Si-Imidazole-HSO4 Functionalized Magnetic Fe3O4 Nanoparticles as an Efficient and Reusable Catalyst for the Regioselective Ring Opening of Epoxides in Water

Document Type: Research Paper


Department of Chemistry, Payame Noor University, P.O. BOX: 19395-4697 Tehran, Iran


An efficient and simple method for the preparation of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs) and used as an efficient and reusable magnetic catalysts for the regioselective ring opening of epoxides under green conditions in water. This catalyst was used for the ring opening of epoxide corresponding to the thiocyanohydrins and azidohydrines. Compared to the classical ring opening of epoxides, this new method consistently has the advantage of excellent yields, short reaction times, and methodological simplicity.  



       Magnetic nanoparticles (MNPs) have been considered as attractive and interesting materials because of their high surface area and unique magnetic properties, moreover, they have a wide  range of novel applications in various fields; such as magnetic fluids [1] catalysis [2,3] biology and medical applications [4] magnetic resonance imaging (MRI) [5,6] data storage [7] and environmental remediation [8,9]. MNPs have been recently viewed as attractive materials either as catalysts or as supporters for immobilization of homogeneous and heterogeneous catalysts [10,11]. Magnetic nanocatalysts can easily be separated and recycled from the other products by an external magnet, which achieves simple separation of the catalysts without filtration [12-14]. Over the last few years, Ionic liquids (ILs), have been generally used as solvents for organic synthesis, catalysis, and also media for extraction processes [15-16]. Therefore, catalytic systems developed on MNP supports have been successfully used in catalyzing a wide range of organic reactions including knoevenagel reaction [17,18] nucleophilic  substitution  reactions  of  benzyl  halides [19], epoxidation of alkenes [20], synthesis of α-amino nitriles [21], hydrogenation of alkynes [22], esterifications [23], CO2 cycloaddition reactions [24], Suzuki coupling reactions [25] and three-component condensations [26]. In this research, magnetic nanoparticles which can support ionic liquids will be tested and analyzed as a new heterogeneous catalyst for the regioselective ring opening of epoxides in water.




      Products were characterized by comparison of their spectroscopic data (1H NMR, 13C NMR and IR) and physical properties with those reported in the literature. NMR spectra were recorded in DMSO-d6 on a Bruker advanced DPX 500 and 400 MHz instrument spectrometers using TMS as internal standard. IR spectra were recorded on a Frontier FT-IR (Perkin Elmer) spectrometer using a KBr disk. All yields refer to isolated products. The purity determination of the products and reaction monitoring were accomplished by TLC on silica gel polygram SILG/UV 254 plates. The particle morphology was examined by SEM and TEM. 


      Synthesis of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs). The magnetite nanoparticles were prepared by the conventional co-precipitation method [27]. A schematic representation of the synthesis of magnetic nanoparticles supporting ionic liquids is shown in Scheme 1. Then, 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride (IL), this IL was prepared from the reaction of imidazole with (3-chloropropyl)trimethoxysilane and heated at 120 °C for 8 h with continuous stirring under N2 atmosphere [28]. Then an excess amount of KHSO4 was added into deionized water and stirred for 24 h at room temperature. KCl, prepared during the exchange of chloride anions with HSO4 [29] and MNP-IL-HSO4, was separated by magnetic decantation, washed with acetonitrile and dichloromethane, and left to dry in a desiccator.


     General procedure for the preparation of β-hydroxythiocyanates and 2-azidoalcohols in water. Si-Im-HSO4 MNPs (20 mg) was added to a mixture of the epoxide (1.0 mmol) and KSCN or NaN3 (3 mmol)  in  water (5 ml). The reaction mixture was magnetically stirred at 80 °C for the appropriate time. Progress of the reaction was monitored by TLC using ethylacetate:n-hexane (1:4). After reaction completion, the mixture was extracted with ethyl ether (5 ml × 3), washed with brine, dried with CaCl2and evaporated under reduced pressure. The desired thiocyanohydrins and azidohydrines were obtained in good to excellent isolated yields (83-94%).



 Scheme 1. Synthesis of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs)


      The spectral (1H NMR, 13C NMR and IR) of some representative compounds are given below: Spectral data for 1-azido-3-phenoxy-2-propanol (Entry 1). IR νmax (cm-1):  2103 (N31H 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.

      Spectral data for 3-Phenoxy-2-hydroxypropyl thiocyanate (Entry 1). IR νmax (cm-1): 2156 (SCN); 1H NMR (CDCl3, 400 MHz): 3.13-3.31 (2H, d), 3.78 (1H, s), 4.01-4.05  (2H, d),  4.29  (1H, m),  6.95  (2H, m),  7.02   (1H, m),7.22-7.34 (2H, m); 13C NMR (CDCl3, 100 MHz): 37.39, 68.06, 69.51, 112.99, 114.64, 121.32, 129.88, 158.49.

      Spectral data for 2-azido-2-phenyl-1-ethanol (Entry 2). IR νmax (cm-1):  2102 (N31H 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.

      Spectral data for 1-azido-3-butoxy-2-propanol (Entry 3). IR νmax (cm-1):  2102 (N31H 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): 53.37, 69.87, 71.32, 72.07, 117.36, 134.36.

      Spectral data for 3-allyloxy-2-hydroxypropyl thiocyanate (Entry 3). IR νmax (cm-1):  2155 (SCN) 1H NMR (CDCl3, 400 MHz): 3.04-3.24 (3H, m), 3.53 (2H, d), 4.01-4.08 (3H, m), 5.19-5.29 (2H, m), 5.87 (1H, m); (CDCl3, 100 MHz): 37.35, 69.17, 71.09, 71.59, 113.07, 117.46, 133.66.



 Fig. 1. FT-IR spectra of (a) MNP, (b) IL, (c) Si-Im-HSO4 MNPs.



 Characterization of Si-Im-HSO4 Ionic Liquid Supported on MNP; Preparation, Structural and Morphological Analysis

      Immobilization of Si-Im-HSO4 functionalized MNPs combines the advantages of ionic liquids with those of heterogeneous catalysts. The Si-Im-HSO4 MNPs catalyst was synthesized by a multi-step procedure, as shown in Scheme 1, and characterized by various techniques.

      An infrared spectrum was obtained in the 400-4000 cm-1 range, by a Perkin-Elmer FTIR spectrometer. KBr pellets were used for solid samples. The infrared spectroscopy presents a useful tool to initially detect the success of the immobilization process.

      Figure 1 presents the FTIR spectra of MNPs, IL and Si-Im-HSO4 MNPs. Comparing with the spectra of MNPs without modifiers (curve a), spectrum of Si-Im-HSO4 MNPs curve c) presented a new peak at 1090 cm-1 indicative of the Si-O band on  Fe3O4. The bands at 2948 and 2843 cm-1 wave numbers was assigned to the stretching vibrations of CH3 and CH2 in IL, while new peaks at 1403 and 1287 cm-1 are their bending vibrations. Accordingly, one can be sure that IL has been immobilized successfully on the surface of MNPs.

      The positions and relative intensities of all the peaks in the XRD pattern of Si-Im-HSO4 MNPs conform well with the standard XRD pattern of MNPs (Fig. 2). Peaks of Si-Im-HSO4 MNPs (2θ = 30, 36, 37, 38, 39, 46, 55, 58) and iron oxide phase (2θ = 33, 41, 63, 68) indicate the structure of the catalyst. It is implied that the resultant nanoparticles are pure MNPs with a spinel structure and that the grafting process did not induce any phase change of the MNPs nanoparticles.

      The structural and morphological characterization of Fe3O4 and Si-Im-HSO4 MNPs nanostructure were performed by measuring SEM using a Philips XL30 scanning electron microscope. The surface morphologies of the Fe3O4 nanoparticles without modifiers and Si-Im-HSO4 MNPs are shown in Figs. 3A and 3B.

      The TEM images of MNPs and Si-Im-HSO4 MNPs are presented in Fig. 4, showing almost homogeneous and uniform distribution of these particles in the powder samples.  Figure 5 shows  the  magnetization  curves  of  the prepared MNPs, and Si-Im-HSO4 MNPs. The magnetization curve of MNPs exhibited no eminence effect (indicating the superparamagnetic property) with saturation magnetization of about 60 (emu g-1). As seen in Fig. 5, similar to magnetite particles, MNPs, and Si-Im-HSO4 MNPs nanocomposites also indicate a zero remanence Ms and coercivity, suggesting that the superparamagnetic behavior is still retained with the nanocomposite materials.



 Fig. 2. XRD pattern of (A) MNPs, (B) Si-Im-HSO4 MNPs.


Application of Si-Im-HSO4 Ionic Liquid Supported on MNP as Magnetic Catalyst for the Regioselective Ring Opening of Epoxides in Water

      The catalyst concentration varied over a range of 5-25 mg Si-Im-HSO4 MNPs on the basis of the total volume of the reaction mixture. As mentioned before, we have carried out the reaction of 2,3-epoxypropyl phenyl ether with potassium thiocyanate. Different reaction conditions have been studied for optimization (Table 1). Entry 6 in Table 1 shows optimization of reaction conditions. After optimizing the conditions, we examined the generality of these conditions to other substrates using several epoxides. The reaction proceeds efficiently in all cases. Different epoxides underwent ring opening easily in the presence of Si-Im-HSO4 ionic liquid supported on MNP at 80 °C condition in water  (Table  2).  The  products  were  formed  in  excellent yields. The conversion was completed in 10-40 min.


Fig. 3. SEM images of (A) MNPs, (B) Si-Im-HSO4 MNPs.