Highly efficient and selectivity-controllable aerobic oxidative cleavage of C-C bond over heterogeneous Fe-based catalysts

Article abstract of DOI:10.1016/j.jcat.2021.01.029

A base-free selectivity-controllable aerobic oxidative cleavage of C-C bond with heterogeneous Fe-based catalysts (Fe_xO_y-N@C₃N₄) is developed. In the presence of oxygen, 1,2-diols are selectively transformed to the corresponding aldehyde, while the methyl esters are orientedly produced from 1,2-diones in methanol medium.

Full text of DOI:10.1016/j.jcat.2021.01.029

Journal of Catalysis 395 (2021) 399–403
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Priority Communication
Highly efficient and selectivity-controllable aerobic oxidative cleavage of
C-C bond over heterogeneous Fe-based catalysts
⇑
⇑
Pengfei Guo, Shengyun Liao , Shun Wang, Jing Shi, Xinli Tong
Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, Tianjin Key Laboratory of Drug Targeting and Bioimaging, School of Chemistry and Chemical
Engineering, Tianjin University of Technology, No. 391 Binshuixi Road, Tianjin 300384, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A base-free selectivity-controllable aerobic oxidative cleavage of C-C bond with heterogeneous Fe-based
catalysts (FexOy-N@C3N4) is developed. In the presence of oxygen, 1,2-diols are selectively transformed to
the corresponding aldehyde, while the methyl esters are orientedly produced from 1,2-diones in metha-
nol medium.
Received 10 September 2020
Revised 17 January 2021
Accepted 25 January 2021
Available online 5 February 2021
Ó 2021 Elsevier Inc. All rights reserved.
Keywords:
Oxidative cleavage
1,2-Diols
1,2-Diones
Heterogeneous catalysts
Selectivity-controllable
The selective cleavage of C–C bond in organic molecules with
the suitable oxidant is of fundamental interest and plays a signifi-
cant role in the present organic synthesis and sustainable chem-
istry [1–5]. Oxidative cleavage of vicinal diols and diones is
originally developed and investigated using periodic acid and lead
tetraacetate as oxidants [6–7]. The utilization of classical oxidizing
systems such as chromium trioxide, manganese dioxide, and pyri-
dinium chlorochromate also brings serious environmental prob-
lems. Therefore, the development of green catalytic oxidation
system with a clean oxidant such as molecular oxygen has pro-
voked more interest. A number of homogeneous transition-metal
catalytic systems such as CuBr (10 mol%) and pyridine (50 mol%),
CeCl3Á7H2O (10 mol%), TBACl (50 mol%), AgOTf (10 mol%), and
NaOMe (3 equiv) have been studied recently [8–11]. Although
some good results were acquired on the homogeneous reaction
systems, the recycling of catalyst and the addition of expensive
metal salt restrict their widespread application in the chemical
industry. Solmi and co-workers found that a 45% conversion of
trans-1,2-cyclohexanediol with 87% selectivity of adipic acid was
obtained using the Au/MgO as catalyst at 90 °C for 24 h [12].
Recently, Escande’s group developed a novel heterogeneous cata-
lyst of EcoMnOx derived from the Mn-hyperaccumulating plant
for selective aerobic oxidative cleavage of 1,2-diols, in which 98%
conversion of meso-hydrobenzoin and >99% selectivity of ben-
zaldehyde were attained in 1-butanol at 100 °C for 1 h [13]. The
same group also studied the oxidative transformation of meso-
hydrobenzoin in 1-butanol using a complex heterogeneous cata-
lyst of (Na-Mn-LMO) to produce corresponding aldehydes, and
high efficiency and good selectivity were acquired under the same
reaction conditions [14]. Furthermore, García and co-workers
reported that the oxidative cleavage of hydrobenzoin using MoO2-
Cl2(dmso)2 as catalyst in the presence of DMSO at 120 °C for
120 min, in which the yield of benzaldehyde was up to 89% [15].
Very recently, an atomically dispersed cobalt-based catalyst was
synthesized by Luo et al. for oxidative cleavage of 1-
phenylethane-1,2-diol with additive of K2CO3 under mild condi-
tions (80 °C, 24 h), which provided 100% conversion with 96% yield
of methyl benzoate [16]. However, the additive of base promoter
was still necessary in the reaction systems. Though the aforemen-
tioned homogeneous and heterogeneous catalytic systems in the
presence of molecular oxygen can promote the transformation of
1,2-diols to acid, ketone or ester with high selectivity (see
Scheme 1A and 1B), the development of more efficient and envi-
ronmentally benign catalytic protocols based on low-cost catalytic
system without basic additives for the C-C bond cleavage of diols
still remains of significance.
Herein, a novel low-cost heterogeneous base-free catalytic sys-
tem has been developed for aerobic oxidative cleavage of C-C bond
in 1,2-diols and 1,2-diones, in which a single FexOy-N@C3N4 was
used as the catalyst and the selectivity-regulatable oxidative
⇑
Corresponding authors.
E-mail addresses: 18202587221@163.com (S. Liao), tongxinli@tju.edu.cn (X.
Tong).
https://doi.org/10.1016/j.jcat.2021.01.029
0021-9517/Ó 2021 Elsevier Inc. All rights reserved.

P. Guo, S. Liao, S. Wang et al.
Journal of Catalysis 395 (2021) 399–403
Scheme 1. A and B: previous work; C and D: this work.
cleavage of C-C bond of 1,2-diols and 1,2-diones to produce alde-
hyde and ester, respectively. The typical experiments are shown
in Scheme 1C and 1D. As a result, about 96.6% conversion with
100% selectivity of benzaldehyde is obtained during the oxidative
transformation of hydrobenzoin. Meanwhile, 89.3% conversion of
benzil in 99.9% selectivity of methyl benzoate is attained with
methanol as solvent.
N@C3N4 (Table 1, entries 5 and 6). In benzil-methanol reaction sys-
tem, no methyl benzoate was detected with CuxOy-N@C3N4 and
NixOy-N@C3N4 and benzoic acid was the only product (Table 1,
entries 5 and 6). So FexOy-N@C3N4 was screened as the best cata-
lyst for oxidative cleavage hydrobenzoin and benzil in the medium
of methanol. FexOy-N@C3N4 could not only promote transforma-
tion of hydrobenzoin towards benzaldehyde with 96.6% conversion
and 100% selectivity, but also promote the conversion of benzil
towards methyl benzoate with 89.3% conversion and 99.9% selec-
tivity, when the reaction time was prolonged to 1 h and 10 h,
respectively (Table 1, entries 3 and 4). In addition, g-C3N4 was
replaced by several other supporters (Table1, entries 8–11), the
low conversion and poor selectivity of main product was obtained
in both hydrobenzoin-methanol and benzil-methanol system,
which demonstrated that the synergetic effect between the active
component and the supporters may be responsible for the excel-
lent performance of FexOy-N@C3N4 was the best catalyst for the
two catalytic systems [16–17].
Catalyst precursors were synthesized via introducing the sup-
porters into the reaction mixture of metal nitrate and 1,10-
phenanthroline. These precursors were subjected to 800 °C pyrol-
ysis to give the different catalysts. We altered the types of metal
nitrates and obtained the catalysts such as FexOy-N@C3N4, CuxOy-
N@C3N4, NixOy-N@C3N4, and CoxOy-N@C3N4. Their catalytic perfor-
mance in both hydrobenzoin-methanol system and benzil-
methanol system was shown in Scheme 2 and Table 1. With FexOy-
N@C3N4 as catalyst, 76.7% conversion of hydrobenzoin and 100%
selectivity of benzaldehyde were achieved in the first reaction sys-
tem. At the same time, FexOy-N@C3N4 could also promote the
transformation of benzil to methyl benzoate with 77.4% conversion
and 99.7% selectivity (Table 1, entry 3). CoxOy-N@C3N4 could also
catalyse oxidative cleavage of hydrobenzoin to benzaldehyde, but
it displayed poor performance towards oxidative cleavage of benzil
to methyl benzoate (Table 1, entry 7) with only 50.3% conversion
and 41.6% selectivity. In hydrobenzoin-methanol reaction system,
CuxOy-N@C3N4 and NixOy-N@C3N4 is less active than FexOy-
The performance of several reported catalysts and the present
catalysts were shown in Table S1. It is found the noble metallic cat-
alysts such as AgOTf and Pd(OAc)2 could promote oxidative cleav-
age of C-C bond of hydrobenzoin and benzil with high yield under
the mild reaction conditions, but it can not do without the addi-
tives. Similarly, an atomically dispersed cobalt-based catalyst
(Co-NC-800) could not catalyze this reaction in the absence of
Scheme 2. Aerobic oxidative cleavage of C-C bond: (a) hydrobenzoin-methanol system; (b) benzil-methanol system.
400

P. Guo, S. Liao, S. Wang et al.
Journal of Catalysis 395 (2021) 399–403
Table 1
The catalytic aerobic oxidative cleavage of C-C bond of hydrobenzoin and benzil over different catalysts.a
Catalytic system
Entry
Hydrobenzoin-methanol
Benzil-methanol
Conv. (%)c
Catalyst
Conv. (%)b
Sel. (%)b
Sel. (%)b
1d
3d (2)
1d
2d
3d
1
None
0
0
0
0
0
0
0
2
g-C3N4
1.6
100
100
100
100
40.8
94.6
7.9
100
21.3
8.2
0
0
0
0
0
0
0
0
0
0
100
100
58.4
91.0
58.8
32.7
94.7
3
FexOy-N@C3N4
FexOy-N@C3N4
CuxOy-N@C3N4
NixOy-N@C3N4
CoxOy-N@ C3N4
FexOy-N@Al2O3
FexOy-N@MgO
FexOy-N@TiO2
FexOy-N@ZrO2
76.7
96.6
5.2
68.8
100
32.1
9.5
77.4
89.3
55.3
26.9
50.3
21.1
34.1
24.3
44.3
0.3
0.1
0
0
0
0
0
0
0
99.7
99.9
0
4c
5
6
7
8
9
10
11
59.2
0 (5.4)
92.1
0
78.7
91.8
0
41.6
9.0
41.2
67.3
5.3
37.7
26.1
a
Reaction conditions: 0.1 g substrate, 0.025 g catalyst, in 15 mL methanol under 0.2 MPa of O2 (hydrobenzoin-methanol: at 70 °C for 0.5 h; benzil-methanol at 100 °C for
4 h).
b
These results were obtained by GC analysis with the internal standard technique.
The reaction time was prolonged to 1 h in the hydrobenzoin-methanol system and to 10 h in the benzil-methanol system, respectively.
Compounds 1, 2, and 3 are referred to benzaldehyde, methyl benzoate, and benzoic acid, respectively.
c
d
the basic promoter. For the reported Mn-based catalysts, a large
amount of NaOH was added during the preparation of the catalyst,
too. However, the present catalyst (FexOy-N@C3N4) still displays
good performance in the absence of any basic additive.
We extended the types of substrates to explore the versatility of
FexOy-N@C3N4 and the results are shown in Table 2. Benzaldehyde
was stabilized under the as-established catalytic condition
(Table 2, entry 1). The additive of K2CO3 played a positive role in
benzil-methanol system (Table 1, entry 3 and Table 2, entry 5).
The data from entries 2 and 3 in Table 2 demonstrated that
2-phenylacetophenone and benzoin were not only directly cleaved,
but also can be oxidized to benzil. Subsequently, benzil was further
transformed into methyl benzoate (Scheme S1 in Supporting Infor-
mation). The extra-evidence for the mentioned possible pathways
is the mole ratio of benzaldehyde and methyl benzoate about 1:3
(Table 2, entries 6 and 7), when the additive of K2CO3 was intro-
duced into the reaction system. Although in the presence of
K2CO3 as promoter, the catalyst of FexOy-N@C3N4 can’t catalyze
Table 2
The detailed investigation to the performance of the as-established catalytic system towards different substrates.a
Entry
Substrate
Conv. (%)b
Sel. (%)b
1
2
benzil
0
Others
100d
1c
2
1.2
100
100
0
0
0
29.7
0
44.5
17.6
0
23.6
2.2d
3
27.9
0
54.5d
4
0
0
0
0
0
0
0
5e
6e
7e
8e
9f
100
100
100
0
2.8
26.8
22.7
0
97.2
73.2
77.3
0
0
0
0
0
0
0
0
0
10f
0
0
0
0
0
0
0
11h
22.2
6.2i
12h
28.3
0
5.1j
0
a
b
c
d
e
f
Reaction conditions: 0.1 g substrate, 0.025 g catalyst, in 15 mL methanol, under 0.2 MPa of O2, at 100 °C for 4 h.
These results were obtained by GC analysis with the internal standard technique.
Reaction conditions: 0.1 g substrate, 0.025 g catalyst, in 15 mL methanol, under 0.2 MPa O2, at 70 °C for 0.5 h.
(dimethoxymethyl)benzene.
With 0.025 g K2CO3.
Reaction conditions: 0.1 g substrate, 0.025 g catalyst, in 15 mL methanol, under 0.2 MPa of O2, at 70 °C for 4 h.
Reaction conditions: 0.1 g substrate, 0.025 g catalyst, in 15 mL methanol, under 0.2 MPa of O2, at 100 °C for 0.5 h.
The yield of methyl acetate.
h
i
j
The yield of methyl acetate and methyl butyrate.
401

P. Guo, S. Liao, S. Wang et al.
Journal of Catalysis 395 (2021) 399–403
the aerobic oxidative cleavage of 1,2-diphenylethane (Table 2,
entries 4 and 8). Obviously, the type of functional groups on the
C-C bond has important effects on the mode of C-C cleavage and
the selectivity of the products. The addition of K2CO3 reduces the
difference of the selectivity of products, in which the mole ratio
benzaldehyde and methyl benzoate are almost the same in 2-
phenylacetophenone and benzoin reaction system. Several alipha-
tic diols or diones were investigated under the same reaction con-
ditions. It was found the as-synthesized catalyst doesn’t work for
aliphatic diol or diones (Table 2, entries 9–12). So the ortho aro-
matic groups play an important role in the cleavage of C-C bonds
in diols and diketones.
In addition, the effects of reaction medium, reaction atmo-
sphere and reaction time on the catalytic aerobic oxidative cleav-
age of C-C bond of hydrobenzoin and benzil were investigated.
As shown in Table S2 of the Supporting Infromation, the aerobic
oxidative cleavage of C-C bond of hydrobenzoin can happen both
in alcohol and non-alcohol media, but the activity is very low in
the long chain alcohols or non-alcohols media. Benzil does not
react under the established reaction condition, when the solvents
were switched to acetonitrile or dichloromethane. In long chain
alcohols, K2CO3 can promote the aerobic oxidative cleavage of ben-
zil (Tables S2 and S3 of the Supporting Information). Besides (R,S)
hydrobenzoin, the enantionmers (R,R) hydrobenzoin and (S,S)
hydrobenzoin were also tested as the substrates and the lower
us make sure the Fe(0) or FeOx on the surface (0 < x < 1.5) is pos-
sibly the main active site (Entry 5 in Table S6 of the Supporting
Information). But when the reduction temperature was elevated
to 600 °C, such low activity further identifies the probable active
species as FeOx (0 < x < 1.5) (Entry 6 in Table S6 of the Supporting
Information). Based on the above results and the action of MOx and
M-Nx in the oxidative cleavage C-C bond provided from the refe-
ence [18–25], we conclude that FeOx (0 < x < 1.5) and Fe-Nx
may be the active species. The synergic effects between FeOx and
Fe-Nx may be responsible for the great performance of the as-
synthesized catalysts.
In summary, a base-free heterogeneous catalytic system has
been developed for aerobic oxidative cleavage of C-C bond based
on FexOy-N@C3N4, which was fabricated through a facile and con-
venient method. In our catalytic reaction system, benzaldehyde
and methyl benzoate is almost the only product for oxidative
cleavage of hydrobenzoin and benzil under the mild conditions,
respectively. This will provide a promising, cost-effective and
green technology for preparation aldehydes and esters in the
organic synthesis and chemical industry.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
conversion indicated that
a-hydroxyl in the opposite direction of
(R,S) hydrobenzoin was adsorbed easily by the catalyst, which
plays an important role in course of C-C bond cleavage (Table S4,
entries 1–3 of the Supporting Information). The data from Tables
S4 and S5 of the Supporting Information showed oxygen played a
significant role in C-C bond cleavage of hydrobenzoin and benzil.
Only the product and substrate were detected during the course
of the reaction. As the reaction time was prolonged, the selectivity
of the product increased, while the quantity of substrate decreased
greatly (Figure S1 and S2 of the Supporting Information). In addi-
tion, FexOy-N@C3N4 shows good stability in these reaction systems
(Figure S3 of the Supporting Information). The diffraction peaks of
the fresh and used catalyst are overlapped, which can verify the
remained structure of catalyst. In addition, the component and
morphology of the catalyst remained unchanged before and after
use (Figure S4, S6 and S7 of the Supporting Information).
Acknowledgement
This work was financially supported by National Natural
Science Foundation of China (21601135 and 21878235), Tianjin
Research Program of Application Foundation and Advanced Tech-
nology (No. 17JCYBJC20200), and Natural Science Foundation of
Tianjin Municipal Education Commission (2017KJ256).
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2021.01.029.
References
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N@C3N4 catalyst (Figure S2, S3 S6 and S7 in Supporting Informa-
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as the acid washing, oxidation and reduction were used to study
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the Supporting Information), which shows Fe2O3 does not work
in this reaction system. Thirdly, when the catalyst was reduced
in H2 atmosphere at 500 °C for 4 h, the increased activity may help
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