Highly efficient oxidation of 2,2′-hydrazobis-isobutyronitrile to 2,2′-Azobis-isobutyronitrile over a CrO: X/TiO2catalyst with hydrogen peroxide

Article abstract of DOI:10.1039/d1cc00380a

Green oxidation of 2,2′-hydrazobis-isobutyronitrile (HAIBN) to 2,2′-Azobis-isobutyronitrile (AIBN) over a recyclable solid catalyst was a significant challenge. A titanium dioxide-supported chromium oxide (CrOx/TiO2) catalyst was, for the first time, developed for oxidation of HAIBN with hydrogen peroxide and achieved complete conversion of HAIBN with a high (94.8%) yield of AIBN.

Full text of DOI:10.1039/d1cc00380a

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
Highly efficient oxidation of 2,20-hydrazobis-
isobutyronitrile to 2,20-azobis-isobutyronitrile
over a CrOx/TiO2 catalyst with hydrogen
peroxide†
Cite this: Chem. Commun., 2021,
57, 4576
Received 22nd January 2021,
Accepted 31st March 2021
Hu Zhang, Shengnan Yue,
Xionggang Lu*
Xiujing Zou, Xueguang Wang, * Xingli Zou * and
DOI: 10.1039/d1cc00380a
rsc.li/chemcomm
Green oxidation of 2,20-hydrazobis-isobutyronitrile (HAIBN) to 2, For the catalytic oxidation of HAIBN with H2O2 using the catalyst
20-azobis-isobutyronitrile (AIBN) over a recyclable solid catalyst HBr or KBr, the reactions can be performed only in solutions
was a significant challenge. A titanium dioxide-supported chro- containing highly-concentrated sulfuric acid. Accordingly, the bro-
mium oxide (CrOx/TiO2) catalyst was, for the first time, developed mide catalyst is difficult to recover for reuse, resulting in environ-
for oxidation of HAIBN with hydrogen peroxide and achieved mental pollution and high cost.20 The most desirable production of
complete conversion of HAIBN with a high (94.8%) yield of AIBN.
AIBN should be the oxidation of HAIBN through a highly efficient
and reusable solid catalyst using a green oxidizing agent such as
2,20-Azobis-isobutyronitrile (AIBN) has been widely applied as H2O2 or O2 under mild low-temperature conditions. Compared to
an important initiator or foaming agent for the synthesis of O2, H2O2 has a better oxidation ability for HAIBN, and thus has
various organic polymers like polyvinyl chloride, polyvinyl been recognized as a preferred oxidizing agent for this reaction.
acetate, polymethyl methacrylate, rubber and plastics.1–5 However, up to now, there has not been a report on an active solid
Besides, AIBN has also been used to synthesize some new catalyst for the catalytic oxidation of HAIBN to AIBN with H2O2.
water-soluble azo initiators for aqueous solutions and emulsion
polymerization.6–9
In this study, we demonstrated for the first time that a
titanium dioxide-supported chromium oxide (CrOx/TiO2)
Industrially, AIBN is produced mainly by the condensation catalyst prepared by a simple impregnation method exhibited
of hydrazine hydrate and acetone cyanohydrin, followed by high catalytic activity for the oxidation of HAIBN to AIBN with
oxidation of 2,20-hydrazobis-isobutyronitrile (HAIBN) using H2O2 in organic solvents without any acid or base at low
chlorine as an oxidizing agent.10–13 In the reaction process of temperatures. Importantly, the CrOx/TiO2 catalyst and solvents
HAIBN, large amounts of toxic chlorine gas required to generate can be easily recovered for reuse by simple treatments almost
AIBN would inevitably cause serious safety and environmental without any environmental pollution.
concerns. In addition, it is difficult to control the reaction end-
point for the oxidation of HAIBN with chlorine, affecting the yield tion method and calcined at different temperatures (denoted
and quality of the products.14,15
CrOx/TiO2-T; T = 300 1C, 400 1C, 500 1C, 600 1C). Other catalysts
The CrOx/TiO2 catalyst was prepared through an impregna-
Recently, much attention has been paid to the oxidation of mentioned for comparison were synthesized using the same
HAIBN to AIBN with hydrogen peroxide (H2O2), a green oxidizing method with a 400 1C calcination temperature. All details about
agent, which only generates water as a byproduct in the reaction.16 catalysts and their synthesis processes can be found in the ESI.†
However, the high activation energy between HAIBN and H2O2 Note that the mass of catalytic metallic element (such as Cr in
makes this reaction sluggish at low temperature. Heating up to CrOx) to supports (such as TiO2, MgO, etc.) was 5.5 wt% for all
increase the frequency of collisions between molecules and speed of the catalysts prepared in this study.
up the chemical reaction is also not advisable for this reaction
The X-ray diffraction (XRD) patterns of the CrOx/TiO2-T
owing to the easy decomposition of AIBN at high temperature.17–19 catalysts (Fig. 1a) all have diffraction peaks at 25.31, 37.81,
48.01, 55.11, 62.71, and 75.01, which can be indexed to the
(101), (004), (200), (211), (204), and (215) crystal facets of
State Key Laboratory of Advanced Special Steel, School of Materials Science and
the anatase phase (JCPDS No. 21-2172), respectively.21,22 As
Engineering, Shanghai University, Shanghai 200444, China.
the calcination temperature increased, there was no peak of
E-mail: wxg228@shu.edu.cn, xinglizou@shu.edu.cn, luxg@shu.edu.cn
rutile in the prepared catalyst, demonstrating its excellent
stability. No chromium oxides were found in the CrOx/TiO2
† Electronic supplementary information (ESI) available: Experimental details. See
DOI: 10.1039/d1cc00380a
4576 | Chem. Commun., 2021, 57, 4576–4579
This journal is © The Royal Society of Chemistry 2021

View Article Online
Communication
ChemComm
Table 1 Catalytic performances of the synthesized catalysts for the
oxidation of HAIBNa
Entry
Catalyst
Conv.b (%)
1
2
3
4
5
6
7
8
9
10
No catalyst
CrOx/TiO2
CoOx/TiO2
NiOx/TiO2
CuOx/TiO2
CrOx/MgO
CrOx/ZrO2
CrOx/CeO2
CrOx/La2O3
CrOx/y-Al2O3
o0.5
55.7
5.8
4.6
6.1
11.1
15.5
15.5
8.6
Fig. 1 (a) The wide-angle XRD patterns and (b) the XPS spectra (Cr 2p3/2
of the synthesized CrOx/TiO2-T catalysts.
)
catalysts synthesized at calcination temperatures in the range
from 300 1C to 500 1C, indicating that CrOx exists in an
amorphous form on the surface of titanium dioxide. Peaks at
33.91, 36.61, 41.91 and 50.71 marked in the pattern represent
the (104), (110), (113) and (024) planes of Cr2O3 (JCPDS No.
38-1479).23 This result revealed that the increase of calcination
temperature is not beneficial to the formation of a homoge-
neous dispersion of CrOx, which was consistent with the
result of scanning electron microscope (SEM) characterization
(Fig. S1, ESI†).21 X-ray photoelectron spectroscopy (XPS) was
used to analyze the chemical states of the CrOx/TiO2-T catalysts.
The XPS spectra of the Cr 2p3/2 regions are shown in Fig. 1b,
and the related content proportions of Cr(III) and Cr(VI) calcu-
lated based on the XPS spectra are summarized in Table S1,
ESI.† The Cr 2p3/2 peaks located at binding energies of 576.8 eV
and 579.4 eV represent Cr(III) and Cr(VI), respectively.24–26 As the
calcination temperature increased, the content of Cr(VI) first
increased and then decreased. When the temperature reached
400 1C, the proportion of Cr(VI) reached the highest value
(26.2%). It could be speculated that some Cr(III) on the surface
was oxidized to Cr(VI) during the calcination as the precursors
would inevitably be exposed to air. With the further increase of
calcination temperature, Cr(VI) was decomposed into Cr(III) in
the form of Cr2O3, as confirmed by the XRD analysis (Fig. 1a).
To investigate the catalytic performance of the synthesized
CrOx/TiO2 catalyst, we first tested different catalysts for the
oxidation of HAIBN to AIBN using 30 wt% H2O2 in acetonitrile,
and the results are summarized in Table 1. Obviously, the CrOx/
TiO2 catalyst exhibited the best catalytic performance com-
pared with the other catalysts such as Co, Ni and Cu oxides
supported on TiO2 (entries 2–5). In addition, different supports
including MgO, ZrO2, CeO2, La2O3 and y-Al2O3 loaded chro-
mium oxides were also tested for the same reaction (entries 2
and 6–10). The results showed that TiO2 as the support exhib-
ited the best catalytic effect among these catalysts. This result
suggested that the special binding force between CrOx and TiO2
may strongly affect the oxidation of HAIBN to AIBN with H2O2.
Notably, except for CrOx/TiO2, using the other catalysts it is
difficult to completely transform HAIBN even by extending the
reaction time.
13.3
a
Reaction conditions: HAIBN 1a (10 mmol), 30 wt% H2O2 2a (20 mmol),
b
catalyst 200 mg, acetonitrile 20 mL, 40 1C, 1 h. The conversion rate of
HAIBN was measured by liquid chromatography; the details are given in
the ESI.
CrOx/TiO2-T catalysts can achieve entire conversion of HAIBN
by extending the reaction time, but AIBN existed in a liquid
phase at 40 1C for long time would be decomposed. It was
suggested that the CrOx/TiO2 catalyst with the best catalytic
performance was the one synthesized at 400 1C (CrOx/TiO2-
400). As the treatment temperature further increased, the
reaction rate decreased and more time was required for com-
pletion of the reaction. Surprisingly, the catalytic performances
of the CrOx/TiO2-T catalysts were well consistent with the
content of Cr(VI) in CrOx on the surface of TiO2. It could be
speculated that the calcination temperature could change the
content of Cr(VI) in the CrOx/TiO2 catalyst, and a high ratio of
Cr(VI) would be beneficial to improve the performance of the
catalysts.
The oxidation of HAIBN under different conditions was
further performed to optimize the reaction conditions for the
CrOx/TiO2-400 catalyst, and the results are listed in Table 2. The
increase of reaction temperature could accelerate the conver-
sion rate but the yield would decrease gradually (entries 1–4).
Accordingly, 40 1C is a relatively optimal reaction temperature
for this reaction. Note that even if the complete reaction time is
far more than 4 h, a high yield of AIBN is still maintained,
indicating that the decomposition of AIBN depends strongly on
The complete conversion of HAIBN and its yield based on
the CrOx/TiO2 catalysts synthesized at different calcination
temperatures were also evaluated, as shown in Fig. 2. All
Fig. 2 Catalytic performances of the synthesized CrOx/TiO2-T catalysts
and their corresponding yields for complete reaction.
This journal is © The Royal Society of Chemistry 2021
Chem. Commun., 2021, 57, 4576–4579 | 4577

View Article Online
ChemComm
Communication
Table 2 Influences of reaction conditions on the catalytic performance of CrOx/TiO2-400 for the oxidation of HAIBN to AIBN
Entry
Temp. (1C)
H2O2 (equiv.)
Solvent (mL)
Conv.a (%)
Yieldb (%)
Timec (h)
1
2
3
4
5
6
7
8
20
30
40
50
40
40
40
40
40
40
40
40
2
2
2
2
1.2
1.5
3
2
2
Acetonitrile (20 mL)
Acetonitrile (20 mL)
Acetonitrile (20 mL)
Acetonitrile (20 mL)
Acetonitrile (20 mL)
Acetonitrile (20 mL)
Acetonitrile (20 mL)
Alcohol (20 mL)
Methanol (20 mL)
Water (20 mL)
Acetonitrile (10 mL)
Acetonitrile (30 mL)
23.3
32.6
55.6
65.3
45.3
50.2
55.7
48.3
45.8
13.2
39.4
53.7
95.6
95.2
94.8
72.3
88.2
90.2
95.1
91.2
89.8
–
412
8
4
2
412
9
4
8
8
–
6
4
9
10
11
12
2
2
2
93.2
95
a
b
c
The conversion rate of HAIBN for 1 h. The yield of complete conversion of HAIBN to AIBN. The time for the complete conversion.
temperature. The HAIBN conversion rate and AIBN yield fifth cycle reaction, nuclear magnetic resonance (NMR) was
increase with increasing H2O2 content and reach stable values used to accurately detect the raw substrate and the product, as
at a H2O2/substrate molar ratio of 2 : 1 (entries 3, 5–7). Several shown in Fig. S2, ESI.† Through the 1H NMR spectrum, the
widely used solvents such as acetonitrile, alcohol, methanol synthesis of AIBN was confirmed, and no side product was
and water were applied to this reaction (entries 3 and 8–10). detected. The XPS characterization of the spent CrOx/TiO2-T
The result shows that acetonitrile with the highest solubility of catalysts after being recycled 5 times and the proportion of
hydrazine has the highest reaction rate. The poor solubility Cr(VI) in CrOx are shown in Fig. 3b. Notably, there were no
between the substrate and the inorganic solvent (water) would peaks of other valence states in the XPS spectra of Cr element,
reduce the reaction rate, as a result of which this reaction only indicating that only Cr(III) and Cr(VI) appeared during the whole
progressed for 1 h. It is suggested that a mixed solution of reaction process. In addition, the Cr(VI) contents of the spent
20 mL acetonitrile and 2 mmol HAIBN is the most suitable for CrOx/TiO2-T catalysts all slightly increased compared to their
the reaction (entries 3, 11 and 12). The concentration of the corresponding initial catalysts, which may be caused by the
substrate would have a certain impact on this reaction process. oxidation of hydrogen peroxide added into the reaction pro-
Typically, a low substrate concentration is beneficial to get a cess. This observation suggests that a slight conversion from
stable reaction rate and yield; in contrast, a high substrate Cr(III) to Cr(VI) occurred during the oxidation of HAIBN to AIBN
concentration system needs more time for complete conversion with H2O2.
of HAIBN owing to the high proportion of water brought by
30 wt% H2O2.
It is generally accepted that the hydroxyl group existing on the
surface of TiO2 can affect the reaction activity of the catalyst.27,28
The stability and reusability of the CrOx/TiO2-400 catalyst In this catalytic reaction process, whether the fresh or spent
was investigated, as shown in Fig. 3. The details about the CrOx/TiO2 catalysts, only the valence of Cr(III) and Cr(VI) could be
recovery process of the spent CrOx/TiO2-400 catalyst are pro- found. Therefore, it is deduced that Cr(III) and Cr(VI) ions played
vided in the ESI.† It could be clearly seen from Fig. 3a that the a dominant catalytic role in the oxidation of HAIBN, and the
conversion rate is 94% and the yield is 89% even in the fifth hydroxyl oxygen groups on the surface of TiO2 could provide
cycle, which suggested that the CrOx/TiO2-400 catalyst has active sites for the Cr ions to successfully connect to the surface
excellent stability. After extending for a certain time for the of TiO2, as schematically shown in Fig. 4. Hence, the superior
catalytic performance of the synthesized CrOx/TiO2 catalyst
could be attributed to the cooperative effect between Cr ions
and the unique active sites created by unique Cr(VI)–O–Ti bonds
Fig. 3 (a) Reuse profiles of CrOx/TiO2-400. Reaction conditions in the
first step: HAIBN (10 mmol), 30 wt% H2O2 (20 mmol), catalyst (200 mg),
acetonitrile (20 mL), 40 1C, 4 h. (b) The XPS spectra of the spent CrOx/
TiO2-T (T = 300, 400, 500 1C) and the inset shows the proportions of Cr(VI)
in the spent catalysts compared to the fresh CrOx/TiO2-T catalysts.
Fig. 4 The possible reaction mechanism of the CrOx/TiO2 catalyst for
oxidation of HAIBN.
4578 | Chem. Commun., 2021, 57, 4576–4579
This journal is © The Royal Society of Chemistry 2021

View Article Online
Communication
ChemComm
and Cr(III)–O–Ti bonds.29 Moreover, as the calcination tempera- (Eastern Scholar) at Shanghai Institutions of Higher Learning
ture increased, some Cr(VI) would convert to Cr(III), as shown in (TP2019041) for financial support.
Fig. 1. Combining the experimental results in Fig. 2, it is
speculated that some of the Cr(VI)–O–Ti bonds and Cr(III)–O–Ti
bonds might break, and then Cr2O3 crystals would form at an
Conflicts of interest
elevated calcination temperature. Additionally, the Cr(III) in the
form of Cr2O3 crystals on the surface of TiO2 cannot catalyse the
oxidation of HAIBN to AIBN with H2O2, but the synergy between
Cr(VI)–O–Ti and Cr(III)–O–Ti plays a real catalytic role. Therefore,
based on the experimental data and previous work,30 the possi-
ble catalytic mechanism of the CrOx/TiO2 catalyst for the oxida-
tion of HAIBN to AIBN is shown in Fig. 4. Cr(VI)–O–Ti can easily
oxidize HAIBN and it itself would transform into Cr(III)–O–Ti.
Generally, Cr(III) can be oxidized to Cr(VI) by H2O2 in alkaline
solution or in Fenton-like systems, but this process can also
happen over the CrOx/TiO2 catalyst in a neutral environment and
at 40 1C.31 The reasons might be that the electron cloud in the
Ti–O–Cr(III) structure is more biased towards O–Ti, and Cr(III)
preferably loses electrons and becomes Cr(VI), which make it
possible for H2O2 to oxidize Ti–O–Cr(III) in the mild reaction
environment. Hence, these two steps led to the smooth progress
of the cycle reaction because of the participation of the CrOx/TiO2
catalyst, as shown in Fig. 4. We note that more details about the
reaction mechanism (including density functional theory calcula-
tion) need further investigations, which are currently underway.
In summary, we have demonstrated that a novel TiO2-
supported CrOx catalyst can be prepared by a simple impreg-
nation method, and the synthesized CrOx/TiO2 catalyst exhibits
superior catalytic activity and a high yield for the oxidation of
HAIBN using 30 wt% H2O2 at 40 1C. Compared with the
traditional chlorine oxidation method, this safe, green, effi-
cient, and reusable CrOx/TiO2-400 catalyst shows comparable
catalytic performance with complete conversion of HAIBN and
an 89% yield of AIBN even in the fifth cyclic reaction. Moreover,
the possible catalytic reaction mechanism and the formation
pathways of the products over the CrOx/TiO2 catalyst have been
proposed. This catalytic system may also afford an environmen-
tally green and general route for the synthesis of other azo
compounds, and has significant industrial application prospects.
Data curation – Hu Zhang; investigation – Hu Zhang and
Shengnan Yue; supervision – Xiujing Zou and Xueguang Wang;
writing the original draft – Hu Zhang; writing, review & editing –
Xueguang Wang; Xingli Zou and Xionggang Lu.
There are no conflicts to declare.
Notes and references
1 B. V. K. J. Schmidt, Polym., 2019, 12, 39.
2 J. Kreutzer and Y. Yagci, Polym., 2018, 10, 35.
3 X. Wang, S. Lascelles, R. Jackson and S. Armes, Chem. Commun.,
1999, 1817–1818.
4 L. Androvic, J. Bartacek and M. Sedlak, Res. Chem. Intermed., 2016,
42, 5133–5145.
5 C. J. Hawker, G. G. Barclay, A. Orellana, J. Dao and W. Devonport.,
Macromolecules, 1996, 29, 5245–5254.
6 M. Sedlak and K. Tauer, Mol., 2000, 5, 730.
7 H. Mutlu, C. M. Geiselhart and C. Barner-Kowollik, Mater. Horiz.,
2018, 5, 162–183.
8 J. Lalevee and J. P. Fouassier, Overview of Radical Initiation, Encyclo-
pedia of Radicals in Chemistry, Biology and Materials, John Wiley &
Sons, Ltd, 2012.
9 K. Taued and S. Kosmella, Polym. Int., 2010, 30, 253–258.
10 C. G. Overberger, P. Huang and M. B. Berenbaum, Org. Synth., 1963,
4, 274.
11 J. Schirmann and P. Bourdauducq. Ullmann’s Encyclopedia of Indus-
trial Chemistry, Wiley-VCH, Weinheim, 2002.
12 C. G. Overberger, M. T. O’shaughnessy and H. Shalit, J. Am. Chem.
Soc., 1949, 71, 2661–2666.
13 J. Thiele and K. Heuser, Justus Liebigs Ann. Chem., 1896, 290, 1.
14 C. Winder, Environ. Res., 2001, 85, 105–114.
15 G. L. Squadrito, E. M. Postlethwait and S. Matalon, Am. J. Physiol.:
Lung Cell. Mol. Physiol., 2010, 299, 289–300.
16 R. Ciriminna, L. Albanese and F. Meneguzzo, ChemSusChem, 2016,
9, 3374–3381.
17 B. Roduit, M. Hartmann, P. Folly, A. Sarbach, P. Brodard and
R. R. Baltensperger, Thermochim. Acta, 2015, 621, 6–24.
18 S. Guo, W. Wan, C. Chen and W. Chen, J. Therm. Anal. Calorim.,
2013, 113, 1169–1176.
19 S. Liu, C. Cao, W. Lin and C. Shu, J. Hazard. Mater., 2019, 365, 164–177.
20 X. L. Bao, L. F. Cui and B. Chen, Chinese Pat., CN108484444B, 2019.
21 Q. Wang, X. Fang, P. Hao, H. Ren, Y. Zhao, F. Huang, J. Xie, G. Cui
and B. Tang, Chem. Commun., 2020, 56, 11827–11830.
22 S. Wu, X. Tan, J. Lei, H. Chen, L. Wang and J. Zhang, J. Am. Chem.
Soc., 2019, 141, 6592–6600.
23 H. Du, X. Guo, R. Kong and F. Qu, Chem. Commun., 2018, 54,
12848–12851.
24 F. Chen, K. Shen, Y. Yang, H. Huang and Y. Li, ACS Appl. Mater.
Interfaces, 2020, 12, 48691–48699.
25 M. Tian, Y. Jian, M. Ma, C. He, C. Chen and C. Liu, Appl. Catal.,
2019, 570, 62–72.
26 Y. Huang, H. Konnerth, J. Yeh, M. H. G. Prechtl, C. Wen and
K. C. Wu, Green Chem., 2019, 21, 1889–1894.
27 S. Liu, K. You, J. Song, R. Deng, F. Zhao, P. Liu, Q. Ai and H. Luo,
Appl. Catal., A, 2018, 568, 76–85.
28 P. Du, A. Bueno-Lopez, M. Verbaas, A. R. Almeida, J. A. Moulijin and
G. Mul, J. Catal., 2008, 260, 75–80.
29 F. Meng, M. Zhang, F. Zhou, B. Zhu, Y. Zeng, S. Zhang and Q. Zhong,
Catal. Lett., 2020, 150, 1–11.
30 S. Yu, S. Xu, B. Sun, Y. Lu, L. Li, W. Zou, P. Wang, F. Gao, C. Tang
and L. Dong, RSC Adv., 2018, 8, 3858–3868.
This work was supported by the National Natural Science
Foundation of China (No. 52022054; 51974181), the Shanghai
Rising-Star Program (19QA1403600), the Iron and Steel
Joint Research Fund of National Natural Science Foundation
and China Baowu Steel Group Corporation Limited (U1860203),
and the Program for Professor of Special Appointment
31 A. D. Bokare and W. Choi, J. Hazard. Mater., 2014, 275, 121–135.
This journal is © The Royal Society of Chemistry 2021
Chem. Commun., 2021, 57, 4576–4579 | 4579