HIO3 in the presence of wet SiO2: A mild and efficient reagent for selective oxidation of sulfides to sulfoxides under solvent-free conditions

Article abstract of DOI:10.1081/SCC-200050940

In the presence of wet SiO₂, HIO₃ is highly efficient for the selective oxidation of sulfides to sulfoxides. It may be applied to any type of dialkyl and alkyl aryl sulfides. It develops under solvent-free conditions, and gives high yield in the presence of different functional groups on the sulfide at room temperature.

Full text of DOI:10.1081/SCC-200050940

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HIO3 in the Presence of Wet SiO2: A Mild and
Efficient Reagent for Selective Oxidation of
Sulfides to Sulfoxides under Solvent‐Free
Conditions
M. M. Lakouraj a , M. Tajbakhsh a , F. Shirini b & M. V. Asady Tamami a
a Department of Chemistry, Faculty of Science , University of Mazandaran ,
Babolsar, Iran
b Department of Chemistry , Guilan University , Rasht, Iran
Published online: 20 Aug 2006.
To cite this article: M. M. Lakouraj , M. Tajbakhsh , F. Shirini & M. V. Asady Tamami (2005) HIO3 in the
Presence of Wet SiO2: A Mild and Efficient Reagent for Selective Oxidation of Sulfides to Sulfoxides under
Solvent‐Free Conditions, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 35:6, 775-784, DOI: 10.1081/SCC-200050940
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Synthetic Communicationsw, 35: 775–784, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200050940
HIO3 in the Presence of Wet SiO2: A Mild
and Efficient Reagent for Selective
Oxidation of Sulfides to Sulfoxides under
Solvent-Free Conditions
M. M. Lakouraj and M. Tajbakhsh
Department of Chemistry, Faculty of Science, University of Mazandaran,
Babolsar, Iran
F. Shirini
Department of Chemistry, Guilan University, Rasht, Iran
M. V. Asady Tamami
Department of Chemistry, Faculty of Science, University of Mazandaran,
Babolsar, Iran
Abstract: In the presence of wet SiO2, HIO3 is highly efficient for the selective
oxidation of sulfides to sulfoxides. It may be applied to any type of dialkyl and alkyl
aryl sulfides. It develops under solvent-free conditions, and gives high yield in the
presence of different functional groups on the sulfide at room temperature.
Keywords: HIO3/wet SiO2, selective oxidation, solvent-free, sulfide, sulfoxide
Organic sulfoxides are useful synthetic intermediates for the construction of
various chemically and biologically significant molecules.[1] To date the
synthesis of sulfoxides from sulfides has been widely explored and
numerous oxidation procedures have been developed in an effort to achieve
Received in the U.K. June 10, 2004
Address correspondence to M. M. Lakouraj and M. Tajbakhsh, Department of
Chemistry, Faculty of Science, University of Mazandaran, Babolsar 47415, Iran.
E-mail: lakouraj@umz.ac.ir

776
M. M. Lakouraj et al.
a facile, efficient, cheap, and selective method.[2] There are several reagents
available for this conversion.[3] However, most reagents need carefully con-
trolled reaction conditions, including the quantity of oxidants, because of
the formation of sulfone as a side product.[4] Despite a number of alternative
methods available for the synthesis of sulfoxides, oxidation of sulfides is the
most favored method.[5]
Popularity of this method is due to the availability of a wide variety of
sulfides that can be utilized in such reaction. However, some of the
oxidation procedures suffer from poor selectivity.[6] Unfortunately one or
more equivalents, often hazardous or toxic oxidizing agents, and inert atmos-
phere or microwave assistance are usually required. Otherwise over-oxidation
of sulfide, which results in sulfone formation and undesired reactions of other
functional groups, are common problems.[7] As a consequence, the introduc-
tion of new, simple, less expensive, and safer methods and/or further work on
technical improvements to overcome these limitations are still important
experimental challenges.[8] Along this, recently much attention has been
paid to methods and reactions that are performed either in solid phase or in
the absence of solvents.[9] These reactions are of interest from different
points of views and have developed into useful techniques for a variety of
applications in organic chemistry, especially the solventless reactions
conducted on solid supports.[10] Recently, we have reported HIO3 as a mild,
inexpensive, and efficient reagent for the coupling of thiols, and the con-
venient regeneration of carbonyls from oximes and hydrazones.[11] In the
course of our study on oxidation of sulfides,[12] we herein explore the utility
of this reagent for selective oxidation of sulfides to sulfoxide in the
presence of wet SiO2 under solvent-free conditions (Scheme 1). This
reagent is readily prepared by adding HIO3 to wet SiO2, which is stable and
could be stored for months without any activity lost at room temperature.
This storable and easily handled reagent allows the conversion of sulfides to
sulfoxides in mild conditions. These reactions share the virtues of ease of
operation, simplicity of product isolation, formation of products in high
yields, and the absence of side reactions including over-oxidation.
As shown in Table 1, a wide variety of sulfides are easily oxidized to the
corresponding sulfoxides in high yields. The oxidation of methyl phenyl
sulfide as the model compound was examined under solvent-free conditions
Scheme 1.

Table 1. Oxidation of sulfides to sulfoxides by HIO3/wet SiO2 under solvent-free conditiona
Time
(min)
Sulfoxideb
(%)
Mp or bp (8C)
found
Mp or bp (8C)
Entry
R1
R2
reported(ref)
1
2
3
4
5c
6
7
Ph
PhCH2–
Me
50
170
2
95
92
87
89
93
91
86
30–32
132–134
73–75.1
29–31.6
123
33–34[13]
133–135[13]
75.05[14]
32.6[15]
PhCH2–
n-Pr
n-Bu
n-Pr
n-Bu
15
170
80
1
Ph
n-Oct
–CH2CH2CH2CH2–
PhCH2
n-Oct
117–121[14]
71–72[13]
105–107[16]
(12 mmHg)
135–136[17]
—
74–75
102–105
8c
9
4-MeC6H4
Me
Ph
PhCH2
140
1
92
84
85
86
89
134–135
oil
–CH2CH2CHO
–CH2CH2OH
–CH2COOH
PhCH2
10
11
12
80
90
147–150.2
106–109
oil
150–152.2[18]
—
4-MeC6H4
205
oil[19]
13
Me
295
275
84
85
200–206
69–73
—
—
14c
–CH2CN
15c
16
Ph –CH2CH55CH2
–CH2CH2 O CH2 CH2–
25
2
86
85
—
43–45
0.385[20]
46–47.2[21]
aReactions are carried out at room temperature using substrate/oxidant (1:3).
bYields of isolated pure products.
cReaction are carried out in a steam bath (45–50 8C).

778
M. M. Lakouraj et al.
at room temperature. The optimum ratio of sulfide to oxidant (1:3) is found to
be ideal for complete conversion of sulfides to sulfoxides. Results show no
sulfone formation in this reaction. By using this oxidation system, a variety
of alkyl aryl, dialkyl, and diaryl sulfides were transformed to their correspond-
ing sulfoxides. This solid-phase procedure is also applicable to long-chain
aliphatic sulfides, which are normally insoluble in polar solvent and are
therefore difficult to obtain by conventional methods (Table 1, entry 6). The
selectivity of this procedure is remarkable toward sulfides. As evident from
the results presented in the Table 1, chemoselective oxidation of sulfides to
the corresponding sulfoxides has been achieved in the presence of a variety
of functional groups, including alcohol, ether, alkene, aldehyde, and nitrile.
In all the above experiments only sulfoxides were formed with no oxidation
of other functional groups. Oxidation of 2-thiophenyl ethanol (Table 1,
entry 10) to the corresponding sufoxide without any interference of
oxidation of alcohol is notable, and allyl phenyl sulfide (Table 1, entry 15)
afforded allyl phenyl sulfoxide in excellent yield without any complication
from oxidation of carbon–carbon double bond.
To test the effectiveness of SiO2, a model run was carried out with methyl
phenyl sulfide in the absence of wet SiO2 and we found that no sulfoxidation
reactions took place within typical reaction time.
To show the strong and weak points of our method, we have compared the
results of oxidation of methyl phenyl sulfide by our method with some of those
reported in the literature under solvent-free conditions (Table 2). As indicated
in Table 2, this method gives higher yield in shorter reaction time at ambient
temperature without microwave assistance.
In conclusion, we have found a new and selective oxidation reaction of
sulfides to sulfoxides with HIO3 in the presence of wet SiO2 that has many
desirable features commending its use as an oxidantion method. This
method offers the following advantages: a) the procedure is highly efficient
and occurs under solvent-free conditions, b) the yield of sulfoxide is high,
c) the reagent is cheap, safe, and easily prepared, and d) the selectivity of
Table 2. Comparison of our method with some of those reported in the
literature[22(a,b,c,d)]
Reagent (condition)
Yield (%)/time (min)
MnO2/H2SO4/SiO2/Neat (1:2)[22a]
80/60
92/75
80/2
[22b]
.
Fe(NO3)3 9H2O/Neat (1:2)
NaIO4/SiO2/MW (1:1.7)[22c]
PhI(OAc)2/Alumina/MW
(1:65:1.5)[22d]
82/0.75
Clayfen/MW[22e]
HIO3/Wet SiO2 (1:3)
90/0.25
95/50

HIO3 in the Presence of Wet SiO2
779
this method is remarkable with regard to sulfides. Summing up, its high
chemoselectivity together with features mentioned above makes this method
a good alternative for conversion of sulfides to sulfoxides.
EXPERIMENTAL
Chemicals were purchased from Merck, Fluka, and Aldrich chemical
companies. All sulfides were prepared using the standard synthetic
method.[23] Products were separated and purified by different chromatographic
techniques and were also identified by the comparison of their mp, IR, NMR,
and bp with those reported for the authentic samples. 1H NMR spectra were
recorded on JNM-EX 90A or Bruker-DRX MH2 NMR spectrometers.
General Procedure
To a mixture of HIO3 (0.528 g, 3 mmol) and wet SiO2 [(SiO2/H2O; 20% ww),
0.24 g] was added sulfide (1 mmol). The resulting mixture was stirred with a
magnate bar at a room temperature or on a steam bath for the definite time
(Table 1). The reaction was monitored by TLC (silica gelpolygram SiLG/
UV 254 plates). After completion of the reaction, diethyl ether (5 ml) and
sodium thiosulfate solution were added to the mixture and the resultant
mixture was filtered after 15 min. Anhydrous Na2SO4 was added to the
filtrate and filtered. Evaporation of the solvent gave the corresponding sulfox-
ides in good to high yields.
Products 1 to 16 are known compounds and their identities are established
1
by comparison of their HNMR and IR spectra with the data reported in the
literature.[1,8,24–28]
Methyl Phenyl Sulfoxide (1)
1HNMR: d ¼ 2.70 (3H, s), 7.35–7.71 (5H, m).
IR (film): n ¼ 1050, 1093, 1406, 1450, 2920, 3070m cm21
.
Dibenzyl Sulfoxide (2)
1HNMR: d ¼ 3.85 (4H, s), 7.10–7.40 (10H, m).
IR (film): n ¼ 1035, 1080, 1410, 1450, 1500, 2960, 3025, 3070, cm21
.
Dipropyl Sulfoxide (3)
1HNMR: d ¼ 1.08 (6H, t), 1.85 (4H, sext), 2.50–2.74 (4H, m).

780
M. M. Lakouraj et al.
Dibutyl Sulfoxide (4)
1HNMR: d ¼ 0.99 (6H, t), 1.19–1.82 (8H, m), 2.70 (4H, t).
IR (film): n ¼ 1015, 1272, 1400, 1450, 2887, 2950, 2980, cm21
.
Benzyl Phenyl Sulfoxide (5)
1HNMR: d ¼ 3.97 (1H, d), 4.07 (1H, d), 6.88–7.00 (2H, m), 7.2–7.37 (3H,
m), 7.38–7.50 (5H, m).
IR (film): n ¼ 696, 753, 1042, 1086, 1447, 1500, 2914, 2972, 3064, cm21
.
Diocthyl Sulfoxide (6)
1HNMR: d ¼ 0.89 (6H, t), 1.08–2.05 (24H, m), 2.67 (4H, t).
IR (film): n ¼ 993, 1014, 1082, 1461, 2900, 2910, cm21
.
Tetrahydrothiophen Oxide (7)
1HNMR: d ¼ 1.80–2.50 (4H, m), 2.55–2.90 (4H, m).
IR (film): n ¼ 1028, 1225, 1236, 1618, 1775, 1735, 2887, 2952, cm21
.
Benzyl (4-Methyl Phenyl) Sulfoxide (8)
1HNMR: d ¼ 2.38 (3H, s), 3.78–4.20 (2H, m), 7.52–7.45 (5H, m), 7.8 (4H, m).
3-(Methyl Sulfinyl) Propanal (9)
1HNMR: d ¼ 2.51 (3H, s), 2.84 (2H, m), 2.94–3.18 (2H, m), 10.16 (1H, s).
IR (film): n ¼ 970, 1045, 1148, 1210, 1620, 1742, 2620, 2960, cm21
.
2-(Phenyl Sulfinyl)-1-Ethanol (10)
1HNMR: d ¼ 2.98–3.2 (2H, m) 3.4 (1H, s), 3.9–4.3 (2H, m), 7.42–7.89
(5H, m).
IR (film): n ¼ 745, 990, 1033, 1429, 1610, 2869, 3726, cm21
.
2-[(4-Methyl Phenyl) Sulfinyl] Acetic Acid (11)
1HNMR: d ¼ 2.4 (3H, s), 3.84–3.95 (2H, s), 7.25–7.96 (4H, m), 9.98 (1H, s).

HIO3 in the Presence of Wet SiO2
781
IR (film): n ¼ 885, 1016, 1049, 1093, 1236, 1271, 1398, 1488, 1627,
1703, 1745, 2559, 2999, 3449, cm21
.
MS (EI): m/z ¼ 198, 181, 165, 162, 160, 148, 139, 128, 107, 91, 67, 62, 40.
Benzyl Cyclohexyl Sulfoxide (12)
1HNMR: d ¼ 1.52–1.60 (6H, m), 2.57 (1H, s), 2.87–2.95 (4H, m), 3.78–4.25
(2H, q), 7.22–7.48 (5H, m).
IR (film): n ¼ 698, 789, 892, 921, 922, 966, 1028, 1070, 1116, 1157,
1265, 1359, 1452, 1496, 1602, 2931, 3085, 3438, cm21
.
1-H-1,3-Benzimidazol-2-yl Methyl Sulfoxide (13)
1HNMR: d ¼ 2.85 (3H, s), 7.02–7.75 (4H, m), 10.4 (1H, s).
IR (film): n ¼ 738, 882, 964, 1014, 1099, 1147, 1220, 1267, 1317, 1359,
1440, 1498, 1589, 1618, 2385, 2686, 2923, 3053, cm21
.
MS (EI): m/z ¼ 180, 165, 150, 132, 131, 118, 104, 90, 91, 62, 38.
[(4-Chloro Phenyl) Sulfinyl] Methyl Cyanide (14)
1HNMR: d ¼ 3.53–3.64 (2H, s), 7.36, 7.95 (4H, m).
IR (film): n ¼ 636, 742, 821, 1012, 1097, 1394, 1475, 1573, 2113, 2248,
2976, cm21
.
MS (EI): m/z ¼ 185, 183, 173, 161, 159, 145, 111, 108, 99, 91, 81, 74,
67, 47, 46.
1-Allylsulfinylbenzene (15)
1HNMR: d ¼ 3.55 (2H, m, CH2), 5.1 (1H, d, CH, J ¼ 15 Hz), 5.32 (1H, d, CH,
J ¼ 11 Hz), 5.65 (1H, m, CH), 7.55 (5H, m).
IR: nmax (neat)/cm21 ¼ 1044.
4-Oxo-1,4-Thioxane (16)
1HNMR: d ¼ 2.40–3.10 (m, 4H), 3.50–4.50 (m, 4H).
IR: n–1025, 1038, 1081, 1124, 1234, 1289, 1398, 1409, 1485, 1665,
2871, 2936, 2980.

782
M. M. Lakouraj et al.
ACKNOWLEDGMENT
We greatly acknowledge the research councils of Mazandran University for
their financial support.
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