SnO 2 nanoparticles: Preparation and evaluation of their catalytic activity in the oxidation of aldehyde derivatives to their carboxylic acid and sulfides to sulfoxide analogs

Article abstract of DOI:10.1080/10426507.2012.717139

A variety of aromatic and aliphatic aldehydes were converted to the corresponding carboxylic acid derivatives with 30% H₂O₂ and tert-butyl hydroperoxide as the oxidant in the presence of a catalytic amount of SnO₂ nanoparticles as a precursor. These nanoparticles were also used for the efficient catalytic oxidation of sulfides to sulfoxides using 30% H₂O₂. The present methodology offers several advantages such as applicability to a wide range of aldehydes/sulfides, convenient work-up, mild reaction conditions as well as good yields and reasonable time of the reactions. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426507.2012.717139

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SnO Nanoparticles: Preparation and
2
Evaluation of their Catalytic Activity in
the Oxidation of Aldehyde Derivatives
to their Carboxylic Acid and Sulfides to
Sulfoxide Analogs
a
a
Mohsen Dehbashi , Mousa Aliahmad , Mohammad Reza Mohammad
b
b
Shafiee & Majid Ghashang
a
Department of Physics, Faculty of Sciences , University of Sistan
and Baluchestan , Zahedan , Iran
b
Department of Chemistry, Faculty of Sciences, Najafabad Branch ,
Islamic Azad University , Najafabad , Esfahan , Iran
Accepted author version posted online: 09 Aug 2012.Published
online: 05 Jul 2013.
To cite this article: Mohsen Dehbashi , Mousa Aliahmad , Mohammad Reza Mohammad Shafiee
&
Majid Ghashang (2013) SnO Nanoparticles: Preparation and Evaluation of their Catalytic
2
Activity in the Oxidation of Aldehyde Derivatives to their Carboxylic Acid and Sulfides to
Sulfoxide Analogs, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:7, 864-872, DOI:
10.1080/10426507.2012.717139
To link to this article: http://dx.doi.org/10.1080/10426507.2012.717139
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Phosphorus, Sulfur, and Silicon, 188:864–872, 2013
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.717139
SNO NANOPARTICLES: PREPARATION AND
2
EVALUATION OF THEIR CATALYTIC ACTIVITY IN THE
OXIDATION OF ALDEHYDE DERIVATIVES TO THEIR
CARBOXYLIC ACID AND SULFIDES TO SULFOXIDE
ANALOGS
1
1
Mohsen Dehbashi, Mousa Aliahmad, Mohammad Reza
2
2
Mohammad Shafiee, and Majid Ghashang
Department of Physics, Faculty of Sciences, University of Sistan and Baluchestan,
Zahedan, Iran
1
2
Department of Chemistry, Faculty of Sciences, Najafabad Branch, Islamic Azad
University, Najafabad, Esfahan, Iran
GRAPHICAL ABSTRACT
SnO nanoparticles
2
(
R)Ar CHO
(R)Ar COOH
tert-BuOOH or H O ;
2
2
o
6
0 C; CH CN
3
O
S
SnO nanoparticles
2
S
(R)Ar
Ar(R)
(R)Ar
Ar(R)
o
H O ; 30 C; CH CN
2
2
3
Abstract A variety of aromatic and aliphatic aldehydes were converted to the corresponding
carboxylic acid derivatives with 30% H2O2 and tert-butyl hydroperoxide as the oxidant in
the presence of a catalytic amount of SnO2 nanoparticles as a precursor. These nanoparticles
were also used for the efficient catalytic oxidation of sulfides to sulfoxides using 30% H2O2.
The present methodology offers several advantages such as applicability to a wide range of
aldehydes/ sulfides, convenient work-up, mild reaction conditions as well as good yields and
reasonable time of the reactions.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords Oxidation; acid; sulfide; sulfoxide; H2O2; tert-BuOOH; SnO2 nanoparticles
Received 13 May 2012; accepted 27 July 2012.
The authors are indebted to the Najafabad Branch, Islamic Azad University for financial support of this
research.
Address correspondence to Majid Ghashang Department of Chemistry, Faculty of Sciences, Najafabad
Branch, Islamic Azad University, P.O. Box: 517, Najafabad, Esfahan, Iran. E-mail: ghashangmajid@gmail.com
8
64

SULFIDE OXIDATION CATALYZED BY SnO2 NANOPARTICLES
865
1. INTRODUCTION
The developments of nanosized metal oxides have attracted a great deal of attention
due to their unique properties such as high surface area, stability and effectively as catalyst in
1
some organic transformations. Tin oxide (SnO2) is one of the most important metal oxides
with unique electronic, optical, electrochemical, and catalytic properties.2 It has been used
–4
in semiconductors with wide band gap (3.6 eV at 300 K), flat panel displays, transparent
2
–4
conducting electrodes, solar cells, gas sensors, and rechargeable Li-ion batteries.
This work has been expanded the library applications of SnO2 to the catalytic oxi-
dation of aldehydes to the corresponding carboxylic acid derivatives with 30% H2O2 and
tert-butyl hydroperoxide as the oxidant and also sulfides to sulfoxides using 30% H2O2.
The oxidation of sulfides to sulfoxides is one of several fundamental research area
5
in organic chemistry, and has been explored for a wide range of applications. For ex-
6
–9
ample, sulfoxides are valuable in molecular rearrangements and C-C bond-formation.
Some sulfoxides are biologically active compounds and therapeutic agents. In addition
sulfoxides are valuable synthons for the synthesis of chemically and biologically important
1
0–14
molecules.
Thus, although a number of methods for the oxidation of sulfides to sulfox-
ides have been reported, the search for efficient, mild reaction conditions, and environment
friendly catalysts is a much needed area of pursuit. Various oxidants have been intensively
1
5–20
studied for the oxidation of sulfides to sulfoxides.
The most common of these oxidants
is aqueous hydrogen peroxide that contains some advantages such as low cost, ease of
handling, and a high percentage of available oxygen. In this context, a number of catalytic
procedures for H2O2 oxidation have been developed.
The present paper deals with the use of SnO2 nanoparticles as a catalyst in the
oxidation of sulfides to sulfoxides in acetonitrile as a solvent and also aldehydes to the
corresponding carboxylic acids in acetonitrile as solvent (Scheme 1).
SnO nanoparticles
2
(
R)Ar CHO
(R)Ar COOH
tert-BuOOH or H O ;
2
2
o
6
0 C; CH CN
3
O
S
SnO nanoparticles
S
2
(R)Ar
Ar(R)
(R)Ar
Ar(R)
o
H O ; 30 C; CH CN
2
2
3
2
. RESULTS AND DISCUSSION
.1. XRD Analysis
The crystalline structure and phase composition of the SnO2 nanoparticles was re-
2
vealed by X-ray diffraction (Figure S1, available online). Pure SnO2 nanoparticles exhibits
three strong peaks at 26.6, 33.4, and 51.8 (2θ) due to (1 0 0), (1 0 1), and (2 1 1) reflection
lines and some weaker signals corresponding to (2 0 0), (2 2 0), (0 0 2), (3 1 0), (1 1 2), and
(
(
3 0 1) reflections, indicating the formation of tetragonal structure of the SnO2 nanoparticles
Figure S1, available online). The average crystalline size estimated by using the Scherrer
formula (λ = 0.154056 nm) from the (1 1 0) reflection line of the XRD was 30 nm.

8
66
M. DEHBASHI ET AL.
2.2. TEM Analysis
The nanoparticles mean size and sample homogeneity were estimated by TEM anal-
◦
ysis. Figure 1illustrates the TEM image of SnO2 nanoparticles calcined at 350 C for 2 h; it
is shown that the powder is uniform in size and the particle shape of the sample is spherical.
These particles are found to be agglomerated. The diameter of particles is evaluated to be
in the range of 23–40 nm (Figure S2, available online).
2.3. FT-IR Analysis
The FT-IR spectrum of SnO2 nanoparticles is presented in Figure S3 (available
−
1
online). The absorption bands at 528 and 643 cm arise from stretching vibrations of
Sn–O and the O–Sn–O bending vibration, respectively.
2.4. Catalytic Activity
The catalytic activity of SnO2 nanoparticles has been studied in the mild oxidation of
various sulfides to sulfoxides using H2O2 as oxidant (Scheme 1). Additionally, the prepared
nanoparticles have been found to be effective for the oxidation of aromatic and aliphatic
2
1–37
aldehydes to the respective carboxylic acids using H2O2 and tert-BuOOH as oxidants
Scheme 1).
In an initial screening, the oxidation of methylphenylsulfide in acetonitrile as solvent
(
◦
at 30 C was investigated (Table 1). In the absence of a catalyst and oxidant the conversion
of sulfides to sulfoxides did not occur (Table 1, Entries 1–2). The results revealed that the
presence of H2O2 as a co-catalyst is required for the oxidation reaction. In order to find an
optimal reaction medium, the effect of various common organic solvents was investigated
which deduced that acetonitrile appears to be the most favorable solvent (Table 1, Entry
7
0
). In continuance, the oxidation reaction was carried out in the presence of 0.3, 0.25, 0.1,
.05, and 0.025 mmol of SnO2 nanoparticles with other parameters kept constant. Among
the tested various amount of the catalyst, the best oxidation reaction was 0.25 mmol of
catalyst (Table 1, Entry 9). The results are summarized in Table 1.
Table 1 Optimization of the reaction conditions in the synthesis of 1-(methylsulfinyl)benzene
◦
Yield (%)a
Entry
Catalyst (mmol)
T ( C)
Solvent (5 mL)
1
2
3
4
5
6
7
8
9
0.1
-
0.1
0.1
0.1
0.1
0.1
0.30
0.25
0.05
0.025
30
30
30
30
30
30
30
30
30
30
30
CH3CN
CH3CN
n-Hexane
CH2Cl2
Et2O
- (without H2O2)
-
7
15
35
60
91
87
94
88
75
EtOAc
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
1
1
0
1
aIsolated yields after purification, reaction time: 3 h.

SULFIDE OXIDATION CATALYZED BY SnO2 NANOPARTICLES
867
Table 2 Oxidation of sulfides to sulfoxides using SnO2 nanoparticles as catalyst
Entry
1
Sulfide
Time (h)
3
Yield (%)a
94
S
S
2
3
4
3
93
92
S
S
4
5
6
3
90
85
89
S
S
3
3.5
7
8
3
80
93
S
3.5
S
9
3
85
87
88
S
OCH3
O
1
1
0
1
3
S
3.5
S
a
a
Isolated yields after purification; The pure isolated product(s) was characterized by comparison of their
physical data with those of known compounds.1
5–20
Using these optimized reaction conditions the efficiency of SnO2 nanoparticles was
explored for the oxidation of various sulfides. The results are summarized in Table 2.
Reaction times are relatively short, and the sulfoxides are obtained in excellent yields.
To exhibit the merit of the present work in comparison with previously reported
results, we compared the results of SnO2 nanoparticles with some of other metal salts
catalysts reported in the literature in the synthesis of 1-(methylsulfinyl)benzene. As shown
in Table 3, SnO2 nanoparticles can act as an effective catalyst with respect to reaction times
and the yield of the product.
Encouraged by the results from oxidation of sulfides, we expanded our library to
oxidation of aldehydes to carboxylic acids. Initiallly the oxidation of aldehydes were
performed with 4-chlorobenzaldehyde as a model of substrate in the presence of different
solvents and different amount of catalyst (Table 4). In the absence of a catalyst and oxidant
the conversion of aldehyde to carboxylic acid occurred in a low yield (Table 4, Entries 1–2).
The results revealed that the presence of H2O2 as a co-catalyst is required for the oxidation
reaction. At room temperature, the conversion of 4-chlorobenzaldehyde to product was
found to be low (50%) (Table 4, Entry 3). The conversion of 4-chlorobenzaldehyde is

8
68
M. DEHBASHI ET AL.
Table 3 Comparison results of SnO2 nanoparticles with other catalysts reported in the literature a
Entry
Catalyst / Oxidant
MTO/ H2O2
Mont. K 10 / H2O2
Bentonite / H2O2
CuCl2 / H2O2
CaO / H2O2
MgO / H2O2
CuO / H2O2
Fe2O3 / H2O2
Condition
Time
Yield (%)b
References
◦
1
2
3
4
5
6
7
8
9
CDCl3, 20 C
24 h
2.5 h
4 h
10 h
7 h
7 h
7 h
10 h
10 h
5 h
97
98
60
65
70
77
65
64
37
61
94
19d
18d
18d
CH3OH, r.t.
CH3OH, r.t.
CH3CN; 30 C
CH3CN; 30 C
CH3CN; 30 C
CH3CN; 30 C
CH3CN; 30 C
CH3CN; 30 C
CH3CN; 30 C
◦
◦
◦
◦
◦
◦
◦
◦
This work
This work
This work
This work
This work
This work
This work
This work
Na2O / H2O2
BaO / H2O2
SnO2 nano-particles / H2O2
1
1
0
1
CH3CN; 30 C
3 h
aBased on the preparation of 1-(methylsulfinyl)benzene; b Isolated yields after purification.
facile in the presence of 0.25 mmol of SnO2 nanoparticles and H2O2 as the oxidant at
◦
6
0 C. Among the different solvents used in this study, acetonitrile yielded best results
(Table 4). The results are summarized in Table 4. Using these conditions, the efficiency of
SnO2 nanoparticles was explored for the oxidation of various aldehydes. The results are
summarized in Table 5.
Generally, all of the oxidation reactions proceeded well and afforded the de-
sired products (Table 5, Entries 1–17) in good to excellent yields. As shown in Ta-
ble 5, the reaction was compatible successfully with a variety of aryl aldehydes having
electron-donating and electron-withdrawing substituent. Aromatic aldehydes substituted
with electron-withdrawing groups react slowly (Table 5, Entries 12–14). The results show
that aliphatic aldehydes can be successfully oxidized in good yields (Table 5, Entries
1
6–17).
Under the same optimized reaction conditions (Table 4) and using tert-butyl hy-
droperoxide as oxidant, aldehydes can be oxidized to the corresponding carboxylic acids
in excellent yields (Scheme 1). The results are summarized in Table 5.
Table 4 Optimization of the reaction conditions in the synthesis of 4-Chlorobenzoic acid
◦
Yield (%)a
Entry
Catalyst (mmol)
T ( C)
Solvent (5 mL)
1
2
3
4
5
6
7
8
9
0.1
-
0.1
0.1
0.1
0.1
0.1
0.1
0.30
0.25
0.05
0.025
60
60
25
60
35
35
60
60
60
60
60
60
CH3CN
CH3CN
CH3CN
n-Hexane
CH2Cl2
Et2O
5 (without H2O2)
12
50
61
45
67
84
87
85
91
62
51
EtOAc
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
1
1
1
0
1
2
aIsolated yields after purification, reaction time: 90 min

SULFIDE OXIDATION CATALYZED BY SnO2 NANOPARTICLES
869
Table 5 Synthesis of carboxylic acid derivatives using SnO2 nanoparticles as catalyst
Time (min)
Yield (%)a
Entry
1
Aldehyde
Benzaldehyde
H2O2/tert-BuOOH
H2O2/tert-BuOOH
60/100
90/150
120/180
120/190
90/140
45/70
89/85
91/90
83/90
87/86
89/80
86/87
77/79
91/84
89/82
92/91
85/86
91/94
93/90
81/86
75/74
77/80
87/85
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
9
4-Chlorobenzaldehyde
2-Chlorobenzaldehyde
2,4-Dichlorobenzaldehyde
2,4-Dimethoxybenzaldehyde
4-Methoxybenzaldehyde
2-Methoxybenzaldehyde
4-Methylbenzaldehyde
2-Methylbenzaldehyde
4-Bromobenzaldehyde
3-Bromobenzaldehyde
4-Nitrobenzaldehyde
3-Nitrobenzaldehyde
2-Nitrobenzaldehyde
Furfural
100/120
50/80
100/135
80/110
85/120
180/240
180/240
200/250
120/150
70/100
60/95
0
1
2
3
4
5
6
7
Butyraldehyde
Cyclohexanecarbaldehyde
a
a
Isolated yields after purification; The pure isolated product(s) was characterized by comparison of their
physical data with those of known compounds.2
1–37
The reusability of the catalyst was tested in the oxidation of benzaldehyde to benzoic
acid, as shown in Figure 1. The catalyst was recovered after each run, washed three times
with CH2Cl2, dried prior to use and tested for its activity in the subsequent run and fresh
catalyst was not added. The catalyst was tested for 10 runs. It was seen that the catalyst
displayed very good reusability.
In conclusion, SnO2 nanoparticles was prepared and characterized on the basis of
XRD, TEM, and FT-IR analysis. The catalytic activity of these nanoparticles has been
studied in the mild oxidation of various aromatic and aliphatic aldehydes and also sulfides.
Figure 1 Reusability of SnO2 nanoparticles (yield for product).

8
70
M. DEHBASHI ET AL.
H2O2 and tert-butyl hydroperoxide were used as co-oxidants. In addition catalyst could
recover and reused several times.
3. EXPERIMENTAL
3.1. Material and Instrumentation
All reagents were purchased from Merck and Aldrich and used without further
purification. All yields refer to isolated products after purification. The NMR spectra were
recorded on a Bruker Avance DPX 400 MHz instrument (Germany). The spectra were
measured in CDCl3 relative to TMS (0.00 ppm). IR spectra were recorded on a Perkine
Elmer 781 spectrophotometer (Japan). TLC was performed on silica gel polygram SIL
G/UV 254 plates (Merck, KGaA, Germany). The powder X-Ray diffraction patterns were
measured with Rigaku-Miniflex X-ray diffractometer (Japan) with CuKα radiations (λ =
◦ ◦
.15406 nm) in 2θ range from 20 to 70 . TEM image was taken by a PHILIPS CM20
0
microscope (Holland) to examine the shape and size of SnO2 nanoparticles.
3.2. Preparation of SnO2 Nanoparticles
The preparation of SnO2 nanoparticles was based on the homogeneous hydrolysis
4f-g
of SnCl4.5H2O according to the procedure that was reported previously
with some
modifications. Typically, SnCl4.5H2O was added to distilled water (50 mL) followed by
the drop-wise addition of Na2CO3 (2 M) over 1 h with magnetic stirring. The dropping rate
must be well controlled (one drop per 4 s) for the chemical homogeneity. The resulting
◦
precipitate was washed with distilled water and dried at 120 C for 15 h. The dried powder
◦
was further calcined at 350 C in air for 2 h resulting in the formation of SnO2 nanoparticles.
3.3. Typical Procedure for the Oxidation of Sulfides to Sulfoxides
To a solution of methylphenylsulfide (1 mmol) and SnO2 (0.25 mmol) in CH3CN
(
5 mL) was added aqueous H2O2 (0.5 mL, 30% in water). The resulting reaction mixture
◦
was stirred at 30 C until the disappearance of starting material (TLC). After completion
of the reaction, the solvent was evaporated and the resulting crude reaction mixture was
purified by plate chromatography (n-hexane / ethyl acetate 95/5) to give the pure product
(
Table 3).
3.4. Typical Procedure for the Oxidation of Aldehydes to Carboxylic
Acid Analogous
To a solution of 4-chlorobenzaldehyde (1 mmol) and SnO2 (0.25 mmol) in CH3CN
5 mL) was added aqueous H2O2 (0.5 mL, 30% in water). The resulting reaction mixture
(
◦
was stirred at 60 C until the disappearance of starting material (TLC). After completion
of the reaction, the solvent was evaporated and to the resulting crude reaction mixture
NaHCO3 (10%) was added and then the reaction mixture was extracted with ethyl acetate.
The aqueous layer was acidified to pH 2.0 using 2 N HCl and extracted with ethyl acetate.
The organic layer was concentrated and purified by plate chromatography (n-hexane / ethyl
acetate 95/5) to give the pure product (Table 2).

SULFIDE OXIDATION CATALYZED BY SnO2 NANOPARTICLES
871
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