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Synthesis of 1,3-dithiane and 1,3dithiolane derivatives by tungstate sulfuric acid: recyclable and green catalyst a

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Bahador Karami , Mahbubeh Taei , Saeed Khodabakhshi & Masih Jamshidi

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Department of Chemistry, Yasouj University, PO Box 353, Yasouj, 75918-74831, Iran Version of record first published: 28 Nov 2011.

To cite this article: Bahador Karami , Mahbubeh Taei , Saeed Khodabakhshi & Masih Jamshidi (2012): Synthesis of 1,3-dithiane and 1,3-dithiolane derivatives by tungstate sulfuric acid: recyclable and green catalyst, Journal of Sulfur Chemistry, 33:1, 65-74 To link to this article: http://dx.doi.org/10.1080/17415993.2011.629659

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Journal of Sulfur Chemistry Vol. 33, No. 1, February 2012, 65–74

Synthesis of 1,3-dithiane and 1,3-dithiolane derivatives by tungstate sulfuric acid: recyclable and green catalyst Downloaded by [University of Sussex Library] at 06:29 14 March 2013

Bahador Karami*, Mahbubeh Taei, Saeed Khodabakhshi and Masih Jamshidi Department of Chemistry, Yasouj University, PO Box 353, Yasouj 75918-74831, Iran (Received 9 August 2011; final version received 2 October 2011 ) An efficient, novel, and environmentally benign procedure for the thioacetalization of aliphatic and aromatic carbonyl compounds in the presence of catalytic amounts of tungstate sulfuric acid under solvent-free conditions to afford 1,3-dithianes and 1,3-dithiolanes was reported. This method has many advantages including excellent yields, short reaction time, and simple work-up procedure.

Keywords: tungstate sulfuric acid; thioacetalization; 1, 3-dithiane, 1,3-dithiolane; solvent-free; carbonyl compound

1.

Introduction

The chemistry of molecules containing sulfur attracts continuous attention as a consequence of the potential biological activity of this class of compounds (1). For example, tiapamil is an antianginal agent used in the treatment of angina pectoris (2). The protection of carbonyl functionality as a dithioacetal or a thioketal is an important tool in the multistep total synthesis of complex natural and non-natural products and has attracted special attention in recent years (3). Synthetic organic chemists have found 1,3-dithianes to be versatile systems of great applicability, natural products being the main targets in organic synthesis (4). In addition, these compounds are also utilized as masked acyl anions (5) or masked methylene functional groups in carbon–carbon *Corresponding author. Email: [email protected]

ISSN 1741-5993 print/ISSN 1741-6000 online © 2012 Taylor & Francis http://dx.doi.org/10.1080/17415993.2011.629659 http://www.tandfonline.com

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66 B. Karami et al.

bond forming reactions (6). Among carbonyl protecting groups, 1,3-dithianes, 1,3-dithiolanes, and 1,3-oxathiolanes are inherently stable under both acid and alkaline media (pH 2–12) (7). Several reagents for the synthesis of dithiolane and dithiane derivatives such as SO2 (8), SOCl2 – SiO2 (9), p-TsOH (10) in refluxing benzene, p-toluenesulfonic acid and silica gel in refluxing dichloromethane (11), P2 O5 /Al2 O3 under microwave irradiation (12), nano-sized nickel under a N2 atmosphere (3), Bi(OTf)3 (13), LiOTf (14), LiBF4 (15), InCl3 (16), In (OTf)3 (17), selenonium ionic liquid (18), lanthanum(III) nitrate hexahydrate (19) etc., have been used. Recently, Perin et al. (20) reported the catalyst-free thioacetalization of carbonyl compounds using glycerol as a recyclable solvent. Although some of these methods have been carried out under mild reaction conditions, most of them suffer from drawbacks such as long reaction times, the use of stoichiometric, expensive, and toxic reagents, tedious work-up procedure, the use of toxic organic solvents, and low yield of the products.

2.

Results and discussion

The challenge in chemistry to develop the practical methods, reaction media, conditions, and/or the use of materials based on the idea of green chemistry is one of the important issues in the scientific community. However, the concept of “Green Chemistry” has emerged as one of the guiding principles of the environmentally organic synthesis (21). A solvent-free or solid-state reaction obviously reduces pollution and brings down handling costs due to simplification of experimental procedures including work-up technique and also provides a savings in labor cost. These are especially important during industrial production. Recently, silica sulfuric acid and Nafion-H (22) have been used for a wide variety of reactions (23). Accordingly, we found that anhydrous sodium tungstate reacts with chlorosulfonic acid (1:2 mole ratio) to give tungstate sulfuric acid (TSA, 1). The reaction is easy, clean, and performed without any work-up (Scheme 1). It is also noteworthy that there is no gas production during the reaction.

Scheme 1.

Preparation of TSA (1).

Figure 1 shows the X-ray diffraction (XRD) patterns of TSA (1). It was reported that a high degree mixing of W–S in chlorosulfonic acid often led to the absence of an XRD pattern for anhydrous sodium tungstate. The broad peak around 25.7◦ (2θ ) (θ is the Bragg’s angle) from the smaller inset could be attributed to insertion of W into the framework of chlorosulfonic acid. The XRF data for TSA (1) indicates the presence of WO4 and SO3 in this catalyst (Table 1). The FT-IR spectra of anhydrous sodium tungstate and TSA (1) are shown in Figure 2. The spectrum of TSA (1) shows bands for the characteristic bonds of anhydrous sodium tungstate and chlorosulfonic acid. The absorptions at 3406, 1820, 1725, 1702, 1620, 1290, 1060, 1005, and 860 cm−1 in the catalyst spectrum are those expected for bonds in anhydrous sodium tungstate and in the −OSO3 H group. In connection with our previous work on developing use of TSA (1) in organic transformations (24), in this manuscript, we wish to report a simple and convenient route for the thioacetalization

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Journal of Sulfur Chemistry 67

Figure 1. The powder XRD pattern of the TSA (1). Table 1. XRF data of HO3 SO (WO2 ) OSO3 H (TSA, 1). Compound

Concentration (% w/w)

WO4 SO3 Na2 O Cl CuO Fe2 O3 CaO LOI Total Note: LOI, loss on ignition.

Figure 2.

FT-IR spectra of H3 OSO(WO2 )OSO3 H (TSA, 1).

19.49 0.317 0.190 0.056 0.023 0.015 0.014 79.82 99.93

68 B. Karami et al.

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of carbonyl compounds (2) using catalytic amounts of TSA (1) under solvent-free conditions to afford the 1,3-dithiane (3) and 1,3-dithiolane (4) derivatives (Scheme 2). TSA is a strong solid acid so that it can activate the carbonyl group to decrease the transition state energy of the nucleophilic attack step.

Scheme 2.

Synthesis of 1,3-dithiane and 1,3-dithiolane using TSA (1).

As shown in Table 2, several aromatic and aliphatic carbonyl compounds carrying either electron-releasing or electron-withdrawing substituents in the ortho, meta, and para positions afforded good to excellent yield of the products. Aliphatic ketones, however, did not produce the corresponding thioacetals under the same reaction conditions. The 1 H NMR (CDC13 , 400 MHz) spectrum of (3d) exhibited a singlet for the protons of a methyl group (δ = 1.67 ppm) and a triplet for the protons of two methylene groups (δ = 2.57 ppm). Also, the resonance of the aromatic protons appeared at δ = 7.29–8.20 ppm as four distinct signals. The proton-decoupled 13 C NMR spectrum of (3d) showed 13 distinct resonances in agreement with the proposed structure. Obviously, in the spectrum of compound (3d), the absence of a resonance for the carbonyl group is also consistent with the formation of the 1,3-dithiolane. In another variation, we investigated the chemoselectivity of methods A and B. It is noteworthy that very few of the reported methods have demonstrated chemoselective thioacetalization of aldehydes in the presence of ketones. Consequently, we explored this possibility using our method. As can be seen in Scheme 3, when an equimolar mixture of methoxybenzaldehyde and acetophenone was allowed to react with 1,2 ethanedithiol in the presence of a catalytic amount of TSA (1), benzaldehyde was exclusively protected, whereas acetophenone was left intact. Not only the ecological benefit of decreasing hazardous industrial waste but also the economic benefit of the elimination of an expensive organic solvent is further improved if the catalyst is recyclable and reaction conditions are solvent-free. In fact, the main disadvantage of almost all the above-mentioned methods for the synthesis of 1,3-dithianes and 1,3-dithiolanes is that the catalysts are destroyed in the work-up procedure and cannot be recovered or reused. In this process, as indicated in Figure 3, the recycled catalyst was used for four cycles during which time no appreciable loss in the effectiveness of the catalyst was observed. Mechanistically, the reaction starts with the protonation of the oxygen of the carbonyl group by TSA (1) acting as a Brønsted acid. Subsequent nucleophilic attack of the dithiole at the carbonyl followed by an intramolecular cyclization reaction afforded the products (Scheme 4).

3.

Conclusion

In summary, the main target of this study was the development of a green synthetic procedure for 1,3-dithiane and 1,3-dithiolane formation by employing TSA as a solid sulfur-containing acid.

Journal of Sulfur Chemistry 69 Table 2.

Synthesis of (3) and (4) using TSA (1) through methods A and B. Yielda (%)

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Entry

Product

Time (min)

Ab

Bc

Ab

Bc

Mp (◦ C) (lit.)

1

3a

90

88

5

45

Oil (25)

2

3b

82

90

5

25

73–74

3

3c

85

76

5

30

Oil (25)

4

3d

87

85

25

55

102–103

5

3e

96

90

8

44

62–63 (17)

6

3f

70

68

5

25

61–62 (25)

7

3g

88

85

22

45

Oil (3)

8

4a

91

94

5

90

67–68 (26)

9

4b

95

95

12

45

114–115 (26)

Continued

70 B. Karami et al. Table 2.

(Continued). Yielda (%)

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Entry

Product

Time (min)

Ab

Bc

Ab

Bc

Mp (◦ C) (lit.)

10

4c

90

97

8

96

140–141 (27)

11

4d

90

87

10

45

Oil (26)

12

4e

85

85

5

36

75–76 (28)

13

4f

90

86

10

75

Oil (29)

14

4g

88

85

10

80

Oil (29)

15

4h

76

84

10

65

111–112

16

4i

90

95

5

60

84–85 (25)

17

4j

92

97

5

12

103–104

18

4k

74

98

10

60

110–111 (25)

Continued

Journal of Sulfur Chemistry 71 Table 2.

(Continued). Yielda (%)

Entry

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19

Product

4l

Time (min)

Ab

Bc

Ab

Bc

Mp (◦ C) (lit.)

82

82

12

45

121–122

Notes: a Isolated yields. b Method A: Grinding at rt conditions. c Method B: Stirring under thermal (80◦ C) conditions.

Scheme 3. Chemoselectivity of methods A and B for the thioacetalization of benzaldehyde in the presence of acetophenone.

Figure 3. Recyclability of TSA (1) as a catalyst for the synthesis of 3a: (a) Grinding, rt, reaction time = 5–10 min; (b) solvent-free, 80◦ C, reaction time = 45–60 min.

The simple experimental procedure, solvent-free reaction conditions, utilization of an inexpensive, recoverable and eco-friendly catalyst, short reaction time, and good to excellent yields make this method a valuable contribution to existing methodologies.

4.

Experimental

4.1. General All chemicals were purchased from Merck, Fluka, and Aldrich companies. The reactions were monitored by TLC (silica gel 60 F254 , n-hexane: ethyl acetate). XRD patterns were obtained with a Philips X Pert Pro X diffractometer operated with a Ni-filtered CuKα radiation source. X-ray fluorescence (XRF) spectroscopy was recorded with an XRF Analyzer, Bruker, S4 PIONEER,

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72 B. Karami et al.

Scheme 4.

Proposed mechanism for the thioacetalization of carbonyl compound using TSA (1).

Germany. Melting points were measured on an electrothermal KSB1N apparatus. IR spectra were recorded on an FT-IR JASCO-680 and the 1 H NMR spectra were obtained on a Bruker-Instrument Avance 2 DPX-400 MHz NMR. 4.2. Preparation of the catalyst A 0.588 g (2 mmol) sample of anhydrous sodium tungstate was added to 25 ml of dry n-hexane in a 100 ml round-bottom flask, equipped with ice bath and overhead stirrer, then 0.266 ml (4 mmol) of chlorosulfonic acid was added dropwise to the flask over a 30 min period. This solution was stirred for 1.5 h. Afterwards the reaction mixture was gradually poured with agitation into 25 ml of chilled distilled water. The yellowish solid that separated out was filtered. Then the catalyst was washed five times with distilled water until the filtrate showed a negative test for chloride ion and dried at 120◦ C for 5 h. The catalyst was obtained in 98% yield as a yellowish solid, which decomposed at 285◦ C. 4.3.

General procedure for the preparation of compounds (3) and (4)

Method A: A mixture of 1 mmol of aldehyde or ketone, 1 mmol of dithiol, and TSA (1) (10 mol%) was stirred and added to a mortar. The mixture was thoroughly ground with a pestle at room temperature. The progress of the reaction was monitored by TLC (ethyl acetate/n-hexane, 1:5). After the completion of the reaction, the reaction mixture was dissolved in CHCl3 and the catalyst was filtered. The pure products (3) and (4) were crystallized from ethanol. The catalyst was washed with diethyl ether, dried at 70◦ C for 45 min and reused in another reaction. Method B: A mixture of aldehyde or ketone (1 mmol), dithiol (1 mmol), and TSA (10 mol%) was stirred and heated at 80◦ C in a preheated oil bath for an appropriate time (Table 2). After completion of the reaction (monitored by TLC), ethanol or chloroform (30 ml) was added, and the solid catalyst was removed by filtration. The solvent was evaporated and the crude products (3) and (4) were purified by recrystallization in ethyl acetate or ethanol. The catalyst was washed with diethyl ether, dried at 70◦ C for 45 min and reused in another reaction. 4.4. Spectral data for selected compounds 4.4.1. 2-(2,6-Dichlorophenyl)-1,3-dithiolane (3b) IR (KBr) νmax (cm−1 ): 3086, 2975, 1576, 1436, 1071; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 7.10 (d, 2H, J= 8 Hz), 6.93 (t, 1H, J = 8 Hz), 6.48 (d, 1H, J = 8 Hz), 3.49–3.42 (m, 2 H), 3.25–3.18 (m, 2H); 13 C-NMR (CDC13 , 100 MHz) δ (ppm): 137.39, 134.32, 130.88, 130.41, 51.05, 42.56.

Journal of Sulfur Chemistry 73

4.4.2.

2-Methyl-2-(naphthalen-2-yl)-1,3-dithiolane (3d)

IR (KBr) νmax (cm−1 ): 3050, 2958,1624, 1499, 1436, 1362; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 8.20 (d, 1H, J = 11.2), 7.87–7.84 (m, 1H), 7.71–7.64 (m, 3H), 7.32–7.39 (m, 2H), 2.58–2.55 (t, 4H, J = 5.6), 1.68 (s, 3H); 13 C-NMR (CDC13 , 100 MHz) δ (ppm): 141.10, 133.29, 132.36, 128.44, 128.34, 127.41, 127.10, 126.24, 126.17, 125.75, 54.13, 28.16, 24.67.

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4.4.3.

2-(3-Nitrophenyl)-1,3-dithiolane (3f)

IR (KBr) νmax (cm−1 ): 3081, 2922, 1614, 1533, 1471, 1346, 852, 769; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 8.20 (s, 1H), 7.92 (m, 1H), 7.62 (d, 1H, J = 8 Hz), 7.29 (t, 1H, J = 8 Hz), 5.47 (s, 1H), 3.34 (m, 2H), 3.21 (m, 2H); 13 C-NMR (CDC13 , 100 MHz) δ (ppm): 149.41, 144.68, 135.88, 130.58, 124.21, 124.12, 56.11, 41.65. 4.4.4.

2-Phenyl-1,3-dithiane (4a)

IR (KBr) νmax (cm−1 ): 3095, 2920, 1610, 1500, 1480, 1650, 1140; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 7.51 (d, 2H, J = 8 Hz), 7.39–7.31 (m, 3H), 5.20 (d, 1 H, J = 4 Hz), 3.09–2.88 (two m, 4 H), 2.14 (d, 1H, J = 4 Hz), 1.95–1.91 (m, 1 H). 4.4.5.

2-p-Tolyl-1,3-dithiane (4b)

IR (KBr) νmax (cm−1 ): 3057, 2901, 1607, 1462, 1440, 1413, 815; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 7.39, 7.35 (two d, 2H, J = 8 Hz), 7.19 (d, 2H, J = 7.8 Hz), 5.18 (s, 1H), 3.10–3.03 (m, 1H), 2.94–2.88 (m, 1H), 2.36 (s, 3H), 2.16–2.15 (m, 1H), 1.95–1.92 (m, 1H); 13 C-NMR (CDC13 , 100 MHz) δ (ppm): 138.30, 136.24, 129.45, 127.88, 51.23, 32.9, 25.16, 21.27. 4.4.6. 2-(Naphthalen-1-yl)-1,3-dithiane (4c) IR (KBr) νmax (cm−1 ): 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 8.36 (d, 1 H, J = 8 Hz), 7.90–7.83 (m, 3 H), 7.63–7.59 (m, 3H), 7.54–7.48 (m, 3H), 5.96 (s, 1 H), 3.24–3.18 (m, 2H), 3.02–2.97 (m, 2H), 2.21 (d, 1H, J = 2 Hz), 2.05 (t, 1H, J = 2.8 Hz). 4.4.7.

2-(2-Nitrophenyl)-1,3-dithiane (4h)

IR (KBr) νmax (cm−1 ): 3073, 2923, 1599, 1524, 1441, 1345, 744; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 7.67 (t, 2H, J = 6.8 Hz), 7.41 (t, 1H, J = 7.6 Hz), 7.24 (t, 1H, J = 8 Hz), 5.68 (d, 1H, J = 16.4 Hz), 2.91 (t, 2H, J = 12.8 Hz), 2.73–2.70 (m, 2H), 2.00–1.96 (m, 1H), 1.77–1.68 (m, 1H); 13 C-NMR (CDC13 , 100 MHz) δ(ppm): 148.86, 134.57, 132.13, 131.89, 130.27, 125.89, 47.10, 33.41, 26.15. 4.4.8. 2-Methyl-2-(naphthalen-2-yl)-1,3-dithiane (4j) IR (KBr) νmax cm−1 ): 3050, 2957, 1593, 1499, 1459, 1362; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 8.23 (s, 1H), 7.89–7.86 (m, 1H), 7.72–7.65 (m, 3H), 7.32–7.30 (m, 2H), 2.57 (t, 4H, J = 5.2 Hz), 1.78 (t, 2H, J = 3.6 Hz), 1.70(s, 3H); 13 C-NMR (CDC13 , 100 MHz) δ (ppm): 141.13, 133.31, 132.38, 128.47, 128.36, 127.43, 127.12, 126.28, 126.21, 125.78, 54.16, 36.83, 28.18, 24.70.

74 B. Karami et al.

4.4.9.

2-(3-Nitrophenyl)-1,3-dithiane (4k)

IR (KBr) νmax (cm−1 ): 3070, 2905, 1610, 1523, 1432, 1343, 675, 771, 871; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 8.36 (d, 1H, J = 1.9 Hz), 8.17–8.15 (m, 1H), 7.83–7.81 (m, 1H), 7.55–7.51 (m, 1H), 5.25 (d, 1H, J = 4), 3.11–3.04 (m, 2H), 2.97–2.91 (m, 2H), 2.19–2.17 (m, 1H), 1.96– 1.93 (m, 1H); 13 C-NMR (CDC13 , 100 MHz) δ (ppm): 148.33, 141.17, 134.08, 129.77, 123.40, 123.11, 50.17, 31.77, 31.60, 24.77.

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4.4.10. 2-(2,6-Dichlorophenyl)-1,3-dithiane (4l) IR (KBr) νmax (cm−1 ): 3090, 2900, 1630, 1550, 1475, 1340, 850, 770; 1 H-NMR (CDC13 , 400 MHz) δ (ppm): 7.12–7.07 (m, 2 H), 6.92 (t, 1H, J= 8 Hz), 5.86 (s, 1H), 2.96–2.75 (m, 2H), 2.74–2.71 (m, 2H), 2.00–1.95 (m, 2H), 1.84–1.76 (m, 1 H). Acknowledgement The authors gratefully acknowledge partial support of this work by the Yasouj University Iran.

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