The Cu(I)- and HNO3-catalyzed oxidation of substituted toluenes to the benzoic acid based on NOx recycling

Article abstract of DOI:10.1007/s11696-017-0256-y

Based on the recycling of NO_x, the Cu(I)- and HNO₃-catalyzed oxidation of 2-chloro-4-(methylsulfonyl)toluene to 2-chloro-4-(methylsulfonyl)benzoic acid has been developed with an excellent yield of 84.2% and a purity of 99.7%. The optimized reaction conditions (160?°C, oxygen pressure 1.5?MPa, HNO₃ concentration 25?wt%, HNO₃: substrate 0.5:1) use 1.0?mol% CuI as catalyst. The dosage of HNO₃ in the new process is only 25% of the stoichiometric amount and 12.5% of the amount of the traditional process. The NO_x emission is 5% amount of the traditional process. The oxidation of several additional toluene derivatives with comparable yields demonstrates the generality to these reaction conditions.

Full text of DOI:10.1007/s11696-017-0256-y

Chem. Pap.
DOI 10.1007/s11696-017-0256-y
ORIGINAL PAPER
The Cu(I)- and HNO3-catalyzed oxidation of substituted toluenes
to the benzoic acid based on NOx recycling
Mengyi Wei1 Chao Qian1
Xinzhi Chen1
•
•
Received: 3 May 2017 / Accepted: 21 July 2017
Ó Institute of Chemistry, Slovak Academy of Sciences 2017
Abstract Based on the recycling of NOx, the Cu(I)- and
HNO3-catalyzed oxidation of 2-chloro-4-(methylsul-
fonyl)toluene to 2-chloro-4-(methylsulfonyl)benzoic acid
has been developed with an excellent yield of 84.2% and a
purity of 99.7%. The optimized reaction conditions
(160 °C, oxygen pressure 1.5 MPa, HNO3 concentration
25 wt%, HNO3: substrate 0.5:1) use 1.0 mol% CuI as
catalyst. The dosage of HNO3 in the new process is only
25% of the stoichiometric amount and 12.5% of the
amount of the traditional process. The NOx emission is 5%
amount of the traditional process. The oxidation of several
additional toluene derivatives with comparable yields
demonstrates the generality to these reaction conditions.
economy. Hence, our objective was a green, process-scale
synthesis (Figs. 1, 2).
The preparation of 2-chloro-4-(methylsulfonyl)benzoic
acid from 2-chloro-4-(methylsulfonyl)toluene is a typical
example of the benzylic oxidation of a substituted toluene—
a reaction widely used in the synthesis of pesticides, phar-
maceuticals, spices, dyes and other fields. This oxidation
may be performed using chemical oxidation, electrolytic
oxidation, or microbial biochemical oxidation. Chemical
reagent oxidation (Brown et al. 1994; Li et al. 2012; Wu et al.
2008; Fukunaga et al. 1995) is difficult to control, and typi-
cally generates the reduced oxidation agent as waste liquid, a
form that is difficult to treat. Stoichiometric oxidation by
HNO3 (Di Somma et al. 2017) does not require the presence
of nitrite ions or HNO2 in solution, and is a simple and fea-
sible reaction, but needs high temperature, large quantities of
HNO3, and produces too much NOx pollution. The
Co(OAc)2/NaBr/AcOH catalytic system (Roehrscheid 1992;
Roehrscheid 1990; Yan et al. 2011) uses cheap air as an
oxidant. However, the oxidation ability of oxygen is limited,
resulting in low conversion of the reagent unless high con-
centrations are used. However, it is difficult to regenerate the
catalyst and to suppress side reactions. Electrolytic oxidation
(Kreh et al. 1987, 1989) and microbial oxidation (Ishii and
Sakaguchi 2006; Sheldon and Arends 2006; Paul et al. 2005;
Cull et al. 2000) of aromatic hydrocarbons have the advan-
tages of high selectivity, little environmental pollution, and
simple operation. But electrolytic oxidation requires the
development of electrolytic equipment and uses large power
consumption. For microbial oxidation, finding a specific and
robust (not easily inactivated) catalytic enzyme is extremely
hard. Both of above methods are not mature enough to meet
industrial requirements.
Keywords HNO3-catalyzed oxidation Á NOx recycling Á
Benzylic oxidation Á 2-Chloro-4-(methylsulfonyl)benzoic
acid
Introduction
3-[2-Chloro-4-(methylsulfonyl)benzoyl]bicyclo[3.2.1]oc-
tane-2,4-dione is a new type of triketone herbicide (Ko-
matsubara et al. 1996) with high economic value and
good market prospects. Therefore, the development of a
practical synthesis of its intermediate, 2-chloro-4-
(methylsulfonyl)benzoic acid, was needed. Its literature
synthesis (Brown 1995; Siddall et al. 2001; Adachi et al.
2007) is environmentally unfriendly with low atom
& Chao Qian
qianchao@zju.edu.cn
1
In this paper, we report the preparation of 2-chloro-4-
(methylsulfonyl)benzoic acid by an improved HNO3-
College of Chemical and Biological Engineering, Zhejiang
University, Zhejiang, China
123

Chem. Pap.
Results and discussion
The route leading to 2-chloro-4-(methylsulfonyl)benzoic
acid is illustrated (Fig. 4).
To improve the product yield and to optimize the
reaction conditions, the one-variable method was used to
analyze process parameters. In the reaction, HNO3
decomposes and produces reactive oxygen species.
Because temperature has great influence on this decom-
position and the ensuing oxidation reactions, the selection
of the correct reaction temperature is critical to the reaction
optimization. The conversion of NO and O2 to NO2 occurs
in the gas phase, and the reaction pressure also reflects the
amount of oxygen in the system, so identifying the best
reaction pressure is also important. Lastly, reaction time
greatly influences the selectivity of the reaction and the
yield of the product. We identified a significant improve-
ment in the reaction with different concentrations of HNO3
at a temperature of 160 °C, an oxygen pressure of 1.5 MPa,
and a reaction time of 4 h (Tables 1, 2; Fig. 5).
Fig. 1 The structure of the triketone herbicide
Fig. 2 Oxidation of 2-chloro-4(methylsulfonyl)toluene to 2-chloro-
4-(methylsulfonyl)benzoic acid
It is important to note that the reduction product of
concentrated HNO3 is mainly NO2, while the reduction
product of less concentrated HNO3 is mainly NO, and the
reduction products of dilute HNO3 are mainly N2O, N2,
and ammonium nitrate. The concentration of HNO3
determines whether the reduction product can combine
with oxygen to produce HNO3 and recycle. Using the
above optimal conditions, the best concentration of HNO3
for the reaction was explored. In an initial experiment,
5 wt% HNO3 gave a yield of the benzoic acid that was only
38.5%. At this low concentration of HNO3, the
catalyzed oxidation method (Chen et al. 2015), that is
fundamentally different from the traditional HNO3 oxida-
tion method. HNO3/CuI is used as catalysts in a pressurized
oxygen atmosphere, realizing the transfer of oxygen and
regeneration of NOx. The HNO3 initiates a chain oxidation
of the benzyl alcohol, mediated by (H)NOx species, and O2
as the terminal oxidant. The experimental operation is
simple, and the dosage of HNO3 and NOx emission is
reduced compared with the traditional process. The gen-
erality of the reaction with respect to different substituents
was proven, and this generality promotes the possible
application of this CuI/HNO3-catalyzed for application to
other aromatic hydrocarbon oxidations (Fig. 3).
CH3
COOH
Cl
Cl
O2
HNO3
NOx
CuI
SO2CH3
SO2CH3
N2O, N2
Fig. 4 Oxidation of 2-chloro-4(methylsulfonyl)toluene to 2-chloro-
4-(methylsulfonyl)benzoic acid
HNO3
CH3
Cl
Table 1 The effect of reaction temperature on the oxidation
reactions
O2, H2O
O2
Entry Temperature
(°C)
Conversion rate
(%)
Selectivity
(%)
Yield
(%)
SO2CH3
CuI
NO, NO2, N2O, N2
1
2
3
4
5
6
7
100
120
140
150
160
170
180
0
0
0
COOH
Cl
23.5
69.8
93.5
98.7
99.2
99.6
90.3
88.3
87.5
85.3
80.2
75.3
21.2
61.6
81.8
84.2
79.6
75.0
SO2CH3
Fig. 3 Reuse of the NOx to synthesize 2-chloro-4-(methylsul-
fonyl)benzoic acid
123

Chem. Pap.
110
100
90
80
70
60
50
40
30
20
110
100
90
80
70
60
50
40
30
20
Table 2 The effect of pressure on the oxidation reactions
Entry Oxygen pressure
(MPa)
Conversion
rate (%)
Selectivity
(%)
Yield
(%)
1
2
3
4
5
6
0
17.9
47.8
77.9
98.7
99.0
99.7
86.3
85.9
87.3
85.3
85.5
85.8
15.4
41.1
68.0
84.2
84.6
85.5
0.5
1.0
1.5
2.0
2.5
Conversion rate of raw material
Product yield
100
90
80
70
60
50
40
30
0.0
0.2
0.4
0.6
0.8
1.0
mole ratio
Fig. 6 The effects of quantity of HNO3 on the oxidation reaction
concentration of HNO3 is higher than 25 wt%, the corro-
sion effect on the equipment is not acceptable. Table 3
reveals that 25 wt% HNO3 gives both an excellent con-
version rate and an excellent product yield. The amount of
HNO3 directly relates to economic performance and NOx
emission. At atmospheric O2 pressure, the molar amount of
HNO3 required is four times that of the toluene. As a result,
the treatment of the tail gas is necessary to prevent pollu-
tion of the environment. For this reason, reducing the
dosage of HNO3 has great practical significance. Figure 6
shows that the best molar ratio of HNO3 to raw material is
0.5–0.6. The conversion rate and yield are not improved
when the molar ratio exceeds 0.6 because the amount of
HNO3 in the system and the amount of recycled HNO3 are
exactly enough at the 0.5–0.6 molar ratio for successful
oxidation.
1
2
3
4
5
6
7
Reaction time/h
Fig. 5 The effect of reaction time on the oxidation reactions
Table 3 Different concentration of HNO3 in the oxidation reactions
Entry HNO3 concentration
(wt%)
Conversion rate
(%)
Yield
(%)
These optimal oxidation conditions—25 wt% (concen-
tration), 0.5 equivalent (dosage) HNO3, 160 °C, 1.5 MPa
O2 pressure, 1.0 mol% CuI—were examined for nine
electronically and sterically varied toluenes (Table 4). The
conversion rate of the toluene and the product yield are
higher when the substituents are in the para-position
compared to the ortho-position, presumably for steric
reasons. In addition, HNO3 oxidation is a free radical
reaction. If the intermediate free radicals are stable, the
reaction will be fast and will have good selectivity. Elec-
tron-withdrawing groups (–NO2 or –Cl) have a conjugation
effect on the para-methyl groups, which stabilize the para-
methyl radical making the reaction rate fast and the
selectivity good. Electron-withdrawing groups at the meta-
positions of toluene are more reactive than the ones with
electron-donating groups (Table 4, entries 2, 5, 7–9). With
decreasing electron-withdrawing ability, the reaction time
is shortened, the conversion rate increases, and the yield
increases. The one exception (with the poorest yield) is
meta-xylene. Its two methyl groups oxidize simultaneously
1
2
3
4
5
6
7
65
40
25
20
15
10
5
99.4
99.0
98.7
96.2
87.2
78.7
45.3
84.0
83.8
84.2
80.3
73.7
66.1
38.5
stoichiometry of HNO3 is just 0.5 times of the toluene
starting material, and the primary reduction products (N2O
and N2) are unreactive with oxygen. Hence, we explored
increased HNO3 concentrations to allow a better combi-
nation of NOx, oxygen, and water so as to recycle the
HNO3. The results for these different concentrations are
given in Table 3.
Concentrations of HNO3 lower than 25 wt% are not
sufficient to oxidize the toluene completely, because HNO3
recycling is inefficient during the reaction. When the
123

Chem. Pap.
Yield (%)
80.3
Table 4 The results for
different substituted toluenes
Entry
1
Substrate
Product
Conversion
rate (%)
COOH
CH3
NO2
NO2
90.3
H3C
H3C
NO2
HOOC
NO2
NO2
2
3
95.7
98.6
83.2
89.7
NO2
HOOC
HOOC
CH3
COOH
Cl
Cl
4
94.5
83.6
H3C
Cl
Cl
Cl
Cl
5
6
97.2
99.8
86.5
93.2
H3C
H3C
HOOC
HOOC
Br
F
Br
F
7
8
9
98.9
95.9
100
89.0
84.7
53.4
H3C
H3C
HOOC
HOOC
CH3
CH3
and meta-phthalic acid is a co-product (although the con-
version rate is 100%).
new process the dosage of HNO3, the NOx emission, and
reaction temperature are all decreased. The operation is
simpler, the yield is higher, and the system is more
stable compared with the traditional process (Li et al.
2012).
The advantages of this new HNO3-catalyzed oxidation
of toluenes to the benzoic acids compared with the tradi-
tional method are listed in Table 5, using 2-chloro-4-
(methylsulfonyl)benzoic acid as the example. Notably, for
Table 5 Comparision of new
Comparison
New process
Traditional process
and traditional processes
Dosage of HNO3
NOx emission (mol%)
Adding method
Operation
0.5 equivalent
4.0 equivalent
3.8
0.2
All reagents combined
Drop
Simple
1.5 MPa
160 °C
Stable
84.2
Complex
Pressure
Atmospheric pressure
180–200 °C
not easy to control
75.6
Reaction temperature
Stability
Product yield (%)
123

Chem. Pap.
1H NMR and 13C NMR spectra were recorded using
Bruker DRX-400 spectrometer. For 2-chloro-4-(methyl-
Experimental section
1
sulfonyl)benzoic acid, H NMR (400 MHz, d6-Acetone) d
All the organic reagents were commercial products from
AladdinÒ with the highest purity available ([98%) and
were used without further purification. HNO3, CuI, NaOH
and HCl were commercial products from Sinopharm
Chemical Reagent Co.,Ltd with a purity of over 99% and
were used as received.
8.10 (t, J = 6.4 Hz, 1H), 8.06 (d, J = 1.6 Hz, 1H), 8.01
(dd, J = 8.1, 1.7 Hz, 1H), 3.26 (s, 3H); 13C NMR
(101 MHz, d6-Acetone) d 166.79, 146.52, 137.50, 135.07,
133.66, 131.17, 127.64, 44.88.
2-Nitrobenzoic acid: m.p. 145–146 °C; 1H-NMR
(400 MHz, d6-DMSO) d 7.97 (d, J = 8.0 Hz, 1H), 7.85 (d,
J = 6.8 Hz, 1H), 7.74–7.81 (2H, m); 13C-NMR (101 MHz,
d6-DMSO) d 165.9, 148.4, 133.1, 132.4, 129.9, 127.3
123.7.
3-Nitrobenzoic acid: m.p. 139–140 °C; 1H-NMR
(400 MHz, d6-DMSO) d 8.61 (s, 1H), 8.46 (d, J = 8.0 Hz,
1H), 8.34 (d, J = 8.0 Hz, 1H), 7.80 (t, J = 8.0 Hz, 1H);
13C-NMR (101 MHz, d6-DMSO) d 165.9, 148.4, 133.1,
132.4, 129.9, 127.3, 123.7.
4-Nitrobenzoic acid: m.p. 238–240 °C; 1H NMR
(400 MHz, d6-DMSO) d 8.12 (d, J = 8.4 Hz, 2H), 8.27 (d,
J = 8.0 Hz, 2H); 13C NMR (101 MHz, d6-DMSO) d
123.7, 130.7, 136.4, 150.0, 165.8.
2-Chloro-4-(methylsulfonyl)toluene
(0.100 mol,
20.50 g), CuI (0.001 mol, 0.19 g) and 25 wt% HNO3
(12.60 g) were added in sequence to a 100 mL high
pressure reaction kettle equipped with stirrer and a tem-
perature measuring device. Oxygen gas filled the kettle
until the pressure was 1.5 MPa. The reaction solution was
heated to 160 °C slowly (approximately 0.7 h). The
autoclave pressure was raised to 2.5 MPa. The reaction
was continued for 4 h with stirring at keeping 160 °C
(thermostated). At the conclusion of the reaction the
pressure declined to 0.8 MPa and was stable (9 mol%
NO2 and 5 mol% NO, gaseous species concentration
-
-
determined by the concentration of NO2 and NO3 after
passing the gas through NaOH solution). Thin layer
chromatography (TLC) was used to determine reaction
conversions in some instances. After the reaction was
finished, a 25 wt% NaOH solution (0.200 mol NaOH)
was added into the reaction solution and stirring was
continued. After reduced pressure filtering, 36 wt%
hydrochloric acid was used to adjust the pH of the filtrate
to pH 2. The resulting precipitate was collected by fil-
tration. This precipitate was added to MeOH (110 mL)
containing 3.00 g of activated carbon. The mixture was
heated gently to reflux temperature (60 °C). The precipi-
tate dissolved completely. Stirring was continued for 1 h.
The mixture was filtered, and allowed to cool at 10 °C.
After 8 h at -5 °C the reaction was filtered. The solid
precipitate was dried at 80 °C for 5 h to give 19.70 g
(0.084 mol) of the product as white crystals. The yield
was 84.2% and the product purity was 99.7%.
2-Chlorobenzoic acid: m.p. 141 °C; 1H NMR
(400 MHz, CDCl3) d 9.26 (s, br, 1H), 8.09–7.84 (m, 1H),
7.47–7.35 (m, 2H), 7.29 (tt, J = 6.3, 4.0 Hz, 1H); 13C
NMR (101 MHz, CDCl3) d 169.90, 133.74, 132.57,
131.46, 130.48, 127.42, 125.68.
3-Chlorobenzoic acid: m.p. 137–138 °C; 1H NMR
(400 MHz, CDCl3) d 13.29 (s, br, 1H), 8.02 (t, J = 1.8 Hz,
1H), 7.93 (dd, J = 7.8, 1.1 Hz, 1H), 7.52 (ddd, J = 8.0,
2.0, 1.0 Hz, 1H), 7.35 (t, J = 7.9 Hz, 1H); 13C NMR
(101 MHz, CDCl3) d 169.98, 133.69, 132.88, 129.96,
129.24, 128.82, 127.30.
4-Chlorobenzoic acid: m.p. 250 °C; 1H NMR
(400 MHz, CDCl3) d 12.01 (s, br, 1H), 8.10–7.83 (m, 1H),
7.39 (d, J = 6.7 Hz, 1H), 7.19 (d, J = 2.1 Hz, 2H); 13C
NMR (101 MHz, CDCl3) d 166.5, 137.8, 131.3, 129.6,
128.7.
3-Bromobenzoic acid: m.p. 155–156 °C; 1H NMR
(400 MHz, CDCl3) d 8.18 (d, J = 1.3 Hz, 1H), 7.98 (d,
J = 7.8 Hz, 1H), 7.67 (d, J = 7.9 Hz, 1H), 7.29 (td,
J = 7.9, 2.0 Hz, 1H); 13C NMR (101 MHz, CDCl3) d
169.84, 135.79, 132.17, 130.14, 129.06, 127.74, 121.56.
3-Fluorobenzoic acid: m.p. 122–123 °C; 1H NMR
(400 MHz, CDCl3) d 7.32 (s, 1H), 7.45 (d, J = 5.6 Hz,
1H), 7.80 (d, J = 8.4 Hz, 1H), 7.91 (d, J = 6.8 Hz, 1H);
13C NMR (101 MHz, CDCl3) d 116.9, 117.1, 120.8, 121.0,
125.9, 130.1, 130.2, 131.5, 131.4, 161.3, 163.7, 171.2.
3-Methylbenzoic acid: m.p. 112–114 °C; 1H NMR
(400 MHz, CDCl3) d 10.52 (s, br, 1H), 7.85 (d,
J = 7.8 Hz, 2H), 7.34 (d, J = 7.5 Hz, 1H), 7.28 (t,
J = 7.6 Hz, 1H), 2.34 (s, 3H); 13C NMR (101 MHz,
CDCl3) d 171.61, 137.27, 133.57, 129.68, 128.23, 127.35,
126.35, 20.22.
Product analysis
TLC was carried out using commercial aluminum-backed
plates of silica gel 60 F-254, visualized under 254 and
365 nm radiation. The product and reactant were analyzed
through expanding agent (methanol: chloroform = 1:1,
plus two drops of acetic acid). Standard sample of
2-chloro-4-(methylsulfonyl)benzoic acid (Rf = 0.4), reac-
tant (Rf = 0.6) and product (Rf = 0.4). Melting points
were determined in open capillaries using an Electrother-
mal 9100 without further corrections. The melting point of
the product is 193.8–194.3 °C, consistent with the litera-
ture value.
123

Chem. Pap.
Acknowledgements The authors are grateful for the financial sup-
port from The National Key Research and Development Program of
China (2016YFB0301800) and the Natural Science Foundation of
China (21376213, 21476194).
Komatsubara K, Sato T, Mikami K et al (1996) Preparation of
substituted benzoyl cyclic enones as herbicides. AU 672058,
1996
Kreh RP, Spotnitz RM, Lundquist JT (1987) Selective oxidations with
ceric methanesulfonate and ceric trifluoromethanesulfonate.
Tetrahedron Lett 28(10):1067–1068. doi:10.1016/S0040-
4039(00)95912-4
Kreh RP, Spotnitz RM, Lundquist JT (1989) Mediated electrochem-
ical synthesis of aromatic aldehydes, ketones, and quinones
using ceric methanesulfonate. J Org Chem 54(7):1526–1531.
doi:10.1002/chin.198943075
Li G, Xu X, Miao Y (2012) Process for preparation of 2-chloro-4-
(methyl sulfonyl) benzoic acid. CN 102627591, 2012
Paul A, Mandal PK, Samanta A (2005) How transparent are the
imidazolium ionic liquids? A case study with 1-methyl-3-
butylimidazolium hexafluorophosphate, [bmim][PF6]. Chem
Phys Lett 402(4–6):375–379. doi:10.1016/j.cplett.2004.12.060
Roehrscheid F (1990) Preparation of alkanesulfonylbenzoic acid
derivatives. DE 3914390, 1990
References
Adachi H, Ueda A, Aihara T et al (2007) Synthesis and herbicidal
activity of bicyclo[4.1.0]heptane-2,4-dione derivatives (Part I):
synthesis of new bicyclo[4.1.0]heptane-2,4-dione derivatives and
their herbicidal activity.
32(2):112–119. doi:10.1584/jpestics.G06-30
J
Pestic Sci (Tokyo, Jpn)
Brown RW (1995). Process and catalysts for the preparation of
4-(methylsulfonyl)benzoic acids from phenols. WO 9513265,
1995
Brown SM, Bowden MC, Moorhouse K (1994) Preparation of p-
alkyl- and p-arylsulfonylbenzoic acids by catalytic oxidation of
alkyl(sulfonyl)benzenes. WO 9427959, 1994
Chen X, Wang L, Qiao C et al (2015) Method for preparing 2-chloro-
4-(methylsulfonyl)benzoic acid. CN 105017101, 2015
Cull SG, Holbrey JD, Vargas-Mora V et al (2000) Room-temperature
ionic liquids as replacements for organic solvents in multiphase
bioprocess operations. Biotechnol Bioeng 69(2):227–233.
doi:10.1002/(SICI)1097-0290(20000720)69:23.3.CO;2-S
Di Somma I, Russo D, Andreozzi R et al (2017) Kinetic modelling of
benzyl alcohol selective oxidation in aqueous mixtures of nitric
and sulfuric acids. Chem Eng J 2017(308):738–744. doi:10.
1016/j.cej.2016.09.113
Roehrscheid F (1992 Process for the preparation of alkanesulfonyl
benzoic acids. EP 505965, 1992
Sheldon RA, Arends IWCE (2006) Catalytic oxidations mediated by
metal ions and nitroxyl radicals. J Mol Catal A Chem
251(1–2):200–214. doi:10.1016/j.molcata.2006.02.016
Siddall TL, Krumel KL, Emonds MVM et al (2001) Process for
preparing 1-alkyl-4-(2-chloro-3-alkoxy-4-alkylsulfonylbenzoyl)-
5-hydro xypyrazole and related com-pounds. US 6211403, 2001
Wu J, Deng J, Wang H et al. (2008). Method for oxidating benzene
ring lateral chain containing electron-withdrawing group by
combined use of ozone and nitric acid. CN 101177369, 2008
Yan H, Yin Q, Zhao R et al (2011). Method for preparing 2-chloro-4-
(methylsulfonyl)benzoic acid with 2-chloro-4-(methylsulfonyl)
toluene as raw material. CN 102126996, 2011
Fukunaga T, Hanabusa T, Tatsumi H et al (1995) Preparation of
2-chloro-4-methylsulfonylbenzoic acid as intermediate for her-
bicides. JP 07048341, 1995
Ishii Y, Sakaguchi S (2006) Recent progress in aerobic oxidation of
Today
hydrocarbons
117(1–3):105–113. doi:10.1002/chin.200705236
by
N-hydroxyimides.
Catal
123