Journal of Molecular Liquids 183 (2013) 14–19

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Journal of Molecular Liquids

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Short Communication

Synthesis, characterization and application of magnetic room temperature dicationicionic liquid as an efficient catalyst for the preparation of 1,2-azidoalcohols

Bijan Mombani Godajdar a,⁎, Ali Reza Kiasat b, Mohammad Mahmoodi Hashemi c

a Department of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iranb Department of Chemistry, College of Science, Shahid Chamran University, Ahwaz, Iranc Department of Chemistry, Sharif University of Technology, Tehran, Iran

⁎ Corresponding author. Tel.: +98 916607003; fax: +E-mail address: bmombini@gmail.com (B.M. Godajd

0167-7322/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.molliq.2013.03.022

a b s t r a c t

a r t i c l e i n f o

Article history:Received 24 December 2012Received in revised form 24 March 2013Accepted 26 March 2013Available online 18 April 2013

Keywords:RegioselectiveMagnetic room temperature dicationic ionicliquid1,2-azidoalcoholsGreen chemistry

An environmentally benign, aqueous synthesis of 1,2-azidoalcohols via regioselective ring opening of theirepoxides using magnetic imidazolium based dicationic room temperature ionic liquid, [pbmim](FeCl4)2, asan efficient magnetic phase transfer catalyst in water has been described. The present approach offers the ad-vantages of clean reaction, simple methodology, short reaction time, high yield, easy purification and reus-able catalyst.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

In recent years, the concept of green chemistry has been playingan important role for meeting the fundamental scientific challengesof protecting the living environment [1]. Green chemistry, alsoknown as sustainable chemistry, is the design of chemical productsand processes that reduce or eliminate the use or generation of haz-ardous substances. Again, organic synthesis in aqueous media is rap-idly gaining importance in view of the fact that the use of many toxicand volatile organic solvents, particularly chlorinated hydrocarbons,contributes to pollution [2]. Consequently, it is highly desirable to de-velop environmentally benign processes that can be conducted inaqueous media. Furthermore, using water as a solvent offers manyadvantages, such as simple operation, abundant in nature, has virtual-ly no cost, and the safest among all available solvents. However, itsuse is limited by the low solubility of organic compounds. One ofthe most important strategies to overcome this limitation is the utili-zation of phase transfer catalyst such as ionic liquid (IL).

Room temperature ionic liquids (RTILs) are generally defined assalts that are liquid at or below room temperature. The combinationof ammonium, pyridinium, phosphonium or imidazolium cations withvarious inorganic or organic anions led to a large amount of liquidsalts with numerous possible applications e.g. in the field of organicsynthesis, catalysis, biocatalysis,material science, chemical engineering,electrochemistry or separation processes [3]. The increasing interest in

98 611 3738044.ar).

rights reserved.

RTILs is related to their possible exploitation as environmentally friend-ly neoteric solvents because of their vanishing vapor pressure, thermaland chemical stability, air and moisture stability, wide liquidus range,solvent capability, etc. [4]. However the large scale application of ionicliquids is still far from realization because of their high cost and difficultrecovery [5].

Magnetic ILs not only have the excellent properties of IL but alsoexhibit an unexpectedly strong response to an additional magnet.These properties make magnetic ILs have more advantages and po-tential application prospects than conventional ILs in the fields of cat-alytic reactions, solvent effects and separation processes [6].

Vicinal azidoalcohols are an important class of organic compoundsand they serve as precursors in the synthesis of vicinal aminoalcohols,carbohydrates, nucleosides [7–9], lactames [10], and oxazolines [11].They are usually prepared through ring opening of epoxides byusing different kinds of azides in suitable solvents. The reactionsoften carried out under either alkaline or acidic conditions and sever-al different methods have been devised in order to obtain the directazidolyses of epoxides in the presence of sodium azide [12]. Underthese conditions, azidolyses are usually carried out over a long reac-tion times and azidohydrin is often accompanied by isomerization,epimerization, and rearrangement of products [13,14]. In order toovercome some of these limitations, a number of alternative proce-dures have been reported over the past few years using a variety ofcatalysts [15–18]. However, most of these methods have limitationsincluding use of expensive catalyst or solvent, strong acidic condi-tions, low regioselectivity, longer reaction time, and harsh reactionconditions. Thus, the development of a new and efficient protocol

Scheme 1. Synthesis of [pbmim]Cl2 (1a), and [pbmim](FeCl4)2 (2a).

Fig. 1. Visible spectrum of [pbmim](FeCl4)2 (1b).

Fig. 2. Raman spectrum of [pbmim](FeCl4)2 (1b).

Fig. 3. Magnetic susceptibility of [pbmim](FeCl4)2 (1b).

Fig. 4. Magnetic susceptibility of FeCl3.

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Scheme 2. Synthesis of 1-azido-3-phenoxypropan-2-ol (Entry 2) as a model study.

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for this transformation under mild and more convenient conditions isstill needed.

With this expectation in mind, a novel and green approach forthe preparation of 1,2-azidoalcohols using a catalytic amount of[pbmim](FeCl4)2, as a novel magnetic dicationic ionic liquid (MDIL) inwater under reflux conditions is described.

2. Results and discussion

1-Butyl-3-methylimidazolium tetrachloroferrate ([bmim]FeCl4)with magnetism was synthesized and first reported by Hayashi etal. [19] in 2004. Since then, the syntheses of magnetic ILs have beenfocused on expanding synthesis with different alkyl chain length ofimidazole cations or different magnetic metal anions. To the best ofour knowledge, there is no report for the preparation of magneticroom temperature dicationic ionic liquid (MRTDIL). Scheme 1 illus-trates the synthetic route for the preparation of MRTDIL synthesizedand characterized in this study.

As shown in Scheme1, the synthesis ofmagnetic imidazoliumbaseddicationic room temperature ionic liquid (2a), [pbmim](FeCl4)2, in-volves two steps. First, 1,3-dichloropropane reacted with two equiva-lents of N-methylimidazole in methanol and under reflux conditionsto afford dicationic RTILs in quantitative yields [20]. In the secondstep, the anions of imidazolium based dicationic room temperatureionic liquid, Cl-, were easily changed with FeCl4- anions by the simplemixing with FeCl3 under neat conditions.

Due to the paramagnetic nature of the [pbmim](FeCl4)2, nuclearmagnetic resonance technique could not be used to confirm its structure.Instead, UV and Raman spectroscopes were used to characterize the[pbmim](FeCl4)2 structure. The UV spectrum is shown in Fig. 1.[Pbmim](FeCl4)2 spectra exhibited absorption bands in the visible regionat 534, 620 and 680 nm which are characteristic for the FeCl4- anion(Fig. 1).

Moreover, this MRTDIL was characterized via Raman spectroscopyand proved to be identical with authentic material reported in litera-ture [21]. The peak at 333 cm−1 is due to FeCl4-, indicating that theanion of this MRTDIL is FeCl4- (Fig. 2).

The magnetic properties of the [pbmim](FeCl4)2 and FeCl3 weremeasured by a vibrating sample magnetometer, VSM, at the room tem-perature (Figs. 3, 4). The VSM technique is used tomeasure themagne-tization value of magnetic particles under applied magnetic field. Forparticles with magnetic properties when the applied magnetic field isremoved, they should exhibit no Coercivity and reminiscences. In(Figs. 3 & 4), the paramagnetic linear response of [pbmim](FeCl4)2 is

Table 1Efficiency of solvents on azidolysis of epoxides.a

Entry Solvent Time (min) Yield (%)

1 CH2Cl2 180 282 n-hexane 180 353 CH3CN 180 504 EtOAc 180 605 Et2O 180 306 H2O 60 92

a 2,3-epoxypropyl phenyl ether (1 mmol), NaN3 (3 mmol) and 20%mmol of MRTDILwere used under reflux conditions.

similar to iron (Ш) chloride. FromMvs.H curves, the saturationmagne-tization is the value at the same field was found to be 0.4 emu g−1,lower than of FeCl3 (0.7 emu g−1). Magnetic susceptibility of IL is re-duced due to the presence of alkyl groups in the structure of IL.

We examined the catalytic ability of [pbmim](FeCl4)2 for conver-sion of 2,3-epoxypropyl phenyl ether (1 mmol) to the correspondingazidoalcohol with NaN3 (3 mmol) in various solvents (Scheme 2).The reaction was carried out in diethyl ether, n-hexane, acetonitrile,dichloromethane, ethyl acetate and water. From the results given inTable 1, it fallows that the best solvent for this reaction is water.Thus, water is an excellent solvent in terms of cost, availability, andenvironmental impact and shorter reaction times.

As show in Tables 1 and 2, interestingly this catalyst acted efficientlyinwater, and it was observed that 20%mmol of the catalyst is enough toconvert 1 mmol of different epoxides to their corresponding vicinalazidohydrin in good to excellent isolated yields (Scheme 3).

The regioselectivity of the ring opening of epoxides is dependenton the mechanism of the reaction and particularly on steric and elec-tronic factors. Azide anion underwent the reaction with styrene oxide inthe presence of [pbmim](FeCl4)2 in a regioselective manner to give thecorresponding vicinal azidohydrin with preferential nucleophilic attackat benzylic position and produced 2-phenyl-2-azidoethanol (ΙΙ) as majorproduct (Table 2, entry 1). Epoxides carrying electron-withdrawinggroups reacted under similar reaction conditions with azide anion andtheir corresponding 1,2-azidoalcohols were produced with preferentialattack at the non-benzylic terminal carbon of the epoxide (Table 2, entries2–6). Furthermore, cyclic epoxides, such as cyclohexene oxide reactedsmoothly in SN2 fashion to afford the corresponding 1, 2 azidoalcohols(Table 2, entries 7). The stereochemistry of the ring opening productswas found to be in the trans-configuration as determined from the cou-pling constants associated with the 1H NMR spectral resonances of thering protons in.

The structures of the products were established from their spec-tral (1H NMR & 13C NMR, IR) data.

MRTDIL showed remarkable reactivity as a Lewis acid reagent andconsiderably accelerated the reactions. We have proposed the plausi-ble mechanism for the ring opening of epoxide in the presence ofMRTDIL (Scheme 4). As shown in Scheme 4, FeCl4- groups at the IL,probably, facilitate the ring opening of epoxide.

The success of the above reactions promptedus to investigate the re-cyclability of catalyst. We carried out our study by using the reaction2,3-epoxypropyl phenyl ether with NaN3 and under optimal conditionsas a model study. The aqueous phase was then subjected to distillationat 80 °C under reduced pressure (10 mm Hg) for 4 h to recover theMRTDIL almost completely. The MRTDIL, thus recovered could bereused six times without loss of activity for the typical reaction (Fig. 5).

In order to show the merit of our procedure for the synthesis ofvicinal azidoalcohols, we have shown the advantages of the presentprocedure by comparing our results with those previously reportedin the literature (Table 3).

In summary, [pbmim](FeCl4)2 as a magnetic imidazolium baseddicationic room temperature ionic liquid was synthesized, character-ized and its catalytic activity in the ring opening of epoxides withNaN3 in water was investigated. This method offers several advan-tages including high yield, short reaction time, simple work-up proce-dure, ease of separation, and recyclability of the magnetic catalyst, as

Table 2Reaction of different epoxides with NaN3 using MRTDIL in water.a

Entry Substrate Producta Time (min) Yield (%)b

1 60 85c

2 60 92

3 75 88

4 60 91

5 60 90

6 60 86

7 60 89

a All of products were identified by comparison of their physical and spectral data with authentic samples.b Isolated yields.c According to GC analysis.

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well as the ability to tolerate a wide variety of substitutions in thestarting materials.

3. Experimental

3.1. General remarks

1H NMR & 13C NMR spectra were recorded on a Bruker AdvancedDPX 400 MHz instrument spectrometer using TMS as the internalstandard in CDCl3. IR spectra were recorded on a BOMEM MB-Series1988 FT-IR spectrometer. Substrates were purchased from MerckCompany in high purity. All Products were characterized by compar-ison of their physical and spectroscopic data with those of knownsamples. The purity of products and reaction monitoring was accom-plished by TLC on silica gel Poly GramSILG/UV 254 plates.

3.2. Procedure for the preparation of [pbmim]Cl2

1,3-Dicholoropropane (1 mmol) reacted with 1-methylimidazole(2 mmol), respectively, stirred in methanol, refluxed for 24 h, andthen precipitated from ethyl acetate to obtain the required product(white solid 1a, yield 94%). 1H NMR (400 MHz, D2O): δ 2.56 (quin,

Scheme 3. Synthesis of vicinal azidoalcohols from epoxide

J = 7.3 Hz, 2H), 3.90 (s, 6H), 4.35 (t, J = 7.3 Hz, 4H), 7.48 (s, 2H),7.52 (s, 2H), and 8.62 (s, 2H).

3.3. Procedure for preparation of [pbmim](FeCl4)2 as a magnetic roomtemperature dicationic ionic liquid

[Pbmim](FeCl4)2, MRTDIL, was prepared by mixing crystal powderof [pbmim]Cl2 (1 mmol) with anhydrous FeCl3 (2 mmol) at roomtemperature for 3 h, a dark brown liquid was obtained. The obtainedMRTDIL was extracted with small amount of ethyl acetate. The sol-vent was evaporated and the resulting clear brown liquid was driedin vacuum oven at 60 °C for 24 h. The MRTDIL was obtained in highyield (89%). Elem. Anal. Calc. for C11H18Cl8Fe2N4: C, 21.9; H, 2.99; N,9.3O. Found: C, 20.4; H, 3.1; N, 9.05%.

3.4. General procedure for the preparation of 1,2-azidoalcohols in water

A solution of epoxide (1 mmol), NaN3 (3 mmol), [pbmim](FeCl4)2(20% mmol), and water (5 ml) were heated and stirred under refluxconditions for appropriate time (Table 2). The progress of the reactionwas monitored by TLC (eluent: n-hexane-EtOAc 80:20). After com-pletion of the reaction, the mixture was extracted with ether(2 × 10 ml). The combined organic extracts (dried over CaCl2) were

s in the presence of magnetic phase transfer catalyst.

Table 3Comparison of some epoxides with different catalysts.

Entry Epoxide Catalyst/reagent/solvent Time(h)

Yield(%)

Ref

1 Zr(OTf)4/TMGA/CH3CNa 42 84 [16]Polymeric PTC/NaN3 H2Ob 6 95 [17]LiClO4/NaN3/CH3CN 5 92 [18]Mg(ClO4)2/NaN3/CH3CN 2 78 [18]NH4Cl/NaN3/CH3OH–H2O 20 94 [18]CeCl3/NaN3/CH3CN–H2O 3 89 [12][Pbmim](FeCl4)2/NaN3/H2Oc 1 90 –

2 Zr(OTf)4/TMGA/CH3CN 42 84 [16]Polymeric PTC/NaN3/H2O 8 89 [17]LiClO4/NaN3/CH3CN 36 95 [18]Mg(ClO4)2/NaN3/CH3CN 24 94 [18]NH4Cl/NaN3/CH3OH–H2O 36 92 [18]CeCl3/NaN3/CH3CN–H2O 3 98 [12][Pbmim](FeCl4)2/NaN3/H2O 1 89 –

3 Zr(OTf)4/TMGA/CH3CN 2 88 [16]Polymeric PTC/NaN3/H2O 12 94 [17]LiClO4/NaN3/CH3CN 5 97 [18]Mg(ClO4)2/NaN3/CH3CN 2 96 [18]NH4Cl/NaN3/CH3OH–H2O 12 95 [18]CeCl3/NaN3/CH3CN–H2O 3 99 [12][Pbmim](FeCl4)2/NaN3/H2O 1 92 –

a TMGA: 1,1,3,3-tetramethylguanidinium azide.b Polymeric PTC: poly[N-(2-aminoethyl)acrylamido]-trimethyl ammonium iodide.c Present method.

Scheme 4. Plausible mechanism for the ring opening of epoxide catalyzed by MRTDIL.

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evaporated under reduced pressure. The desired azidohydrin wasobtained in good to excellent isolated yields. For styrene oxide, furtherpurification was achieved by column chromatography.

3.4.1. Selected spectroscopic data2-Azido-2-phenyl-1-ethanol (Entry 1): IR (neat): νmax N3

(2103 cm−1); 1H NMR (400 MHz, CDCl3): 3.36 (s, 1H), 3.73 (m, 2H),4.65 (m, 1H), 7.33–7.44 (m, 5H). 13C NMR (100 MHz, CDCl3): 66.27,68.03, 127.47, 128.40, 128.51, 136.27 ppm.

1-Azido-3-phenoxypropan-2-ol (Entry 2): IR (neat): νmax N3

(2100 cm−1); 1H NMR (400 MHz, CDCl3): 3.51 (d, 2H), 3.88–3.98(m, 1H), 4.00 (d, 2H), 4.16 (s, 1H), 6.93–7.00 (m, 2H), 7.01–7.06 (m,1H), 7.26–7.36 (m, 2H). 13C NMR (100 MHz, CDCl3): 53.50, 69.23,69.20, 114.29, 121.15.

1-Azido-3-isopropoxypropan-2-ol 9 (Entry 3) liquid; IR (neat):νmax N3 (2103 cm−1); 1H NMR (CDCl3, 400 MHz): δ: 1.40 (d, J =6.5 Hz, 6H), 3.01 (m, 1H), 3.20 (dd, J = 7.0, 11.5 Hz, 1H), 3.25 (dd,J = 4.0, 11.5 Hz, 1H), 3.30–3.50 (m, 2H), 3.96 (brs, 1H, OH), 3.97–4.0 (m, 1H). 13C NMR (CDCl3, 100 MHz) δ: 72.1, 71.3, 70.3, 53.4,25.7 ppm.

1-Azido-3-propoxypropan-2-ol (Entry 4): IR (neat): νmax N3

(2102 cm−1); 1H NMR (400 MHz, CDCl3): δ:1.07 (t, 3H), 1.70–1.78(m, 2H), 3.82 (s, 1H), 3.30 (m, 2H), 3.38 (t, 2H), 3.42 (d, 2H), 3.86(m, 1H). 13C NMR (100 MHz, CDCl3): δ: 19.15, 31.74, 53.50, 69.73,70.59, 71.71 ppm.

1-Azido-3-Allyloxypropan-2-ol (Entry 5): IR (neat): νmax

N3(2103 cm−1); 1H NMR (400 MHz, CDCl3): δ: 3.45–3.54 (m, 2H), 3.8(m, 1H), 3.96–4 (m, 2H), 4.18 (sbr, 1H), 3.7 (m, 2H), 5.2 (dd, 1H), 5.3(dd, 1H), 5.8 (dd, 1H). 13C NMR (100 MHz, CDCl3): δ: 53.37, 69.87,71.32, 72.07, 117.36, 134.36 ppm.

1-Azidobutan-2-ol (Entry 6): IR (neat): νmax N3 (2098 cm−1); 1HNMR (400 MHz, CDCl3): δ: 0.96 (t, 3H), 1.48(m, 2H), 3.2 (m, 1H), 3.4(d, 2H), 3.97 (br, 1H). 13C NMR (100 MHz, CDCl3): δ: 8.1, 27.7, 71.2,53 ppm.

2-Azidocyclohexan-1-ol (Entry 7): IR (neat): νmax N3 (2097 cm−1);1H NMR (400 MHz, CDCl3): 1.20–1.36 (m, 4H), 1.72–1.78 (m, 2H),

Fig. 5. Recyclability

2.00–2.07 (m, 2H), 2.52 (s, 1H), 3.10–3.22 (m, 1H), 3.28–3.42 (m,1H). 13C NMR (100 MHz, CDCl3): 24.38, 24.48, 24.51, 33.14, 62.14,73.79 ppm.

Acknowledgments

We gratefully acknowledge financial support from the ResearchCouncil of Islamic Azad University, Science and Research BranchTehran.

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