Heterogeneous swern oxidation. Selective oxidation of alcohols by DMSO/SiO2-Cl system

Article abstract of DOI:10.1080/10426500307777

Dimethyl sulfoxide in the presence of solid SiO₂-Cl in CH₂Cl₂ at -60°C rapidly converts benzyl alcohols to their corresponding carbonyl compounds in high yields.

Full text of DOI:10.1080/10426500307777

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Heterogeneous Swern Oxidation. Selective Oxidation of
Alcohols by DMSO/SiO 2 -Cl System
a
a
a
H. Firouzabadi , H. Hassani & H. Hazarkhani
a
Shiraz University, Shiraz, Iran
Version of record first published: 27 Oct 2010.
To cite this article: H. Firouzabadi , H. Hassani & H. Hazarkhani (2003): Heterogeneous Swern Oxidation. Selective Oxidation
of Alcohols by DMSO/SiO 2 -Cl System, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:1, 149-153
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:149–153
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DOI: 10.1080/10426500390170282
HETEROGENEOUS SWERN OXIDATION.
SELECTIVE OXIDATION OF ALCOHOLS BY
DMSO/SiO -Cl SYSTEM
2
H. Firouzabadi, H. Hassani, and H. Hazarkhani
Shiraz University, Shiraz, Iran
(
Received July 16, 2002; accepted)
�
Dimethyl sulfoxide in the presence of solid SiO -Cl in CH Cl at � 60 C
2
2
2
rapidly converts benzyl alcohols to their corresponding carbonyl com-
pounds in high yields.
Keywords: Alcohols; carbonyl compound; dimethyl sulfoxide; oxidation;
silica chloride; swern oxidation
INTRODUCTION
Oxidation of primary and secondary alcohols to the corresponding car-
bonyl compounds using dimethyl sulfoxide (DMSO) is widely used in or-
1
ganic synthesis. The first procedure for alcohol oxidation using DMSO
is reported by Pfitzner and Moffatt, and involves activation of the DMSO
2
by dicyclohexylcarbodiimide (DCC). In the Swern procedure, dimethyl
3,4
4
sulfoxide (DMSO) in the presence of oxalyl chloride, thionyl chloride,7
5
6
trifluoro acetic anhydride, sulfur trioxide/Py, and acetic anhydride
can be used for the oxidation of alcohols. Handling of oxalyl chloride,
thionyl chloride, and acid anhydrides especially for the large-scale op-
erations is hazardous and not so easy. The dimethyl sulfoxide/acetic
anhydride procedure needs long reaction times (18–48 h) and is usu-
ally contaminated with thiomethyl ethers as by products.7 In order to
reduce the hazards and also to improve the selectivity of Swern oxida-
tion, in this article, we have presented a new method in which DMSO
in the presence of solid silica chloride conducts selective oxidation of
benzyl alcohols.
,8
The authors are thankful to the Shiraz University Research Council for the partial
support of this work.
Address correspondence to H. Firouzabadi, Department of Chemistry, College of
Sciences, Shiraz University, Shiraz 71454, Iran, E-mail: firouzabadi@chem.susc.ac.ir
1
49

1
50
H. Firouzabadi et al.
RESULTS AND DISCUSSION
Silica chloride has been prepared from the reaction of silica gel with
thionyl chloride and reported to be an efficient reagent for the selective
thioacetalization of carbonyl compounds and transformation of sulfox-
9
ides to the thioethers. Very recently, we have modified the preparation
10
of silica chloride in order to increase the capacity of the reagent. Ac-
cording to this modification, the reagent can be prepared by the reac-
tion of thionyl chloride (SOCl2) and silica gel under reflux conditions for
4
8 h in a quantitative yield. SiO2-Cl is a grayish and stable powder that
should be stored in the absence of moisture. Nevertheless, a literature
survey shows that less attention has been paid to solid silica chloride
as a potential heterogeneous inorganic reagent in organic synthesis.
We have explored new applications of solid silica chloride as a cata-
lyst for transthioacetalization of acetals and transformation of acylals
into the 1,3-dithiolanes, 1,3-dithianes and 1,3-oxathiolanes.1 Now, we
report a modified Swern oxidation using dimethyl sulfoxide (DMSO) in
the presence of solid silica chloride for the selective oxidation of ben-
zylic alcohols. The handling and storage of solid silica chloride is much
easier than oxalyl chloride; thionyl chloride, trifluoro acetic anhydride,
sulfur trioxide/Py, and acetic anhydride that are corrosive liquids with
high vapor pressures. Solid silica chloride also is a suitable reagent for
the large-scale operations.
0
A solution of DMSO in dry CH2Cl2 was added dropwise to the pre-
�
viously cooled SiO2 Cl (� 60 C) and then a solution of an alcohol in
CH2Cl2 was added to the mixture of DMSO/SiO2 Cl while the temper-
�
ature was kept at � 60 C. By the addition of triethylamine (TEA) to
�
the mixture and raising the temperature to 25 C the desired carbonyl
compounds were produced in high yields (Scheme 1 and Table I). We
also have proposed a mechanism (Scheme 2) for this system in which
the role of solid silica chloride is clarified.
SCHEME 1
As shown in Table I, various types of benzylic alcohols with electron-
releasing and electron-withdrawing groups were converted efficiently
to their corresponding carbonyl compounds in 85–93% yields. Cinnamyl

Swern Oxidation
151
SCHEME 2
alcohol was converted to cinnamaldehyde in a high yield without the
cleavage of the benzylic double bond. Surprisingly, 3-phenyl-1-propanol
(
Table I, entry 14) was converted to the corresponding carbonyl com-
pound in 80% yield whereas, 2-phenylethanol remained almost intact.
We do not have any reasonable explanation for this result.
�
TABLE I Oxidation of Alcohols by DMSO/-SiO
2
Cl in CH
2
Cl
2
at � 60 C
Conversiona
-
SiO2-Cl
(gr)
Yieldb,c,d
(%)
Entry
R1
R2
RCH2OH
RCHO
1
2
3
4
5
6
7
8
9
Ph
H
H
H
H
H
H
Ph
CH3
Ph
H
0
0
0
0
5
7
0
0
0
7
5
100
100
100
100
95
1.5
1.5
2
2
2
2
2
2
2
85
88
90
90
90
85
93
92
90
90
85
4-(CH3O)C6H4
4-(CH3)C6H4
4-(Cl)C6H4
4-(NO2)C6H4
2-(NO2)C6H4
Ph
Ph
PhCO
PhCH CH
93
100
100
100
93
1
1
0
1
2
2
95
12
13
14
15
CH3(CH2)5CH2
CH3(CH2)4CH2
PhCH2CH2
PhCH2
H
CH3
H
50
70
15
85
50
30
85
15
2
2
2
2
35
25
80
5
H
a
Conversion was determined by GC and NMR.
b
c
Yields refer to isolated products.
Structures are confirmed by IR, H-NMR, 13C-NMR, mp/bp.
1
d
Benzaldehyde was isolated as its 2,4-dinitrophenyl-hydrazine derivative.

1
52
H. Firouzabadi et al.
TABLE II Selective Oxidation of Alcohols by DMSO/-SiO
2
Cl
�
in CH
2
Cl
2
at � 60 C
Entry
1
Substrate
Product
Yielda
100
CH3(CH2)6CH2OH
CH3(CH2)6CHO
0
2
3
100
CH3(CH2)6CH2OH
CH3(CH2)6CHO
0
100
CH3(CH2)5CH(OH)CH3
CH3(CH2)5COCH3
0
4
90
Ph(CH2)2CH2OH
Ph(CH2)2CH2OH
CH3(CH2)6CH2OH
Ph(CH2)2CHO
Ph(CH2)2CHO
CH3(CH2)6CHO
10
80
5
5
6
80
0
aGC yield.
In order to show the chemoselectivity of the method for the oxi-
dation of different alcohols, we have performed a number of compet-
itive reactions and their results are tabulated in Table II. These re-
sults clearly show that the presented method is potentially applicable
for the chemoselective oxidation of benzylic alcohols versus saturated
alcohols (Table II, entries 1–4). 3-phenyl-1-propanol was easily con-
verted to the corresponding aldehyde in a good yield in the presence of
1
2
-octanol (Table II, entry 5). 3-Phenyl-1-propanol in the presence of
-phenylethanol was oxidized with high selectivity in 80% yield
whereas, 2-phenylethanol remained intact (Table II, entry 6).
EXPERIMENTAL SECTION
General Procedure
Methylene chloride (10 ml) and SiO2-Cl (1.5–2 g) were placed in a 100 ml
flask equipped with a magnetic stirrer. The contents of the flask were
�
cooled below � 60 C and DMSO (3–5 mmol) in CH2Cl2 (5 ml) was added

Swern Oxidation
153
dropwise to the stirred cold solution in 5 min. Steering was continued
�
at � 60 C for 20 min. To the resulting mixture, a solution of an alcohol
(
1 mmol) in CH2Cl2 (5–10 ml) was added dropwise in 5 min. The mixture
�
was stirred at � 60 C for 10 min followed by the dropwise addition of
TEA (5 ml) in CH2Cl2 for 5 min. The reaction mixture was allowed to
warm up to room temperature and then H2O (50 ml) was added to the
mixture. The aqueous layer was separated and extracted with another
portion of CH2Cl2 (50 ml). The organic extracts were combined and
washed with dilute aqueous solution of HCl (1%, 50 ml), H2O (50 ml),
dilute aqueous solution of NaHCO3 (5%, 50 ml) and H2O (50 ml). The
resulting organic solution was evaporated to dryness to give the highly
pure corresponding carbonyl compound (Table I).
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