Oxidation of organic compounds by sulfonated porous carbon and hydrogen peroxide

Article abstract of DOI:10.1016/S1872-2067(10)60127-1

The oxidation of organic compounds by sulfonated porous carbon and H ₂O₂ was studied at room temperature. Alkyl and aryl sulfides were oxidized to the corresponding sulfoxides or sulfones in excellent yields. Secondary alcohols were also converted to the corresponding esters/lactones and aldehydes to methyl esters in good yields. Moreover, aliphatic tertiary amines and substituted pyridines were oxidized to N-oxides.

Full text of DOI:10.1016/S1872-2067(10)60127-1

CHINESE JOURNAL OF CATALYSIS
Volume 31, Issue 12, 2010
Online English edition of the Chinese language journal
Cite this article as: Chin J Catal, 2010, 31: 1427–1432.
RESEARCH PAPER
Oxidation of Organic Compounds by Sulfonated Porous
Carbon and Hydrogen Peroxide
Arash SHOKROLAHI*, Abbas ZALI, Mohammad Hossein KESHAVARZ
Chemistry Department, Malek-Ashtar University of Technology, Shahin-Shahr, P.O.Box 83145-115, Iran
2 2
Abstract: The oxidation of organic compounds by sulfonated porous carbon and H O was studied at room temperature. Alkyl and aryl
sulfides were oxidized to the corresponding sulfoxides or sulfones in excellent yields. Secondary alcohols were also converted to the cor-
responding esters/lactones and aldehydes to methyl esters in good yields. Moreover, aliphatic tertiary amines and substituted pyridines were
oxidized to N-oxides.
Key words: sulfonated porous carbon; oxidation; hydrogen peroxide; sulfoxides; sulfones; ester; N-oxide
It is important to use industrial catalysts that are eco-
friendly, green, and can be recycled easily from reaction mix-
tures. Therefore, green chemistry is defined as a set of princi-
ples that reduces or eliminates the use or generation of haz-
ardous substances throughout the lifetime of chemical materi-
als. Furthermore, solid acid catalysts have a prominent role in
organic synthesis under heterogeneous conditions. For the
applications considered here, an ideal solid material should
have high stability and numerous strong protonic acid sites
[5–8].
Oxidation is an important chemical process and is prevalent
throughout chemistry. Studies in this area have focused on the
use of transition-metal catalyzed processes [9–18]. However, a
large number of oxidation reactions require the use of toxic
metal reagents or catalysts. Therefore, from a green chemistry
standpoint, green oxidation systems are required for chemical
manufacturing. Because hydrogen peroxide is a strong oxidant
and does not lead to toxic byproducts, it is considered to be an
ideal green oxidant [19–26]. The purpose of this work is to
study the oxidation of various organic compounds using SPC
as a new medium and heterogeneous catalyst with H O .
[
1–4].
Hara and co-workers [5] reported the synthesis of a sul-
fonated (SO H-bearing) carbon catalyst with a mesoporous
3
2
2
structure and a high specific surface area, which was prepared
by impregnating the cellulosic precursor (wood powder) with
1 Experimental
ZnCl before activation and sulfonation. The specific surface
2
area of the porous carbon catalyst was found to increase with
Melting points were measured on an Electrothermal 9100
apparatus. All chemicals were commercial products. All melt-
ing points were obtained using a Stuart Scientific apparatus and
are uncorrected. Thin layer chromatography (TLC) was used to
monitor all reactions and all yields refer to isolated products.
2
carbonization temperature to a maximum of 1 560 m /g at ca.
5
00 °C. The resulting black powder is insoluble in solvents
such as water, methanol, ethanol, benzene, and hexane even at
their boiling temperatures and it is referred to as a sulfonated
porous carbon (SPC) catalyst. This catalyst has some advan-
tages: (1) It is insoluble in common organic solvents, is weakly
corrosive, and is environmentally friendly; (2) Reaction
products are easily separated from the reaction mixture and the
catalyst is recoverable without a decrease in activity; (3) SPC
can be successfully used instead of sulfuric acid as a catalyst
1
H NMR spectra were recorded on a Bruker Avance AQS 300
MHz using tetramethylsilane (TMS) as an internal standard.
Fourier transform infrared (FT-IR) spectra were recorded on a
Nicolet IMPACT 400D instrument. X-ray diffraction (XRD)
patterns were obtained on a Bruker D8 Advance instrument.
The specific surface area and mean pore diameter were calcu-
Received date: 19 May 2010.
*
Corresponding author. Tel: +98-312-5225071; Fax: +98-312-5225068; E-mail: arshokrolahi@gmail.com
Foundation item: Supported by the Malek-Ashtar University of Technology.
Copyright © 2010, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.
DOI: 10.1016/S1872-2067(10)60127-1

Arash SHOKROLAHI et al. / Chinese Journal of Catalysis, 2010, 31: 1427–1432
lated using nitrogen adsorption isotherms at –196 °C with the
standard Brunauer-Emmett-Teller (BET) equation and were
obtained on a Nova 2200, Quantachrome Corporation. Ele-
mental analysis was obtained using a Vario EL III instrument.
1
.1 Preparation of SPC
Pine wood powder was used as the starting material in the
preparation of the porous carbon material. In a typical proce-
dure, wood powder (10 g) was impregnated with ZnCl by
2
10
20
30
40
2T/( )
50
60
70
o
immersion into a 50 ml aqueous solution of 1.0 mol/L HCl
containing 20 g ZnCl under mechanical agitation at 25 °C for
2
Fig. 1. XRD pattern of the prepared SPC.
1
0 h. The supernatant liquid was then separated by filtration
and the remaining solid was oven-dried at 80 °C for 24 h.
The pattern had one broad and weak diffraction peak (2ș =
10°–30°) attributed to amorphous carbon, which consists of
small polycyclic aromatic carbon sheets.
The ZnCl -impregnated wood powder was placed in a
2
boat-like small size ceramic container and heated from room
temperature to the maximum heat treatment temperature. The
heating rate was 10 °C/min. The heating time at the maximum
heat (450 °C) treatment temperature was 1 h. The sample was
washed with aqueous HCl solution by heating in the wash
solution at 100 °C for 1 h. The sample was then filtered and
rinsed with warm distilled water to confirm that the wash so-
lution was free of zinc ions. The resultant activated porous
carbon material was finally dried at 80 °C in an oven for ap-
proximately 24 h. The activated porous carbon material (5 g)
The BET surface area, mean pore diameter, and pore size
distribution were calculated from the adsorption isotherms of
nitrogen at –196 °C. The surface area and the mean pore di-
2
ameter were 925 m /g and 2–8 nm, respectively. The FT-IR
spectrum of the SPC (Fig. 2) shows a broad band at
–
1
3
300–3 500 cm , which is assigned to OH groups (3 437
–
1
–1
cm ). The vibration bands at 1 040 and 1 193 cm in the
spectrum indicate that the resulting material possesses SO H
3
groups. The density of the SO H groups was determined by
3
was heated for 10 h in 100 ml of oleum (18–24 wt% SO ) at 80
3
elemental analysis. The total acid density (SO H + COOH) and
3
°
C under N to introduce SO H. After heating and then cooling
+
2
3
(SO H + COOH + OH) were estimated by exchange with Na
3
to room temperature, 400 ml distilled water was added to the
mixture. A black precipitate formed and it was washed re-
peatedly with boiling distilled water until all the impurities
such as sulfate ions were no longer detected in the wash water.
The sample was finally dried overnight in an oven at 80 °C to
afford the sulfonated acid catalyst [6–8].
in aqueous NaCl and NaOH solutions, respectively.
The results reveal that the sample composition is
CH0.43O0.29S0.024 and that the amounts of SO H, COOH, and
3
phenolic OH groups are 1.34, 0.28, and 2.51 mmol/g, respec-
tively.
The SPC provides a valuable tool for the oxidation of sul-
fides, tertiary amines, and secondary alcohols. The reaction
probably involves the in situ formation of peracid by reaction
of the acid group of the SPC with hydrogen peroxide, followed
by oxygen transfer to the organic substrate as shown in Scheme
1
.2 Activity test
In a general procedure, a mixture of the SPC (0.5 g, 2.0
+
mmol H ) and substrate (1 mmol) was pulverized in a mortar
for 1 min. The mixture was introduced into a 25 ml
flat-bottomed flask and hydrogen peroxide (aq. 30%, 4 mmol)
was added. The reaction mixture was then stirred magnetically
at room temperature over the time given in Table 1. For alde-
1
.
hyde oxidation, excess methanol (4 mmol) and 1 g MgSO as a
4
water trapping agent were used. Reaction progress was moni-
tored by TLC. After completion of the reaction, the mixture
was washed with CHCl (10 ml) and filtered to recover the
3
catalyst. The solvent was evaporated under reduced pressure.
Finally, the crude product obtained was purified by column
chromatography on silica gel.
4
000 3500 3000 2500 2000 1500 1000 500
2
Results and discussion
ꢀ1
Wavenumber (cm )
Fig. 2. FT-IR spectrum of the prepared SPC.
The XRD pattern of the prepared SPC is shown in Fig. 1.

Arash SHOKROLAHI et al. / Chinese Journal of Catalysis, 2010, 31: 1427–1432
R
OH
R
R'
O
R'
O
O
OH
OOH
O
S
O
S
RCHO + CH OH
3
RCOOCH3
R
H O
2
2
Porous carbon
Porous carbon
R
N
R''
R'
R'
N
O
O
H
O
O
O
R''
OH
O
S
O
O
RSR'
S
R
R'
R
R'
2 2
Scheme 1. Oxidation of various organic compounds with SPC and H O .
We used the SPC as a heterogeneous catalyst in the presence
of hydrogen peroxide, which acts as an oxidizing agent for the
oxidation of both aliphatic and aromatic sulfides to the corre-
sponding sulfoxides or sulfones. The optimum ratio of sulfide
to H O was found to be 1:1 in the presence of SPC (0.5 g) and
vents or highly concentrated hydrogen peroxide.
From Table 1 (entries 21–24), aldehydes were also studied
using a method consisting of the dropwise addition of hydro-
gen peroxide to the stirred aldehyde mixture, SPC and
methanol at room temperature in the presence of anhydrous
2
2
this ratio was ideal for the complete conversion of sulfides to
sulfoxides (with low amounts of sulfone). The reaction was
incomplete for lesser amounts (Table 1, entries 1–8). At higher
molar ratios of H O to sulfide (4:1) and in the presence of SPC
MgSO . All aldehydes were selectively converted into the
4
corresponding methyl esters in excellent yields. Furthermore,
the corresponding acids were obtained as major products in the
absence of a water trapping agent (MgSO4).
2
2
(
0.5 g), the use of excess reagent affords the corresponding
The oxidation of several tertiary amines was carried out
under similar reaction conditions and those results are shown in
Table 1 (entries 25–31). The employed tertiary amines were
oxidized to the corresponding N-oxides in high yields. How-
ever, aliphatic tertiary amines and pyridines containing elec-
tron-donating groups were found to be more reactive and re-
quired less reaction time.
sulfone in a clean reaction (Table 1, entries 9–15).
As indicated in Table 1 (entries 16–20), secondary alcohols
were converted into the corresponding esters/lactones in good
yields. The reaction shows that carbonyl compounds can be
effectively converted into corresponding esters in
a
Baeyer-Villiger-type reaction without the use of organic sol-
Table 1 Oxidation of various organic compounds using SPC/H
2
O
2
at room temperature
a
Yield
%)
Time
(min)
25
mp or bp (°C)
found (reported)
28–29 (30–30.5)
1
Entry
Substrate
S
Product
H NMR spectral data (G)
(
b
O
S
1
CH3
90
2.78 (3H,s),
CH3
7.44–7.66 (5H,m)
b
S
O
S
2
CH3
CH3
85
30
45
2.43 (3H,s), 2.72 (3H,s),
7.35 (2H,d), 7.54 (2H,d)
140 (138–140)
CH
3
H3C
Cl
H3C
Cl
b
S
O
3
85
2.79 (3H,s), 7.01 (2H,d),
7.40 (2H,d)
133–135 (136–137)
S
CH3
b
S
O
S
4
87
90
30
35
7.43–7.65 (10H,m)
148–151 (153–155)
42–43 (43–45)
b
5
O
S
3.96 (2H,s),
S
6
.95–7.33 (10H,m)
(
To be continued)

Arash SHOKROLAHI et al. / Chinese Journal of Catalysis, 2010, 31: 1427–1432
Table 1 (Continued)
a
Yield Time
mp or bp (°C)
found (reported)
148–151 (153–155)
1
Entry
Substrate
S
Product
H NMR spectral data (G)
(%)
(min)
180
b
O
S
6
91
7.02–7.24 (8H,m)
O
S
O
O
b
7
90
92
25
25
1.27 (6H,t), 2.75 (4H,q)
104 (103–106)
S
O
b
8
S
S
0.84–0.91 (6H,t), 1.57 (8H,m),
23–25 (24.5–25.5)
S
2
.48–2.63 (4H,m)
O
O
9
CH3
91
87
35
45
3.00 (3H,s) 7.44–7.64 (3H,m),
7.84–7.95 (2H,d)
86–88 (89–90)
86–88 (88)
S
CH3
S
O
O
S
1
0
1
CH3
CH3
2.71 (3H,s), 3.01 (3H,s),
CH
3
7
.36 (2H,d), 7.83 (2H,d)
H3C
Cl
3
H C
S
O
O
1
90
60
3.11 (3H,s), 7.01 (2H,d),
.53 (2H,d)
96–98 (95–97)
S
CH
3
7
Cl
c
S
O
S
O
1
2
90, 91,
40
35
7.47–7.56 (6H,m),
7.92–7.96 (4H,m)
125–128 (128–129)
142–144 (144–145)
S
8
8, 88
1
3
90
4.29 (2H,s), 7.08 (2H,d),
O
O
S
7
7
.21–7.30 (3H,m),
.43–7.48 (2H,m),
7
.59–7.62 (3H,m)
O
O
O
1
1
4
5
S
S
S
S
90
89
30
30
1.41 (6H,t), 3.02 (4H,m)
0.93 (6H,t), 1.47 (4H,m),
71–74 (73–75)
29 (29–30)
O
1
.79 (4H,m), 2.91 (4H,t)
1.57–1.83 (6H,m),
OH
O
1
6
92
420
250–253 (253)
O
O
2
.63 (2H,m), 4.23 (2H,m)
OH
OH
O
1
1
7
8
91
73
240
720
1.81 (4H,m), 2.34 (2H,m),
4.12 (2H,m)
203–207 (207–208)
65–69 (68–70)
O
6.81–7.24 (5H,m),
7
.65–7.96 (5H,m)
O
OH
O
CH3
1
2
9
0
75
90
85
87
660
330
300
240
2.42 (3H,s), 6.87–7.41 (5H,m)
193–197 (196)
CH3
O
0.98 (6H,s), 1.08–1.41 (5H,m),
1.85 (3H,s), 1.89–2.05 (2H,m)
205–208 (209–210)
196–199 (198–199)
215–219 (220–223)
OH
O
O
d
O
O
2
1
2
3.91 (3H,s), 7.34–7.43 (3H,m),
7.89–8.22 (2H,m)
CH
3
H
O
O
d
d
O
2
2
2.38 (3H,s), 3.88 (3H,s),
7.18–7.24 (2H,d),
CH3
H
O
7
.89–7.95 (2H,d)
H3C
H3C
O
O
3
4
85
87
150
180
3.86 (3H,s), 4.12 (3H,s),
6.81–7.03 (2H,d),
239–243 (244–245)
227–229 (231)
CH3
H
O
7
.80–8.11 (2H,d)
3.91 (3H,s), 7.33–7.40 (1H,t),
.49–7.90 (2H,m), 7.99 (1H,s)
H CO
H CO
3
3
d
O
O
2
CH3
H
O
7
Cl
Cl
(
To be continued)

Arash SHOKROLAHI et al. / Chinese Journal of Catalysis, 2010, 31: 1427–1432
Table 1 (Continued)
a
Yield
%)
Time
(min)
240
mp or bp (°C)
found (reported)
59–61 (61–62)
1
Entry
Substrate
N
Product
N
H NMR spectral data (G)
(
2
2
5
6
90
7.39–7.44 (3H,m),
O
O
8
.26–8.41 (2H,m)
2.45 (3H,s), 7.10–7.20 (3H,m),
.07–8.23 (1H,m)
91
240
210
255–259 (259–261)
43–49 (37–49)
N
N
8
CH3
N
CH
N
3
2
7
89
2.33 (3H,s), 7.13–7.22 (2H,m),
.16–8.20 (2H,m)
O
8
H C
H3C
H3C
3
2
2
3
8
9
0
87
73
89
300
330
150
2.39 (3H,s), 7.12–7.23 (2H,d),
.09–8.21 (2H,d)
7.87–8.01 (2H,d),
.43–8.45 (2H,d)
182–185 (182–185)
178–180 (180–182)
134–136 dec.
H3C
N
N
O
8
NC
N
CN
N
O
8
C
C
2
2
H
H
5
5
C H
2
5
1.21 (6H,t), 3.28 (4H,q),
6.92 (3H,m), 7.32 (2H,m)
N
N
O
C H
2
5
CH3
3
1
83
180
3.27 (5H,m), 3.43–3.54 (3H,m),
~150 dec.
O
N CH
3
O
N
4
.11–4.20 (3H,m)
4 mmol. Isolated yield. Experiments were carried out in the presence of 1 mmol
. The same reagent was used for each of the four runs. 4 mmol methanol and 1 g MgSO as a water trapping agent were added.
O
+
a
b
2 2
Reaction conditions: SPC 05 g (2.0 mmol H ), substrate 1 mmol, H O
c
d
H
2
O
2
4
8
9
0
1
Trost B M, Fleming I. Comprehensive Organic Synthesis. Vol. 7.
st Ed. Oxford: Pergamon Press, 1991
The recyclability of the SPC was also investigated using a
1
model oxidation of diphenyl sulfide under similar reaction
conditions. The SPC was separated by filtration after reaction
completion. Subsequent experiments with fresh substrate and
oxidant under similar reaction conditions were conducted over
four run cycles. The activity of the SPC did not show any
significant decrease after three runs. In subsequent recycle
experiments, the reaction time needed to be increased gradually
to obtain comparable yields of diphenyl sulfone.
Buchner W, Schliebs R, Winter G, Buchel K H. Industrielle
Anorganische Chemie, 2nd Ed. Weinheim: VCH, 1986
Venkataramanan N S, Kuppuraj G, Rajagopal S. Coord Chem
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1
Shul’pin G B, Suss-Fink G, Shul’pina L S. J Mol Catal A, 2001,
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Shaabani A, Lee D G. Tetrahedron Lett, 2001, 42: 5833
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Conclusions
1
5
Sheldon R A, Kochi J K. Metal-Catalyzed Oxidations of Organic
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In summary, we have shown that SPC, which can be easily
prepared from commercially available starting materials, effi-
ciently catalyzes the oxidation of sulfides to sulfoxides or
sulfones, tertiary amines to N-oxides, secondary alcohols to
esters/lactones, and aldehydes to methyl esters.
16 Zhu Z L, Espenson J H. J Org Chem, 1995, 60: 1326
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