Stereoselective oxidation of methyl phenyl sulfide in the presence of chiral ionic liquids

Article abstract of DOI:10.1134/S1070363214070093

Several ionic liquids containing a chiral center either in the cation or in the anion have been prepared. They have been applied as catalysts and solvents for stereoselective oxidation of methyl phenyl sulfide to obtain the respective sulfoxide.

Full text of DOI:10.1134/S1070363214070093

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 7, pp. 1302–1307. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.V. Akopyan, E.V. Rakhmanov, D.A. Grigor’ev, M.V. Ryzhov, A.V. Tarakanova, A.V. Anisimov, 2014, published in Zhurnal Ob-
shchei Khimii, 2014, Vol. 84, No. 7, pp. 1105–1111.
Stereoselective Oxidation of Methyl Phenyl Sulfide
in the Presence of Chiral Ionic Liquids
A. V. Akopyan, E. V. Rakhmanov, D. A. Grigor’ev, M. V. Ryzhov,
A. V. Tarakanova, and A. V. Anisimov
Lomonosov Moscow State University, Moscow, 119992 Russia
e-mail: anis@petrol.chem.msu.ru
Received December 16, 2013
Abstract—Several ionic liquids containing a chiral center either in the cation or in the anion have been
prepared. They have been applied as catalysts and solvents for stereoselective oxidation of methyl phenyl sulfide
to obtain the respective sulfoxide.
Keywords: ionic liquid, oxidation, chirality, sulfide
DOI: 10.1134/S1070363214070093
Development of efficient and environmentally
friendly oxidants of organic sulfides and disulfides is a
topical task, as the so obtained products (sulfoxides,
sulfones, and thiosulfonates) may act as promising
complexing agents, surfactants, plant growth factors,
and drugs. Many of the biologically active compounds
contain a chiral sulfinyl group; hence, catalytic
systems allowing for asymmetric oxidation of sulfides
into sulfoxides with high enantioselectivity are on
demand. The application of ionic liquids for chiral
oxidation of sulfur-containing substrates has been
reported in [1]. Nowadays, conventional Bolm and
Kagan catalytic systems are widely used; however,
such methods are not universal, and they are
technologically sophisticated [2–6].
racemization should be avoided at any stage of the
ionic liquid preparation.
Taking
into
account
the
above-listed
considerations, in this work we used imidazolinium
salts of organic acids prepared via the ion exchange.
Many of such salts are liquid at room temperature;
containing carboxylic groups, they can be converted
into the peracid salts under conditions of the oxidation,
they can then act as an oxidant bearing an asymmetric
center. The following acids were used for the ionic
liquids preparation: L-serine, L-lactic acid, and L-
tartaric acid (they are commercially available in the
enantiopure form).
The following oxidants were used: tert-butyl
hydroperoxide, cumene hydroperoxide, hydrogen
peroxide (30 wt % aqueous solution), hydrogen
peroxide–urea complex, and benzoyl peroxide. Ionic
liquids Ia–Ic containing chiral center in the anion were
prepared via ion exchange between 1-butyl-3-
methylimidazolinium chloride and sodium salts of L-
lactic acid, L-tartaric acid, and L-serine (Scheme 1).
In this work we studied asymmetric oxidation of
organic sulfide in the presence of chiral ionic liquids
containing an asymmetric center either in the cation or
in the anion. Being the chirality source, they were used
as oxidant or as solvent. In the literature, there have
been published examples of asymmetric sulfides
oxidations where the same molecule acted both as
oxidant and as asymmetric center [7, 8].
Ionic liquids containing chiral center in the cation
were prepared starting from commercially available
asymmetric natural alcohols: L-menthol and L-borneol
To be used in asymmetric oxidation of sulfides, a
ionic liquid with a chiral center in the anion should be
easily prepared; it should possess a low melting point
(IIa, IIb) [9] (Scheme 2).
(
sulfoxides racemization is substantially accelerated
Firstly, ester of chloroacetic acid and the
corresponding alcohol was prepared; the second stage
was 1-methylimidazole alkylation with the so prepared
above room temperature); it should contain functional
groups participating in the oxidation process; the
1
302

STEREOSELECTIVE OXIDATION OF METHYL PHENYL SULFIDE
1303
Scheme 1.
H C
H C
3
3
N
Na Х
N
n
Х
2
4 h
N+
_
N+
Cl
H C
H C
3
3
n
Ia−Ic
_
O
OH
OH
O
O
HO
O
_
Х = H C
, n = 1 (a); Х = H N
, n = 1 (b); Х =
, n = 2 (c).
3
2
OH
_
O
O
O
_
O
Scheme 2.
N
N
CH
3
dicyclohexylcarbodiimide/
dimethylaminopyridine
O
O
O
N+
N
CH3
ROH +
Cl
Cl
o
o
_
HO
CH Cl , 20 C
RO
20 C, 4 h
RO
2
2
Cl
IIa, IIb
IIIa, IIIb
IVa, IVb
O
KBF4
N+
N
CH3
0oC
_
2
RO
BF4
Va, Vb
O
_
Na WO
CH3 WO42
2
4
N+
N
2
0oC, 24 h
RO
2
VIa
CH3
H
3
C
CH
3
R =
(a),
(b).
C3H3
H C
CH3
3
esters. The reaction yields were 82% (menthol) and
To prepare ionic liquid containing tungstate anion
we performed ion exchange of the menthol derivative
chloride with sodium tungstate.
5
6% (borneol). The second stage implied ion exchange
between the prepared ionic liquids and potassium
tetrafluoroborate.
Mass spectrometry (inductively coupled plasma)
revealed 7 mg of tungsten in 1 mL of 2 wt % aqueous
solution of the ionic liquid; that corresponded to the
2 : 1 complex composition and evidenced the complete-
ness of anion exchange reaction.
Following the scheme, we obtained tetrafluoro-
borate of the menthol derivative (yellow oil) with the
yield of 77%; in the case of borneol, yield of the
product (brown oil) was 92%.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 7 2014

1
304
AKOPYAN et al.
Scheme 3.
_
_
O
O
O
S
ROOH
S+
S+
S
+
+
kt
H C
Ph
H C
Ph
H C
Ph
H C
Ph
3
3
3
3
O
Oxidation of the model substrate, methyl phenyl
the sulfoxide yield above 50%. In all cases the
enantiomeric excess did not exceed 10%; the best
result (ее 10%) was achieved when ionic liquid Ia was
used as solvent (see table).
sulfide, was performed using the ionic liquid with
chiral center in the anion, allowing for high
enantiomeric excess at substantial yield of the
sulfoxide (up to 80%) [1]. The following oxidants
were used: hydrogen peroxide–urea complex, aqueous
hydrogen peroxide (37 wt %), 3-chloro-perbenzoic
acid, and benzoyl peroxide (Scheme 3). The results
obtained under varied conditions are shown in the table.
Oxidation of methyl phenyl sulfide under
conditions of the modified Sharpless reaction [diethyl
tartrate being substituted with 1-butyl-3-methylimida-
zolinium (R,R)-tartrate] allowed for the increased
methyl phenyl sulfoxide yield of 87%, the enantio-
meric excess being of 79% (HPLC).
The oxidation practically did not occur when
hydrogen peroxide–urea was used as oxidant (the
sulfoxide yield was below 1%).
To conclude, in this work we prepared a number of
ionic liquids, and they were used in model reaction of
methyl phenyl sulfide oxidation. So far we were not
able to achieve high enantiomeric excess of the
product by using the ionic liquids as chiral solvent.
Using ionic liquids in conventional systems of asym-
metric oxidation of sulfides was successful and helped
improving the sulfoxide yield. The properties of ionic
liquids like easy preparation, excellent solubility in
most of organic solvents, etc may further extend the
possibilities of the developed synthetic methods by
substitution of conventional chirality sources with the
chiral ionic liquids.
Addition of 1 mol % of sodium tungstate as co-
catalyst increased the sulfoxide yield up to 13%, other
conditions being the same. Running the oxidation
during 24 h instead of 3 h further increased the
sulfoxide yield up to 80%; however, still longer run
did not lead to higher sulfoxide yield. The highest
yield of the sulfoxide (90%) was achieved using
benzoyl peroxide as oxidant and sodium tungstate as
co-catalyst. The oxidant and methyl phenyl sulfide
were readily soluble in the ionic liquids, and 24 h
stirring at room temperature in all cases gave more
than 60% of methyl phenyl sulfoxide.
EXPERIMENTAL
Ionic liquids with chiral center in the cation
containing metal atom in the anion (for example,
tungstate ion) act as oxidation catalysts in nonpolar
medium, under conditions of contact ion pairs
formation. Even though there are examples of using
ionic liquids as catalyst of asymmetric sulfide oxida-
tion [1], in all the reported cases the asymmetric center
was in the anion of the ionic liquid. We attempted
comparative study of methyl phenyl sulfoxide
oxidation using the above-mentioned ionic liquids with
chiral center in the cation and 3-chloroperbenzoic acid
as oxidant; however, the results were poor (the
sulfoxide yield was below 5%). Variation of the
oxidant and the reaction duration did not improve the
sulfoxide yield.
The starting chemicals and solvents used in this
work were commercially available products (Reakhim,
Aldrich, and Acros Organic). The solvents were
purified by distillation using standard methods [10].
1Н NMR spectra were recorded with the Bruker
Avance 400 spectrometer at 400 MHz. 2 wt %
solutions in CDCl
or DMSO-d were studied. Chemical
3
6
shifts were referenced to internal hexamethyldisiloxane.
Electrospray ionization mass spectra (ESI-МS)
were recorded with the AB Sciex QTRAP 3200
instrument (cations registration mode). The samples
were prepared in the form of 2 wt % solution in
methylene chloride or in water (LS MS Grade
Аldrich). Other conditions were as follows: direct
input with a syringe, source voltage 5.5 kV, source
temperature 300°С, mass range 100–500 Da.
The enantiomeric composition of the oxidation
products was analyzed in the cases of reactions with
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 7 2014

STEREOSELECTIVE OXIDATION OF METHYL PHENYL SULFIDE
1305
Oxidation of methyl phenyl sulfide with various oxidants in the presence of ionic liquids at 25°С
Yield
of sulfoxide/ee, %
Comp. no. Co-catalyst Reaction time, h
Oxidant
Solvent
Ia
Ib
Ic
Ia
Ia
Ib
Ic
Ia
-
1/–
3
CH
2
Cl
2
/
13/–
80/4
78/5
82/5
90/6
Hydrogen peroxide–urea
Benzoyl peroxide
2
2
wt % EtOH
24
Na
2
WO
WO
4
4
Na
2
24
CH
wt % EtOH
-
2
Cl /
2
Ia
Ib
Ic
Ia
-
-
-
65/10
61/8
68/8
54/6
m-Chloroperbenzoic acid
30% Hydrogen peroxide
Hydrogen peroxide–urea
CH
wt % EtOH
CH Cl
wt % EtOH
CH CN
Cl
2 2
/
2
2
Ia
Ia
2
2
/
75/5
55/3
Na
2
WO
4
48
3
The products composition and purity were
monitored by gas-liquid chromatography (Kristall-2000M
chromatograph with flame ionization detector, Zebron
column (l = 30 m, d = 0.32 mm), ZB-1 as liquid phase,
temperature ramp 100 to 230°С (sulfides analysis).
TLC analysis was performed using the Silufol UV
254 or cellulose plates. Depending of the reaction
mixture composition, eluents of various polarity were
used. The plates were developed in iodine vapor, with
UV irradiation, or with potassium permanganate
solution.
Tungsten content was determined by mass
spectrometry with inductively coupled plasma (the
Agilent 7500c instrument, generator power 1500 W,
the rate of plasma forming gas 15 L/min, sample rate
Enantiomeric excess was determined by means of
HPLC using the chiral column with Kromacil 3-
Cellucoat CT8032 as the stationary phase; the
Shimadzu 231 chromatograph with spectrophotometric
detector, λ = 220 nm; hexane–isopropyl alcohol, 40 : 1,
as eluent; Р = 1 MPa.
1
.15 L/min, resolution 0.7 a. w. u., pressure without
–5
plasma 4 × 10 Torr, pressure with plasma 4 ×
–4
1
3
0
Torr, measurement time 0.05–0.1 s per point,
182 184
points per peak, 3 replicates, W and W isotopes
1
-Butyl-3-methylimidazolium lactate (Ia) [11].
were used).
Sodium L-lactate (1.23 g, 11 mmol) was added to
solution of 1-methyl-3-butylimidazolium chloride
(1.91 g, 11 mmol) in anhydrous acetone (10 mL) at
room temperature. After 24 h stirring, the reaction
mixture was filtered through porous glass filter with
1 cm layer of zeolite. The solvent was removed, and
the residue was dried in a vacuum (2 mmHg) during
Calibration was run using the ICP-MS-68 multiele-
ment reference, solution B containing 10 mg/L of
tungsten. Calibration plots were obtained via suc-
cessive dilution of the stock solution with 1 wt %
aqueous HNO to concentration of 1, 10, and 100 µg/L.
3
The background signal was measured using 1 vol %
1
aqueous HNO (Merck, Germany). For the measure-
24 h. Yield 1.30 g (52%), yellow liquid. Н NMR
3
ment, a sample to be analyzed was diluted to 1 : 50 and
spectrum (DMSO-d ), δ, ppm: 0.81 t (3Н, J 7.3 Hz),
6
1
: 1000, and then the signal was measured.
1.19 m (2Н), 1.71 m (2Н), 3.59 m (1Н), 3.87 s (3Н),
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 7 2014

1
306
AKOPYAN et al.
4
.02 m (3Н), 4.18 t (2Н, J 7.1 Hz), 7.80 s (1Н), 7.88 s
(3Н, J 7.0 Hz), 0.81 m (1Н), 0.85 t (6Н, J 6.7 Hz),
0.98 m (2Н), 1.36 m (2Н), 1.62 m (2Н), 1.81 m (1Н),
1.95 m (1Н), 3.98 m (2Н), 4.70 m (1Н).
(
1Н), 9.63 s (1Н). Mass spectrum: m/z 140 [M −
+
lactate] .
1
-Butyl-3-methylimidazolium 2-amino-3-hydroxy-
1
,7,7-Trimethylbicyclo[2.2.1]hept-2-ylchloro-
propionate (Ib) [11]. Sodium salt of L serine (1.21 g,
acetate (IIIb) [9]. Chloroacetic acid (1.58 g, 20 mmol),
dicyclohexylcarbodiimide (5.16 g, 20 mmol), and
dimethylaminopyridine (0.23 g, 1 mmol) were added
at 0ºC upon stirring to solution of L-borneol (2.00 g,
9
.5 mmol) was added at room temperature to solution
of 1-methyl-3-butylimidazoluim chloride (1.65 g,
9
.5 mmol) in 50 mL of anhydrous acetone, and the
mixture was stirred during 24 h. Then the reaction
mixture was filtered through a filter with a zeolite
2
0 mmol) in anhydrous CH Cl (15 mL). The mixture
2
2
was stirred during 12 h at room temperature. The
suspension was filtered, and the residue was washed
with anhydrous CH Cl (10 mL). The organic phase
layer, and the solvent was distilled off. Yield 1.90 g
1
(
(
(
83%). Н NMR spectrum (DMSO-d ), δ, ppm: 0.86 t
6
2
2
3Н, J 7.5 Hz), 1.23 m (3Н), 1.74 m (2Н), 3.33, 3.47 m
2Н), 3.79 m (1Н), 3.87 s (3Н), 4.18 t (2Н, J 7.2 Hz),
was washed with 10 wt % HCl (10 mL), then with
saturated NaHCO solution (10 mL), and with
3
7
.77 s (1Н), 7.84 s (1Н), 9.36 s (1Н). Mass spectrum:
saturated NaCl solution (10 mL). The product was
dried with Na SO , filtered, and the solvent was
+
m/z 140 [М
] .
cation
2
4
1
distilled off. Yield 1.66 g (36%), dark-yellow oil. Н
1
-Butyl-3-methylimidazolium (R,R)-tartrate (Ic)
NMR spectrum (DMSO-d ), δ, ppm: 0.76 s (3Н), 0.80
[
11]. 1.82 g (2 eq.) of sodium hydroxide was added to
6
d (6Н, J 11.0 Hz), 0.94 m (1Н), 1.15 m (2Н), 1.65 m
solution of 3.42 g (23 mmol) of tartaric acid in 30 mL
of water; the solution was stirred during 30 min, and
then concentrated by solvent evaporation. Then the so
prepared solution of sodium (R,R)-tartrate was added
to the solution of 1-methyl-3-butylimidazolium
chloride (10.00 g, 46 mmol) in 100 mL of anhydrous
acetone, and the mixture was stirred at room
temperature during 24 h. The solution was evaporated
to dryness, 50 mL of CH Cl was added; the organic
(
4
2Н), 1.86 m (1Н), 2.24 m (1Н), 4.35 d (2Н, J 3.7 Hz),
.85 m (1Н).
-Methyl-3-[(1R,2S)-5-methyl-2-(prop-2-yl)cyclo-
hexyloxycarbonylmethyl]-1Н-imidazol-3-ium chloride
1
(
IVa) [9]. 0.78 g (1 equiv.) of 1-methylimidazole was
added to ester IIIa (2.22 g, 9.5 mmol); the solution
was stirred during 4 h at 80°С. After that, the formed
solid white substance was washed with benzene (2 ×
2
2
fraction was separated, washed with water (2 × 20 mL),
and dried over Na SO . The solvent was then removed,
1
(
0 mL), filtered, and dried in a vacuum. Yield 2.48 g
1
2
4
82%), dark-yellow powder, mp 72–73°С. Н NMR
and the residue was dried in vacuum. Yield 8.10 g
spectrum (DMSO-d ), δ, ppm: 0.70 d (3Н, J 6.9 Hz),
6
1
(
(
(
(
83%), viscous yellow liquid. Н NMR spectrum
0
.81 m (1Н), 0.86 t (6Н, J 6.9 Hz), 0.99 m (2Н), 1.33
DMSO-d ), δ, ppm: 0.86 t (6Н, J 7.3 Hz), 1.21 m
6
m (2Н), 1.61 m (2Н), 1.83 m (1Н), 1.99 m (1Н), 3.90 s
4Н), 1.74 m (2Н), 3.40 s (2Н), 3.85 s (6Н), 4.18 m
(
(
3Н), 4.66 m (1Н), 5.19 m (2Н), 7.75 m (2Н), 9.18 s
1Н).
2Н), 7.75 s (2Н), 7.83 s (2Н), 9.31 s (2Н). Mass
+
spectrum: m/z 140 [M
] .
cation
1
-Methyl-3-{(1,7,7-trimethylbicyclo[2.2.1]-hept-
(
1R,2S)-5-Methyl-2-(propan-2-yl)cyclohexyl-
chloroacetate (IIIa) [9]. Chloroacetic acid (2.35 g,
5 mmol), dicyclohexylcarbodiimide (5.16 g, 25
2
(
-yl)oxycarbonylmethyl}-1Н-imidazol-3-ium chloride
IVb) [9]. 0.43 g (1 equiv.) of 1-methylimidazole was
2
added to ester IIIb (1.20 g, 5.2 mmol); the solution
was stirred during 4 h at 80°С. After that, the formed
brown oil was washed with benzene (3 × 10 mL) and
mmol), and dimethylaminopyridine (0.23 g, 1.9 mmol)
were added at 0ºC upon stirring to solution of L-
menthol (3.00 g, 19 mmol) in anhydrous CH Cl
2
2
1
dried in a vacuum. Yield 0.91 g (56%). Н NMR
(
15 mL). The mixture was stirred during 12 h at room
spectrum (DMSO-d ), δ, ppm: 0.76 s (3Н), 0.80 d (6Н,
6
temperature. The suspension was filtered, and the
residual was washed with anhydrous CH Cl (10 mL).
J 7.2 Hz), 0.94 m (1Н), 1.09 m (2Н), 1.63 m (3Н),
2
2
1
5
.86 m (1Н), 2.20 m (1Н), 3.86 s (3Н), 4.83 m (1Н),
.25 m (2Н), 7.72 m (2Н), 9.15 s (1Н).
The organic phase was washed with 10 wt % HCl
(
(
10 mL), then with saturated NaHCO solution
3
10 mL), and with saturated NaCl solution (10 mL).
1-Methyl-3-[(1R,2S)-5-methyl-2-(prop-2-yl)cyclo-
The product was dried with Na SO , filtered, and the
hexyloxycarbonylmethyl]-1Н-imidazol-3-ium tetra-
2
4
solvent was distilled off. Yield 2.22 g (50%), yellow
fluoroborate (Va) [9]. 0.88 g (1 equiv.) of KBF
4
was
1
oil. Н NMR spectrum (DMSO-d ), δ, ppm: 0.72 d
added to a solution of 2.22 g (7 mmol) of compound
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 7 2014

STEREOSELECTIVE OXIDATION OF METHYL PHENYL SULFIDE
1307
IVa in 10 mL of water, and the mixture was stirred
during 5 h at room temperature. After that, water was
distilled off; CH Cl was added to the residue; the
or CH CN). The mixture was stirred at room tem-
3
perature during 3–48 h. The mixture was decanted or
filtered, washed with water, and analyzed.
2
2
mixture was filtered through zeolite layer; the filtrate
was dried over Na SO ; the solvent was distilled off;
Methyl phenyl sulfide oxidation in the Kagan
system [2]. Titanium tetraisopropylate (0.14 mg,
2
4
and the residue was dried in a vacuum. Yield 2.00 g
0
.5 mmol) and the ionic liquid Ic (0.42 g, 1 mmol)
1
(
77%), pale-yellow powder, mp 37–38°С. Н NMR
were dissolved in 5 mL of anhydrous CH Cl Under
2
2
spectrum (DMSO-d ), δ, ppm: 0.70 d (3Н, J 7.1 Hz),
6
argon. 9 µL of water were added dropwise through the
septum. The reaction mixture was stirred during
0
.81 m (1Н), 0.86 t (6Н, J 7.1 Hz), 0.99 m (2Н), 1.33
m (2Н), 1.61 m (2Н), 1.83 m (1Н), 1.99 m (1Н), 3.90 s
3
0 min till homogenization; and methyl phenyl sulfide
(
(
3Н), 4.66 m (1Н), 5.19 m (2Н), 7.72 m (2Н), 9.14 s
(
0.062 g, 0.5 mmol) was added. The solution was
+
1Н). Mass spectrum: m/z 280 [M – BF ] .
4
cooled to –20°С, and 200 µL (1 mmol) of 5 mol/L
solution of tert-butyl hydroperoxide was added. The
mixture was stirred at –20°С during 12 h. The reaction
was then quenched by addition of 2 mL of water; the
mixture was filtered, and the organic phase was
analyzed.
1
-Methyl-3-{(1,7,7-trimethylbicyclo[2.2.1]hept-2-
yl)oxycarbonylmethyl}-1Н-imidazol-3-ium tetra-
fluoroborate (Vb) [9]. 0.37 g (1 equiv.) of KBF was
4
added to a solution of 0.91 g (2.9 mmol) of compound
IVb in 10 mL of water, and the mixture was stirred
during 48 h at room temperature. After that, water was
distilled off; CH Cl was added to the residue; the
ACKNOWLEDGMENTS
2
2
mixture was filtered through zeolite layer; the filtrate
was dried over Na SO ; the solvent was distilled off;
This work was financially supported by the Russian
Foundation for Basic Research (project no. 12-03-
00260).
2
4
and the residue was dried in a vacuum. Yield 0.87 g
1
(
92%), brown oil. Н NMR spectrum (DMSO-d ), δ,
6
ppm: 0.76 s (3Н), 0.80 d (6Н, J 7.3 Hz), 0.94 m (1Н),
REFERENCES
1
3
9
.09 m (2Н), 1.63 m (3Н), 1.86 m (1Н), 2.20 m (1Н),
.86 s (3Н), 4.83 m (1Н), 5.25 m (2Н), 7.69 m (2Н),
1
. Bigi, F., Nimal Gunaratne, H.Q., Quarantelli, C., and
Seddon, K.R.C.R., Chimie, 2011, no. 14, p. 685.
+
.10 s (1Н). Mass spectrum: m/z 278 [M – BF ] .
4
1
-Methyl-3-[(1R,2S)-5-methyl-2-(prop-2-yl)cyclo-
hexyloxycarbonylmethyl]-1Н-imidazol-3-ium tungstate
VIa) [9]. 10.56 g (32 mmol) of Na WO ·2H O was
2. Pitchen, Ph. and Kagan, H.B., Tetrahedron Lett., 1984,
vol. 25, no. 10, p. 1049.
3
4
. Sivik, M.R., Stanton, K.J., and Paquette, L.A., Org.
(
2
4
2
Synth., 1996, no. 73, p. 57.
added to a solution of 20.00 g (64 mmol) of compound
IVa in 100 mL of water, and the mixture was stirred
during 24 h at room temperature. After that, water was
distilled off; CH Cl was added to the residue; the
. Baraldi, P.G., Barco, A., Benetti, S., Ferretti, V., Pol-
lini, G.P., Polo, E., and Zanirato, V., Tetrahedron, 1989,
vol. 45, no. 5, p. 1517.
2
2
5
. Bolm, C., Bienewald, F., and Harms, K., Synlett., 1996,
p. 775.
mixture was filtered through zeolite layer; the filtrate
was dried over Na SO ; the solvent was distilled off;
2
4
6
7
. Bolm, C., Coord. Chem. Rev., 2003, vol. 237, p. 245.
the residue was dried in a vacuum. Yield 10.87 g
1
. Doskocil, E.I., Nopdawekar, S.V., Kaya, B.G., and
Davis, R.J.J., Phys. Chem. (B), 1999, vol. 103, no. 30,
p. 6277.
(
4
0
42%), yellow-green oil. Н NMR spectrum (DMSO-d ,
6
00 MHz), δ, ppm: 0.68 d (3Н, J 7.0 Hz), 0.81 m (1Н),
.86 t (6Н, J 6.9 Hz), 0.99 m (2Н), 1.33 m (2Н), 1.61
8
. Bordawekar, S.V. and Davis, R.J., J. Catal., 2000, vol. 189,
no. 1, p. 79.
m (2Н), 1.83 m (1Н), 1.91 m (1Н), 3.89 s (3Н), 4.63 m
(
1Н), 5.24 m (2Н), 7.72 m (2Н), 9.12 s (1Н). Mass
+
9. Matos, R.A.F., Andrade, C.K.Z., Tetrahedron Lett.,
spectrum: m/z 280 [M – BF ] .
4
2
008, vol. 49, p. 1652.
Methyl phenyl sulfide oxidation [1]. Methyl phenyl
sulfide (0.20 g, 1.6 mmol), 1 mol % of the chiral ionic
liquid and 1.15 equiv. of the oxidant (hydrogen
peroxide–urea, 30 wt % hydrogen peroxide solution, 3-
chloroperbenzoic acid, or benzoyl peroxide) were
added to 5 mL of the solvent (CH Cl −C H OH 50 : 1
1
0. Becker, H. and Berger, W., Organikum, Berlin: VEB
Deutscher Verlag Der Wissennschaften, 1976. Trans-
lated under the title Organikum, Мoscow: Mir, 2008,
vol. 2.
11. Earle, M.J., McCormac, P.B., and Seddon, K.R., Green
Chem., 1999, no. 1, p. 23.
2
2
2
5
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 7 2014