Tungstate-exchanged Mg-Al-LDH catalyst: An eco-compatible route for the oxidation of sulfides in aqueous medium

Article abstract of DOI:10.1039/b205292j

The catalytic oxidation of sulfides selectively to sulfoxides and/or sulfones is realised for the first time with heterogeneous tungstate-exchanged Mg-Al-LDH catalyst using 30% hydrogen peroxide in aqueous media at a faster rate in quantitative yields at room temperature. The heterogeneous catalyst showed higher activity (TOF) over its homogeneous analogues and other heterogeneous catalysts reported so far. The catalyst is well characterised by various instrumental techniques such as FT-IR spectroscopy, thermal analysis (TGA and DTA), powder XRD and chemical analysis. The catalyst is reused for six cycles with consistent activity and selectivity.

Full text of DOI:10.1039/b205292j

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Tungstate-exchanged Mg-Al-LDH catalyst: an eco-compatible
route for the oxidation of sulfides in aqueous medium†
B. M. Choudary,* B. Bharathi, Ch. Venkat Reddy and M. Lakshmi Kantam
1
Indian Institute of Chemical Technology, Hyderabad-500007, India.
E-mail: choudary@iict.ap.nic.in; Fax: 91-40-7160921
Received (in Cambridge, UK) 31st May 2002, Accepted 24th July 2002
First published as an Advance Article on the web 13th August 2002
The catalytic oxidation of sulfides selectively to sulfoxides and/or sulfones is realised for the first time with
heterogeneous tungstate-exchanged Mg-Al-LDH catalyst using 30% hydrogen peroxide in aqueous media at a
faster rate in quantitative yields at room temperature. The heterogeneous catalyst showed higher activity (TOF)
over its homogeneous analogues and other heterogeneous catalysts reported so far. The catalyst is well characterised
by various instrumental techniques such as FT-IR spectroscopy, thermal analysis (TGA and DTA), powder XRD
and chemical analysis. The catalyst is reused for six cycles with consistent activity and selectivity.
makes the process cumbersome. Moreover the catalyst could
Introduction
not be recovered for further cycles.
The vast chemistry of sulfoxides and sulfones makes them very
An ideal system for such reactions is the use of solid catalysts
useful reagents in organic synthesis in general and useful syn-
under heterogeneous conditions, which allows easy separation
thetic intermediates for the construction of various chemically
of the catalysts from the reaction mixture and adaptability in
large-scale production to conform to the class of greener tech-
and biologically significant molecules in particular.1 For this
reason the oxidation of sulfides to chiral/achiral sulfoxides or
nologies. In recent years selective oxidation of sulfides to sulf-
sulfones has been the subject of extensive studies and a number
oxides or sulfones has been carried out with a large number
of synthetic procedures are now available.2–18 To date the most
of supported reagents or catalysts.28 For instance, titanium
important method for preparing sulfoxides or sulfones involves
silicates (TS-1 and TS-2)28g promote sulfide oxidation, but the
the oxidation of sulfides. Various oxidising reagents used for
use of bulky sulfides is precluded by their limited access to the
this purpose include nitric acid,3 KMnO4,4 MnO2,5 NaClO4,6
Ti active sites. In order to overcome this limitation, mesoporous
m-chloroperbenzoic acid,7 sodium metaperiodate,8 bromine,9
materials have been used. Ti-MCM-41 allows the oxidation
nitrogen tetraoxide,10,11 oxaziridine,12 benzeneseleninic per-
of bulky sulfides29 but with the loss of selectivity. Recently
acid,13 tert-butyl hydroperoxide,14 sulfinyl peroxy compounds,15
Fraile et al. introduced Ti(OiPr)4 supported on silica as an
iodosobenzene diacetate16 and 4-methylmorpholine N-oxide
efficient and selective catalyst for the oxidation of sulfides to
with osmium tetraoxide.17 Unfortunately most of these reagents
sulfoxides,30 but the drawback is the gradual leaching of
are not satisfactory for medium to large scale synthesis because
of the low content of effective oxygen, the formation of environ-
mentally unfavourable by-products, and high cost. Singlet
titanium during the reaction.
With an ever-increasing level of global competition and
environmental consciousness, there is much incentive to find
new and strategically important processes using a highly robust
oxygen or molecular oxygen combined with 2-methylpropanal
and Co() complexes18,19 has also been used.
and recyclable catalyst that provides higher atom utilisation,
Catalytic homogeneous reactions are preferred over reactions
preferably close to theoretical values, to eventually minimise
that use stoichiometric quantities, since the stoichiometric reac-
pollution levels using greener ingredients. The challenge is to
tions are not only corrosive and hazardous, but they also gener-
ate copious amounts of heavy metal waste. Aqueous hydrogen
peroxide (30%) is an ideal oxidant in view of its high effective-
oxygen content (as high as 47%), cleanliness (it produces only
perform a truly heterogeneous catalytic reaction for the
oxidation of sulfides in the laboratory, bulk and fine chemical
industries. Layered double hydroxides (LDHs) or hydrotalcite-
like compounds (HTLCs)31 have recently received much atten-
water as by-product), safety in storage and operation, and low
tion in view of their potential usefulness as adsorbents, anion
cost of production and transportation.20 These obvious advan-
exchangers and most importantly as catalysts.32 The hydro-
tages have spurred the development of useful procedures for
philicity of the LDH material makes the hosted oxidation
H2O2 mediated oxidation of sulfides catalysed by tungsten
catalyst water compatible to conduct the reactions using water
as a solvent. Recently we reported the catalytic N-oxidation of
tertiary amines by tungstate-exchanged Mg-Al-LDH catalyst
systems comprising H2WO4,21 [C5H5N(n-C16H33)]3PO4[W(O)-
(O2)2]4,22 and Na2WO4 ϩ [n-C4H9)4N]Cl23 in addition to Na2-
MoO4 ϩ (n-C4H9)3PO,24 Ti()Cl,25 CH3ReO3.26 However, there
(LDH-WO4) in quantitative yields at faster rate in aqueous
remains much room for improvement, because many of these
procedures require chlorohydrocarbon solvents that affect
human health and the environment. In order to address this
media.33 We report in this paper an efficient and heterogeneous
tungstate-exchanged Mg-Al-LDH catalyst for the oxidation of
sulfides using H2O2 as an oxidant and water as a solvent with
issue recently, Noyori et al. reported oxidation of sulfides to
good to excellent yields for the first time (Scheme 1).
sulfoxides and sulfones with 30% H2O2 using Na2WO4 under
solvent and halogen free conditions.27 A phosphonic acid
promoter, and an acidic quaternary ammonium salt, [CH3-
(n-C8H17)3N]HSO4, are used along with the catalyst which
Results and discussion
The structure of layered double hydroxides (LDH) consists of
brucite [Mg(OH)2] type octahedral layers in which some of the
M() cations are isomorphously substituted by M() cations.
† IICT Communication No: 020222
DOI: 10.1039/b205292j
J. Chem. Soc., Perkin Trans. 1, 2002, 2069–2074
This journal is © The Royal Society of Chemistry 2002
2069

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Table 1 The oxidation of thioanisole using various transition metal oxide exchanged LDH catalysts and their homogeneous analoguesa
Entry
Catalyst
Time/h
Conversion (%)
1a : 1b
TOF/hϪ1 b
1
2
3
4
5
6
7
8
LDH-WO42Ϫ (cat 1)
LDH-MoO42Ϫ (cat 2)
LDH-VO3Ϫ (cat 3)
LDH-{PO4WO(O2)]4} (cat 4)
Na2WO4
NaVO3
Na2MoO4
None
0.5
3.0
3.5
4.0
2.5
4.0
3.5
6.0
94
80
42
90
95
35
89
88 : 12
94 : 6
100 : 0
40 : 60
70 : 30
80 : 20
94 : 6
—
42.72
4.4
1.53
15
9
4.2
1.12
—
No reaction
a All reactions were carried out with 2 mmol of substrate, 200 mg of catalyst in 10 cm3 of water, 0.66 cm3 (6 mmol) of aqueous hydrogen peroxide
(30% w/w). b TOF (turnover frequency) = mmol of product per mmol of catalyst per hour.
layered double hydroxides supported catalysts is cat 1 > cat 2 >
cat 4 > cat 3. The heterogeneous catalysts displayed superior
activity over their homogeneous counterparts. LDH-WO4
(cat 1) exhibited the highest (molar) turnover frequency of
21.7 hϪ1 over the other exchanged LDH catalysts. Besides
this, the exchanged LDH catalysts showed 2–5 fold activity
over the analogous homogeneous catalytic systems. This is a
Scheme 1
very significant result over Noyori’s recently reported pro-
The excess positive charge of the octahedral layers resulting
from this substitution is compensated by interstitial layers built
of anions such as carbonate, nitrate, chlorides, cyanide and
crystal water. The redox properties of LDH can be tunable or
imparted according to the requirements. This can be done in
different ways, one being the introduction of redox properties
by incorporating a redox divalent or trivalent transition metal
ion or both. The other option is the change in the ratios of
redox metal ions chosen for the preparation of a specific
catalyst. Yet another manner by which the redox properties
of the LDH can be tuned or introduced is by incorporating
transition metal oxides as anions to neutralise the positive
charge developed as a result of the isomorphous substitution of
Mg in the brucite main frame as discussed above. These LDHs
are thus represented by the general formula [M()(1Ϫx)
cedure,27 an analogous reaction conducted with Na2WO4
wherein the additives and moderate temperatures are required
to accomplish the reaction in excellent yields. Thus LDH-WO4
(cat 1) is proved to be the best catalyst among the various
exchanged LDH catalysts and their homogeneous analogues,
for the oxidation of sulfides. No reaction occurred without
catalyst, in the oxidation of thioanisole (Table 1, entry 8).
The enrichment of sulfides on the surface of water compatible
ionic LDH and the ready formation of peroxide with the
tungstate of LDH are likely to contribute to the enhancement
of reactivity in the oxidation of sulfides using LDH-WO4
catalyst.
In an effort to understand the scope of the reaction, a
series of sulfides having different kinds of R groups attached to
the sulfur atom were subjected to the oxidation using the LDH-
WO4–H2O2 system and the results are presented in Table 2.
Aromatic sulfides, which are selectively oxidised to sulfoxides at
lower conversions and lower time intervals, are converted to
sulfones on prolonged reaction times (Table 2, entries 1–8).
On the other hand aliphatic sulfides are oxidised at faster rate
than the aromatic sulfides (Table 2, entries 10–12). Further, the
oxidations of aliphatic sulfides do not proceed to form sulfones
selectively even on prolonged reaction times. It is known that
organic sulfides are oxidised by hydrogen peroxide in a hetero-
lytic process involving the nucleophilic attack of the sulfur
atom on the oxygen according to Scheme 2.28f The rate of the
M()x(OH)2]xϩ[(AyϪ
)
ؒnH2O]xϪ where M() is a divalent
x/y
cation such as Mg, Cu, Ni, Co, Mn, Fe, Zn; M() is a trivalent
cation such as Al, Fe, Cr, V, Ru, Rh, Ga, In; AnϪ is the interlayer
2Ϫ
anion such as OHϪ, ClϪ, CO32Ϫ, NO3Ϫ, SO4 and the value
of x is in the range of 0.1 to 0.33. The small hexagonal LDH
crystals with Mg1ϪxAlx(OH)2(Cl)xؒzH2O composition were
synthesized following existing procedures (here, x = 0.25).34
The anionic species tungstate, molybdate, vanadate and
{PO4WO(O2)]4}Ϫ2 were exchanged on to LDH-Cl to give a
series of LDH oxidant catalysts, LDH-WO4 (cat 1),32e LDH-
MoO4 (cat 2) LDH-VO3 (cat 3) and LDH-{PO4WO(O2)]4}
(cat 4) respectively.
All these catalysts are well characterised by XRD, TGA–
DTA and chemical analysis. The X-ray powder diffraction
patterns of the LDH and LDH-WO4 (cat 1), LDH-MoO4
(cat 2), LDH-VO3 (cat 3), LDH-{PO4WO(O2)]4} (cat 4) hardly
differ in the range of 2θ = 3–65Њ. These data clearly indicate that
the above anions are not intercalated but present at the edge-on
positions of the LDH in the solid catalyst. Chemical analysis of
the catalysts shows that the tungstate content (%) in cat 1 = 11
and cat 4 = 21, molybdate content in cat 2 = 9.9, and vanadate
content in cat 3 = 7.8. The thermogravimetric profiles and the
relative derivative curves (TGA and DTA) for the tungstate,
molybdate and vanadate exchanged LDH catalysts cat 1, cat 2,
cat 3 and cat 4 show two stages of weight loss associated with
two endotherms, which represents the characteristic pattern of
the LDH structure. These results indicate that there was no
structural disorder after the ion exchange.
Scheme 2
oxidation of thioethers increases with the increased nucleo-
philicity on the sulfur atom. The dialkyl sulfides are thus indeed
more easily oxidised than the diaryl sulfides using the LDH-
WO4–H2O2 catalytic system. Similarly, due to the decreased
nucleophilicity prompted by conjugation, the allylic and vinylic
sulfides (Table 2, entries 6, 8) are less reactive than the dialkyl
sulfide. It is significant to note that the allylic and vinylic
sulfides form corresponding sulfoxides without the breaking of
carbon–carbon bonds.
The studies on the conversion/selectivity as a function of
time in the oxidation of sulfides was carried out with three of
the substrates (Table 2, entries 2, 6 and 7). The studies show
higher selectivities towards sulfoxides at lower conversions.
With increasing time, the conversion increases while the
The exchanged LDH catalysts (cat 1–4) and their homo-
geneous analogues were evaluated for the oxidation of thio-
anisole in order to identify the best catalytic system using H2O2
in aqueous medium (Table 1). The order of the activity of
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Table 2 The oxidation of sulfides by tungstate-exchanged Mg-Al-LDH catalysta
Entry
1
Sulfide1–12
Time/h
0.5
Conversion (%)
Sulfoxide1a–12a
Sulfone–10b
94
88
85
12
15
90b
2
3.0
7.0
12.0
87
95
99
88
60
1
12
40
99
3
4
3.0
3.0
99
90
10
91
95
5
5
3.0
91
95
5
6
7
8
9
3.0
7.0
12.0
81
94
98
70
45
1
30
55
99
3.0
7.0
12.0
78
96
99
83
43
1
17
57
99
3.0
99
71
29
2.0
99
90
10
10
11
12
1.5
1.5
1.5
99
99
98
80
100
100
20
—
—
a Reaction conditions are as exemplified in Table 1, in footnote a. b Conversion after 6th cycle.
Scheme 3
selectivity is reduced. The maximum selectivity of 100% is
achieved at 54–62% of conversion. It is always better to
terminate the reaction at these conversions in order to obtain
sulfoxides of high purity.
III with hydrogen peroxide II.32e A shift of λmax from 250 nm
(LDH III) to 325 nm (IV) in UV–diffusion reflectance spectra
confirms the formation of peroxotungstate species. Our system
and hydrogen peroxide directed oxidation of sulfides show simi-
lar trends in reactivity i.e. aliphatic sulfides are oxidised at faster
rate than aromatic sulfides due to the higher nucleophilicity
of aliphatic sulfides. In the present reaction the facilitation of
the transfer of electrophilic oxygen from the peroxotungstate
species, IV, to sulfide V forming sulfoxide VI, is commensurate
with the nucleophilicity of the sulfides, i.e., the rate of the reac-
tion is increased as the nucleophilicity increases. Further, the
electrophilicity of the peroxotungstate is much higher than that
of H2O2. Therefore the electrophilic attack of oxygen in the
bridged tungsten oxide is faster, which is in agreement with
earlier results.35 In case of sulfone formation, the sulfoxide VI
further reacts with the another mole of active peroxotungstate,
IV to form sulfone VII and the eventual regeneration of the
catalyst III.
The solvent effect was also studied in the oxidation of thio-
anisole using LDH-WO4 catalyst; the activity is in the following
order: H2O ≅ CH3OH > CHCl3 > CH3CN > CH2Cl2. Thus
water gave the best results among the solvents examined in the
oxidation of sulfides. Furthermore the reusability was checked
for several cycles with the best catalyst, cat 1, which showed
consistent activity and selectivity for six cycles as detailed in
Table 2, entry 1. During the oxidation with WO42Ϫ 0.3% of the
total amount of tungsten was found in solution and the use of
recycled catalysts resulted in unaltered activity, supporting the
oxidative stability of the catalyst.
The plausible catalytic cycle in the oxidation of sulfides to
sulfoxides or sulfones as described in Scheme 3 involves the easy
formation of peroxotungstate, IV, on interaction of LDH-WO4
J. Chem. Soc., Perkin Trans. 1, 2002, 2069–2074
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LDH (1 g) was added and stirred at 293 K for 24 h. The solid
catalyst was filtered, washed with deionised and decarbonated
water and lyophilized to dryness.
Conclusions
In conclusion, the present study represents the first example
wherein the heterogenised tungstate-exchanged Mg-Al-LDH is
used in catalytic amounts for the oxidation of sulfides to sulf-
oxides and/or sulfones. With the broader scope of utility as
applied for bulky sulfoxides and consistent activity over a
number of cycles, the present catalytic system is superior to
the other heterogeneous catalysts reported so far. The high
throughput of the product obtained using the LDH-WO4
catalyst lowers the inventories of the process to offer a potential
competitive economically viable process. The use of water as
solvent and H2O2 as an oxidant, which are greener ingredients,
conforms to the stringent environmental specifications.
Mg-Al-LDH-{PO4WO(O2)]4} (cat 4). The preparation of
{PO4[WO(O2)2]4} ((n-Bu)4N)3 was carried out according to
the literature procedure.36 To a solution of isolated {PO4[WO-
(O2)2]4} ((n-Bu)4N)3 (0.46 mmol) in acetone (3 cm3) was added
an aqueous solution of 30% (w/w) H2O2 (1 cm3) and Mg-Al-Cl
LDH (1 g) and the mixture was stirred for 16 h at room
temperature. The obtained material (cat 4) was treated
consecutively with water–acetone (1 : 1) and acetone.
Typical procedure for the oxidation of thioanisole
To the stirred solution of thioanisole (280 mg, 2 mmol)
and catalyst (200 mg, 0.088 mmol of WO4 content) in water
Experimental
2Ϫ
Proton nuclear magnetic resonance (1H NMR) spectra were
recorded on a Gemini Varian at 200 or 400 MHz, as solutions
in CDCl3 at 25 ЊC; δ were in ppm downfield from tetramethyl-
silane (TMS). Mass spectra were obtained at an ionization
potential of 70 eV, scanned on a VG 70–70H (micro mass); only
selected ions are reported here. Infrared spectra were recorded
on a Bio-RAD FT-IR spectrometer either as neat liquids or
KBr pellets. Thin layer chromatography was performed on
silica gel 60F254 plates procured from E. Merck. ACME silica
gel (60–120 mesh) was used for column chromatography.
Starting materials, metal salts were purchased from Aldrich,
Fluka, and Lancaster or prepared by known methods. Solvents
purchased from commercial sources were purified prior to use.
Thermogravimetric (TG) and differential thermogravimetric
(DT) analysis of thermal decomposition of catalyst was studied
by means of a TG-DTA Mettler Toledo Star system using open
aluminium crucibles with a sample weight of about 8–10 mg
and nitrogen as purge gas at a linear heating rate of 10 K minϪ1
for all measurements. X-Ray diffraction patterns were deter-
mined on a powder X-ray diffractometer Siemens, D-5000 (dif-
fraction geometry; θ–2θ, in the range of 5–65Њ) instrument,
using sealed Cu tube (2.2 kW). CHN analysis was performed on
a Vario EL analyser.
(10 cm3), was added an aqueous solution of 30% (w/w) hydro-
gen peroxide (0.66 cm3, 6 mmol) in 2 to 3 portions at room
temperature. After completion of the reaction (followed by
TLC), the catalyst was filtered off and washed with ethyl
acetate (2 × 10 cm3). To the filtrate a small amount of MnO2
was added to decompose the unreacted H2O2. The treated reac-
tion mixture was filtered to remove solid MnO2, and the
product is extracted with ethyl acetate, dried over anhydrous
Na2SO4 and evaporated in vacuo to afford the sulfoxide or
sulfone. Analytically pure compound was obtained after
column chromatography (silica gel, hexane–ethyl acetate)
The products were characterised by their 1H NMR, mass, IR
spectroscopy and elemental analysis and the data are presented
below.
Methylsulfinylbenzene 1a.37 Pale yellow liquid (Found: C,
59.84; H, 5.67; S, 22.63. C7H8SO requires C, 60.0; H, 5.71;
S, 22.85%); νmax(neat)/cmϪ1 1047; δH (200 MHz; CDCl3;
Me4Si) 2.78 (3H, s, Me), 7.44–7.66 (m, 5H, Ph); m/z (EI),
140 (Mϩ, 87%), 125 (100), 109 (71), 77 (69), 65 (19) 51 (70),
39 (15).
Methylsulfonylbenzene 1b. White solid, mp 85–86 ЊC (lit.,37
85–86 ЊC) (Found: C, 53.62; H, 5.01; S, 20.32. C7H8SO2 requires
C, 53.84; H, 5.12; S, 20.51%); νmax(KBr)/cmϪ1 1320, 1164;
δH (200 MHz; CDCl3; Me4Si) 3.0 (3H, s, Me), 7.44–7.64 (m, 3H,
Ph), 7.84–7.95 (2H, d, Ph–H, J = 8.1 Hz); m/z (EI), 156 (Mϩ,
22%), 142 (27), 77 (100), 65 (8), 51 (37).
Preparation of catalysts
Mg-Al-LDH chloride.34 Mg-Al-Cl LDH (3 : 1) was prepared
as follows: a mixture of solutions of AlCl3ؒ9H2O (12.07 g,
0.25 mol lϪ1) and MgCl2ؒ6H2O (30.49 g, 0.75 mol lϪ1) in
deionised and decarbonated water (200 cm3) and an aqueous
solution of sodium hydroxide (16 g, 2 mol lϪ1) in deionised and
decarbonated water (200 cm3) were added simultaneously
dropwise from the respective burettes into the round bottomed
flask. The pH of the reaction mixture was maintained con-
stant (10.00–10.2) by the continuous addition of NaOH solu-
tion. The suspension thus obtained was stirred for two hours
under nitrogen atmosphere. The solid product was isolated by
filtration, washed thoroughly with deionised and decarbonated
water, and dried at 70 ЊC for 15 h.
1-Benzylsulfinyl-4-methylbenzene 2a. White solid, mp 122–
124 ЊC (Found: C, 73.25; H, 6.12; S, 13.81. C14H14SO
requires C, 73.04; H, 6.08; S, 13.91%); νmax(KBr)/cmϪ1 1038;
δH (200 MHz; CDCl3; Me4Si) 2.4 (3H, s, Me), 3.9 (1H, d, CH2,
J = 12.7 Hz), 4.05 (1H, d, CH2, J = 12.7 Hz), 6.9 (m, 2H, Ph–H)
7.18 (m, 7H, Ph–H); m/z (EI), 230 (Mϩ, 5%), 91 (100), 65 (81),
51 (12).
1-Benzylsulfonyl-4-methylbenzene 2b. White solid, mp 142–
144 ЊC (Found: C, 68.32; H, 5.68; S, 13. 28. C14H14SO2 requires
C, 68.29; H, 5.69; S, 13.00%); νmax(KBr)/cmϪ1 1309, 1151;
δH (200 MHz; CDCl3; Me4Si) 2.42 (3H, s, Me), 4.22 (2H, s,
CH2), 7.06 (m, 2H, Ph–H), 7.22 (m, 3H, Ph–H), 7.4 (m, 2H,
Ph–H), 7.62 (m, 2H, Ph–H); m/z (EI), 246 (Mϩ, 6%) 230 (4), 91
(100), 65 (82) 51 (15), 39 (45).
Mg-Al-LDH tungstate (cat 1).32e To a solution of sodium
tungstate (0.616 g, 1.87 mM) in water (100 cm3), Mg-Al-Cl
LDH (1 g) was added and stirred at 293 K for 24 h. The solid
catalyst was filtered, washed with deionised and decarbonated
water and lyophilized to dryness.
1-Benzylsulfinyl-4-chlorobenzene 3a. White solid, mp 120–122
ЊC (Found: C, 62.24; H, 4.47; S, 12.72; Cl, 14.13. C13H11SOCl
requires C, 62.40; H, 4.40; S, 12.80; Cl, 14.20%); νmax (KBr)/
cmϪ1 1040; δH (200 MHz; CDCl3; Me4Si) 3.98 (1H, d, CH2,
J = 12.7 Hz), 4.04 (1H, d, CH2 J = 12.7 Hz), 6.95 (2H, d, Ph–H,
J = 6.8 Hz), 7.3 (5H, m, Ph–H), 7.38 (2H, d, Ph–H, J = 6.8 Hz);
m/z (EI), 252 (Mϩ, (37Cl) 2%), 250 (Mϩ, (35Cl) 6), 234 (66), 143
(10), 108 (11), 91 (100), 65 (62), 51 (7).
Mg-Al-LDH molybdate (cat 2). To a solution of sodium
molybdate (0.452 g, 1.87 mM) in water (100 cm3), Mg-Al-Cl
LDH (1 g) was added and stirred at 293 K for 24 h. The solid
catalyst was filtered, washed with deionised and decarbonated
water and lyophilized to dryness.
Mg-Al-LDH vanadate (cat 3). To a solution of sodium
vanadate (0.228 g, 1.87 mM) in water (100 cm3), Mg-Al-Cl
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1-Benzylsulfonyl-4-chlorobenzene 3b. White solid, mp 142–
145 ЊC (Found: C, 58.88; H, 4.17; S, 11.97; Cl, 13.38.
C13H11SO2Cl requires C, 58.64; H, 4.13; S, 12.03; Cl, 13.34%);
νmax(KBr) /cmϪ1 1310, 1150; δH (400 MHz; CDCl3; Me4Si) 4.24
(2H, s, CH2), 7.01 (2H, d, Ph–H, J = 6.8 Hz), 7.32 (3H, m,
Ph–H), 7.42 (2H, d, Ph–H, J = 6.8 Hz), 7.58 (2H, d, Ph–H,
J = 6.8 Hz); m/z (EI), 268 (Mϩ, (37Cl) 4%), 266 (Mϩ, (35Cl) 12),
250 (8), 91 (100), 65 (42), 51 (11).
7.5 (3H, m, Ph–H), 7.9 (2H, m, Ph–H); m/z (EI), 170(Mϩ, 30%),
154 (35), 126 (50), 109 (65), 77 (100), 51 (60).
1-Vinylsulfinylbenzene 8a.38 Pale yellow liquid (Found: C,
62.28; H, 5.22; S, 21.13. C8H8SO requires C, 63.15; H, 5.26; S,
21.05%); νmax(neat) /cmϪ1 1053; δH (200 MHz; CDCl3; Me4Si)
5.89 (1H, d, CH, J = 10.2 Hz), 6.2 (1H, d, CH, J = 15.3 Hz),
6.5–6.8 (1H, m, CH), 7.5–7.8 (m, 5H, Ph–H); m/z (EI), 152
(Mϩ, 3%), 135 (26), 125 (70), 109 (30), 91 (37), 77 (100), 51 (60),
40 (28).
Methyl 2-methylsulfinylbenzoate 4a. Pale yellow liquid
(Found: C, 54.36; H, 5.36; S, 16.25. C9H10SO3 requires C, 54.54;
H, 5.05; S, 16.16%); νmax(KBr) /cmϪ1 1067; δH (200 MHz;
CDCl3; Me4Si) 2.85 (3H, s, SOMe), 3.95 (s, 3H, OMe), 7.58
(1H, t, Ph–H, J = 7.2 Hz), 7.85 (1H, t, Ph–H, J = 7.2 Hz), 8.05
(1H, d, Ph–H, J = 6.8 Hz), 8.32 (1H, d, Ph–H, J = 7.2 Hz); m/z
(EI), 198 (Mϩ, 30%), 183 (100), 167 (10), 152 (45), 77 (12).
(tert-Butylsulfinylmethyl)benzene 9a. Pale yellow solid, mp
72–73 ЊC (lit.,39 72–73 ЊC) (Found: C, 66.49; H, 8.20; S, 16.49.
C11H16SO requires C, 67.34; H, 8.16; S, 16.32%); νmax(KBr)/
cmϪ1 1032; δH (200 MHz; CDCl3; Me4Si) 1.3 (9H, s, t-Butyl), 3.7
(1H, d, CH2, J = 12.7 Hz), 3.85 (1H, d, CH2, J = 12.7 Hz), 7.35
(5H, m, Ph–H); m/z (EI), 196 (Mϩ, 8%), 140 (39), 91 (100),
65 (8).
Methyl 2-methylsulfonylbenzoate 4b. Pale yellow viscous
liquid (Found C, 50.62; H, 4.68; S, 14.98. C9H10SO4 requires C,
50.46; H, 4.67; S, 14.96%); νmax(neat)/cmϪ1 1311, 1153; δH (400
MHz; CDCl3; Me4Si) 3.3 (3H, s, SO2Me), 3.98 (3H, s, OMe),
7.62 (3H, m, Ph–H), 8.1 (1H, d, Ph–H, J = 6.4 Hz); m/z (EI),
214 (Mϩ, 6%), 199 (10), 183 (100), 135 (8), 77 (36).
(tert-Butylsulfonylmethyl)benzene 9b. Pale yellow solid, mp
117–120 ЊC (Found: C, 62.42; H, 7.56; S, 15.29. C11H16SO2
requires C, 62.26; H, 7.54; S, 15.09%); νmax(neat)/cmϪ1 1284,
1153; δH (200 MHz; CDCl3; Me4Si) 1.4 (s, 9H, t-Butyl), 4.15
(2H, s, CH2), 7.4 (m, 5H, Ph–H); m/z (EI), 212 (Mϩ, 3%),
141 (2.5), 91 (32), 57 (100).
Ethyl 2-phenylsulfinylacetate 5a. Pale yellow liquid (Found:
C, 56.58; H, 5.54; S, 15.22. C10H12SO3 requires C, 56.60;
H, 5.66; S, 15.09%); νmax(neat)/cmϪ1 1043; δH (200 MHz;
CDCl3; Me4Si) 1.3 (3H, t, Me, J = 7.5 Hz), 3.62 (1H, d, SCH2,
J = 12.5 Hz), 3.85 (1H, d, SCH2, J = 12.5 Hz), 4.15 (2H, q,
OCH2, J = 7.5 Hz), 7.55 (m, 3H, Ph–H), 7.7 (m, 2H, Ph–H);
m/z (EI), 212 (Mϩ, 12%), 196 (7), 140 (8), 125 (100), 110 (25),
77 (86), 65 (14), 51 (47).
1-Methylsulfinyldodecane 10a. White solid, mp 63–65 ЊC
(Found: C, 66.49; H, 12.26; S, 13.68. C13H28SO requires C,
67.24; H, 12.06; S, 13.79%); νmax(KBr)/cmϪ1 1082; δH (200 MHz;
CDCl3; Me4Si) 0.9 (3H, t, Me, J = 6.6 Hz), 1.2–1.6 (18H, m,
CH2), 1.7–1.95 (2H, m, CH2), 2.56 (3H, s, SMe), 2.6–2.8
(m, 2H, CH2); m/z (EI), 232 (Mϩ, 2), 216 (20), 201(11), 57 (75),
43 (100) 41 (89).
Ethyl 2-phenylsulfonylacetate 5b. Pale yellow liquid (Found
C, 52.48; H, 5.48; S, 14.23. C10H12SO4 requires C, 52.63; H,
5.26; S, 14.03%); νmax(neat)/cmϪ1 1318, 1145; δH (200 MHz;
CDCl3; Me4Si) 1.25 (3H, t, Me, J = 6.4 Hz), 4.08 (2H, s, SCH2),
4.18 (q, 2H, OCH2, J = 6.4 Hz), 7.6 (2H, t, Ph–H, J = 7.2 Hz),
7.7 (1H, t, Ph–H, J = 7.2 Hz), 7.95 (2H, d, Ph–H, J = 7.2 Hz);
m/z (EI), 228 (Mϩ, 2%), 150 (16), 141 (38), 125 (15), 77 (100),
51 (35).
1-Methylsulfonyldodecane 10b. White solid, mp 80–83 ЊC
(Found: C, 62.79; H, 11.42; S, 13.02. C13H28SO2 requires C,
62.90; H, 11.29; S, 12.90%); νmax(KBr) /cmϪ1 1281, 1118; δH (200
MHz; CDCl3; Me4Si) 0.98 (3H, t, CH3, J = 7.0 Hz), 1.28 (18H
m, CH2), 1.82 (2H, m, CH2), 2.82 (3H, s, Me), 2.86 (2H, t, CH2,
J = 7.0 Hz); m/z (EI), 248 (Mϩ, 8%), 108 (46), 81(100), 69(25),
57(35).
1-Allylsulfinylbenzene 6a.28h Pale yellow liquid (Found: C,
65.28; H, 6.12; S, 19.32. C9H10SO requires C, 65.06; H, 6.02; S,
19.27%); νmax(neat)/cmϪ1 1044; δH (200 MHz; CDCl3; Me4Si)
3.55 (2H, m, CH2), 5.1 (1H, d, CH, J = 15 Hz), 5.32 (1H, d, CH,
J = 11 Hz), 5.65 (1H, m, CH), 7.55 (5H, m, Ph–H); m/z (EI), 166
(Mϩ, 12%), 141 (10), 125 (56), 117 (30), 109 (8), 97 (25), 65 (10),
51 (53), 41 (100).
1-Ethylsulfinyldodecane 11a. White solid, mp 68–70 ЊC
(Found: C, 68.44; H, 12.05; S, 13.26. C14H30SO requires C,
68.29; H, 12.19; S, 13.00%); νmax(KBr)/cmϪ1 1046; δH (200 MHz;
CDCl3; Me4Si) 0.9 (3H, t, CH3, J = 6.3 Hz), 1.2–1.5 (m, alkyl,
21H), 1.7–1.9 (2H, m, CH2), 2.55–2.75 (2H, m, CH2), 2.95–
3.0 (2H, m, CH2); m/z (EI), 246 (Mϩ, 2%), 229 (100), 95 (25),
71 (50).
1-Allylsulfonylbenzene 6b. Pale yellow liquid (Found: C,
59.46; H, 5.68; S, 17.62. C9H10SO2 requires C, 59.34; H, 5.49;
S, 17.58%); νmax(neat)/cmϪ1 1319, 1147; δH (200 MHz;
CDCl3; Me4Si) 3.8 (d, 2H, CH2, J = 6.6 Hz), 5.18 (1H, d, CH,
J = 16.6 Hz), 5.38 (1H, d, CH, J = 11 Hz), 5.8 (1H, m,
CH), 7.43–65 (m, 5H, Ph–H); m/z (EI), 182 (Mϩ, 8%), 166 (4),
141 (30), 125 (100), 117 (28), 97 (45), 65 (10), 51 (48), 41 (80).
Methylsulfinylcyclohexane 12a. Pale yellow liquid (Found: C,
57.66; H, 9.69; S, 21.85. C7H14SO requires C, 57.53; H, 9.58; S,
21.91%); νmax(neat) /cmϪ1 1036; δH (200 MHz; CDCl3; Me4Si)
1.2–1.5 (6H, m, CH2), 1.7–2.2 (4H, m, CH), 2.5 (3H, s, CH), 2.8
(1H, m, CH); m/z (EI), 146 (Mϩ, 4%), 83 (95), 55 (100), 41(39).
Acknowledgements
B. B. and Ch. V. R. thank the Council of Scientific and Indus-
trial Research (CSIR), India, for providing a research grant.
1-Ethylsulfinylbenzene 7a. Pale yellow liquid (Found: C,
62.49; H, 6.52; S, 21.03. C8H10SO requires C, 62.33; H, 6.49; S,
20.77%); νmax(neat)/cmϪ1 1062; δH (200 MHz; CDCl3; Me4Si) 1.2
(3H, t, Me, J = 6.6 Hz), 2.7–2.75 (1H, q, CH2, J = 6.6 Hz), 2.9
(1H, q, CH2, J = 6.6 Hz), 7.1–7.45 (m, 3H, Ph–H), 7.45–7.8
(m, 2H, Ph–H); m/z (EI), 154 (Mϩ, 34%), 138 (14), 126 (62),
109 (86), 77 (100), 51 (94).
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J. Chem. Soc., Perkin Trans. 1, 2002, 2069–2074
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