1,1,2,2-Tetrahydroperoxy-1,2-diphenylethane as new oxidant for chemoselective and catalyst free oxidation of sulfides to sulfoxides and sulfones

Article abstract of DOI:10.1080/10426507.2016.1237951

A catalyst free and chemoselective oxidation of sulfides to sulfoxides or sulfones was developed using 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane as a new oxidant. This scope has shown the achievement of various sulfoxides and sulfones which were obtained selectively in high yields at room temperature.

Full text of DOI:10.1080/10426507.2016.1237951

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1,1,2,2-tetrahydroperoxy-1,2-diphenylethane as New Oxidant for Chemoselective and
Catalyst Free Oxidation of Sulfides to Sulfoxides and Sulfones
Kaveh Khosravi,a* Shirin Naserifar,a Boshra Mahmoudi,b Kobra Khalajia
a Department of Chemistry, Faculty of Science, Arak University, Arak 38156-8-8349, Iran
b
Chemical Engineering Department, Faculty of Engineering, Soran University, Erbil/Soran
440018, Iraq-Kurdistan Region
Abstract
A catalyst free and chemoselective oxidation of sulfides to sulfoxides or sulfones was developed
using 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane (THPDPE) as a new oxidant. This scope has
shown the achievement of various sulfoxides and sulfones which were obtained selectively in
high yields at room temperature.
Keywords
Catalyst free, Chemoselective oxidation, Sulfides, Sulfoxides, Sulfones, 1,1,2,2-
tetrahydroperoxy-1,2-diphenylethane
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INTRODUCTION
Sulfides and their oxygenated derivatives play an important role in organic chemistry due to
their various utilities. Oxygenated sulfide derivatives are potential intermediates in the
production of chemically and biologically active compounds.1-3 These molecules take part in the
synthesis of antibacterial, antifungal, anti-atherosclerotic,4 anti-ulcers (proton pump inhibitors),5
antihypertensive,6 psychotropic7, vasodilators8 and cardio tonic agents.9 So, due to their
extensive usages, many studies have been carried out continuously. The most straightforward
method for preparation of sulfoxides and sulfones is the oxidation of sulfides.10, 11 Different
oxygen donors have been used to carry out this process but generally, many of them suffer from
several deficiencies such as low oxygen content, toxic waste products and high cost.1 H2O2,12-14
O215, 16 and BuOOH17, 18 are the most efficient oxygen sources which have been used up to now.
Among these mentioned peroxides, H2O2 has been used widely since it has a low cost and is an
environmentally benign oxidant with high atom efficiency (47%) which leaves water as its only
by-product.19-21 But due to the low reactivity of H2O2, some acids,22 peroxycarbonate,23 tungstate
and molybdate,24 vanadium,25 titanium,26 platinum,27 and magnesium28 is required in order to
activate this reagent. Although all the reported processes could transform sulfides to sulfoxides
and sulfones, but only a few methods had the adequate selectivity to stop the reaction at intended
stage and avoid further oxidation by using the same oxidant under controlled conditions.
Therefore, finding an optimized methodology is still important.
Recently, gem-dihydroperoxides have been synthesized and applied as a suitable oxidant in some
organic reactions.29 In continuation of our interest in the synthesis and application of gem-
dihydroperoxides30 we wish to report a simple, efficient and versatile synthesis of a gem-
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dihydroperoxide namely 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane30i and its use in the
oxidation of sulfides (Schemes 1 and 2). This new oxidant has potential oxygen sources that
accelerate the selective conversion of sulfides to sulfoxides or sulfones in high yields at room
temperature and in the absence of any catalyst.
RESULTS AND DISCUSSION
Phenyl methyl sulfide was chosen as the starting material to optimize the reaction conditions
and all conditions including the solvent, the amount and type of the oxidant were optimized. As
shown in Table 1, THF was found to be the best solvent and further optimization of the reaction
was made by this solvent. Different common oxidants including liquid oxidants (H2O2 and
TBHP) and solid oxidants (UHP and m-CPBA) were tested and it was observed that THPDPE
was the best oxidant (Table 1, entries 15-19). Therefore, as it can be seen, the optimized
conditions were obtained using THF (4 mL) as the solvent and THPDPE as the oxidant (Table 1,
entry 8).
All of the reactions with substituted sulfides proceeded very cleanly and no undesirable side-
reaction was observed, although the yields and reaction times were highly dependent on the
substituents. Aryl-alkyl, aryl-aryl and benzyl-alkyl sulfides were readily oxidized giving high
yields. As summarized in Table 2, dialkyl sulfides were oxidized easier than aryl sulfides (Table
2, entry 18a). Also, electron releasing groups accelerated sulfides oxidation to their
corresponding sulfoxides or sulfones (Tables 2, entries 2a, 7a and 9a and Table 3, entries 2b, 7b
and 9b), while electron with-drawing groups decelerated the reaction in both sulfides and
sulfoxides to afford corresponding sulfoxides or sulfones respectively (Table 2, entries 3-6a and
11a, Table 3, entries 3-6b). Therefore, due to the electron-withdrawing nature of S=O bond in
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sulfoxides, generally, sulfoxides were oxidized to sulfones harder and slower than sulfides and
needed more amounts of the oxidant. The chemoselectivity of the reaction was compatible with a
range of functional groups, including hydroxyl, methoxy, nitro, halide, ester, aldehyde, ketone,
olefin and double bonds (Tables 2, entries 3-7a, 11a, 15a and 16a and table 3, entries 3-7b, 15b
and 16b). Some aromatic sulfides including thiophene, benzothiophene and dibenzothiophene
were also oxidized. It was notable that because of the participation of sulphur atom in
aromaticity, no reaction was detected for thiophene (Table 3, entry 10b). While due to the fusion
of thiophene and benzene rings and the resulting low aromaticity in benzothiophene and
dibenzothiophene, theses substrates were oxidized to their corresponding sulfones, but the
reaction times were much longer than aliphatic and aryl sulphides (Table 3, entries 11b and 12b).
Also, for sulphides which had ketone functional group, no Baeyer-Villiger oxidation was
detected (Tables 2 and 3, entry 6a and 6b respectively). In addition, nitrile group was remained
unreactive (Tables 2, 3, entry 15a and 15b respectively). Finally, no isomerized or dimerized
products were observed in this protocol.
The suggested mechanism is illustrated in Scheme 3. As this scheme shows, sulfur atom
attacks the peroxide as an efficient nucleophile and sulfoxide is obtained. In the presence of
enough peroxide, oxidation continues to yield the corresponding sulfones. This mechanism was
established by detecting 2,2-dihydroperoxy-1,2-diphenylethan-1-one (Scheme 3, intermediate 1)
and benzil in the reaction waste. Also, similar mechanism was reported for H2O2 [39].
Finally, this procedure for the synthesis of (methylsulfinyl)benzene has (Table 2, entry 2 a)
was compared with some reported methodologies in Table 4. Based on the results, this method
clearly improved the yields and reaction times.
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EXPERIMENTAL
Chemicals were purchased from Fluka, Merck, Riedeldehaen AG and Aldrich chemical
1
13
companies. H NMR and C NMR spectra were recorded in CDCl3 and DMSO-d6 on Bruker
300 MHz and JEOL FX 90 MHz spectrometers. IR spectra were recorded on Shimadzu
435‐U‐04 spectrophotometer. Melting points were measured by a Büchi 530 melting point
apparatus. Sulfoxides and sulfones obtained by this protocol were proved to be known by
comparison of their physical and spectral data with those collected from known products.
CAUTION
Although we did not encounter any problems with THPDPE, THPDPE as a peroxidic
compound is potentially explosive and requires precautions in handling (shields, fume hoods,
absence of transition metal salts and heating above room temperature).
General procedures for synthesis of 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane
Benzil (1 mmol, 0.210 g) was added to acetonitrile (5 mL), followed by addition of SbCl3 (0.2
mmol, 0.046 g) which serves as the catalyst of this reaction. To this stirred solution, H2O2 30%
(4 mL, 19.5 mmol) was added and the mixture stirred for the 24 h at room temperature. After
completion (monitored by TLC), water (5 mL) was added to the solution and extracted using
ethyl acetate (3x 5 mL) and dried using MgSO4. After evaporation of the solvent under reduced
pressure, a pure crystalline product was obtained. The Supplemental Materials contains sample
IR, 1H and 13C NMR spectra of 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane (Figures S 1 – S
3).
Spectra data for 1,1,2,2-tetrahydroperoxy-1,2-diphenylethane:
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◦
White solid, 89% yield, Mp: 100-102 C. IR νmax /cm-1 (KBr pellet): 3304, 2924, 1614, 1513,
1
1457, 1375, 1115, 1033, 929; H NMR (CDCl3, 90 MHz): δ= 8.81 (br, s, 4 H, OOH), 7.32-7.99
(m, 10 H); 13C NMR (DMSO-d6, 75 MHz): δ= 167.7, 133.3, 131.2, 129.7, 129.0; Anal. Calcd for
C14H14O8: C, 54.20; H, 4.55 %; Found: C, 54.15; H, 4.63 %.
General procedures for selective oxidation of sulfides to sulfoxides or sulfones
To a stirred solution of sulfide (1 mmol) and THF (4 mL), 1,1,2,2-tetrahydroperoxy-1,2-
diphenylethane (1 up to 5.5 mmol (0.310 up to 1.70 g) depending on the substrates and products)
was added and the mixture was stirred at room temperature for an appropriate time. After
completion of the reaction as monitored by TLC, a saturated aqueous solution of Na2SO3 (2 mL
of 1 M solution) was added to quench the excessive oxidant that was remained in the mixture.
Water (10 mL) was added to the mixture and extracted using chloroform (3 × 5 mL) and dried
over anhydrous MgSO4. After evaporation of solvent under reduced pressure chromatography on
silica gel was used to give pure products.
CONCLUSION
In conclusion, the present protocol presents the potential of 1,1,2,2-tetrahydroperoxy-1,2-
diphenylethane as a new, efficient, cheap, environmentally friendly and comparatively non-toxic
oxidant. The reactions were carried out under a catalyst free conditions. In contrast to some other
peroxides, this oxidant is a stable solid which can be stored for several months at room
temperature without any loss of its activity. Also this methodology had a simple workup and
therefore, complex and inexpensive purification methods were not necessary. Finally, this
method is a chemoselective method since several sensitive functional groups such as alkyl, vinyl
and other substituents remained intact.
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ACKNOWLEDGEMENT
Financial support from Arak University is gratefully acknowledged.
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Table 1 Optimization of reaction conditions
Ent
ry
Amount of oxidant
(mmol)
Time
(min)
Sulfoxide
(%)a
Sulfone
(%)a
Solvent ( Oxidant
THPDP
CH3OH
E
1
15
16
14
30
17
120
20
12
11
20
20
20
25
45
91
90
92
74
82
41
73
96
95
80
65
35
5
-
-
1
THPDP
MeCN
E
1
2
THPDP
DMF
E
1
3
THPDP
E
Ethylace THPDP
CH2Cl2
1
-
4
1
5
tate
E
THPDP
E
THPDP
E
THPDP
E
THPDP
E
THPDP
E
THPDP
E
THPDP
E
THPDP
E
Toluene
1
-
6
THF
THF
THF
THF
THF
THF
THF
THF
0.5
1
-
7
-
8
1.2
1.5
2
3
9
15
32
62
90
92
10
11
12
13
14
2.5
3
THPDP
E
3.5
-
THPDP
E
THF
THF
THF
4
6
5
45
-
90
-
15
16
17
UHP
30%
H2O2
TBHP
(70%)
m-
30
10
5
200
-
THF
THF
5
2
120
120
10
55
-
18
19
10
12
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CPBA
a Isolated Yield
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Table 2 Oxidation of several sulfides to their corresponding sulfoxides
Entrya
Substrate
product
Ref
Oxidant
amount
(mmol)
1
Time (min)
Yield (%)b
1a
2a
40b
40c
12
11
96
97
1
3a
4a
5a
40c
40f
32
1.3
28
32
32
88
87
88
2
1.5
6a
7a
40f
1.5
1
27
11
86
94
40d
8a
9a
40b
40c
1
1
33
32
90
93
10a
11a
40e
40g
1
2
12
60
96
81
12a
40g
1
11
97
13a
14a
15a
40c
40c
40e
1
13
11
22
92
98
90
1
1.2
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16a
40b
1
12
95
17a
18a
40b
40c
2
1
100
10
82
95
a Conditions: Sulfide (1 mmol) and THF (4 mL), oxidant (as the table), r.t.
b Isolated Yield.
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Table 3 Oxidation of several sulfides to their corresponding sulfones
Ref
40b
41a
oxidant amount
Time
(min)
Yield
(%)b
Entrya
1b
Substrate
Product
(mmol)
4
59
54
90
90
78
73
4
2b
120
145
3b
41e
41e
41b
5
5.5
4b
5
5
130
125
78
80
5b
6b
41d
41b
4
4
4
50
66
65
90
81
82
7b
8b
9b
41a
41f
-
5
4
200
140
-
10b
11b
40a
40a
85
4
4
90
50
88
84
12b
13b
41a
41c
41c
4
5
61
89
72
14b
15b
110
40b
4
60
80
16b
40b
41a
5
4
95
48
80
90
17b
18bb
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a Conditions: Sulfide (1 mmol) and THF (4 mL), oxidant (as the table), r.t. b
Isolated Yield.
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Table 4 Comparison of this method with some reported methodologies for the synthesis of
compound 2a
Entr
y
1
Solv
ent
THF
MeC
N
Time Sulfoxide Sulfone
R
ef
-
3
1
3
2
Oxidant
This method
30% H2O2
Catalyst
(min)
12
(%)
96
(%)
-
-
Chromium (III)
72
93
71
-
2
3
THF
30% H2O2
Cerium (IV) triflate
48(h)
29
cyclohexyliden
ebishydroperox
ide
Diketopiperazi
ne-derived
MeC
N
3
3
-
30
89
67
-
-
4
5
MeO
H
3
4
-
24(h)
hydroperoxide
MeC
N
MeO
H
1
2
3
5
30% H2O2
30% H2O2
NBS
300
300
93
96
-
-
6
7
bisflavinium
perchlorates
sodium
perborate or
sodium
CH2
Cl2
3
6
SSA/KBr
120
57
-
8
percarbonate
MeO
H
3
7
30% H2O2
UHP
niobium(V)
30
86
85
-
-
9
Tetrabutylammonium
phosphomolybdate on
fluorapatite
3
8
-
72 (h)
10
18
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Scheme 1 Synthesis of THPDPE catalysed by SbCl3
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Scheme 2 Selective oxidation of sulfides to corresponding sulfoxides or sulfones
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Scheme 3 Suggested mechanism for preparation of sulfoxides and sulfones
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