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

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

[email protected] b

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Department of Chemistry, Malek Ashtar University of Technology, Tehran, Iran, e-mail:

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a

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Yadollah Bayat*a, Farhad Shirini*b, Omid Goli-Jolodarb

Department of Chemistry, University of Guilan, Rasht, Iran, e-mail: [email protected]

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Abstract:

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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

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was prepared with available starting materials, and characterized by FT-IR, 1H-NMR, 13C-NMR,

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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

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condition. A simple method, short reaction times, high yields, green and easy work-up of the

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products, use of commercial cheap starting materials and excellent selectivity are attractive features of the present method.

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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

ACCEPTED MANUSCRIPT 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

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[9], antibacterial [10], antifungal [11], anti-HIV1 [12] and antiviral [13] activity. Furthermore,

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sulfoxides were used in Swern oxidation, Diels–Alder reaction, and C–C bond-formation reactions

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[14].

Oxidation of sulfides is one of the prevalent methods for preparation of sulfoxides. Various

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reagents and oxidizing media are employed for conversion of sulfides to sulfoxides [15-26]. In

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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

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regioselectivity, long reaction times, low yields and over oxidation. Therefore, the new research

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and continues effort is needed to overcome of these difficulties. 2. Experimental Material

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2.1.

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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

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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

ACCEPTED MANUSCRIPT 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(. The 1H-NMR (400 MHz) and

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C-NMR (100 MHz) were run on a Bruker AVANCEIII-400

spectrometer in DMSO by TMS as an internal reference (δ in ppm). Catalyst preparation

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2.3.

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[C4(DABCO)2]Cl2 was prepared according to the reported method in the literature [27]. At the

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next step, sulfuric acid (0.53 mL, 10 mmol, 98%) was added drop-wise to a solution of

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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

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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,

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5mmol) in dry CH2Cl2 (25 mL) within 30 min in an ice bath (0 ℃). In continue, the mixture was

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warmed to room temperature and refluxed for 2 h. The solid product was washed with Et2O (3×5

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mL) and dried under vacuum to give a 1,1'-(butane-1,4-diyl)bis(1,4-diazabicyclo[2.2.2]octane-1,4diium) bis(hydrogen sulfate) dinitrate ([C4(DABCO-H)2].[HSO4]2[Cl]2) as a yellowish solid (mp

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58-60 ℃ ) (Scheme 1).

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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

ACCEPTED MANUSCRIPT 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.

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2. 4. 2. 1H-NMR and 13C-NMR analysis

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The 1H-NMR of [C4(DABCO)2].Cl2 (b) and [C4(DABCO-H)2].[HSO4]2[NO3]2 are shown in Figs.

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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,

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the 13C-NMR spectra of [C4(DABCO-H)2].[HSO4]2[NO3]2 showed four aliphatic carbons which

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provided additional evidence to confirm its structure (Fig. 4). 2. 4. 3. TGA and DSC analysis

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The thermal stability of [C4(DABCO-H)2].[HSO4]2[NO3]2 was measured by TGA analysis (Fig.

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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,

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can associated to the decomposition of sulfonic and nitrate groups. The final step which stated at

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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,

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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

ACCEPTED MANUSCRIPT The surface morphology of DABCO (a), [C4(DABCO)2].Cl2 (b) and [C4(DABCOH)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

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attributed to high charge and great intermolecular interactions. The FESEM of [C4(DABCO-

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2. 5. General procedure for the oxidation of sulfides:

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H)2].[HSO4]2[NO3]2 (d) show that the molecular size of the catalyst is 80-100 nm.

A mixture of an sulfide (1 mmol), [C4(DABCO-H)2].[HSO4]2[NO3]2 (0.5 mmol) and KBr (0.05

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mmol) was vigorously grind using a mortar and pestle at room temperature. After completion of

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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.

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3. Result and discussion

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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-

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H)2].[HSO4]2[NO3]2 for selective oxidation of sulfides to sulfoxides under mild conditions.

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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

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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(DABCOH)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

ACCEPTED MANUSCRIPT 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

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obtained results showed that all of substrates were converted to the corresponding sulfoxide

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products in good to excellent yields. Alkyl aryl sulfides bearing 4-bromo and 4-nitro groups on the

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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

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methyl p-tolyl sulfide gave good results under the presented conditions (Table 2, entry 4). A series

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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

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in almost quantitative yields. Notably, dimethylsulfane and dibutylsulfane as an aliphatic sulfides

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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).

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It should be noted that in the presence of various functional groups such as OH, C=C,

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COOCH3 (Table 2, entries 13-15), the sulfides were only oxidized, which proved the chemoselectively of the present method.

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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.

ACCEPTED MANUSCRIPT 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].

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4. Conclusions

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The [C4(DABCO-H)2].[HSO4]2[NO3]2, as a novel and nano oxidation agent, were prepared simply

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from available starting materials. This nano reagent acted efficiently with highly performance in

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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

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temperature, non-solvent, short reaction times, high yields and good selectivity are advantages of

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the presented method which make it a useful and beneficial methodology.

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ACCEPTED MANUSCRIPT 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(DABCOH)2].[HSO4]2[NO3]2 (c).

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

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

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

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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-

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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-

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H)2].[HSO4]2[NO3]2.

ACCEPTED MANUSCRIPT Table. 1. Oxidation of methyl phenyl sulfide under various conditions: Equivalents of reagent

KBr

Solvent

Temperature (ᵒC)

Time (min)

Conversion (%)

1

0.5

0.05

n-hexane

r.t.

120

50

2

0.5

0.05

CH3CN

r.t.

120

60

3

0.5

0.05

CH2Cl2

r.t.

4

0.5

0.05

Grinding

5

0.5

0.05

Grinding

6

0.25

0.05

7

1

8

100

r.t.

10

100

40-50

8

100

Grinding

r.t.

25

50

0.05

Grinding

r.t.

10

100

0.5

0.025

r.t.

30

50

9

0.5

0.1

Grinding

r.t.

10

100

10

0.5

0

Grinding

r.t.

30

0

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Yield (%)a

1

10

94

2

12

93

3

16

94

4

8

Substrate

m.p. (ᵒC) Found Report [Ref.]

Products

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30-32 [18]

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Entry

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Time (min)

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H)2].[HSO4]2[NO3]2 as oxidation agent

79–81 [19]

101-103

—

95

42-44

43-45 [18]

180

85

67-69

68-70 [18]

140

91

115-117

—

7

12

95

121-123

120-122 [18]

8

30

92

175-177

—

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AN

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78-80

CE AC

6

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5

94

130-132

133-135 [18]

10

7

90

19-21

—

11

10

93

12

5

92

13

17

93

14

10

15

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15

T

10

Oil [18]

Oil

Oil

151-153

150-152 [18]

95

Oil

Oil [18]

90

Oil

—

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AN

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Oil

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Yields refer to pure isolated products and the products were characterized by m.p. and FT-IR.

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a

9

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ACCEPTED MANUSCRIPT 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 [ref.] (Solvent/reagent/temperature) (min) (%)

1

PyHBr3-H2O (0.3 mmol)

CH3CN/t-BuONO-Air/ r.t.

2

Au/CTN-silica (0.02 g)

MeOH/H2O2/60 ℃

3

Ru(PVP)/γ-Al2O3 (2.0 mmol)

CH3CN/H2O2/ r.t.

4

Fe(NO3)3.9H2O (5 mol%)

TFE/Air/ 80 ℃

5

UHP (1 mmol)

CH3CN/ (NCCl)3/ 25 ℃

6

VO2F(dmpz)2 (0.02 mmol)

7

[35]

2h

100a

[36]

120

98

[37]

4h

95

[38]

2.5 h

86

[39]

CH3CN/ H2O2/ 0-5 ℃

5h

95

[40]

2NaBO3.4H2O-SSA (6 mmol)

CH2Cl2/KBr, wet SiO2 / r.t.

14 h

55

[41]

8

Ru(TPP)Cl (0.02 mmol)

Toluene/ t-Bu-OOH/O2/80 ℃

30

94

[42]

9

TUD (2 mol%)

CH2Cl2/ t-Bu-OOH/r.t.

3.5 h

95

[43]

10

[C4(DABCOH)2].[HSO4]2[NO3]2 (0.5 mmol)

Solvent-free/KBr/ r.t.

10

94

This work

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Conversion

3h

T

91

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a

Entry Catalyst (amount of catalyst)

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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(DABCOH)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-

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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-

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H)2].[HSO4]2[NO3]2.

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Graphical abstract

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[C4(DABCO-H)2].[HSO4]2[NO3]2 is prepared and introduced as a new nano-sized dicationic ionic liquid.

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The catalyst is characterized by FT-IR, 1H NMR, 13C-NMR, TGA, DSC, SEM and FESEM

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Selective oxidation of sulfides to sulfoxides is performed efficiently using [C4(DABCO-

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analysis.

H)2].[HSO4]2[NO3]2.

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The reactions are performed with high yields of the products in high reaction rates under

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grinding conditions.

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