Silica sulfuric acid catalysis the oxidation of organic compounds with sodium bromate

Article abstract of DOI:10.1081/SCC-200030562

The oxidation of organic compounds by sodium bromate/silica sulfuric acid under solvent-free conditions and in CH₂Cl₂ have been studied at room temperature.

Full text of DOI:10.1081/SCC-200030562

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Silica Sulfuric Acid Catalysis
the Oxidation of Organic
Compounds with Sodium
Bromate
a
a
Ahmad Shaabani , Kamal Soleimani & Ayoob
a
Bazgir
a
Department of Chemistry, Shahid Beheshti
University, 1983963113, Tehran, Iran
Version of record first published: 10 Jan 2011
To cite this article: Ahmad Shaabani, Kamal Soleimani & Ayoob Bazgir (2004): Silica
Sulfuric Acid Catalysis the Oxidation of Organic Compounds with Sodium Bromate,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 34:18, 3303-3315
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w
SYNTHETIC COMMUNICATIONS
Vol. 34, No. 18, pp. 3303–3315, 2004
Silica Sulfuric Acid Catalysis the Oxidation of
Organic Compounds with Sodium Bromate
*
Ahmad Shaabani, Kamal Soleimani, and
Ayoob Bazgir
Department of Chemistry, Shahid Beheshti University, Tehran, Iran
ABSTRACT
The oxidation of organic compounds by sodium bromate/silica sulfuric
acid under solvent-free conditions and in CH
room temperature.
2 2
Cl have been studied at
Key Words: Sulfides; Sulfoxides; Alkylarenes; Solvent-free; Thiols;
Disulfides; Oxidation; Silica sulfuric acid.
Sodium bromate is commercially available as a stable solid, which poten-
tially is an interesting candidate for the oxidation of organic compounds
because of its capability in multi-electron transfer. Thermodynamically
sodium bromate is a strong oxidant, but according to the literature, bromate
*
Correspondence: Ahmad Shaabani, Department of Chemistry, Shahid Beheshti
University, 1983963113 Tehran, Iran; Fax: þ98-21-2403041; E-mail: a-shaabani@
cc.sbu.ac.ir.
3
303
DOI: 10.1081/SCC-200030562
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3
304
Shaabani, Soleimani and Bazgir
itself is not able to oxidize organic compounds. It is usually used in aqueous
[3]
[1]
[2]
media in the presence of co-reactants such as: NaHSO , HBr, Br2,
3
[4–6]
NH Cl,
[7]
[8]
[9]
FeCl3, cerium(IV) ammonium nitrate (CAN), H SO ,
2 4
4
[10]
[11]
[12]
KHSO4,
Mg(HSO ) ,
(CH (CH ) ] NHSO ,
4
ion exchange resin (IER),
In most of these oxidation systems, the
NaBrO3/
3
2 3 4
[13]
[14]
and HClO4.
4
2
removal of excess sodium bromate from reaction mixture and separation of
bromate or bromide from co-reactant salts is difficult (except of HBr, Br2,
and IER).
In continuation of our studies on the oxidation of organic compounds with
[
4–7,11–13,15]
sodium bromate,
catalytic reaction in the oxidation of the wide range of organic compounds
we have introduced a solid silica sulfuric acid
under solvent-free and heterogeneous conditions in CH Cl2 by sodium
2
bromate. This reaction not only overcomes the above-mentioned disadvan-
tages but also has other advantages: easy and quick separation of the products
from the oxidant and catalyst, high yields, and faster reactions. Because of a
higher concentration of oxidant, lower reaction temperature, less toxic effluent
can be used and other waste problems can be minimized. In addition, the
catalyst does not have the problem of the limited use of bromate due to its
insolubility in almost all organic solvents.
As can be seen in Table 1, alkylarenes are converted into the corre-
sponding a-ketones in good yields under solvent-free conditions at room
temperature. As indicated in Sch. 1, the reaction displays an interesting
selectivity for compounds containing oxygen as part of a cyclic side chain
without C–O bond cleavage. The unique selectivity in the oxidation reaction
demonstrated in Sch. 1 is an attractive synthesis, since the resulting ketones
are useful intermediates for preparing indenes and their homologues
via reduction and dehydration and dihydroisocoumarines and similar
[16]
compounds.
As shown in Table 1, similar results are obtained when reactions are
carried out under heterogenous conditions in which the reductant is dissolved
in an inert solvent such as CH Cl . However, the reaction times are increased
2
2
from 2–4.45 hr to 4–6.30 hr at room temperature.
Also, we obtained this reagent capable of oxidizing toluene and
p-xylene to corresponding carboxylic acid under solvent-free conditions and
in CH Cl .
2
2
A great number of oxidizing agents can affect the conversion of sulfides
However, the susceptibility of sulfoxides to further oxi-
[17–21]
into sulfoxides.
dation narrows the choice of reagents for the oxidation of sulfides to sulfox-
ides. As a consequence, the introduction of new methods and/or further
work on technical improvements to overcome the limitations are still impor-
tant experimental challenges.

Silica Sulfuric Acid Catalysis
3305

3
306
Shaabani, Soleimani and Bazgir

Silica Sulfuric Acid Catalysis
3307
Scheme 1. Oxidation of alkylarenes.
As can be seen from Table 2, aryl and alkyl sulfides are converted into the
corresponding sulfoxides with NaBrO /SiO -OSO H in good yields under
3
2
3
solvent-free conditions and in CH Cl at room tempereture. This is a highly
2
2
useful reaction for the preparation of sulfoxides (Sch. 2), which are important
[22]
intermediates in the synthesis of many organic compounds. The observation
that benzyl phenyl sulfide and dibenzyl sulfide (entries 8 and 9) are oxidized to
the corresponding sulfoxides indicates the reactions proceed by way of an
oxygen transfer mechanism. If the reaction involved electron transfer instead
of oxygen transfer, substantial amounts of benzaldehyde would have been
[23,24]
formed.
We found that NaBrO in the absence of silica sulfuric acid in CH Cl is
3
2
2
able to transform dialkyl sulfides to corresponding sulfoxides (entries 11–13),
but under the same conditions, this reagent is not capable of oxidizing aryl sul-
fides (entries 14–16). Both alkyl and aryl sulfides are not oxidized by NaBrO3
in the absence of silica sulfuric acid under solvent-free conditions at room
temperature (entries 11–16).
Thus, we examined the possibility of the oxidation of sulfoxides to sul-
fones with NaBrO /SiO -OSO H under solvent-free conditions and CH Cl
2
3
2
3
2
at room temperature. As indicated in Table 2 (entries 17 and 18), both alkyl
and aryl sulfoxides are resistant to oxidation after a few days.
As indicated in Table 3, thiols are converted into the corresponding dis-
ulfides in good yields under very mild conditions (Sch. 3). The times required
compared favorably with those for solvent-free oxidation of thiols using other
[
25,26]
oxidants.
conditions and in CH Cl is about equal.
The times required for complete reaction under solvent-free
2
2

3
308
Shaabani, Soleimani and Bazgir

Silica Sulfuric Acid Catalysis
3309
Scheme 2. Oxidation of sulfides.
EXPERIMENTAL
All products are known compounds, which were identified by comparison
of their physical and spectral data with literature values. Melting points were
measured on an Electhrothermal 9100 apparatus and are uncorrected. Infrared
spectra were recorded as neat films or as KBr pellets on a Shimadzu IR-470
spectrometer. NMR spectra were recorded on a Bruker DRX-500 Avance
spectrometer at 500 MHz with CDCl as the solvent and (CH ) Si as the
3
3 4
internal standard. Yields refer to isolated products or 2,4-dinitrophenylhydra-
zone derivatives (2,4-DNP) of carbonyl compounds. Silica sulfuric acid was
[
27]
prepared according to published procedure.
Oxidation of Alkylarenes in Solid State—Typical Procedure
Indan (0.12 g, 1 mmol) was added to a mixture of NaBrO (0.47 g,
3
3
mmol), SiO -OSO H (1.10 g, 3 mmol), and wet SiO (0.60 g, 50% w/w)
2
3
2
and stirred at room temperature. The progress of reaction was followed by
thin layer chromatography (TLC) (eluant: n-hexane/EtOAc: 5/1). When the
reaction was complete (4.45 hr), methylene chloride (15 mL) was added and
the product mixture was filtered through a sinter glass funnel and the
residue washed with methylene chloride (10 mL). The filtrate was treated
with saturated aqueous sodium thiosulfate (2.5 mL) in order to reduce any
residual oxidant. The organic layer was separated and the aqueous layer
extracted with methylene chloride (10 mL). The combined organic layers
were dried over anhydrous magnesium sulfate. Evaporation of the solvent
gave the pure 1-indanone (0.11 g, 0.83 mmol, 83%). This product was ident-
ified by comparison with authentic 1-indanone using TLC, melting point
[28]
1
(41–428C; lit.
428C) and H NMR (500 MHz, CDCl ): d 2.63 (t, J
3
6
.10 Hz, 2H), 3.09 (t, J 6.08 Hz, 2H), 7.08–7.80 (m, 4H).

3
310
Shaabani, Soleimani and Bazgir

Silica Sulfuric Acid Catalysis
3311
Scheme 3. Oxidation of thiols.
Oxidation of Alkylarenes in CH Cl —Typical Procedure
2
2
Indan (0.12 g, 1 mmol) was added to a mixture of NaBrO (0.47 g, 3 mmol),
3
SiO -OSO H (1.10 g, 3 mmol), and wet SiO (0.60 g, 50% w/w) in CH Cl
2
2
3
2
2
(
20 mL) and stirred at room temperature. The progress of reaction was followed
by TLC (eluant: n-hexane/EtOAc: 5/1). When the reaction was completed
6hr), the product mixture was filtered through a sinter glass funnel and the
(
residue washed with methylene chloride (15mL). The filtrate was treated with
saturated aqueous sodium thiosulfate (2.5 mL) in order to reduce any residual
oxidant. The organic layer was separated and the aqueous layer extracted with
methylene chloride (10 mL). The combined organic layers were dried over anhy-
drous magnesium sulfate. Evaporation of the solvent gave the pure 1-indanone
(
0.112g, 0.85mmol, 85%). This product was identified by comparison with
[28]
authentic 1-indanone using TLC, melting point (418C–428C; lit. 428C).
Oxidation of 4-Bromothioanisol in Solid State—
Typical Procedure
4-Bromothioanisol (0.21 g, 1 mmol) was added to a mixture of NaBrO3
0.47 g, 3 mmol), SiO -OSO H (1.10 g, 3 mmol), and wet SiO (0.60 g, 50%
(
2
3
2
w/w) and stirred magnetically for 0.45 hr. The product was separated by
washing with methylene chloride (15 mL). This filtrate was washed with satu-
rated aqueous sodium thiosulfate (2.5 mL) in order to reduce any residual
oxidant and dried over anhydrous MgSO and filtered. Evaporation of the
4
filtrate afforded the corresponding sulfoxide as a pale yellow solid compound,
which was purified by recrystallization from EtOH to afford the pure product;
[
29]
yield, 0.20 g (90%); mp 828C–838C (lit.
838C–848C).
Oxidation of Dioctyl Sulfide in CH Cl —Typical Procedure
2
2
Dioctyl sulfide (0.26 g, 1 mmol) was added to a mixture of NaBrO3
0.47 g, 3 mmol), SiO -OSO H (1.10 g, 3 mmol), and wet SiO (0.60 g, 50%
(
2
3
2

3
312
Shaabani, Soleimani and Bazgir
w/w) in CH Cl (20 mL) and stirred at room temperature for 1.10 hr. The
2
2
resulting mixture was filtered and washed with methylene chloride (20 mL).
The combined organic layers were washed with saturated aqueous sodium
thiosulfate (2.5 mL) in order to reduce any residual oxidant and dried over
anhydrous MgSO and filtered. Evaporation of the filtrate afforded dioctyl
4
sulfoxide as a colorless solid, which was purified by recrystallization from
EtOH to afford the pure product; yield, 0.26 g (96%); mp 718C–738C
[
29]
(
lit.
718C–728C).
Oxidation of Benzyl Thiol in Solid State—Typical Procedure
Benzyl thiol (0.12 g, 1 mmol) was added to a mixture of NaBrO (0.47 g,
3
3
mmol), SiO -OSO H (1.10 g, 3 mmol), and wet SiO (0.40 g, 50% w/w) and
2 3 2
stirred magnetically for 3.30 hr. The resulting mixture was filtered and washed
with methylene chloride (20 mL). The combined organic layers were washed
with saturated aqueous sodium thiosulfate (2.5 mL) in order to reduce any
residual oxidant and dried over anhydrous MgSO and filtered. The solvent
4
was evaporated to give benzyldisulfide (0.11 g, 0.46 mmol, 93%), which pro-
718C–728C).
[30]
duced only one TLC spot and melted at 708C–718C (lit.
Oxidation of Benzyl Thiol in CH Cl —Typical Procedure
2
2
Benzyl thiol (0.12 g, 1 mmol) was added to a mixture of NaBrO (0.47 g,
3
3
CH Cl (20 mL) and stirred at room temperature for 5 hr. The resulting
mmol), SiO -OSO H (1.10 g, 3 mmol), and wet SiO (0.40 g, 50% w/w) in
2
3
2
2
2
mixture was filtered and washed with methylene chloride (20 mL). The com-
bined organic layers were washed with saturated aqueous sodium thiosulfate
(
MgSO and filtered. The solvent was evaporated to give benzyldisulfide
2.5 mL) in order to reduce any residual oxidant and dried over anhydrous
4
(
0.12 g, 0.48 mmol, 96%), which produced only one TLC spot and melted at
98C–718C (lit.
[30]
6
718C–728C).
ACKNOWLEDGMENT
Financial support by the Research Council of Shahid Beheshti University
is gratefully acknowledged.

Silica Sulfuric Acid Catalysis
3313
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Received in the UK May 14, 2003