VO(acac)2-catalyzed oxidation of sulfoxides to sulfones using chlorine dioxide

Article abstract of DOI:10.1016/j.mencom.2008.07.021

The catalytic effect of VO(acac)₂ in the oxidation of sulfoxides to sulfones with chlorine dioxide was found.

Full text of DOI:10.1016/j.mencom.2008.07.021

Mendeleev
Communications
Mendeleev Commun., 2008, 18, 225–226
VO(acac)2-catalyzed oxidation of sulfoxides
to sulfones using chlorine dioxide
Denis V. Sudarikov,* Svetlana A. Rubtsova and Aleksandr V. Kutchin
Institute of Chemistry, Komi Scientific Centre, Ural Branch of the Russian Academy of Sciences, 167982 Syktyvkar,
Russian Federation. Fax: +7 8212 21 8477; e-mail: sudarikov-dv@chemi.komisc.ru
DOI: 10.1016/j.mencom.2008.07.021
The catalytic effect of VO(acac)2 in the oxidation of sulfoxides to sulfones with chlorine dioxide was found.
Chlorine dioxide (ClO2) is a convinient industrial oxidant. The
oxidation of amines, phenols, olefins and carbonyl compounds
by chlorine dioxide was described.1
Previously,2–5 it was shown that the oxidation of sulfides with
ClO2 at a substrate-to-oxidant molar ratio of 1:0.5 in CH2Cl2,
CCl4, AcOEt or without solvent results in 95–100% conversion
of the sulfide to give the corresponding sulfoxide in 80–95%
yields; the formation of sulfones does not exceed 2–3%.
In the oxidation of dipropyl and methyl phenyl sulfoxides
at a substrate-to-oxidant molar ratio of 1:0.5 in CH2Cl2 and
AcOH at room temperature, the conversion of sulfoxides does
not exceed 20–25%. The reaction products are sulfones and
monochlorinated sulfoxide derivatives (Scheme 1).† At 80 °C,
the conversion of sulfoxides was 98–100% in AcOH. In the
case of methyl phenyl sulfoxide, the yields of methyl phenyl
sulfone and (chloromethylsulfinyl)benzene are 25 and 75%,
respectively. Dipropyl sulfoxide gave a sulfone (yield 15%) and
two monochlorinated sulfoxide derivatives (10 and 75%).
Previously,18 it was found that chlorine dioxide oxidizes the
vanadyl ion to a vanadium(V) dioxo cation at a high rate.
Among the products of this reaction are the chlorate ion and
chlorine, which oxidize the vanadyl ion to vanadium(V) dioxo
cation at a lower rate. Note that, in comparison with the chlorate
ion, chlorine dioxide reacts with vanadium(IV) approximately
100 times faster.
·
fast
mVO2+ + ClO2
mVO+2 + products (ClO3–, Cl2)
Presumably, among the reaction intermediates, there is a radical
of chlorine which also rapidly oxidizes vanadium(IV).19
·
fast
VO2+ + Cl
VO+2 + Cl– + 2H+
H2O
Here, we report on the oxidation of sulfoxides with chlorine
dioxide in the presence of catalytic amounts of VO(acac)2. The
catalytic oxidation of dipropyl and methyl phenyl sulfoxides
with VO(acac)2 at a substrate-to-oxidant molar ratio of 1:0.5
leads to the formation of sulfones in CH2Cl2 or AcOH at room
temperature (Scheme 2).† The yields of sulfones in product
mixtures are 80–95%. The minor products are mono-chlorinated
sulfoxides.
O
S
O
S
O
S
ClO2
R1
CH2 R2
R1
CH R2
Cl
R1
CH2 R2
+
80 °C
O
R1 = Ph, Pr
R2 = H, Et
O
S
O
S
Scheme 1
ClO2, 20 °C
R1
CH2 R2
R1
CH2 R2
1 mol% VO(acac)2
Probably, the formation of chlorinated derivatives is associated
with the reactions of radicals formed on the thermolysis of
chlorine dioxide. For instance, among the oxidation products
of substituted phenols with chlorine dioxide, the following
products have been identified: 2-chloro-1,4-benzoquinone and
2,6-dichloro-1,4-benzoquinone.1 Cycloalkanes and benzene
homologues slowly interact with chlorine dioxide to form
chlorinated products.6 The main oxidation products of lower
alcohols at 70–80 °C are ketones and chloroketones.7,8
O
R1 = Ph, Pr
R2 = H, Et
Scheme 2
†
GC analysis was performed on a Chrom 5 chromatograph; argon was
used as a carrier gas, and the column was packed with 5% SKTFT-50 on
Chromaton N-AW-DMCS. The mass spectra were acquired on a Finnigan
Trace DSQ instrument (column RM-5MS, 30 m×0.25 mm, Tcol = 50–220 °C,
4 K min–1). IR spectra were recorded on a MIR-8000 instrument in a thin
layer (0.2–0.5 mm) and KBr pellets at 400–4000 cm–1. 1H NMR spectra
were recorded on a Bruker DPX 300 instrument (300.13 MHz).
General procedure for the catalytic oxidation of sulfoxides. A sulfoxide
(5 mmol) and VO(acac)2 (0.05 mmol) were dissolved in 10 ml of acetic acid
(or CH2Cl2) to give a pale green solution. After stirring for 5 min, a solution
of chlorine dioxide in acetic acid was added dropwise with rapid stirring
at room temperature to produce a brown solution. The mixture was stirred
for 3–4 h at ambient temperature to give afresh pale green solution.
After removing the solvent at low pressure, the residue was diluted with
100 ml of diethyl ether and washed with 50 ml of a saturated aqueous
solution of NaHCO3. The organic phase was dried with Na2SO4, and the
solvent was evaporated. The concentrations of the products were deter-
mined by GLC and GC/MS. Sulfone was recrystallized from ethanol.
The yields were 80–95%.
Therefore, the oxidation of sulfoxides to sulfones can be a
useful model for catalytic oxidation.
The preparation of sulfones usually involves the direct
oxidation of sulfides and sulfoxides using hydrogen peroxide,
peracids, hydroperoxides, chlorine, nitrogen oxides, oxygen or
ozone.9–11 The most common oxidant is hydrogen peroxide,
generally in acetic acid.12–13 Various transition metal compounds
are utilised in the preparation of sulfones from sulfoxides with
homogeneous catalysts (W, Mo, V).14–16
Vanadium(V) compounds are one-electron oxidants (VV–VIV)
widely used in organic reactions. VO(acac)2 is used as a catalyst
for oxygen transfer in the oxidation reactions of alkanes, alkenes,
alcohols, amines, sulfides, sulfoxides, etc. in the presence of
TBHP or molecular oxygen as an oxidant.17
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© 2008 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2008, 18, 225–226
The batchwise addition of an oxidant changed the colour
References
of the reaction mixture from pale green to brown; after the
exhaustion of the oxidant, the colour became light green.
The direct oxidation of methyl phenyl sulfide and dipropyl
sulfide at a substrate-to-oxidant molar ratio equal to 1:1 in AcOH
with catalytic amounts of VO(acac)2 gives corresponding sulfones
in 75–92% yields.
1
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therein.
3
4
5
Thus, the ClO2–VO(acac)2 system is suitable for the oxidation
of sulfoxides to sulfones.
Methyl phenyl sulfoxide: 1H NMR (80 MHz, CDCl3) d: 2.5 (s, 3H,
Me), 7.23–7.41 (m, 5H, Ar). IR (n/cm–1): 1046 (S=O). MS, m/z (%): 140
6
7
8
9
+
+
+
+
·
(40) [M] , 125 (100) [PhSO] , 109 (10) [PhS] , 97 (40), 77 (27) [Ph] .
Methyl phenyl sulfone: mp 86–88 °C. 1H NMR (CDCl3) d: 2.96 (s,
3H, Me), 7.44–7.60 (m, 3H, Ar), 7.79–7.91 (m, 2H, Ar). IR (n/cm–1):
+
+
·
1151, 1306 (O=S=O). MS, m/z (%): 156 (65) [M] , 141 (32) [PhSO2] ,
125 (5) [PhSO]+, 94 (45), 77 (100) [Ph]+.
(Chloromethylsulfinyl)benzene: 1H NMR (CDCl3) d: 4.16–4.45 (m, 2H,
CH2Cl), 7.23–7.41 (m, 5H, Ar). IR (n/cm–1): 1058 (S=O). MS, m/z (%):
10 S. Oae, Organic Sulfur Chemistry: Structure and Mechanism, CRP Press,
Boca Raton, 1991, p. 253.
11 O. Bortolini, S. Campestrini, F. Di Furia and G. Modena, J. Org. Chem.,
1987, 52, 5093.
12 M. Portelli and B. Soranza, Ann. Chim., 1962, 52,1280.
13 N. Furukawa, Y. Konno, H. Tsuruoka, H. Fujihara and S. Ogawa, Chem.
Lett., 1989, 1501.
14 O. Bortolini, F. Di Furia and G. Modena, J. Mol. Catal., 1982, 14, 53.
15 O. Bortolini, F. Di Furia and G. Modena, J. Mol. Catal., 1982, 16, 69.
16 K. A. Vassel and J. M. Espenson, Inorg. Chem., 1994, 33, 5291.
17 T. Hirao, Chem. Rev., 1997, 2707.
+
·
+
+
+
174.5 (6) [M] , 125 (100) [PhSO] , 110 (5) [PhS] , 97 (20), 77 (13) [Ph] .
Dipropyl sulfoxide: mp 22–23 °C. 1H NMR (CDCl3) d: 0.85 (t, 3H,
MeCH2CH2, J 7.2 Hz), 1.45–1.76 (m, 2H, MeCH2CH2), 2.45 (t, 2H,
MeCH2CH2, J 7.25 Hz). IR (n/cm–1): 1038 (S=O). MS, m/z (%): 134 (70)
[M] , 117 (14) [Pr2S] , 92 (100) [PrSO] , 77 (8) [CH2CH2SO] , 63 (72)
[CH2SO]+.
Dipropyl sulfone: mp 29.5–30.5 °C. 1H NMR (CDCl3) d: 0.99 (t, 3H,
MeCH2CH2, J 7.2 Hz), 1.54–2.00 (m, 2H, MeCH2CH2), 2.86 (t, 2H,
MeCH2CH2, J 7.2 Hz). IR (n/cm–1): 1125, 1310 (O=S=O). MS, m/z
+
·
+
+
+
18 W. S. Melvin and G. Gordon, Inorg. Chem., 1972, 11, 1912.
19 K. Dreyer and G. Gordon, Inorg. Chem., 1972, 11, 1176.
+
+
+
·
(%): 150 (10) [M] , 134 (11) [Pr2SO] , 108 (100) [PrSO2] , 93 (4)
[CH2CH2SO]+, 63 (6) [CH2SO]+.
1-Chloro-2-(propylsulfinyl)propane [in the mixture with 1-chloro-
3-(propylsulfinyl)propane]: 1H NMR (CDCl3) d: 4.20–4.45 [m, 1H,
+
+
·
MeCH(Cl)CH2]. MS, m/z (%): 168 (10) [M] , 92 (100) [PrSO] , 77 (16)
[CH2CH2SO]+, 63 (37) [CH2SO]+.
1-Chloro-3-(propylsulfinyl)propane [in the mixture with 1-chloro-
2-(propylsulfinyl)propane]: 1H NMR (CDCl3) d: 3.69–3.90 [m, 2H,
+
+
·
CH2(Cl)CH2CH2]. MS, m/z (%): 168 (10) [M] , 92 (100) [PrSO] , 77
(16) [CH2CH2SO]+, 63 (37) [CH2SO]+.
Received: 11th March 2008; Com. 08/3098
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