Selective oxidation of sulfides to sulfoxides using novel nano Br?nsted dicationic ionic liquid as effective reagent under grinding conditions

Article abstract of DOI:10.1016/j.molliq.2018.06.036

In this work, 1,1′-(butane-1,4-diyl)bis(1,4-diazabicyclo[2.2.2]octane-1,4-diium) bis(hydrogen sulfate) dinitrate ([C₄(DABCO-H)₂]·[HSO₄]₂[NO₃]₂) as a novel Br?nsted dicationic ionic liquid w

Full text of DOI:10.1016/j.molliq.2018.06.036

Accepted Manuscript
Selective oxidation of sulfides to sulfoxides using novel nano
Brönsted dicationic ionic liquid as effective reagent under
grinding conditions
Yadollah Bayat, Farhad Shirini, Omid Goli-Jolodar
PII:
DOI:
Reference:
S0167-7322(18)31246-7
doi:10.1016/j.molliq.2018.06.036
MOLLIQ 9234
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
10 March 2018
26 May 2018
10 June 2018
Please cite this article as: Yadollah Bayat, Farhad Shirini, Omid Goli-Jolodar , Selective
oxidation of sulfides to sulfoxides using novel nano Brönsted dicationic ionic liquid
as effective reagent under grinding conditions. Molliq (2017), doi:10.1016/
j.molliq.2018.06.036
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ACCEPTED MANUSCRIPT
Selective oxidation of sulfides to sulfoxides using novel nano
Brönsted dicationic ionic liquid as effective reagent under grinding
conditions
Yadollah Bayat*a, Farhad Shirini*b, Omid Goli-Jolodarb
a Department of Chemistry, Malek Ashtar University of Technology, Tehran, Iran, e-mail:
y_bayat@mut.ac.ir
b Department of Chemistry, University of Guilan, Rasht, Iran, e-mail: shirini@guilan.ac.ir
Abstract:
In this work, 1,1'-(butane-1,4-diyl)bis(1,4-diazabicyclo[2.2.2]octane-1,4-diium) bis(hydrogen
sulfate) dinitrate ([C4(DABCO-H)2].[HSO4]2[NO3]2) as a novel Brönsted dicationic ionic liquid
1
was prepared with available starting materials, and characterized by FT-IR, H-NMR, 13C-NMR,
TGA, DSC, SEM and FESEM techniques. This nano-sized regent was efficiently employed in
selective oxidation of sulfides to sulfoxides at room temperature, under grinding and solvent-free
condition. A simple method, short reaction times, high yields, green and easy work-up of the
products, use of commercial cheap starting materials and excellent selectivity are attractive
features of the present method.
1. Introduction
In the last decade, a growing interest has been observed in the synthesis and application of
dicationic ionic liquids (DILs) instead of traditional ionic liquids due to high thermal stability,
biological activity and excellent selectivity. Actually high molecular weights, viscosities, charge,
and greater intermolecular interactions of DILs cause to make them suitable in electrolytes [1], gas
chromatography [2] and catalyst in various reactions [3-6]. Furthermore, DILs have been used as

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green solvents in high temperature reactions, lubricants with high temperature resistance and
thermal storage in liquid media [7].
Sulfoxides are one of the most important classes of natural products, bioactive compounds,
medicinal compounds, and other functional molecules [8]. These compounds have an anti-ulcer
[9], antibacterial [10], antifungal [11], anti-HIV1 [12] and antiviral [13] activity. Furthermore,
sulfoxides were used in Swern oxidation, Diels–Alder reaction, and C–C bond-formation reactions
[14].
Oxidation of sulfides is one of the prevalent methods for preparation of sulfoxides. Various
reagents and oxidizing media are employed for conversion of sulfides to sulfoxides [15-26]. In
spite of the effectiveness of some of these methods, most of them suffer from disadvantages such
as use of the expensive reagents, metallic or non-environmentally catalyst, hard workup, poor
regioselectivity, long reaction times, low yields and over oxidation. Therefore, the new research
and continues effort is needed to overcome of these difficulties.
2. Experimental
2.1. Material
The chemicals materials and solvents were purchased from Fluka, Merck and Aldrich chemical
companies. All the products were characterized by their physical constants such as melting point
and comparison with genuine samples and FT-IR spectroscopy. Also the purity of the substrate
and determination of reaction progress were accomplished by TLC on silica-gel polygram
SILG/UV 254 plates.
2.2. Instrumentation
The FT-IR spectra were run on a VERTEX 70 Brucker company. Thermogravimetric analyses
(TGA) and differential scanning calorimetry (DSC) were performed on SDT Q600 specifications

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under N2 atmosphere ramp 20 °C/min. Scanning election microphotographs (SEM) were obtained
on a SEM-Philips XL30 and FESEM were performed on MIRA III/TESCAN (Czech Republic(.
1
The H-NMR (400 MHz) and 13C-NMR (100 MHz) were run on a Bruker AVANCEIII-400
spectrometer in DMSO by TMS as an internal reference (δ in ppm).
2.3. Catalyst preparation
[C4(DABCO)2]Cl2 was prepared according to the reported method in the literature [27]. At the
next step, sulfuric acid (0.53 mL, 10 mmol, 98%) was added drop-wise to a solution of
C4(DABCO)2.2Cl (1.4 g, 5 mmol) in dry CH2Cl2 (25 mL) within 30 min in an ice bath. After
completion of the addition, the reaction mixture was stirred for 6 h at room temperature. The
residue was washed with Et2O (3 x 5 mL) and dried under vacuum. Then, nitric acid 100% (0.63
g, 10 mmol) was added drop-wise to the solution of [C4(DABCO-H)2].[HSO4]2[Cl]2 (2.73 g,
5mmol) in dry CH2Cl2 (25 mL) within 30 min in an ice bath (0 ℃). In continue, the mixture was
warmed to room temperature and refluxed for 2 h. The solid product was washed with Et2O (3×5
mL) and dried under vacuum to give a 1,1'-(butane-1,4-diyl)bis(1,4-diazabicyclo[2.2.2]octane-1,4-
diium) bis(hydrogen sulfate) dinitrate ([C4(DABCO-H)2].[HSO4]2[Cl]2) as a yellowish solid (mp
58-60 ℃) (Scheme 1).
2.4. Catalyst characterization
2. 4. 1. FT-IR analysis
The FT-IR spectra of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCO-H)2].[HSO4]2[NO3]2
(c) are shown in Fig. 1. DABCO has different stretching and bending vibrations modes, so various
absorption bands are appeared in its spectrum. However, in the case of [C4(DABCO)2].Cl2 these
bands are reduced or eliminated due to the limitation of vibrations mode. After the treatment with
sulfuric acid and anion exchange, the broad band at 2650-3600 cm-1 was appeared which can be

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related to the OH stretching of the sulfonic group, and the peaks at 1642 and 1289 cm-1 are
attributed to vibrational modes of NO2 bonds (Fig. 1c). Furthermore, the bands at 1176, 1070,
1007, 857 and 579 cm-1 are assigned to the asymmetric and symmetric stretching bands of S=O
and S–O, respectively.
2. 4. 2. 1H-NMR and 13C-NMR analysis
The 1H-NMR of [C4(DABCO)2].Cl2 (b) and [C4(DABCO-H)2].[HSO4]2[NO3]2 are shown in Figs.
2 and 3, respectively. In the case of [C4(DABCO-H)2].[HSO4]2[NO3]2 cyclic hydrogens were
shifted to the higher ppm. Moreover, the acidic hydrogens are appeared at 5.54 ppm. Furthermore,
13
the C-NMR spectra of [C4(DABCO-H)2].[HSO4]2[NO3]2 showed four aliphatic carbons which
provided additional evidence to confirm its structure (Fig. 4).
2. 4. 3. TGA and DSC analysis
The thermal stability of [C4(DABCO-H)2].[HSO4]2[NO3]2 was measured by TGA analysis (Fig.
5, green chart). The weight loss of the catalyst was occurred in 3 steps. The first step that started
below 100 ℃, is related to lose of the absorbed water or moisture. The second step, at 200-255 °C,
can associated to the decomposition of sulfonic and nitrate groups. The final step which stated at
255-330 °C (T max= 297 °C) attributed to the decomposition of carbonic part.
The nitrogen rich compounds can be explosive. In order to show the safety of this reagent,
the sample of [C4(DABCO-H)2].[HSO4]2[NO3]2 was subjected to DSC analysis. As can be seen in
Fig. 5 (blue chart), the decomposition of the catalyst was endothermic before 300 °C, while further
two steps , 310-415 °C and 415-600 °C, were exothermic. The obtained results from this analysis
show that the total released energy of [C4(DABCO-H)2].[HSO4]2[NO3]2 is low (48.32 J/g), which
confirm the safety of this reagent.
2. 4. 4. SEM and FESEM analysis

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The surface morphology of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCO-
H)2].[HSO4]2[NO3]2 (c) was studied by SEM (Fig. 6). As shown in the figure, DABCO has
penicillate structure, which converted to bulky shaped in [C4(DABCO)2].Cl2. However in the case
of [C4(DABCO-H)2].[HSO4]2[NO3]2, the particles size reduced to the nano scale which can be
attributed to high charge and great intermolecular interactions. The FESEM of [C4(DABCO-
H)2].[HSO4]2[NO3]2 (d) show that the molecular size of the catalyst is 80-100 nm.
2. 5. General procedure for the oxidation of sulfides:
A mixture of an sulfide (1 mmol), [C4(DABCO-H)2].[HSO4]2[NO3]2 (0.5 mmol) and KBr (0.05
mmol) was vigorously grind using a mortar and pestle at room temperature. After completion of
the reaction (monitored by TLC), 5 mL water was added to the mortar and the mixture was filtered
to separate the nitrated product. The products were purified with short column chromatography.
3. Result and discussion
In continuation of our research programs on the design, preparation and use of new catalysts for
organic transformation [28-34], herein we wish to introduce the applicability of [C4(DABCO-
H)2].[HSO4]2[NO3]2 for selective oxidation of sulfides to sulfoxides under mild conditions.
At the first step and for the determination of the optimum reaction conditions, oxidation of
methyl phenyl sulfide was carried out under various reaction conditions in the presence of a
catalytic amount of KBr and [C4(DABCO-H)2].[HSO4]2[NO3]2 as oxidation reagent (Table 1). On
the basis of the obtained results, a grinding method using 0.5 mmol of [C4(DABCO-
H)2].[HSO4]2[NO3]2 and 0.05 mmol of KBr at room temperature was selected for the promotion
of the reactions. Furthermore in other to show the catalytic role of KBr, oxidation of methyl phenyl
sulfide was subjected in the presence of [C4(DABCO-H)2].[HSO4]2[NO3]2 without any KBr. As it

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shows in Table 1, entry 10, the reaction did not complete after 30 min and an impurity of sulfone
was observed.
The scope and generality of this procedure was established with oxidation of various
sulfides such as alkyl aryl, dialkyl, diaryl and cyclic sulfide, and also aryl disulfides (Table 2). The
obtained results showed that all of substrates were converted to the corresponding sulfoxide
products in good to excellent yields. Alkyl aryl sulfides bearing 4-bromo and 4-nitro groups on the
aryl ring showed good reactivity, providing the corresponding products in 93−94 % yields (Table
2, entries 2 and 3). Furthermore, aryl sulfide bearing donating groups on the aryl ring such as
methyl p-tolyl sulfide gave good results under the presented conditions (Table 2, entry 4). A series
of diaryl sulfides such as diphenylsulfane, dibenzothiophene and benzyl(phenyl)sulfane (Table 2,
entries 5-7), and dibenzylsulfan (Table 2, entry 9) were also provided the corresponding products
in almost quantitative yields. Notably, dimethylsulfane and dibutylsulfane as an aliphatic sulfides
and also tetrahydrothiophene as a cyclic sulfide were a suitable substrate in this reaction, delivering
the desired products in excellent yields (Table 2, entries 10-12).
It should be noted that in the presence of various functional groups such as OH, C=C,
COOCH3 (Table 2, entries 13-15), the sulfides were only oxidized, which proved the
chemoselectively of the present method.
In order to show the merit of the present work, the obtained results of oxidation of methyl
phenyl sulfide (Table 2, entry 1) in the presence of [C4(DABCO-H)2].[HSO4]2[NO3]2 were
compared with some of the reported results in the literature (Table 3). As can be seen, the present
method avoids some of the difficulties associated with other methods such as long reaction times,
use of toxic solvents, harsh reaction conditions, hard conditions for the catalyst preparation and
great catalyst loading.

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In a possible mechanism, the [C4(DABCO-H)2].[HSO4]2[NO3]2 as oxidation agent
+
generated NO2 which is able to convert bromide ion (Br-) to bromonium (Br+). Afterward, the
bromonium ion and sulfide react with together in the presence of H2O to afford the corresponding
sulfoxide (Scheme 2). The mechanism is confirmed by the literature [15, 16, 20, 21].
4. Conclusions
The [C4(DABCO-H)2].[HSO4]2[NO3]2, as a novel and nano oxidation agent, were prepared simply
from available starting materials. This nano reagent acted efficiently with highly performance in
the oxidation of various sulfides such as alkyl aryl sulfide, dialkyl sulfide, diaryl sulfide, cyclic
sulfide, and aryl disulfides under green condition. Employment of grinding condition, room
temperature, non-solvent, short reaction times, high yields and good selectivity are advantages of
the presented method which make it a useful and beneficial methodology.

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Scheme and Figure Captions
Scheme. 1. Preparation of [C4(DABCO-H)2].[HSO4]2[NO3]2.
Fig. 1. The FT-IR spectra of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCO-
H)2].[HSO4]2[NO3]2 (c).
Fig. 2. The 1H-NMR of [C4(DABCO)2].Cl2.
Fig. 3. The 1H-NMR of [C4(DABCO-H)2].[HSO4]2[NO3]2.
Fig. 4. The 13C-NMR of [C4(DABCO-H)2].[HSO4]2[NO3]2
Fig. 5. The TGA (green) and DSC (blue) diagrams of [C4(DABCO-H)2].[HSO4]2[NO3]2.
Fig. 6. The surface image of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCO-
H)2].[HSO4]2[NO3]2 (c), (d).
Scheme 2. The proposed mechanism for the oxidation of sulfide to sulfoxide using [C4(DABCO-
H)2].[HSO4]2[NO3]2.

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Table. 1. Oxidation of methyl phenyl sulfide under various conditions:
Equivalents of
reagent
Temperature Time Conversion
run
KBr
Solvent
(ᵒC)
(min)
120
120
30
(%)
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.025
0.1
1
2
0.5
0.5
0.5
0.5
0.5
0.25
1
n-hexane
CH3CN
r.t.
50
r.t.
60
3
CH2Cl2
r.t.
100
100
100
50
4
Grinding
Grinding
Grinding
Grinding
Grinding
Grinding
Grinding
r.t.
10
5
40-50
r.t.
8
6
25
7
r.t.
10
100
50
8
0.5
0.5
0.5
r.t.
30
9
r.t.
10
100
0
0
10
r.t.
30

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Table 2. Oxidation of various sulfides to sulfoxides in the presence of [C4(DABCO-
H)2].[HSO4]2[NO3]2 as oxidation agent
m.p. (ᵒC)
Time Yield
(min) (%)a
Entry
1
Substrate
Products
Found Report [Ref.]
10
12
94
93
Oil
30-32 [18]
2
3
78-80
79–81 [19]
16
94
101-103
—
4
5
6
8
95
85
91
42-44
67-69
43-45 [18]
68-70 [18]
—
180
140
115-117
7
8
12
30
95
92
121-123 120-122 [18]
175-177
—

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9
10
7
94
90
93
130-132 133-135 [18]
10
11
19-21
Oil
—
10
Oil [18]
12
13
5
92
93
Oil
Oil
17
151-153 150-152 [18]
14
15
10
15
95
90
Oil
Oil
Oil [18]
—
a Yields refer to pure isolated products and the products were characterized by m.p. and FT-IR.

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Table 3. Comparison of the obtained results for oxidation of methyl phenyl sulfide in the presence
of [C4(DABCO-H)2].[HSO4]2[NO3]2 with some of the other reported methods.
Condition
Time Yield
Entry Catalyst (amount of catalyst)
[ref.]
[35]
(Solvent/reagent/temperature) (min) (%)
1
2
3
4
5
6
7
8
9
PyHBr3-H2O (0.3 mmol)
Au/CTN-silica (0.02 g)
Ru(PVP)/γ-Al2O3 (2.0 mmol)
Fe(NO3)3.9H2O (5 mol%)
UHP (1 mmol)
CH3CN/t-BuONO-Air/ r.t.
MeOH/H2O2/60 ℃
CH3CN/H2O2/ r.t.
3 h
2 h
120
4 h
91
100a [36]
98
95
[37]
[38]
[39]
[40]
[41]
[42]
[43]
TFE/Air/ 80 ℃
CH3CN/ (NCCl)3/ 25 ℃
CH3CN/ H2O2/ 0-5 ℃
2.5 h 86
5 h 95
14 h 55
VO2F(dmpz)2 (0.02 mmol)
2NaBO3.4H2O-SSA (6 mmol) CH2Cl2/KBr, wet SiO2 / r.t.
Ru(TPP)Cl (0.02 mmol)
TUD (2 mol%)
Toluene/ t-Bu-OOH/O2/80 ℃ 30
94
CH2Cl2/ t-Bu-OOH/r.t.
3.5 h 95
[C4(DABCO-
H)2].[HSO4]2[NO3]2 (0.5
mmol)
This
work
10
Solvent-free/KBr/ r.t.
10
94
a Conversion

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Scheme. 1. Preparation of [C4(DABCO-H)2].[HSO4]2[NO3]2.

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Fig. 1. The FT-IR spectra of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCO-
H)2].[HSO4]2[NO3]2 (c).

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Fig. 2. The 1H-NMR of [C4(DABCO)2].Cl2.

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Fig. 3. The 1H-NMR of [C4(DABCO-H)2].[HSO4]2[NO3]2.

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Fig. 4. The 13C-NMR of [C4(DABCO-H)2].[HSO4]2[NO3]2

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Fig. 5. The TGA (green) and DSC (blue) diagrams of [C4(DABCO-H)2].[HSO4]2[NO3]2.

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Fig. 6. The surface image of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCO-
H)2].[HSO4]2[NO3]2 (c), (d).

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Scheme 2. The proposed mechanism for the oxidation of sulfide to sulfoxide using [C4(DABCO-
H)2].[HSO4]2[NO3]2.

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Graphical abstract

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Research Highlights
 [C4(DABCO-H)2].[HSO4]2[NO3]2 is prepared and introduced as a new nano-sized
dicationic ionic liquid.
 The catalyst is characterized by FT-IR, 1H NMR, 13C-NMR, TGA, DSC, SEM and FESEM
analysis.
 Selective oxidation of sulfides to sulfoxides is performed efficiently using [C4(DABCO-
H)2].[HSO4]2[NO3]2.
 The reactions are performed with high yields of the products in high reaction rates under
grinding conditions.