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Original article
12 (
8
); 2098-2103
doi:
10.1016/j.arabjc.2014.12.037

Task specific ionic liquid as solvent, catalyst and reagent for regioselective ring opening of epoxides in water

, , ,
a Department of Chemistry, Payame Noor University, P.O. Box 19395-4697, Tehran, Iran
b Department of Chemistry, Faculty of Sciences, Shahid Chamran University, P.O. Box 6135743337, Ahvaz, Iran

⁎Corresponding author at: P.O. Box: 69971-45641, shahid motahary street, Arkavaz malekshahi, Ilam, Iran. Tel.: 98 916 6018196; fax: 98 841 2221053. e.rezaee66@yahoo.com (Eshagh Rezaee Nezhad),

Received: , Accepted: ,
© The Author(s) 2015
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Task specific ionic liquid as a novel and environmental eco-friendly green catalyst has been synthesized and used in the ring opening of epoxides under green conditions. This ionic liquids as solvent, catalyst and reagent afforded the corresponding thiocyanohydrins and azidohydrines with good regioselectivity and very short reaction times. The desired thiocyanohydrins and azidohydrines in 83–93% isolated yields.

Keywords

Task specific ionic liquid
Regioselectivity
Ring opening of epoxide
Water
Green conditions
1

1 Introduction

Ionic liquids (ILs) are organic salts, consisting only of cations and anions with melting points at or below 100 °C (Wasserscheid and Keim, 2000; Wasserscheid, 2006; Chowdhury et al., 2007). These compounds have attracted rising interest in the last decades for chemists because of their unique properties such as negligible vapor pressure, high thermal stability, wide liquid temperature range, low volatility, nonflammability, large electrochemical window, capability to dissolve various organic and inorganic compounds, and potentially recyclable properties, have attracted considerable attention as environmentally friendly reaction media in the green organic synthesis (Olivier-Bourbigou et al., 2010; Wilkes, 2002). Brønsted acidic ionic liquids (BAILs) wide range of novel applications such as organic synthesis (as solvent, catalyst and reagent) (Hasaninejad et al., 2010; Zare et al., 2009; Iranpoor et al., 2007; Öchsner et al., 2011), extraction (Visser et al., 2001), electrochemistry (Huddleston and Rogers, 1998), and biphasic catalysis (Qiao et al., 2006), spectroscopy and extraction and separation processes (Pavlinac et al., 2009). BAILs once have designed to replace cation-exchange resins, solid acids and traditional mineral liquid acids like to catalyze chemical transformations (Hapiot and Lagrost, 2008; Zolfigol et al., 2011; Zolfigol et al., 2010; Shaterian and Ranjbar, 2011a,b; Khazaei et al., 2010). Task specific ionic liquid (TSILs) are a subclass of ILs which possess unique functional groups. Task-specific ionic liquids used as reaction medium and catalysts in organic synthesis (Wang et al., 2008). Furthermore, the Brønsted-acidic TSILs have been successfully used as acidic catalysts for the esterification (Zhu et al., 2003), protection reaction of carbonyl groups (Fang et al., 2007a,b), Mannich reaction (Zhao et al., 2004a,b), Biginelli and Hantzsch condensation (Fang et al., 2007a,b; Khabazzadeh et al., 2012; Palakshi Reddy et al., 2015), Friedlander annulation (Palimkar et al., 2003), the synthesis of quinoxaline derivatives (Fang et al., 2008), Synthesis of 1,8-dioxo-octahydroxanthenes and bis(indolyl)methanes (Kalantari, 2012), and ring opening of epoxide (Heidarizadeh and Zarei, 2012; Ranu and Banerjee, 2005). The ring opening of epoxides, which have innovation ways to obtain the direct azidolysis and thiocyanation of epoxides in the presence of sodium azide or potassium thiocyanate, is frequently performed under several different conditions (Sajjadifar et al., 2014; Kiasat et al., 2013; Azadia et al., 2012). In view of a practical application for this project, we are attempting to develop a process that is performed without organic solvents in a onepot procedure under green conditions and TSILs as solvent, catalyst occurs in high yield and high regioselectivity and very short reaction times. But some of these methods are limited to specific epoxides and are not applicable as versatile reagents in the preparation of thiocyanohydrins and azidohydrines are suffer from disadvantages such as long reaction times, low regioselectivity, using of organic solvents, using of expensive catalysts or involve high temperature reaction conditions. Therefore, it seems that there is still a need for development of novel methods that proceed under green and eco-friendly conditions.

2

2 Experimental section

2.1

2.1 General

All reagents were purchased from Merck and Aldrich and used without further purification. The acidic ionic liquid 1-hydrogen-3-methylimidazolium chloride [HMIM][Cl] was prepared according to literature (Kore and Srivastava, 2012). All yields refer to isolated products after purification. IR spectra were recorded on a BOMEM MB-Series 1998 FT-IR spectrophotometer. All 1H and 13C NMR data were recorded on a Bruker Advanced DPX 400 MHz instrument spectrometer using TMS as the internal standard in CDCl3. The progress of reaction was followed with thin-layer chromatography (TLC) using silica gel SILG/UV 254 and 365 plates.

2.2

2.2 Procedure for the preparation of task specific ionic liquids [Hmim][X](X: SCN or N3) from [HMIM][Cl]

For the preparation of 1-hydrogen-3-methylimidazolium chloride see (Kore and Srivastava, 2012). [Hmim]Cl (11.80 g, 0.1 mol) dissolved in acetone (35 mL) and stirred at room temperature for 20 min, KSCN or NaN3 (0.1 mol) dissolved in acetone (50 mL) was added dropwise to [Hmim]Cl over a period of 60 min at room temperature (Scheme 1, Fig. 1). After completion of the addition, the mixture was filtered to KCl or NaCl. The solvent was evaporated under low pressure for 45 min.

Synthesis of task specific ionic liquids.
Scheme 1 Synthesis of task specific ionic liquids.
Comparison IR spectrum of [Hmim]Cl, [Hmim]SCN, [Hmim]N3.
Figure 1 Comparison IR spectrum of [Hmim]Cl, [Hmim]SCN, [Hmim]N3.

2.3

2.3 General procedure for the preparation of β-hydroxythiocyanates and 2-azidoalcohols in water

A mixture of epoxide (1 mmol) and [Hmim]X (1 mL) in water (2 mL) was stirred under reflux conditions for the time shown in Table 1 (Scheme 2). Progress of reaction was monitored by TLC using ethyl acetate:n-hexane (1:4). After reaction completion, the mixture was extracted with ethyl ether (5 mL × 3), washed with brine, dried with CaCl2 and evaporated under reduced pressure. The aqueous layer (including ionic liquid) was separated and its solvent was evaporated to obtain pure ionic liquid. The recycled catalyst was used for the next run under identical reaction conditions. The desired thiocyanohydrins and azidohydrines were obtained in good to excellent isolated yields (83–93%).

Table 1 Optimization of reaction conditions for the ring opening of epoxide.
Entry [Hmim]X:water Temperature (°C) Time (min) Yield (%)a
1 1:1 60 90 60:54
2 1:1 Reflux 75 76:70
3 1:2 60 55 72:70
4 1:2 Reflux 20 92:90
5 1:3 60 45 75:68
6 1:3 Reflux 30 83:79
7 1:4 60 60 73:71
8 1:4 Reflux 45 80:80
a Yields of epoxide are X (SCN:N3).
Preparation of thiocyanohydrins and azidohydrines in the presence of TSILs.
Scheme 2 Preparation of thiocyanohydrins and azidohydrines in the presence of TSILs.

2.3.1

2.3.1 Spectral data for phenoxy-2-hydroxypropyl thiocyanate (4a)

IR νmax/cm−1: 2157 (SCN) 1H NMR (CDCl3, 400 MHz): 3.30 (d, 2H,), 3.78 (s, 1H), 4.15 (d, 2H), 4.29 (m, 1H), 6.95 (m, 2H), 7.02 (m, 1H), 7.28 (m, 2H) 13C NMR (CDCl3, 100 MHz): 37.4, 68.1, 69.5, 113.0, 114.6, 121.3, 129.9, 158.5.

2.3.2

2.3.2 Spectral data for 3-allyloxy-2-hydroxypropyl thiocyanate (4c)

IR νmax/cm−1: 2156 (SCN) 1H NMR (CDCl3, 400 MHz): 3.04 (s, 1H), 3.24 (d, 2H), 3.53 (d, 2H), 4.05 (m, 3H), 5.19–5.29 (m, 2H), 5.87 (m, 1H) 13C NMR (CDCl3, 100 MHz): 37.3, 69.2, 71.1, 71.6, 113.1, 117.5, 133.7.

2.3.3

2.3.3 Spectral data for 2-hydroxy-3-thiocyanatopropyl methacrylate (4d)

IR νmax/cm−1: 2157 (SCN) 1H NMR (CDCl3, 400 MHz): 1.85 (m, 3H), 3.01–3.18 (d, 2H), 3.40 (m, 1H), 4.13 (s, 1H), 4.15 (d, 2H), 5.56 (m, 1H), 6.07 (m, 1H) 13C NMR (CDCl3, 100 MHz), 18.4, 37.3, 66.1, 68.1, 112.8, 126.6, 135.2, 167.1.

2.3.4

2.3.4 Spectral data for 3-chloro-2-hydroxypropyl thiocyanate (4e)

IR νmax/cm−1: 2157 (SCN) 1H NMR (CDCl3, 400 MHz): 1.27 (d, 2H), 3.10–3.28 (m, 2H), 3.64–3.84 (m, 1H), 4.20 (s, 1H) 13C NMR (CDCl3, 100 MHz): 37.31, 47.11, 69.88, 112.01.

2.3.5

2.3.5 Spectral data for 2-hydroxycyclohexyl thiocyanate (4g)

IR νmax/cm−1: 2152 (SCN) 1H NMR (CDCl3, 400 MHz): 1.21–1.29 (m, 4H), 1.69 (m, 2H), 1.98 (m, 2H), 3.14 (s, 1H), 3.16 (m, 1H), 3.34 (m, 1H) 13C NMR (CDCl3, 100 MHz): 23.1, 25.2, 30.0, 31.4, 51.5, 79.1, 110.6.

2.3.6

2.3.6 Spectral data for 1-azido-3-phenoxy-2-propanol (5a)

IR νmax/cm−1: 2103(N3) 1H NMR (CDCl3, 400 MHz): 3.45–3.54 (m, 2H), 3.89 (m, 1H), 3.97–4.03 (m, 2H), 4.18 (s, 1H), 6.95–7.00 (m, 2H), 7.02–7.06 (m, 1H), 7.27–7.36 (m, 2H) 13C NMR (CDCl3, 100 MHz): 53.51, 69.21, 69.30, 114.35, 121.16, 129.42, 158.36.

2.3.7

2.3.7 Spectral data for 2-azido-2-phenyl-1-ethanol (5b)

IR νmax/cm−1: 2102(N3) 1H NMR (CDCl3, 400 MHz): 3.37 (s, 1H), 3.74 (m, 2H), 4.65–4.69 (m, 1H), 7.34–7.44 (m, 5H) 13C NMR (CDCl3, 100 MHz): 66.37, 68.03, 127.49, 128.46, 128.61, 136.47.

2.3.8

2.3.8 Spectral data for 1-azido-3-butoxy-2-propanol (5i)

IR νmax/cm−1: 2102(N3) 1H NMR (CDCl3, 400 MHz): 0.87 (t, 3H), 1.31–1.35 (m, 2H), 1.50–1.53 (m, 2H), 3.14 (s, 1H), 3.30–3.32 (m, 2H), 3.39–3.44 (m, 4H), 3.87 (m, 1H) 13C NMR (CDCl3, 100 MHz): 13.78, 19.16, 30.74, 53.52, 69.74, 70.59, 70.71.

3

3 Result and discussion

Herein, we report a developed methodology of the synthesis thiocyanohydrins and azidohydrines in the presence of [Hmim]X (X:SCN or N3) under reflux condition. Herein we have carried out the reaction of 2,3-epoxypropyl phenyl ether and [Hmim]X (X: SCN or N3) as solvent, catalyst and reagent in water. Various reaction conditions have been studied for optimization (Scheme 3, Table 1).

Ring opening of epoxides in the presence of TSILs.
Scheme 3 Ring opening of epoxides in the presence of TSILs.

After optimizing the conditions, we examined the generality of these conditions to other substrates using several epoxides. The results are summarized in Table 2. The reaction proceeds efficiently in all cases.

Table 2 Ring opening of various epoxides in the presence of TSILs in water.
Substrate Productsa,b SCN− N3−
No. Time (min) Yield %c No. Time (min) Yield %c
4a 20 92 5a 20 90
4b 25 86 (13:87)d 5b 25 88(11:89)d
4c 30 87 5c 25 89
8 4d 35 88 5d 30 90
4e 30 83 5e 30 85
4f 25 91 5f 25 93
4 g 35 90 5 g 35 92
4 h 40 84 5 h 35 87
4i 30 88 5i 30 90
4j 40 86 5j 40 84
a Products were identified by comparing their physical and spectral data with those of authentic samples.
b X in all products is SCN or N3.
c Isolated yields.
d According to GC analysis.

Different epoxides easily underwent ring opening in the presence of TSILs at reflux condition in water (Table 2). The products were formed in excellent yields and conversion was completed in 20–40 min.We report the use of acidic ionic liquids (AILs) as highly efficient promoters ring opening of various epoxides. The procedure gives products in good yields, short reaction times and avoids use of organic solvents (handling, cost, safety, pollution). Environmental-friendly ionic liquid afforded a valuable alternative to promote a numerous efficient catalytic systems that have already been proposed for the ring opening of epoxides. Water is a desirable solvent for chemical reactions for reasons of cost, safety and environmental concerns, use of water in this reaction gave only greater regioselectivity ring opening of epoxide.

The acidic hydrogen on carbon 2 of imidazole, between two nitrogen of imidazole (Danten et al., 2009; Cui et al., 2010), and hydrogen on nitrogen, activate the epoxide giving the hydrogen bonds with the oxygen of epoxide, as the critical role of the cation in the reaction (Scheme 4).

Mechanism of epoxide ring-opening reaction by task specific ionic liquid.
Scheme 4 Mechanism of epoxide ring-opening reaction by task specific ionic liquid.

The procedure showed high regioselectivity for thiocyanation and azidation of epoxide in the presence of TSILs as solvent, catalyst and reagent.

As it can be seen in Table 3, [Hmim]X (X:SCN or N3) as a catalyst was afforded good results in comparison with the other catalysts.

Table 3 Comparison of catalytic ability of catalysts.
Entry Catalyst/solvent/temperature/nucleophile Reaction time (h) Yield % References
1 Network polymer/water/80 °C/N3 1.5 89 Mouradzadegun et al. (2012)
2 SiO2-OPEG(300)/water/reflux/N3 2 89 Kiasat and Zayadi (2008)
3 [bmim]PF6([bmim]BF4)/water/65 °C/N3 3(5) 95(89) Yadav et al. (2005)
4 β-cyclodextrin/water/r.t./N3 5 45 Kamal et al. (1999)
5 Al(HSO4)3/solvent-free/r.t./SCN 5 min 91 Kiasat et al. (2010)
6 Selectfluor/CH3CN/r.t./SCN 2.5 95 Yadav et al. (2004)
7 PTC/CH3CN/r.t./SCN 1.5 90 Tamami and Mahdavi, (2002)
8 [Hmim]N3/water/refluxN3 20 min 90 This work
9 [Hmim]SCN/water/reflux/SCN 20 min 92 This work

In order to evaluate the efficiency of our introduced method, some numbers of reported methods were compared with our present method in the yields and reaction times parameters which the results are given in Table 3.

2

2 Conclusion

In conclusion, this new and green methodology provides an easy, eco-friendly and efficient access to highly regioselective synthesis of thiocyanohydrin and azidohydrine. Moreover, the reaction proceeds under green and mild conditions with task specific ionic liquid as solvent, catalyst and reagent. This method offers several advantages including green reaction conditions, high conversions, greater regioselectivity, short reaction times, clean reaction profiles, and high isolated yields which make it a useful and attractive process for the synthesis of thiocyanohydrin and azidohydrines.

Acknowledgment

The authors gratefully acknowledge partial support of this work by Payame Noor University (PNU) of Ilam.

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