation. Peiqing Zhao: Conceptualization, Supervision, Validation,
Funding acquisition, Writing - review & editing. Xu Meng: Conceptu-
alization, Supervision, Validation, Funding acquisition, Writing - review
& editing. Xiang Liu: Conceptualization, Supervision, Validation,
Funding acquisition, Writing - review & editing.
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Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
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We gratefully acknowledge the National Natural Science Foundation
of China (21403256, 21573261, 21805166), the Youth Innovation
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