The Aerobic Oxidation and C=C Bond Cleavage of Styrenes Catalyzed by Cerium(IV) Ammonium Nitrate (CAN)

Article abstract of DOI:10.1002/jccs.201400421

The CAN-catalyzed aerobic oxidation severed the C=C bond selectively through the single electron transfer mechanism, giving a green method to decompose olefins. Compared with the literature reported examples, this method required simple catalyst, cheap, abundant and clean oxidant and was very safe to operate due to the mild conditions. The CAN-catalyzed aerobic oxidative C=C bond cleavage gave a green methodology to decompose olefins into aldehydes and carboxylic acids. Compared with the literature reported examples, this method required simple catalyst, cheap, abundant and clean oxidant and was very safe to operate due to the mild conditions.

Full text of DOI:10.1002/jccs.201400421

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
The Aerobic Oxidation and C=C Bond Cleavage of Styrenes Catalyzed by Cerium(IV)
Ammonium Nitrate (CAN)
Lei Yu,a* Yaping Huang,a Zengbing Bai,a Bingchun Zhu,b Kehong Ding,a Tian Chen,a
Yuanhua Dinga and Yuguang Wanga,b*
aJiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses,
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, 225002, P. R. China
bCollege of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou, 310014, P. R.
China
(Received: Oct. 3, 2014; Accepted: Apr. 27, 2015; Published Online: May 19, 2015; DOI: 10.1002/jccs.201400421)
The CAN-catalyzed aerobic oxidation severed the C=C bond selectively through the single electron trans-
fer mechanism, giving a green method to decompose olefins. Compared with the literature reported exam-
ples, this method required simple catalyst, cheap, abundant and clean oxidant and was very safe to operate
due to the mild conditions.
Keywords: Aerobic oxidation; Single electron transfer (SET); Green chemistry.
INTRODUCTION
Due to the wide applications in organic synthesis and
enough to be kept. After one week’s storage, they might de-
compose to cyclobutanone 3 and aldehydes 4, which could
be observed from NMR and IR spectrums obviously
(Scheme 1, eq. 2). As a neat result, this CAN-catalyzed aer-
obic oxidation and the following decomposition severed
the C=C bond of olefins directly with high atom economic
without waste. The result showed the possibility to severe
the C=C bond of simple olefins with air, which is abundant,
cheap and clean oxidant and intrigued our further investi-
gations. Herein, we wish to report our recent findings on
the CAN-catalyzed aerobic oxidative cleavage of C=C
bond of styrenes.
environment protection, oxidative cleavage of carbon-car-
bon bond is one of the most important topics in organic
methodology research and has attracted chemists’ atten-
tions much for a long time.1 In the past 10 years, a plenty of
novel reactions involving carbon-carbon bond cleavage
have been reported, providing a series of convenient ac-
cesses to many useful and complex compounds.2 However,
many of these reactions require ozone that consumes large
amount of electric energy or chemical oxidants that bring
waste after the reaction. Moreover, expensive or complex
catalysts were always employed in high loadings and spe-
cial factors on substrates were also required, such as the re-
lease of strain energy, the chelation assistance and the func-
tional fragment as the leaving group (e.g. carbonyls, ni-
triles, carboxylic acids et al.). Therefore, developing novel
cheap and clean technologies to sever the simple car-
bon-carbon bond selectively without any cooperated fac-
tors still remains a tremendous challenge. For a long time,
our group aimed to develop novel green synthetic method-
ologies.3-5 During our continuous investigations on oxida-
tion, we preferred to use cheap, abundant and clean oxi-
dant, such as oxygen and hydrogen peroxide.4-5 Recently,
we have reported a novel cerium(IV) ammonium nitrate
(CAN)-catalyzed aerobic oxidation of alkylenecyclobu-
tanes (ACBs), which could generate the interesting pro-
ducts spirocyclobutyl-1,2-dioxethanes 2 (Scheme 1, eq.
1).5 However, unfortunately, compounds 2 were not stable
Scheme 1
RESULTS AND DISCUSSION
We initially chose stryrene 1a as the model compound
and heated it in THF in the presence of 3 mol% of CAN.
After 24 h, the mixture was sent to gas chromatogram (GC)
* Corresponding author. Email: yulei@yzu.edu.cn; yuguangw@zjut.edu.cn
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479

Article
Yu et al.
for analysis. The comparisons with internal standard curve
(biphenyl as internal standard) disclosed that products
benzenealdehyde 4a and benzoic acid 5a were generated in
46% total yield with the molar ratio 54/46 (Table 1, entry
1). Further screening demonstrate that 1,4-dioxane should
be a better solvent (Table 1, entries 2-6) and the yield could
be enhanced to 64% yield (Table 1, entry 6). With 1,4-
dioxane as solvent, experiments employing different dos-
ages of CAN were examined. Results in Table 1, entries
6-10 showed that 5 mol% of CAN should be the better con-
dition and the yield of 4a and 5a could be enhanced to 83%
with the molar ratio 74/26 (Table 1, entry 8).
CHO
COOH
+
MeO
MeO
2
3
MeO
(1c)
(4c, 5c)
58(71/29)
CHO
COOH
+
Cl
Cl
Cl
(1d)
(4d, 5d)
78(80/20)
CHO
COOH
+
Br
Br
(4e, 5e)
72 (76/24)
O
4
5
Br
(1e)
With the optimized conditions in hand, a series of
olefins 1 were employed as substrates. In the presences of 5
mol% CAN, they were heated at 80 °C in 1,4-dioxane with
air. The results were summarized in Table 2. For substituted
styrenes, the results were generally good and the oxidation
product aldehydes and carboxylic acids were obtained in
Ph
Ph
Ph
Ph
(4f), 47%[c]
(1f, 42%)
Me
PhCHO/PhCOOH (4a, 5a)
6
7
66% (70/30)
Ph
(1g)
C3H7
PhCHO/PhCOOH (4a, 5a)
Table 1. Optimization of the CAN catalyzed aerobic oxidation of
styrene[a]
64% (66/34)
Ph
(1h)
C3H7
CHO
COOH
CAN, solvent
PhCHO + PhCOOH
+
Ph
air, 24 h
4a
1a
5a
Me
Me
8
Yield/%(4a/5a)[b]
46 (54/46)
3 (100/0)
(4b, 5b)
Entry
CAN/%
Solvent, T/°C
Me
63% (80/20)
(1i)
1
3
3
THF/60
C4H9
CHO
COOH
2
MeCN/80
+
3
3
Cyclohexane/80
Toluene/110
0 (-)
MeO
MeO
(4c, 5c)
9
4
3
32 (84/16)
5 (80/20)
5
3
EtOH/78
MeO
73% (78/22)
(1j)
6
3
1,4-Dioxane/80
1,4-Dioxane/80
1,4-Dioxane/80
1,4-Dioxane/80
1,4-Dioxane/80
64 (66/34)
61 (61/39)
83 (77/23)
73 (74/26)
56 (80/20)
CHO
COOH
C4H9
+
7
1
Cl
Cl
10
11
8
5
Cl
(4g, 5g)
56% (83/17)
(1k)
C4H9
9
10
20
10
CHO
COOH
+
[a] 1 mmol of styrene 2 mL of solvent were employed; The
amount of CAN was based on styrene. [b] GC yield with
biphenyl as internal standard.
Cl
Cl
(4d, 5d)
Cl
72% (80/20)
(1l)
PhCHO/PhCOOH (4a, 5a)
Table 2. The aerobic oxidations of olefins catalyzed by CAN[a]
5 mol % CAN
12
13
57% (78/22)
Ph
(1m)
COOEt
RCHO + RCOOH
1
1,4-dioxane, 80 oC
air, 24 h
4
5
PhCHO/PhCOOH (4a, 5a)
Ph
24% (62/38)[d]
Entry
1
1[b]
Productsyield / %(4a/5a)[c]
(1n, 65%)
CHO
COOH
[a] Reaction conditions see Table 1, entry 8; [b] Recovered yields
of 1 in parentheses; [c] Isolated yields, compounds identity was
confirmed by comparison with co-injection with authentic
samples and melting point with literature.
+
Me
Me
Me
(1b)
(4b, 5b)
70(75/25)
480
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Aerobic Oxidation of Styrenes
moderate yields with aldehydes as the major product (Table
2, entries 1-4). Generally, the yields and selectivities of al-
dehydes from styrenes with electron withdrawing groups
were higher than that from the styrenes with electron dona-
tion groups, probably due to the lower reactivity of sub-
strates (entries 3,4 VS 1,2). Styrenes with electron donation
groups were more activated, resulting in the generation of
unidentified by-products, especially for 4-methoxylstyrene
1c (Table 1, entry 2). We also tried to oxidize the 1,1-
disubstituted styrenes such as 1f, but it was quite stable and
after 24 h, only 47% of the product 4f was obtained while
42% of 1f was recovered (Table 1, entry 5). Then, 1,2-
disubstituted olefins were also tested, giving aldehydes and
carboxylic acids in moderate yields (Table 1, entries 6-11).
When othor-substituted olefin 1k was employed, the prod-
uct yield decreased while the aldehyde selectivity was en-
hanced, probably due to the decelerated reaction speed (Ta-
ble 1, entry 10). Under the above conditions, ACB 1m
could also be oxidized to benzyl aldehyde and benzoic acid
in moderate yield (Table 1, entry 12) while in our previous
works, it was oxidized to spirocyclobutyl-1,2-dioxethanes
2 at room temperature.5 The electron deficient styrene 1n
was also tested, but gave very low product yield and most
of the starting material could be recovered (Table 1, entry
13).
Compounds 9 was unstable and decomposed to aldehyde
4a under heat.
CONCLUSIONS
In conclusion, CAN catalyzed aerobic oxidation of
olefins provided a clean method to severe the C=C double
bond. The oxidant air is cheaper, cleaner and safer than
other oxidant such as hydrogen peroxide, ozone or pure ox-
ygen. The catalyst loading of this reaction was low and
only 5 mol% of CAN was required. Deeper investigations
on the Ce-catalyzed aerobic oxidations of organic com-
pounds are on the way in our laboratory.
EXPERIMENTAL
General Methods: All of the metal salts and solvents were
purchased from reagent merchant and were analytical grade pure.
The olefins were synthesized through know methodologies10-11 or
purchased from reagent merchant. The purchased styrenes may
contain stabilizer hydroquinone that hinders the free radical reac-
tions. Therefore, they should be purified by distillation or column
chromatography before use. The gas chromatography for the
analysis of the reaction products used a capillary DB1701 column
and a FID. The oven temperature was programmed at 70-260 °C
(heating rate 30 °C/min). Melting points were measured by
WRS-2A digital melting point instrument.
On the basis of our previous experiments as well as
the literature,5 we supposed the possible mechanism
(Scheme 2). Take styrene 1a for example, it was initially
oxidized by CAN and generated the intermediate free radi-
cal cation 6,5-6 which was further oxidized by O2 (in air)
and afforded the intermediate 7.5 Capturing a proton from
the solvent 1,4-dioxane, 7 was transformed to 8,7 which
soon led to 9 through the intramolecular cyclization.8-9
General Procedure for Oxidation of Olefins: To a reac-
tion tube, 1 mmol of olefin 1, 0.05 mmol (NH4)2Ce(NO3)6 and 2
mL of 1,4-dioxane were added. Then, air was slowly introduced
with a tiny glass tunnel. The liquid was heated kept 80 °C for 24 h.
Then, solvent was distilled under vacuum and the residue was pu-
rified by column chromatography to give the corresponding 4 and
5. The products were identified by comparison with co-injection
with authentic samples and melting point with literature (Table
3).
Scheme 2
Table 3. Comparison of melting points of products with literature
Entry
Compd.
5a
m. p./°C
122.0-122.3
180.1-180.9
180.8-182.1
46.1-47.8
Lit. m. p./°C
122-122.5
180-181
181-183
47
Lit.
12a
12b
12c
12d
12e
12f
12g
12h
12i
1
2
3
4
5
6
7
8
9
5b
5c
4d
5d
237.8-238.9
56.7-57.5
238-240
57
4e
5e
251.5-252.8
45.6-47.2
252-253
47.7
4f
5g
137.2-138.4
138-138.5
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ACKNOWLEDGEMENTS
We thank National Science Foundation of China
(21202141, 21202151, 21173182), Yangzhou Nature Sci-
ence Foundation (YZ2014040) and the Priority Academic
Program Development of Jiangsu Higher Education Insti-
tutions for financial support. We also thank the analysis
centre of Yangzhou University for assistance.
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J. Chin. Chem. Soc. 2015, 62, 479-482