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BY-NC-ND 3.0 license Open Access Published by De Gruyter September 19, 2017

Magnetically recoverable nano-catalysts in sulfoxidation reactions

Mosstafa Kazemi and Massoud Ghobadi
From the journal Nanotechnology Reviews

Abstract

The sulfoxidation of sulfides have received special attention in organic synthesis especially in medical chemistry because compounds containing S=O bonds (sulfoxides) are privileged structural scaffolds for building pharmacologically and biologically active molecules. Magnetic separation is an efficient strategy for the rapid separation of catalysts from reaction medium and an alternative to time-, solvent-, and energy-consuming separation techniques. In recent times, many protocols based on using magnetically recoverable nano-catalysts have been reported for the oxidation of sulfides to the sulfoxides. This review is focused on metal complexes, acid, and bromine reagents supported on magnetic nanoparticles and their applications as magnetically recoverable nano-catalysts in the sulfoxidation reactions.

1 Introduction

Catalysis research campaign is a hot research topic in modern organic synthesis. In this category, magnetic separation has received profound attention because catalysts immobilized on magnetic nanoparticles can be readily separated from reaction medium using an external magnet, without the need for filtration, centrifugation, or other tedious work-up processes [1], [2], [3], [4], [5]. Furthermore, recent literature studies clearly have shown that magnetic nanoparticles possess several admirable advantages such as high surface area to bulk ratios, low toxicity, high activity and thermal stability, and the capability of surface modifications and easy dispersion [6], [7], [8], [9], [10], [11], [12]. In fact, magnetic separable catalysts are a well-favored and fascinating strategy to bridge the split between heterogeneous and homogenous catalysis [13], [14]. In describing the magnetic nanoparticles, it can be said that the magnetic separation is, in fact, an admirable and valuable victory in the research of chemistry catalysis. On the other hand, catalysis research under green solvents or solvent-free conditions is always a popular theme from the viewpoint of green synthesis [15]. Considering these issues, in recent times, most of organic chemists focused on organic-synthesis catalysis based on using magnetically recoverable catalysts under benign mediums and mild conditions.

Organosulfur chemistry is always a fascinating research field in organic synthesis because sulfur-containing compounds are prevalent in a broad spectrum of active biological, pharmaceutical, and natural molecules [16], [17], [18]. Sulfoxides are an important class of sulfur-containing compounds that received special attention in organic synthesis. The first report for the synthesis of sulfoxides was presented in 1856 by Marcker [19]. Since then, studies on the sulfoxide applications and activities in various fields, especially medical chemistry, have noticeably increased, and a large number of methods have been reported for their preparation. Organic sulfoxides have been widely applied as a ligand and an oxotransfer reagent in asymmetric synthesis of organic compounds [20], [21], [22]. They play also a vital role in the synthesis of natural products, valuable physiologically and pharmacologically active molecules [23]. Furthermore, sulfoxide derivatives are also prevalent structural motifs in many drugs and biologically active molecules [24], [25]. A nice category of valuable pharmaceutical and biological molecules containing S=O bonds, modafinil (1), adrafinil (2), CRL-40,941 or fladrafinil (3), fipronil (4), oxydemeton-methyl (5), omeprazole (6), pantoprazole (7), lansoprazole (8), and rabeprazole (9), is listed in Figure 1 [26], [27], [28], [29], [30], [31], [32]. The oxidation of sulfides is the most straightforward strategy for the preparation of the sulfoxides [33]. Sulfoxidation catalysis is a well-known and valuable reaction in organic synthesis [33]. Up to now, a wide variety of catalysts have been reported for the oxidation of sulfides to the sulfoxides. However, here, a significant blind spot is glaring, namely, the recovery and reusability of the catalyst because catalysts are often expensive or toxic. The separation of a catalyst from the sulfoxide products or reaction mixture is a difficult, tedious, and time-consuming task and needs a series of costly and specific techniques. Therefore, the search for new recoverable catalysts is a real challenge in sulfoxidation catalysis. In recent times, a wide number of protocols based on using magnetically recoverable nano-catalysts have been reported for the oxidation of sulfides to sulfoxides. Here, in this review, we provided a scientific effort to list the magnetically recoverable nano-catalysts reported in the literature and their activity in sulfoxidation reactions.

Figure 1: A nice category of valuable pharmaceutical and biological molecules containing S=O bonds (sulfoxides).

Figure 1:

A nice category of valuable pharmaceutical and biological molecules containing S=O bonds (sulfoxides).

2 Magnetically recoverable metallic catalysts

Catalysis research based on using transition metal complexes is a well-known research field in organic synthesis because transition metal complexes activate various sites in substrates where reactions can readily take place [34], [35]. Over the last decade, the catalytic activity of transition metal complexes immobilized on solid supports (such as silica, alumina, zeolites, and mesoporous materials) in various chemical reactions were extensively studied by organic chemists [13], [14], [36]. Although these protocols are valuable, there are several drawbacks such as tedious work-up routes, unsatisfactory yields, and difficult separation or recovery. Furthermore, in these catalytic strategies, fewer sites present on the surface are accessible for catalysis; less reactive and selective is the catalytic system, and sometimes, the support, itself, can act as the catalyst of side reactions [13], [14]. Therefore, the development of new support materials and heterogenization strategies for organic synthesis is an important challenge in modern catalysis science. More recently, transition metal complexes immobilized on magnetic nanoparticles have emerged as efficient magnetically recoverable catalysts to overcome these drawbacks. In recent times, a wide number of the sulfoxidation reactions have been developed based on using transition metals complexes immobilized on magnetic nanoparticles as the catalyst.

3 Copper catalysts

Copper complexes are well-known and promising catalysts for oxidation reactions because copper is a less toxic, readily available, and inexpensive metal compared with other transition metals [13], [14]. During the recent years, a number of magnetically recoverable copper catalysts have been investigated for the oxidation of sulfides to sulfoxides. Ghorbani-Choghamarani and his team reported the sulfoxidation of aliphatic and aromatic sulfides based on using Cu(II)-Schiff base complex-functionalized magnetic Fe3O4 nanoparticles (MNPs 1, Figure 2) as magnetically recoverable catalysts. The structure of MNPs 1 was characterized by FT-IR spectroscopy, TGA, and SEM [37]. The SEM analysis showed that the MNPs 1 is prepared in nanometer-sized particles (70–80 nm). Sulfoxidation reaction failed in the absence of the catalyst (MNPs 1). Solvent-free sulfoxidation reactions were catalyzed by MNPs 1 (0.02 mmol) in the presence of H2O2 at ambient temperature (Scheme 1). By this catalytic system, a variety of sulfides can be successfully converted to the corresponding sulfoxides in excellent yields (in less than 180 min). Furthermore, the copper nano-catalyst was found to be highly stable with noticeable catalytic activities, even after 10 runs. In 2015, Ghorbani-Choghamarani and his co-workers developed a magnetically recoverable copper catalyst (MNPs 2, Figure 2) for the sulfoxidation reactions. The structure of the as-prepared catalyst was characterized by TG/DTG, FT-IR, TEM, VSM, ICP, AAS, XRD, EDS, and SEM spectroscopic techniques [38]. Diameters of approximately 10–20 nm for the final MNPs 2 were observed in SEM and TEM images. Successful preparation of the MNPs 2 was well confirmed by EDS analysis. The MNPs 2 was then tested for the oxidation of sulfides to sulfoxides in the presence of H2O2 under thermal ethanol (Scheme 2). Under the described conditions, a variety of asymmetrical and unsymmetrical sulfides were tested, and the desired products were afforded in moderate to high yields. Interestingly, product separation was readily performed using an external magnet, and the recovered catalyst was reused for 12 runs without any notable loss in catalytic activity. In another study, the catalytic activity of chitosan-Schiff base complex of Cu(II) supported on supramagnetic Fe3O4 nanoparticles (MNPs 3, Figure 2) for the oxidation of sulfides was also evaluated by Naghipour and Fakhri. The as-synthesized MNPs 3was characterized by XRD, FT-IR, TGA, SEM, and EDX spectroscopic techniques [39]. The sulfoxidation reaction failed when the process was performed in the absence of MNPs 3. To identify the best reaction medium, a series of solvents such as H2O, EtOH, CH3CN, CH2Cl2, and ethyl acetate was tested. However, the maximums yield of the desired sulfoxide was observed under solvent-free conditions. Under the optimized conditions, room temperature oxidation of a nice library of sulfides with 30% H2O2 leads to afford the corresponding sulfoxides in excellent yields (Scheme 3). This catalytic system was not efficient for the oxidation of diphenylsulfide because the desired product was obtained in unsatisfactory yield even after 48 h. Recycling studies have shown that the recovered catalyst can be reused for four cycles without significant loss of activity. Comparison FT-IR spectra of used MNPs 3 with the fresh MNPs 3 show that the structure of MNPs 3 remained intact after the successive four runs of recoveries.

Figure 2: Magnetically recoverable copper nano-catalysts.

Figure 2:

Magnetically recoverable copper nano-catalysts.

Scheme 1: Solvent-free oxidation of sulfides to sulfoxides catalyzed by Fe3O4-Schiff base of Cu(II)/H2O2 (MNPs 1).

Scheme 1:

Solvent-free oxidation of sulfides to sulfoxides catalyzed by Fe3O4-Schiff base of Cu(II)/H2O2 (MNPs 1).

Scheme 2: Oxidation of sulfides to the sulfoxides with H2O2 catalyzed by Fe3O4/salen of Cu(II) (MNPs 2) in ethanol.

Scheme 2:

Oxidation of sulfides to the sulfoxides with H2O2 catalyzed by Fe3O4/salen of Cu(II) (MNPs 2) in ethanol.

Scheme 3: Oxidation of sulfides to sulfoxides with H2O2 catalyzed by Fe3O4-chitosan-Schiff based Cu complex (MNPs 3).

Scheme 3:

Oxidation of sulfides to sulfoxides with H2O2 catalyzed by Fe3O4-chitosan-Schiff based Cu complex (MNPs 3).

The same group also reported the preparation of magnetically recoverable Fe3O4@chitoasn-based Cu complex (MNPs 4, Figure 2) for the catalytic oxidation of sulfides. The structure of the as-prepared catalyst was characterized by a series of spectroscopic techniques such as XRD, FT-IR, TGA, SEM, and EDX [40]. TGA analysis also showed a high thermal stability of the magnetic nano-catalyst. The EDS analysis confirmed the successful immobilization of copper complex on Fe3O4@chitosan-bond-2-hydroxy-1-naphthaldehyde. The catalytic performance of the MNPs 4 for the oxidation of sulfides to sulfoxides has been evaluated in the presence of H2O2 as the oxidant. The obtained results showed that the target sulfoxides were obtained in excellent yields in less than 90 min. By this catalytic strategy, diphenylsulfoxide was also afforded satisfactory yields (Scheme 4). The catalyst was recycled by simple magnetic separation and reused for four runs without significant loss in efficiency.

Scheme 4: Oxidation of sulfides to sulfoxides with H2O2 catalyzed by Fe3O4@chitosan-based Cu complex (MNPs 4).

Scheme 4:

Oxidation of sulfides to sulfoxides with H2O2 catalyzed by Fe3O4@chitosan-based Cu complex (MNPs 4).

More recently, Ghorbani-Choghamarani et al. reported the fabrication of Cu-S-(propyl)-2-aminobenzothioate immobilized on magnetic Fe3O4 nanoparticles (MNPs 5) for the catalytic sulfoxidation of sulfides. The as-fabricated catalyst has been characterized by TEM, SEM, EDS, AAS, ICP-OES, XRD, FT-IR, VSM, and TGA spectroscopic techniques [41]. The SEM and TEM images of MNPs 5 show that the catalyst consisted of nanometer-sized particles (20 nm). The catalytic activity of MNPs 5 was then examined in the oxidation of sulfides to sulfoxides. Solvent-free sulfoxidation reactions in the presence of H2O2were catalyzed by MNPs 5 at room temperature. As shown in Scheme 5, the desired sulfoxides were obtained in 91–97 yields (in less than 190 min). The catalyst was quickly recovered from solution using handheld magnets. The authors also indicated that this catalyst was recovered and reused for at least five runs without any significant loss of activity.

Scheme 5: Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by Cu-SPATB/Fe3O4 (MNPs 5).

Scheme 5:

Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by Cu-SPATB/Fe3O4 (MNPs 5).

A plausible reaction mechanism for the sulfoxidation reactions catalyzed by organometallic catalysts containing Cu(II) metal ions, based on published previous reports in literature [42], [43], is depicted in Scheme 6. The reaction of H2O2 with the Cu catalyst leads to intermediate A, which is converted to active oxidant B. In the next step, nucleophilic attack of the sulfide on this intermediate gives cation C, which produces the corresponding sulfoxide [41].

Scheme 6: Plausible mechanism for the sulfoxidation reaction catalyzed by MNPs-Cu(II) complex in the presences of H2O2.

Scheme 6:

Plausible mechanism for the sulfoxidation reaction catalyzed by MNPs-Cu(II) complex in the presences of H2O2.

4 Vanadium catalysts

Vanadium catalysts are found to be efficient catalysts for the selective oxidation sulfides to the sulfoxides with oxidizing agents such as H2O2 and UHP. Most of the catalysts investigated for the sulfoxidation reactions are based on the chemistry of vanadium oxides. During recent years, several magnetically recoverable catalysts have been investigated for the sulfoxidation of sulfides. In 2012, Bagherzadeh and co-workers reported the preparation of a magnetically recyclable vanadium (V) catalyst through the covalent anchoring of VO(salen)Cl on silica-coated magnetic Fe3O4 nanoparticles (MNPs 6). The as-prepared catalyst was characterized by FT-IR, XRD, DLS spectroscopic techniques [44]. The DLS analysis demonstrates that the Fe3O4@SiO2@VO(salen) catalyst has particles, which are exactly in the nanosize range. The catalytic potential of the MNPs 6 was evaluated in the sulfoxidation of sulfides in CH2Cl2/MeOH at room temperature using UHP as the oxidant. As shown in Scheme 7, the conversion of diphenyl sulfide, as a result of the electronic and steric effect of the aryl groups, was lower than the others. The catalyst can be recycled six times without a negligible decrease in activity.

Scheme 7: Oxidation of sulfides to the sulfoxides with UHP catalyzed by MNPs 6.

Scheme 7:

Oxidation of sulfides to the sulfoxides with UHP catalyzed by MNPs 6.

Rostami and Atashkar reported that the oxidation of sulfides to the sulfoxides was successfully catalyzed by the chiral oxo-vanadium (+)-pseudoephedrine complex immobilized on magnetic Fe3O4 nanoparticles (MNPs 7). The as-fabricated catalyst has been characterized by UV-Vis spectrophotometer, SEM, XRD, TGA, FT-IR, EDX, and AGFM. The SEM image of the VO(Pseudoephedrine)@MNPs (MNPs 7) confirmed that the catalyst was made up of uniform nanometer-sized particles less than 33 nm [45]. The catalytic performance of the MNPs 7 strongly depends on the amount of catalyst and H2O2. Also, a series of solvents were tested on the sulfoxidation reactions, but the best results were obtained in the absence of a solvent. Under the standardized conditions (Scheme 8), a nice library of alkyl aryl and diaryl sulfides was smoothly converted to the corresponding sulfoxides in good to excellent yields. The catalyst (MNPs 7) was easily recovered by an external magnetic decantation and reused for 20 reaction times without any significant loss of activity and enantioselectivity.

Scheme 8: Selective and solvent-free oxidation of sulfides to the sulfoxides with H2O2 catalyzed by MNPs 7.

Scheme 8:

Selective and solvent-free oxidation of sulfides to the sulfoxides with H2O2 catalyzed by MNPs 7.

Ghorbani-Choghamarani et al. reported the fabrication of oxovanadium(IV)-glycine imine supported on magnetic Fe3O4 nanoparticles (MNPs 8). The structure of the as-synthesized MNPs 8 was well characterized by a series of spectrum techniques such as FT-IR, SEM, TEM, XRD, TGA, VSM, and ICP-OES. The SEM image of MNPs 8 confirmed the formation of nanoparticles with spherical shape and slight agglomeration. TEM analysis of MNPs 8 showed the formation of particles with spherical morphology and size varying in the range of 10–32 nm [46]. MNPs 8 was used in the sulfoxidation reaction of alkylaryl and dialkyl sulfides by H2O2under solvent-free conditions (25–220 min); the corresponding products are furnished in excellent yields (90–99%) (Scheme 9). The MNPs 8 could be used for five successive times without any significant decrease in activity.

Scheme 9: Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 8 at room temperature.

Scheme 9:

Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 8 at room temperature.

Very recently, Ghorbani-Choghamarani and Norouzi reported amine-functionalized magnetic Fe3O4 nanoparticles (MNPs 9) for the immobilization of oxovanadium(IV) complex. As-prepared MNPs 9 was characterized by FT-IR, TGA, XRD, SEM, and EDX spectroscopic techniques. The SEM micrograph of the MNPs 9 exhibits a relatively homogeneous grain distribution, which was made up of particles with the size in the nanosized range (8–20 nm) [47]. Unfortunately, the exact structure of MNPs 9 was not reported in this paper. The catalytic behavior of the MNPs 9 has been evaluated in the sulfoxidation of sulfides. Solvent-free sulfoxidation reaction in the presence of MNPs 9 as the catalyst and H2O2 as the oxidant at ambient temperature was considered as the best conditions for further investigation. A fascinating category of aliphatic and aromatic sulfides was performed well under the described conditions, and the corresponding products were obtained in good to excellent yields in satisfactory times (Scheme 10). Recycling of the catalytic system was also investigated in the oxidation of methyl phenyl sulfide; only a slight loss of activity was observed after 12 times.

Scheme 10: Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 9 at room temperature.

Scheme 10:

Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 9 at room temperature.

The proposed mechanism for this process involves the nucleophilic attack of sulfide on MNPs@VO (salen) complex to form intermediate A. The reaction of intermediate A with hydrogen peroxide affords the sulfoxide and regenerates the vanadium salen complex (Scheme 11) [46].

Scheme 11: Plausible mechanism for the sulfoxidation reaction catalyzed by MNPs@VO (salen) complex in the presences of H2O2.

Scheme 11:

Plausible mechanism for the sulfoxidation reaction catalyzed by MNPs@VO (salen) complex in the presences of H2O2.

5 Manganese catalysts

Oxidation catalysis based on using manganese complexes is a fascinating research field in organic synthesis. A number of manganese complexes are well-known to catalyze the oxidation of sulfides to sulfoxides [48]. In 2014, Ghorbanloo and his colleagues reported the oxidation of sulfides to sulfoxides based on using Mn(II) complex (complex: porphyrin) supported on (3-chloropropyl)-trimethoxysilane-functionalized silica-coated magnetic nanoparticles (MNPs 10, Figure 3) as a magnetically separable catalyst. The structure of the MNPs 10 was characterized by FT-IR, VSM, and SEM spectroscopic techniques [49]. The SEM image of MNPs 10 shows that the catalyst is formed of nanometer-sized particles (63 nm). The oxidation reactions were carried out in the presence of H2O2 under thermal acetonitrile (Scheme 12). The highest yield was observed in the oxidation of methyl phenyl sulfide. The MNPs 10 was readily recovered by simple magnetic decantation and can be reused for four cycles without considerable loss in catalytic activity.

Figure 3: Magnetically recoverable manganese nano-catalysts.

Figure 3:

Magnetically recoverable manganese nano-catalysts.

Scheme 12: Oxidation of sulfides to sulfoxides by the MNPs 10/H2O2 in CH3CN.

Scheme 12:

Oxidation of sulfides to sulfoxides by the MNPs 10/H2O2 in CH3CN.

The utilization of imidazole-functionalized silica-coated magnetic Fe3O4 nanoparticles as support for the immobilization of manganese porphyrin (MNPs 11, Figure 3) was also reported by Bagherzadeh and Mortazavi-Manesh. A series of spectroscopic techniques such as FT-IR, XRD, and UV-Vis was used to analyze the MNPs 11. The SEM image of MNPs 11 confirmed that the particles were well distributed with dimensions about 33 nm [50]. The catalytic activity of the MNPs 11 was checked in sulfoxidation reactions (Scheme 13). Good to high conversions of the sulfoxide products was observed at room temperature for 3 h (UHP as the oxidant and CH2Cl2/MeOH as reaction medium). The MNPs 11 was successively reused for about six runs without significant loss of efficiency.

Scheme 13: Oxidation of sulfides to sulfoxides with UHP catalyzed by MNPs 11 in CH2Cl2/MeOH at room temperature.

Scheme 13:

Oxidation of sulfides to sulfoxides with UHP catalyzed by MNPs 11 in CH2Cl2/MeOH at room temperature.

Very recently, Bagherzadeh et al. prepared a Mn MNPs catalyst via the covalent anchoring of Mn(II)-substituted phosphotungstate on ammonium-modified silica-coated magnetic Fe3O4 nanoparticles. The resulting nanocomposite was characterized by a series of spectroscopic techniques such as FT-IR, XRD, SEM, and EDX. The EDX analysis confirmed the successful synthesis of Fe3O4@SiO2-MnPOWnanocomposite (MNPs 12). The SEM analysis indicates that the particles are approximately spherical with an average diameter of about 50 nm [51]. The MNPs 12 was then tested as a heterogeneous catalyst for room temperature oxidation of sulfides in the presence of UHP as the oxidant under CH2Cl2/MeOH. The collected results are listed in Scheme 14. Under the described conditions, methyl-phenyl sulfide and diethyl sulfide were effectively oxidized to the desired sulfoxides. Leaching and recycling experiments showed that the MNPs 12 can be reused for at least four cycles without any notable loss of activity. Unfortunately, any proposed mechanism for the sulfoxidation reactions using MNPs-Mn (II) catalysts was not reported.

Scheme 14: Oxidation of sulfides to sulfoxides with UHP catalyzed by MNPs 12 in CH2Cl2/MeOH.

Scheme 14:

Oxidation of sulfides to sulfoxides with UHP catalyzed by MNPs 12 in CH2Cl2/MeOH.

6 Other transition metal catalysts

During recent years, the catalytic activity of a number of other metal complexes immobilized on magnetic nanoparticles has been investigated for the oxidation of sulfides to the sulfoxides. In 2015, Bagherzadeh and his team reported the fabrication of two magnetically separable molybdenum catalysts via the immobilization of the molybdenum complex, [MoO2Cl2(DMSO)2], on amino propyl and Schiff base-modified magnetic Fe3O4@SiO2 nanoparticles by covalent linkage (MNPs 13 and 14, Figure 4). The characterization of the as-fabricated catalysts was accomplished by FT-IR, TGA, SEM, ICP/OES, VSM, TEM, EDX, and XPS spectroscopic techniques. The SEM and TEM images of MNPs 13 and 14 show that the catalyst is formed of nanometer-sized particles. The presence of molybdenum in the nanoparticle structure was confirmed by EDX analysis. The loading amount of molybdenum was about 0.7 mmol g−1, which is determined by ICP/OES analysis [52]. The catalytic behavior of MNPs 13 and 14 was then explored in the oxidation of sulfides to sulfoxides. UHP and CH2Cl2/MeOH were used as the oxidant and solvent, respectively. As shown in Scheme 15, the best results in terms of conversion and selectivity were observed when MNPs 14 was used as the catalyst. The catalyst (MNPs 14) could be reused for four times without obvious decrease in the catalytic activity.

Figure 4: Magnetically recoverable molybdenum nano-catalysts.

Figure 4:

Magnetically recoverable molybdenum nano-catalysts.

Scheme 15: Comparison of catalytic activity of MNPs 13 and MNPs 14 in oxidation of sulfides.

Scheme 15:

Comparison of catalytic activity of MNPs 13 and MNPs 14 in oxidation of sulfides.

In another publication, Bezaatpour and his coworkers reported the immobilization of a molybdenum N4-type Schiff base complex on magnetic Fe3O4 nanoparticles (MNPs 15) as a novel heterogeneous catalyst for the oxidation of sulfides. Stepwise preparation of the Mo-salenSi@Si-CoFe2O4 catalyst is shown in Scheme 5. The structure of MNPs 15 was characterized fully by FT-IE, SEM, TEM, DRS, EDX, XRD, XRD, and VSM spectroscopic techniques. The SEM and TEM images of MNPs 15 show that the catalyst is formed of nanometer-sized particles (17–20 nm) [53]. The catalytic activity of MNPs 15 was then tested in the oxidation of various sulfides using H2O2 as the oxidant. The oxidation reactions are performed in the absence of a solvent at 55°C. As shown in Scheme 16, a wide range of sulfides could be efficiently transformed to the corresponding sulfoxides with high chemoselectivity (in less than 5 min). The catalyst could be recycled six times by magnetic separation without any decrease in the catalytic activity.

Scheme 16: Oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 15.

Scheme 16:

Oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 15.

In 2014, Hashemi’s research team reported the preparation of iron(II) acetylacetonate immobilized on amine-modified magnetic Fe3O4@SiO2 nanoparticles (MNPs 16) as an efficient and recyclable heterogeneous catalyst for the selective oxidation of sulfides to the corresponding sulfoxides using H2O2 as a green oxidant at room temperature. The as-prepared catalyst was completely characterized by spectroscopic techniques of TEM, SEM, XRD, EDS, FTIR, TGA, ICP-AES, VSM, and elemental analysis (CHN). The presence of Fe complex in the nanocomposite structure was confirmed by EDX analysis. The Fe content grafted on the Fe3O4@SiO2-amine was measured by plasma atomic emission analysis (ICP-AES), about 0.11 mmol g−1 [54]. The MNPs 16 enabled to catalyze the sulfoxidation of symmetrical and unsymmetrical sulfides with high yield and excellent selectivity in ethanol (Scheme 17). The MNPs 16 can be readily recovered and reused for eight reaction runs without detectable loss of efficiency. Based on suggested mechanism (Scheme 18), the presence of Fe(IV)=O complex (high-valent iron oxo complex) is essential in oxidation reactions. First, the reaction of Fe(II) complex (A) with H2O2 as oxidizing agent, which leads to the formation of intermediate B. Then, the O–O bond homolysis/heterolysis of intermediate B results in the formation of intermediate C, which is involved in the oxygen atom transfer reaction for the oxidation of sulfides to sulfoxides [54].

Scheme 17: Oxidation of sulfides to sulfoxides catalyzed by H2O2/MNPs 15.

Scheme 17:

Oxidation of sulfides to sulfoxides catalyzed by H2O2/MNPs 15.

Scheme 18: Proposed mechanism for the oxidation of sulfides to sulfoxide using H2O2 in the presence of MNPs-Fe (II) catalyst.

Scheme 18:

Proposed mechanism for the oxidation of sulfides to sulfoxide using H2O2 in the presence of MNPs-Fe (II) catalyst.

In another report, Zohreh and co-workers successfully synthesized a heterogeneous tungstate-based catalyst via the immobilization of high amounts of WO4−2 onto the cross-linked poly(ammonium ethyl acrylamide)-coated magnetic Fe3O4 nanoparticles (MNPs 17). FT-IR, TEM, TGA, VSM, XRD, EDX, and CHN spectroscopic techniques were used for the characterization of the MNPs 17. RDP analysis of MNPs 17 also confirmed the crystalline plans of magnetic Fe3O4 nanoparticles. The data obtained by ICP-OES showed that the loading amount of WO42− ions is 0.89 mmol g−1 [55]. The as-synthesized catalyst exhibited high activity in the oxidation of sulfides to sulfoxides. A variety of sulfides were subjected to sulfoxidation reactions in CH3CN/H2O at room temperature (H2O2 used as oxidant). The sulfoxide products were obtained in good to excellent yields (Scheme 19). The MNPs 17 could be readily recovered by magnetic separation six times without loss of catalytic activity.

Scheme 19: Selective oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 16 in H2O/MeCN at room temperature.

Scheme 19:

Selective oxidation of sulfides to sulfoxides with H2O2 catalyzed by MNPs 16 in H2O/MeCN at room temperature.

Later, Ghorbani-Choghamarani and co-workers reported that M-Salen complexes (M=Ni, Co, Cr, Zn or Cd) supported on magnetic Fe3O4 nanoparticles (MNPs 18–22) are efficient recoverable catalysts for the oxidation of sulfides to the sulfoxides. The as-prepared catalysts were characterized by FT-IR, TGA, XRD, SEM, and EDX spectroscopic techniques. The EDX analysis confirmed the successful immobilization of M-Salen complexes on magnetic Fe3O4 nanoparticles. The size of the catalysts was evaluated using scanning electron microscopy; most of the particles formed were nanometer-sized with an average diameter about 15 nm [56]. The application of these catalysts (MNPs 18–22) was tested in the solvent-free sulfoxidation of sulfides by H2O2. The collected results are listed in Scheme 20. The obtained results revealed clearly that all the nano-catalysts are very efficient in these sulfoxidation processes because, generally, all the target sulfoxide products were obtained in both excellent yields (up to 99%) and suitable times (in less than 120 min). The MNPs catalysts were magnetically recovered and reused for 10 cycles without noticeable loss of catalytic activity. Also, the chemo-selective oxidative coupling of thiols to the disulfides in excellent yields could be successfully performed by this catalytic system.

Scheme 20: Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by M-salen-MNPs (M=Ni, Co, Cr, Zn, or Cd).

Scheme 20:

Solvent-free oxidation of sulfides to sulfoxides with H2O2 catalyzed by M-salen-MNPs (M=Ni, Co, Cr, Zn, or Cd).

Very recently, Hajjami and Kolivand immobilized copper and zirconium oxide complexes on imine-bonded magnetic Fe3O4 nanoparticles (MNPs 23–24) and their activity as magnetically separable catalysts evaluated in the oxidation of sulfides to sulfoxides. The as-prepared catalysts were well confirmed by a series of spectroscopic techniques such as XRD, FT-IR spectroscopy, TGA, TEM, SEM, EDX, and VSM [57]. The TEM images disclose the spherical shapes of the MNP catalysts with an average size of 12 nm, which exhibits a close agreement with the values calculated from the XRD analysis. Optimized results were obtained with 0.03 g of catalysts (MNPs 23–24) and use of H2O2 as an oxidant under thermal ethanol. All results are listed in Scheme 21. The collected results in Scheme 21 demonstrated well that both MNPs 23 and 24 are efficient catalysts for the oxidation of sulfides to sulfoxides. Furthermore, the catalysts can be reused many times without any loss in activity.

Scheme 21: Sulfoxidation of sulfides with H2O2 catalyzed by MNPs 23 and 24.

Scheme 21:

Sulfoxidation of sulfides with H2O2 catalyzed by MNPs 23 and 24.

In a nice publication, tungstate-based poly(ionic liquid) entrapped magnetic nanoparticles (MNPs 25) were reported, by Pourjavadi and his research team, as a new and robust magnetically recoverable catalyst for oxidation reactions. The resulting catalyst was characterized by a series of spectroscopic techniques such as FTIR, TGA, SEM, TEM, XRD, XRF, CHN, VSM, and AAS. The TEM analysis confirmed that the size of MNP particles was about 10 nm, and they were dispersed into the polymeric matrix. It was found that the loading amount of WO4 ion in MNP@PILW was calculated by atomic absorption spectroscopy (AAS), about 0.61 mmol g−1 [58]. The catalytic activity of MNPs 25 was evaluated in the oxidation of sulfides to sulfoxides. In the absence of a catalyst (MNPs 25), the sulfoxidation reaction failed. To identify the optimal conditions, the effect of catalyst loading and solvent nature was well studied. Under the standardized conditions, as shown in Scheme 22, a series of symmetrical and unsymmetrical sulfides was smoothly oxidized under solvent-free conditions, and the desired sulfoxides were obtained in high to excellent yields. Under this catalytic system (MNPs 25/H2O2), a fascinating category of substrates including alcohols and olefins were also selectively oxidized with excellent yields. The MNPs 25 can be easily recovered and reused for at least 10 runs without notable loss of activity.

Scheme 22: MNPs 25/H2O2 catalyzed solvent-free oxidation of sulfides to sulfoxides.

Scheme 22:

MNPs 25/H2O2 catalyzed solvent-free oxidation of sulfides to sulfoxides.

Nickel ferrite (NiFe2O4), with an inverse spinel structure, is an important soft magnetic material with remarkable thermal stability, large magnetic anisotropy, and moderate saturation magnetization [59]. In 2014, Desai and coworkers described a fascinating and efficient protocol for the oxidation of sulfides to sulfoxides using magnetically recoverable and reusable NiFe2O4 nanoparticles (MNPs 26). The prepared MNPs 26 was characterized by SEM, TEM, XRD, AAS, and hysteresis loop. The TEM analysis exhibits cubic morphology of the nanoparticles of size ranging between 14 and 20 nm [59]. The synthesized catalyst in the presence of H2O2 showed high catalytic activity and chemoselectivity in the oxidation of symmetrical and unsymmetrical sulfides to sulfoxides. The sulfoxidation reactions were performed in acetonitrile at ambient temperature (Scheme 23). The maximum yield was observed in the sulfoxidation of diphenyl sulfide. It is noteworthy that this oxidizing catalytic system is compatible with the other functional groups in the molecule especially highly sensitive imine bonds that are well retained under this mild condition The MNPs 26 was magnetically separated and reused for five runs without noticeable loss of catalytic activity. Also, the chemo-selective oxidative coupling of thiols to the respective disulfides could be efficiently carried out by this catalytic system in high yields.

Scheme 23: Sulfoxidation of sulfides catalyzed by H2O2/NiFe2O4 (MNPs 26).

Scheme 23:

Sulfoxidation of sulfides catalyzed by H2O2/NiFe2O4 (MNPs 26).

7 Magnetically recoverable acidic catalysts

From past to present, the catalysis of chemical and organic reactions by acids has been always a hot research target in organic-synthesis catalysis. As the acids are often liquid or expensive, their separation from the reaction media is the most important concern of organic chemists [60]. Therefore, the designing and fabricating of strong solid acids and their utility as a catalyst in organic reactions is a nice response to the future of organic synthesis, in particular, from the green chemistry point of view [61], [62]. In fact, the immobilization of the acidic functional groups on the magnetic nanoparticles and their catalytic utility in chemical and organic reactions can be considered an ideal and fascinating solution to overcome this blind spot because the catalyst can be readily separated from the reaction media by an external magnet. Inspired by this strategy, the oxidation of sulfides to sulfoxides have recently been investigated by several research teams. In 2013, Rostami and his research team evaluated the catalytic behavior of N-propylsulfamic acid supported onto magnetic Fe3O4 nanoparticles (MNPs 27) in the oxidation of sulfides to sulfoxides. The as-prepared acidic catalyst was characterized by SEM, XRD, and FT-IR spectroscopic techniques. Sulfoxidation catalysis under solvent-free conditions was the key milestone to attain the optimal conditions. Under the described conditions, a nice category of aliphatic and aromatic sulfides are smoothly and selectively oxidized to the corresponding sulfoxides in high yields (Scheme 24). The MNPs 27 could be recovered via magnetic attraction and could be recycled at least 10 times without appreciable decrease in activity. The SEM images of both the fresh and reused catalyst also revealed that no detectable changes of the catalyst occurred during the reaction and the recycling stages [63].

Scheme 24: MNPs 27 catalyzed solvent-free oxidation of sulfides to sulfoxides using H2O2 at room temperature.

Scheme 24:

MNPs 27 catalyzed solvent-free oxidation of sulfides to sulfoxides using H2O2 at room temperature.

The ability of silica sulfuric acid-coated Fe3O4 magnetic nanoparticles (MNPs 28) to catalyze the sulfoxidation of sulfides was investigated by Rostami and co-workers. The structure of MNPs 28 was characterized by FT-IR spectroscopy, TGA, XRD, and SEM spectroscopic techniques. The SEM image of MNPs 28 shows that the catalyst was formed of nanometer-sized particles [64]. The well grafting of sulfuric acid on Fe3O4 is verified by TGA analysis. Among a number of tested solvents, the highest yield and shortest times were observed under water as the solvent. Sulfoxidation reactions could be then conducted under aqueous medium at ambient temperature; good to excellent yields of the target products were obtained in less than 20 min (Scheme 25). Recycling of the catalytic system was evaluated in the oxidation of methyl phenyl sulfide, and only a slight loss of activity was observed after 15 runs.

Scheme 25: Oxidation of sulfides to sulfoxides catalyzed by H2O2/MNPs 28 in water.

Scheme 25:

Oxidation of sulfides to sulfoxides catalyzed by H2O2/MNPs 28 in water.

In another study, Ghorbani-Choghamarani and his research team immobilized dopamine sulfamic acid on magnetic Fe3O4 nanoparticles (MNPs 29) to fabricate a magnetically recoverable catalyst for the sulfoxidation of sulfides. The structure of MNPs 29 was characterized by FT-IR, XRD, TGA, SEM, TEM, and VSM spectroscopic techniques. TEM analysis confirmed that most of the particles are quasispherical with homogeneous average diameter of about 15–25 nm [65]. The MNPs 29 provided satisfactory yields for a nice library of substrates containing alkylaryl and dialkyl sulfides. Sulfoxidation reactions were carried out by H2O2 in ethanol at ambient temperature. As shown in Scheme 26, excellent yields were observed in the sulfoxidation of asymmetrical sulfides (95–98%) in less than 55 min. The MNP 29 can be magnetically recovered after the reaction and can be reused for four runs with only a minimal loss of activity (first run 97% yield, fourth run 87% yield).

Scheme 26: Oxidation of sulfides to sulfoxides with catalyzed H2O2/MNP 29 in EtOH.

Scheme 26:

Oxidation of sulfides to sulfoxides with catalyzed H2O2/MNP 29 in EtOH.

In 2016, Ghorbani-Choghamarani and Azadi demonstrated that the MNPs 30 consisting of sulfamic acid heterogenized on amine-functionalized magnetic Fe3O4 nanoparticles can be successfully used as a magnetically recoverable catalyst for the sulfoxidation of sulfides. In the absence of a catalyst, only 31% yield of the desired sulfoxide was observed after 65 min. By using MNPs 30, the oxidation of a variety of symmetrical and unsymmetrical sulfides to sulfoxides has been investigated in the presence of H2O2 in thermal ethanol (Scheme 27). High to excellent yields (82–97%) were observed in less than 85 min. The nano-structure of MNPs 30 was characterized by FT-IT, TGA, XRD, SEM, and TEM spectroscopic techniques. The TEM analysis confirmed that most of the particles were monodispersed and uniform with a spherical shape (45 nm) [66]. The authors reported that the MNPs 30could be reused up to 10 times, and no significant loss of activity was observed.

Scheme 27: MNPs 30/H2O2 catalyzed the sulfoxidation of sulfides in ethanol.

Scheme 27:

MNPs 30/H2O2 catalyzed the sulfoxidation of sulfides in ethanol.

Very recently, Shiri and his research team reported the immobilization of sulfamic acid on magnetic Fe3O4 nanoparticles via diethylenetriamine ligand (MNPs 31). The structure of the resulting catalyst was well characterized by a series of spectroscopic techniques such as FT-IR, SEM, EDX, VSM, TGA, and XRD. The SEM analysis revealed the formation of uniformly sized magnetic nanoparticles with spherical morphology and an average size range of 17–21 nm. The catalytic activity of MNPs 31 was then tested in sulfoxidation reactions; it was observed that 15 mg of MNPs 31 and 0.5 ml of hydrogen peroxide (30%) in CH3CN at room temperature are the standardized conditions for further investigation [67]. As shown in Scheme 28, a diverse range of symmetrical and unsymmetrical sulfides was successfully oxidized to the corresponding sulfoxides in high yields (86–98%). It is noteworthy that the activity of the MNPs 31 remains unaltered even after six runs without any significant loss in yield. Furthermore, MNPs 31 showed the high catalytic activity in the oxidative coupling of thiols Knoevenagel condensation of aromatic aldehydes with active methylene compounds.

Scheme 28: MNPs 31/H2O2 catalyzed oxidation of sulfides to the sulfoxides in CH3CN.

Scheme 28:

MNPs 31/H2O2 catalyzed oxidation of sulfides to the sulfoxides in CH3CN.

A plausible mechanistic path for the sulfoxidation reactions is depicted in Scheme 29. The elucidation for this process is the in situ formation of peroxyacid (A) by the reaction of MNPs-NSO3H or OSO3H with hydrogen peroxide, followed by the oxygen transfer to the organic substrate [67].

Scheme 29: Proposed mechanism for the oxidation of sulfides to sulfoxide using H2O2 in the presence of MNPs-NSO3H or OSO3H catalysts.

Scheme 29:

Proposed mechanism for the oxidation of sulfides to sulfoxide using H2O2 in the presence of MNPs-NSO3H or OSO3H catalysts.

8 Magnetically recoverable bromine catalysts

Catalysis research under bromine is a well-known topic in organic synthesis [68]. However, the hazardous and toxic nature of bromine and its negative and deleterious effects on human health has caused organic chemists to avoid working on bromine [69], [70]. Furthermore, the separation of bromine source catalysts from the desired products or reaction media is a difficult, tedious, and time-consuming task and needs a series of costly and specific techniques [69], [70]. The heterogenization of bromine sources on magnetic nanoparticles can be considered as an efficient and fascinating catalytic system to overcome this drawback because the catalyst can be readily separated from the reaction mixture by an external magnet. In this section, we focused on sulfoxidation reactions catalyzed by magnetically recoverable bromine sources.

In 2014, Rostami and co-workers reported a new strategy to immobilize tribromide ion on surface-functionalized magnetic Fe3O4 nanoparticles (MNPs 32, Figure 5) leading to a magnetically recoverable catalyst, which exhibits high catalytic efficiency in a series of sulfoxidation reactions. The as-prepared MNPs 32 was subject to characterization by a series of spectroscopic techniques such as FT-IR, XRD, TGA, EDX, SEM, and VSM. The SEM analysis of MNPs 32 was revealed that the catalyst was made up of uniform nanometer-sized particles less than 26 nm [71]. The presence of bromine in nanocomposite structure was confirmed by EDS analysis. Eighty percent yield of the sulfoxide product was observed when the process was performed under catalyst-free conditions for 24 h. MNPs 32/H2O2 was an efficient catalytic system for the solvent-free oxidation of aliphatic and aromatic sulfides to the sulfoxide at room temperature (Scheme 30). It is noteworthy that the target sulfoxide products were furnished in excellent yields in less than 70 min. The MNPs 32 could be recovered via magnetic attraction and could be reused for at least 15 runs without significant decrease in activity.

Figure 5: Magnetically recoverable bromine nano-catalysts.

Figure 5:

Magnetically recoverable bromine nano-catalysts.

Scheme 30: Solvent-free oxidation of sulfides to sulfoxides catalyzed by H2O2/MNPs 32.

Scheme 30:

Solvent-free oxidation of sulfides to sulfoxides catalyzed by H2O2/MNPs 32.

One year later, Kolvari and his research team described the fabrication of imidazole tribromide supported on magnetic (Y-Fe2O3) nanoparticles (MNPs 33, Figure 5). A series of spectroscopic techniques such as XRD, TGA, FT-IR, EDX, SEM, TEM, and VSM was used to confirm the structure of MNPs 33. The average diameter determined from SEM and TEM images is 10±5 nm for MNPs 33. The strong magnetization of MNPs 33 (54 emu g−1) was also revealed by vibrating sample magnetometer analysis (VSM) [72]. MNPs 33 was then tested in the solvent-free sulfoxidation of sulfides using hydrogen peroxide as the oxidant at room temperature. A nice category of aliphatic and aromatic sulfides were examined, and it was found that the substrate kind had a key role in these transformations (Scheme 31). MNPs 33 can be readily recovered by magnetic decantation and used for sulfoxidation for up to five runs without any detectable loss of activity.

Scheme 31: MNPs 33/H2O2 catalyzed solvent-free oxidation of sulfides to sulfoxides.

Scheme 31:

MNPs 33/H2O2 catalyzed solvent-free oxidation of sulfides to sulfoxides.

In 2016, Shiri and Tahmasbi found that tribriomide ion heterogenized on diethylenetriamine-functionalized magnetic Fe3O4 nanoparticles (MNPs 34, Figure 5) is a highly efficient and selective heterogeneous catalyst for sulfoxidation reactions. MNPs 34 was characterized by FT-IR spectroscopy, TGA, VSM, XRD, TEM, and SEM spectroscopic techniques. The VSM analysis showed that MNPs 34 has a saturated magnetization value of 47.86 emu g−1. The XRD analysis of MNPs 34 showed that the surface modification of the Fe3O4 nanoparticles do not lead to their phase change [73]. The as-synthesized MNPs 34 was then tested for the solvent-free oxidation of sulfides to sulfoxides in the presence of hydrogen peroxide in ethanol at room temperature. By the described catalytic system, a broad spectrum of symmetrical and unsymmetrical sulfides subjected to the sulfoxidation reactions and with high to excellent yields (91–98%) of the desired sulfoxide products were observed in less than 50 min (Scheme 32). Recycling studies on the oxidation of methyl phenyl sulfide have shown that the catalyst can be readily recovered and reused six times without significant loss of activity.

Scheme 32: MNPs 34/H2O2 catalyzed solvent-free oxidation of sulfides to sulfoxides.

Scheme 32:

MNPs 34/H2O2 catalyzed solvent-free oxidation of sulfides to sulfoxides.

In a fascinating publication, Shiri et al. used Fe3O4 MNPs functionalized with (3-aminopropyl)trimethoxysilane as support for the immobilization of a bromine source (MNPs 35, Figure 5). The as-synthesized MNPs 35 was comprehensively characterized by FT-IR, TGA, VSM, XRD, EDX, and SEM spectroscopic techniques. The SEM analysis revealed that the catalyst was made up uniformly, and the average size of MNPs 35 was about 10 nm. The EDX analysis confirmed the successful immobilization of the bromine source on the surface of magnetic Fe3O4nanoparticles [74]. The catalytic activity of MNPs 35 was investigated for the sulfoxidation of sulfides. The oxidation of methyl phenyl sulfide was chosen as a model substrate, and the reaction conditions were optimized (catalyst concentration, solvent effect, etc.). Among all the tested solvents, ethanol proved to be the most efficient in this reaction. Sulfoxidation reactions were carried out by hydrogen peroxide and MNPs 35 in EtOH at ambient temperature. Under the described conditions, a nice library of aliphatic and aromatic sulfides was oxidized to the corresponding sulfoxides in excellent yields (87–97%). As seen in Scheme 33, chemoselectivity of this catalytic system tested in the oxidation of several sulfides containing oxidation-prone functional groups and the obtained results revealed well that these functional groups remained intact during the oxidation process. The recovery of MNPs 35 was simply performed using an external permanent magnet, and no noticeable loss of catalytic efficiency consequently was observed during the five consecutive reactions. The SEM image of the recovered catalyst shows that there are no significant differences in the morphologies of the freshly prepared catalyst and the recovered catalyst after an operation for five consecutive reaction times [74]. Furthermore, MNPs 35 exhibited a high activity in the selective oxidative coupling of thiols to the disulfides.

Scheme 33: MNPs 35/H2O2 catalyzed oxidation of sulfides to sulfoxides in EtOH.

Scheme 33:

MNPs 35/H2O2 catalyzed oxidation of sulfides to sulfoxides in EtOH.

A plausible mechanism for the oxidation of sulfides to sulfoxides in the presence of MNPs-Br3 is outlined in Scheme 34.

Scheme 34: Proposed mechanism for the oxidation of sulfides to sulfoxide using H2O2 in the presence of MNPs-Br3 catalysts.

Scheme 34:

Proposed mechanism for the oxidation of sulfides to sulfoxide using H2O2 in the presence of MNPs-Br3 catalysts.

9 Other report

Finally, Malakooti and Atashin reported the preparation of magnetic Fe3O4 nanoparticles embedded in an SBA-15 silica wall (MNPs 36) as new magnetically recoverable catalyst for oxidation reactions. The structure of MNPs 36 was analyzed by a series of spectroscopic techniques such as FT-IR, XRD, UV/Vis, TEM, VSM, and ICP-AES. The TEM analysis of MNPs 36 confirmed an ordering cylindrical pore structure, which is in accordance with XRD data [75]. Sulfoxidation of a series of sulfides was successfully achieved with a high conversion using H2O2 as the oxidant in the presence of a catalytic amount of MNPs 36 at 80°C in water within 2–8 h (Scheme 35). Separation from the reaction mixture was easily achieved by applying an external permanent magnet, and the separated catalyst could be recycled for at least six runs without any appreciable loss in activity. MNPs 36 exhibited also a high catalytic activity in the oxidation of alcohols to aldehydes.

Scheme 35: MNPs 36/H2O2 catalyzed oxidation of sulfides to sulfoxides in water.

Scheme 35:

MNPs 36/H2O2 catalyzed oxidation of sulfides to sulfoxides in water.

10 Comparison of the catalytic activity of MNPs nano-catalysts

Table 1 enlists a comparative data of various parameters in the sulfoxidation of sulfides catalyzed by MNPs nano-catalysts. As shown in Table 1, in most cases, H2O2 was used as the oxidant. Most of the sulfoxidation reactions were performed in EtOH or under solvent-free conditions. In this category (MNPs nano-catalysts), magnetic Fe3O4 nanoparticles were found to be the most successful. Except for a few cases, in most cases, MNPs were able to catalyze the sulfoxidation of sulfides in satisfactory yields. From the economic point of view, MNPs 7, 26, and 29 are the most reusable catalysts. The highest yields were observed in the presence of MNPs 1, 8, 17, 18, and 31.

Table 1:

Comparison of the activity of all MNPs nano-catalysts in sulfoxidation of sulfides.

EntryMNPs (cat.)ConditionsRecoveryTimeYield (%)
1MNPs 1H2O2, solvent free, 40°C1010–180 min90–99
2MNPs 2H2O2, EtOH, 60°C1220–360 min58–99
3MNPs 3H2O2, solvent free, r.t.410 min–48 h53–97
4MNPs 4H2O2, solvent free, 35oC45 min–24 h75–98
5MNPs 5H2O2, solvent free, r.t55–190 min91–97
6MNPs 6UHP, CH2Cl2/MeOH, r.t.64–24 h60–99
7MNPs 7H2O2, solvent free, r.t.205–300 min80–97
8MNPs 8H2O2, solvent free, r.t.525–220 min90–99
9MNPs 9H2O2, solvent free, r.t.127–600 min70–98
10MNPs 10H2O2, CH3CN, 60°C4120 min23–75
11MNPs 11UHP, CH2Cl2/MeOH, r.t.63 h75–90
12MNPs 12UHP, CH2Cl2/MeOH, r.t.42 h11–95
13MNPs 13UHP, CH2Cl2/MeOH, r.t.430 min45–85
14MNPs 14UHP, CH2Cl2/MeOH, r.t.430 min50–99
15MNPs 15H2O2, solvent free, 55°C65 min40–100
16MNPs 16H2O2, EtOH, r.t.8150–480 min76–96
17MNPs 17H2O2, CH3CN/H2O, r.t.61–4 h68–96
18MNPs 18H2O2, solvent free, 35°C105–60 min90–99
19MNPs 19H2O2, solvent free, 35°C105–120 min91–99
20MNPs 20H2O2, solvent free, 35°C105–30 min92–97
21MNPs 21H2O2, solvent free, 35°C105–60 min88–96
22MNPs 22H2O2, solvent free, 35°C105–30 min90–96
23MNPs 23H2O2, EtOH, 35°C710 min–20 h62–99
24MNPs 24H2O2, EtOH, 45°C.75 min–24 h53–99
25MNPs 25H2O2, solvent free, r.t.1060–150 min82–99
26MNPs 26H2O2, CH3CN, r.t.590–210 min84–92
27MNPs 27H2O2, solvent free, r.t.105–120 min85–95
28MNPs 28H2O2, water, r.t.152–20 min83–97
29MNPs 29H2O2, EtOH, r.t.45–60 min70–98
30MNPs 30H2O2, EtOH, 60°C105–85 min82–98
31MNPs 31H2O2, CH3CN, r.t.615–310 min86–98
32MNPs 32H2O2, solvent free, r.t.155–70 min82–97
33MNPs 33H2O2, solvent free, r.t.515–45 min80–97
34MNPs 34H2O2, solvent free, r.t.65–50 min90–98
35MNPs 35H2O2, EtOH, r.t.510–280 min87–97
36MNPs 36H2O2, H2O, 80°C72–8 h70–100

11 Summary and outlook

The concept of magnetic nanoparticle supporting of catalysts has rapidly developed in recent times. These MNPs nano-catalysts possess a series of admirable advantages such as simple preparation, simplicity of operation, high catalytic activity, easy separation and reusability, and being nontoxic. Magnetic nanoparticles can be readily separated from reaction medium using an external magnet, without the need for filtration, centrifugation, or other tedious work-up processes. The most important aspect in magnetic catalysis is the design and fabrication of a catalyst for a specific organic reaction, considering the mechanistic pathway and the feasibility to perform reactions on a laboratory scale with potential for industrial applications [5]. The recyclability aspects are the salient features due to their popularity and sustainable applications [5]. A broad library of high-pressure and high-temperature organic reactions can be carried out on nano-magnetite supported catalysts because they are highly stable [5]. Because of the sturdy interaction between the support (magnetic nanoparticles) and metals, leaching of metals can be avoided or minimized [5]. The catalytic activity of a large number of MNPs in the oxidation of sulfides to sulfoxides, which are prevalent structural scaffolds in many drugs and biologically active molecules, was investigated in this paper. In most cases, the sulfoxide products were afforded in reasonable yields. The sulfoxidation reactions are often performed under mild conditions without using solvents or by applying ethanol, methanol, and water. Therefore, they are an efficient tool for green chemistry and probably for industrial and pharmaceutical application. Also, the MNP nano-catalysts can be simply separated by magnetic decantation and reused many times. In this category (MNPs nano-catalysts), magnetic Fe3O4 nanoparticles were widely used as a support for the immobilization of catalysts. Accordingly, MNPscan be regarded as an efficient separation technology with great possibilities for applications in the field of catalysis. The combination of two metals (bimetallic) on the magnetic supports (which are difficult to prepare and expensive) would be a new generation of highly stable and selective magnetically recoverable catalysts in the near future, which can be evaluated for a variety of important and valuable chemical reactions from economic and medicinal points of view.

Acknowledgments

This work was supported by the research facilities of Ilam University, Ilam, Iran.

References

[1] Shiri L, Ghorbani-Choghamarani A, Kazemi M. Synthesis and characterization of bromine source supported on magnetic Fe3O4 nanoparticles: a new, versatile and efficient magnetically separable catalyst for organic synthesis. Appl. Organomet. Chem. 2016, 31. DOI: 10.1002/aoc.3634.10.1002/aoc.3634Search in Google Scholar

[2] Karimi B, Mansouri F, Mirzaei HM. Recent applications of magnetically recoverable nanocatalysts in C-C and C-X coupling eeactions. ChemCatChem 2015, 7, 1736–1789.10.1002/cctc.201403057Search in Google Scholar

[3] Polshettiwar V, Luque R, Fihri A, Zhu H, Bouhrara M, Basset JM. Magnetically recoverable nanocatalysts. Chem. Rev. 2011, 111, 3036–3075.10.1021/cr100230zSearch in Google Scholar PubMed

[4] Zhang D, Zhou C, Sun Z, Wu LZ, Tunga CH, Zhang T. Magnetically recyclable nanocatalysts (MRNCs): a versatile integration of high catalytic activity and facile recovery. Nanoscale 2012, 4, 6244–6255.10.1039/c2nr31929bSearch in Google Scholar PubMed

[5] Gawande MB, Brancoa PS, Varma RS. Nano-magnetite (Fe3O4) as a support for recyclable catalysts in the development of sustainable methodologies. Chem. Soc. Rev. 2013, 42, 3371–3393.10.1039/c3cs35480fSearch in Google Scholar PubMed

[6] Shiri L, Ghorbani-Choghamarani A, Kazemi M. Cu(II) immobilized on Fe3O4– diethylenetriamine: a new magnetically recoverable catalyst for the synthesis of 2,-dihydroquinazolin-4(1H)-ones and oxidative coupling of thiols. Appl. Organomet. Chem. 2016, 31. DOI: 10.1002/aoc.3596.10.1002/aoc.3596Search in Google Scholar

[7] Lim CW, Lee IS. Magnetically recyclable nanocatalyst systems for the organic reactions. Nano Today 2010, 5, 412–434.10.1016/j.nantod.2010.08.008Search in Google Scholar

[8] Xu HJ, Wan X, Geng Y, Xu XL. The catalytic application of recoverable magnetic nanoparticles-supported organic compounds. Curr. Org. Chem. 2013, 17, 1034–1050.10.2174/1385272811317100006Search in Google Scholar

[9] Zhu Y, Stubbs LP, Ho F, Liu R, Ship CP, Maguire JA, Hosmane NS. Magnetic nanocomposites: a new perspective in catalysis. ChemCatChem 2010, 2, 365–374.10.1002/cctc.200900314Search in Google Scholar

[10] Baig RBN, Varma RS. Magnetically retrievable catalysts for organic synthesis. Chem. Commun. 2013, 49, 752–770.10.1039/C2CC35663ESearch in Google Scholar PubMed

[11] Ranganath KVS, Glorius F. Superparamagnetic nanoparticles for asymmetric catalysis – a perfect match. Catal. Sci. Technol. 2011, 1, 13–22.10.1039/c0cy00069hSearch in Google Scholar

[12] Shiri L, Rahmati S, Ramezani-Nejad Z, Kazemi M. Synthesis and characterization of bromine source immobilized on diethylenetriamine functionalized magnetic nanoparticles: a novel, versatile and highly efficient reusable catalyst for organic synthesis. Appl. Organomet. Chem. 2017, 31. DOI: 10.1002/aoc.3687.10.1002/aoc.3687Search in Google Scholar

[13] Shiri L, Ghorbani-Choghamarani A, Kazemi M. Sulfides synthesis: nanocatalysts in C–S cross-coupling reactions. Aust. J. Chem. 2016, 69, 585–600.10.1071/CH15528Search in Google Scholar

[14] Shiri L, Ghorbani-Choghamarani A, Kazemi M. S-S bond formation: nano-catalysts in the oxidative coupling of thiols. Aust. J. Chem. 2017, 70, 9–25.10.1071/CH16318Search in Google Scholar

[15] Kazemi M, Kohzadi H, Abdi O. Alkylation of thiols in green mediums. J. Mater. Environ. Sci. 2015, 6, 1451–1456.Search in Google Scholar

[16] Kazemi M, Shiri L. Thioesters synthesis: recent adventures in the esterification of thiols. J. Sulfur Chem. 2015, 36, 613–623.10.1080/17415993.2015.1075023Search in Google Scholar

[17] Kazemi M, Shiri L, Kohzadi H. Recent Achievements in organic trithiocarbonates synthesis. Phosphorus Sulfur Silicon Relat. Elem. 2015, 190, 1398–1409.10.1080/10426507.2014.993035Search in Google Scholar

[18] Kazemi M, Shiri L, Kohzadi H. Recent advances in aryl alkyl and dialkyl sulfide synthesis. Phosphorus Sulfur Silicon Relat. Elem. 2015, 190, 978–1003.10.1080/10426507.2014.974754Search in Google Scholar

[19] Marcker C. Ueber einige schwefelhaltige derivate des toluols. Liebigs Ann. Chem. 1865, 136, 75–95.10.1002/jlac.18651360108Search in Google Scholar

[20] Kagan HB, Toru T, Bolm C. Asymmetric synthesis of chiral sulfoxides. Organosulfur Chem. Asym. Synth. 2009, 1, 1–28.10.1002/9783527623235.ch1Search in Google Scholar

[21] Rowlands JG. Chiral sulfoxide ligands in catalytic asymmetric cyanohydrin synthesis. Synlett 2003, 2, 236–240.10.1055/s-2003-36790Search in Google Scholar

[22] Khenkin AM, Neumann, R. Oxygen transfer from sulfoxides: oxidation of alkylarenes catalyzed by a polyoxomolybdate, [PMo12O40]3-. J. Am. Chem. Soc. 2002, 124, 4198–4199.10.1021/ja0178721Search in Google Scholar PubMed

[23] Bentley R. Role of sulfur chirality in the chemical processes of biology. Chem. Soc. Rev. 2005, 34, 609–624.10.1039/b418284gSearch in Google Scholar PubMed

[24] Hawkins JM, Watson TJN. Asymmetric catalysis in the pharmaceutical industry. Angew. Chem. Int. Ed. 2004, 43, 3224–3228.10.1002/anie.200330072Search in Google Scholar

[25] Federsel HJ. Chemical process research and development in the 21st century: challenges, strategies, and solutions from a pharmaceutical industry perspective. Acc. Chem. Res. 2009, 42, 671–680.10.1021/ar800257vSearch in Google Scholar PubMed

[26] Rao RN, Shinde DD. Talluri, MV, Agawane SB. LC–ESI-MS determination and pharmacokinetics of adrafinil in rats. J. Chromatogr. B. 2008, 873, 119–123.10.1016/j.jchromb.2008.07.025Search in Google Scholar

[27] Tan H, Cao Y, Tang T, Qian K, Chen WL, Li J. Biodegradation and chiral stability of fipronil in aerobic and flooded paddy soils. Sci. Total Environ. 2008, 407, 428–437.10.1016/j.scitotenv.2008.08.007Search in Google Scholar PubMed

[28] Shimatani T, Moriwaki M, Xu J, Tazuma S, Inoue M. Acid-suppressive effects of rabeprazole: comparing 10 mg and 20 mg twice daily in Japanese Helicobacter pylori-negative and -positive CYP2C19 extensive metabolisers. Dig. Liver Dis. 2006, 38, 802–808.10.1016/j.dld.2006.06.002Search in Google Scholar

[29] Strobel S, Kist M. Eradication of H. pylori with pantoprazole, clarithromycin, and metronidazole in duodenal ulcer patients: a head-to-head comparison between two regimens of different duration. Helicobacter 2000, 5, 41–51.10.1046/j.1523-5378.2000.00006.xSearch in Google Scholar PubMed

[30] Katz PO, Gerson LB, Vela MF. Guidelines for the diagnosis and management of gastroesophageal reflux disease. Am. J. Gastroenterol. 2013, 108, 308–328.10.1038/ajg.2012.444Search in Google Scholar PubMed

[31] Thiermann H, Szinicz L, Eyer F, Worek F, Eyer P, Felgenhauer N, Zilker T. Modern strategies in therapy of organophosphate poisoning. Toxicol. Lett. 1999, 107, 233–239.10.1016/S0378-4274(99)00052-1Search in Google Scholar PubMed

[32] Mandal K, Singh B. Persistence of fipronil and its metabolites in sandy loam and clay loam soils under laboratory conditions. Chemosphere 2013, 91, 1596–1603.10.1016/j.chemosphere.2012.12.054Search in Google Scholar PubMed

[33] Kaczorowska K, Kolarska Z, Mitka K, Kowalski P. Oxidation of sulfides to sulfoxides. Part 2: Oxidation by hydrogen peroxide. Tetrahedron 2005, 61, 8315–8327.10.1016/j.tet.2005.05.044Search in Google Scholar

[34] Punniyamurthy T, Rout L. Recent advances in copper-catalyzed oxidation of organic compounds. Coord. Chem. Rev. 2008, 252, 134–154.10.1016/j.ccr.2007.04.003Search in Google Scholar

[35] Hirao, T. Vanadium in modern organic synthesis. Chem. Rev. 1997, 97, 2707–2724.10.1021/cr960014gSearch in Google Scholar PubMed

[36] Chemler SR. Copper catalysis in organic synthesis. Beilstein J. Org. Chem. 2015, 11, 2252–2253.10.3762/bjoc.11.244Search in Google Scholar PubMed PubMed Central

[37] Ghorbani-Choghamarani A, Darvishnejad Z, Norouzi M. Cu(II)–Schiff base complex-functionalized magnetic Fe3O4 nanoparticles: a heterogeneous catalyst for various oxidation reactions. Appl. Organomet. Chem. 2015, 29, 170–175.10.1002/aoc.3266Search in Google Scholar

[38] Ghorbani-Choghamaran A, Ghasemi B, Safari Z, Azadi G. Schiff base complex coated Fe3O4 nanoparticles: a highly reusable nanocatalyst for the selective oxidation of sulfides and oxidative coupling of thiols. Catal. Commun. 2015, 60, 70–75.10.1016/j.catcom.2014.11.007Search in Google Scholar

[39] Naghipour A, Fakhri A. Efficient oxidation of sulfides into sulfoxides catalyzed by a chitosan–Schiff base complex of Cu(II) supported on supramagnetic Fe3O4 nanoparticles. Environ. Chem. Lett. 2016, 14, 207–213.10.1007/s10311-015-0545-zSearch in Google Scholar

[40] Naghipour A, Fakhri A. Fabrication of chitosan-bond-2-hydroxy-1-naphthaldehyde Cu complex covalently linked magnetite nanoparticles as an efficient, reusable and magnetically separable catalyst for the selective oxidation of sulfides to sulfoxides using 30% H2O2 under solvent-free conditions. Mater. Technol. 2016, 31. DOI: 10.1080/10667857.2016.1246233.10.1080/10667857.2016.1246233Search in Google Scholar

[41] Ghorbani-Choghamarani A, Tahmasbi B, Moradi P, Havasi N. Cu–S-(propyl)-2-aminobenzothioate on magnetic nanoparticles: highly efficient and reusable catalyst for synthesis of polyhydroquinoline derivatives and oxidation of sulfides. Appl. Organomet. Chem. 2016, 30, 619–625.10.1002/aoc.3478Search in Google Scholar

[42] Das R, Chakraborty D. Cu(II)-catalyzed oxidation of sulfides. Tetrahedron Lett. 2010, 51, 6255–6258.10.1016/j.tetlet.2010.09.081Search in Google Scholar

[43] Imelda-Jayaseeli AM, Ramdass A, Rajagopal S. Selective H2O2 oxidation of organic sulfides to sulfoxides catalyzed by cobalt(III)–salen ion. Polyhedron 2015, 100, 59–66.10.1016/j.poly.2015.07.020Search in Google Scholar

[44] Bagherzadeh M, Haghdoost MM, Shahbazirad A. Nanoparticle supported, magnetically separable vanadium complex as catalyst for selective oxidation of sulfides. J. Coord. Chem. 2012, 65, 591–601.10.1080/00958972.2012.657188Search in Google Scholar

[45] Rostami A, Atashkar B. Chiral oxo-vanadium (+)-pseudoephedrine complex immobilized on magnetic nanoparticles: a highly efficient and recyclable novel nanocatalyst for the chemoselective oxidation of sulfides to sulfoxides using H2O2. J. Mol. Catal. A Chem. 2015, 398, 170–176.10.1016/j.molcata.2014.12.010Search in Google Scholar

[46] Ghorbani-Choghamarani A, Shiri L, Azadi G. Preparation and characterization of oxovanadium(IV)-glycine imine immobilized on magnetic nanoparticles and its catalytic application for selective oxidation of sulfides to sulfoxides. Res. Chem. Intermed. 2016, 42, 6049–6060.10.1007/s11164-016-2444-8Search in Google Scholar

[47] Norouzi M, Ghorbani-Choghamarani A. Mild and highly efficient method for the oxidation of sulfides and protection of alcohols catalyzed by oxovanadium(IV) supported on modified magnetic nanoparticles as recyclable catalyst. React. Kinet. Mech. Catal. 2016, 119, 537–554.10.1007/s11144-016-1070-1Search in Google Scholar

[48] Bagherzadeh M, Amini M. Synthesis, characterization and catalytic study of a novel iron(III)-tridentate Schiff base complex in sulfide oxidation by UHP. Inorg. Chem. Commun. 2009, 12, 21–25.10.1016/j.inoche.2008.10.023Search in Google Scholar

[49] Ghorbanloo A, Tarasi R, Tao J, Yahiro H. Selective oxidation of sulfides and hydrocarbons with H2O2 over manganese catalyst supported on nanoparticles. Turk. J. Chem. 2014, 38, 488–503.10.3906/kim-1307-50Search in Google Scholar

[50] Bagherzadeh M, Mortazavi-Manesh A. Immobilized manganese porphyrin on functionalized magnetic nanoparticles via axial ligation: efficient and recyclable nanocatalyst for oxidation reactions. J. Coord. Chem. 2015, 68, 2347–2360.10.1080/00958972.2015.1046850Search in Google Scholar

[51] Moradi-Shoeili Z, Zare M, Bagherzadeh M. Synthesis and characterization of magnetic silica-supported Mn(II)-substituted polyoxophosphotungstate as catalyst in sulfoxidation reaction. J. Nanopart. Res. 2016, 18, 298.10.1007/s11051-016-3609-5Search in Google Scholar

[52] Keypour H, Balali M, Haghdoost MM, Bagherzadeh M. Mo(VI) complex supported on Fe3O4 nanoparticles: magnetically separable nanocatalysts for selective oxidation of sulfides to sulfoxides. RSC Adv. 2015, 5, 53349–53356.10.1039/C5RA08653ASearch in Google Scholar

[53] Bezaatpour A, Askarizadeh E, Akbarpour S, Amiri M, Babaei B. Green oxidation of sulfides in solvent-free condition by reusable novel Mo(VI) complex anchored on magnetite as a high-efficiency nanocatalyst with eco-friendly aqueous H2O2. Mol. Catal. 2017, 436, 199–209.10.1016/j.mcat.2017.04.021Search in Google Scholar

[54] Bayat A, Shakourian-Fard M, Ehyaei N, Hashemi MM. A magnetic supported iron complex for selective oxidation of sulfides to sulfoxides using 30% hydrogen peroxide at room temperature. RSC Adv. 2014, 4, 44274–44281.10.1039/C4RA07356HSearch in Google Scholar

[55] Zohreh N, Hosseini SH, Pourjavadi A, Soleyman R, Bennett C. Immobilized tungstate on magnetic poly(2-ammonium ethyl acrylamide): a high loaded heterogeneous catalyst for selective oxidation of sulfides using H2O2. J. Ind. Eng. Chem. 2016, 44, 73–81.10.1016/j.jiec.2016.08.011Search in Google Scholar

[56] Ghorbani-Choghamarani A, Darvishnejad Z, Tahmasbi B. Schiff base complexes of Ni, Co, Cr, Cd and Zn supported on magnetic nanoparticles: as efficient and recyclable catalysts for the oxidation of sulfides and oxidative coupling of thiols. Inorganica Chim. Acta 2015, 435, 223–231.10.1016/j.ica.2015.07.004Search in Google Scholar

[57] Hajjami M, Kolivand S. New metal complexes supported on Fe3O4 magnetic nanoparticles as recoverable catalysts for selective oxidation of sulfides to sulfoxides. Appl. Organomet. Chem. 2016, 30, 282–288.10.1002/aoc.3429Search in Google Scholar

[58] Pourjavadi A, Hosseini SH, Matloubi-Moghaddam F, Koushki-Foroushani B, Bennett C. Tungstate based poly(ionic liquid) entrapped magnetic nanoparticles: a robust oxidation catalyst. Green Chem. 2013, 15, 2913–2919.10.1039/c3gc41307aSearch in Google Scholar

[59] Kulkarni AM, Desai UV, Pandit KS, Kulkarnia MA, Wadgaonkar PP. Nickel ferrite nanoparticles–hydrogen peroxide: a green catalyst-oxidant combination in chemoselective oxidation of thiols to disulfides and sulfides to sulfoxides. RSC Adv. 2014, 4, 36702–36707.10.1039/C4RA04095CSearch in Google Scholar

[60] Koukabi N, Kolvari E, Zolfigol MA, Khazaei A, Shaghasemi BS, Fasahati B. A magnetic particle-supported sulfonic acid catalyst: tuning catalytic activity between homogeneous and heterogeneous catalysis. Adv. Synth. Catal. 2012, 354, 2001–2008.10.1002/adsc.201100352Search in Google Scholar

[61] Rostamnia S, Nuri A, Xin H, Pourjavadi A, Hosseini SH. Water dispersed magnetic nanoparticles (H2O-DMNPs) of γ-Fe2O3 for multicomponent coupling reactions: a green, single-pot technique for the synthesis of tetrahydro-4H-chromenes and hexahydroquinoline carboxylates. Tetrahedron Lett. 2013, 54, 3344–3347.10.1016/j.tetlet.2013.04.048Search in Google Scholar

[62] Safari J, Zarnega Z. A magnetic nanoparticle-supported sulfuric acid as a highly efficient and reusable catalyst for rapid synthesis of amidoalkylnaphthols. J. Mol. Catal. A Chem. 2013, 379, 269–276.10.1016/j.molcata.2013.08.028Search in Google Scholar

[63] Rostami A, Tahmasbi B, Abedi F, Shokri Z. Magnetic nanoparticle immobilized N-propylsulfamic acid: the chemoselective, efficient, green and reusable nanocatalyst for oxidation of sulfides to sulfoxides using H2O2 under solvent-free conditions. J. Mol. Catal. A Chem. 2013, 378, 200–205.10.1016/j.molcata.2013.06.004Search in Google Scholar

[64] Rostami A, Ghorbani-Choghamarani A, Tahmasbi B, Sharifi F, Navasi Y, Moradi D. Silica sulfuric acid-coated Fe3O4 nanoparticles as high reusable nanocatalyst for the oxidation of sulfides into sulfoxides, protection and deprotection of hydroxyl groups using HMDS and Ac2O. J. Saudi Chem. Soc. 2017, 21, 399–407.10.1016/j.jscs.2015.07.007Search in Google Scholar

[65] Ghorbani-Choghamarani A, Rabiei H, Tahmasbi B, Ghasemi B, Mardi F. Preparation of DSA@MNPs and application as heterogeneous and recyclable nanocatalyst for oxidation of sulfides and oxidative coupling of thiols. Res. Chem. Intermed. 2016, 42, 5723–5737.10.1007/s11164-015-2399-1Search in Google Scholar

[66] Ghorbani-Choghamarani A, Azadi G. Synthesis and characterization of sulfamic acid-functionalized nanoparticles and study of its catalytic activity for the oxidation of sulfides to sulfoxides. Croat Chem. Acta 2016, 89, 49–54.10.5562/cca2776Search in Google Scholar

[67] Shiri L, Narimani H, Kazemi M. Synthesis and characterization of sulfamic acid supported on Fe3O4 nanoparticles: a green, versatile and magnetically separable acidic catalyst for oxidation reactions and Knoevenagel condensation. Appl. Organomet. Chem. 2017, DOI: 10.1002/aoc.3938.10.1002/aoc.3938Search in Google Scholar

[68] Jitareanu A, Zbancioc AM., Tuchilus C, Balan M, Stanescu U, Tataringa G. α,β-dibromochalcone derivatives-synthesis and antimicrobial activity. Rev. Med. Chir. Soc. Med. Nat. Iasi. 2015, 119, 1180–1188.Search in Google Scholar PubMed

[69] Saikia I, Borah AJ, Phukan P. Use of bromine and bromo-organic compounds in organic. Chem. Rev. 2016, 116, 6837–7042.10.1021/acs.chemrev.5b00400Search in Google Scholar PubMed

[70] Shiri L, Kazemi M. Recoverable bromine source nano-catalysts in organic synthesis. Mini Rev. Org. Chem. 2017, 14. DOI: 10.2174/1570193X14666170518114613.10.2174/1570193X14666170518114613Search in Google Scholar

[71] Rostami A, Navasi Y, Moradi D, Ghorbani-Choghamarani A. DABCO tribromide immobilized on magnetic nanoparticle as a recyclable catalyst for the chemoselective oxidation of sulfide using H2O2 under metal-and solvent-free conditions. Catal. Commun. 2014, 43, 16–20.10.1016/j.catcom.2013.08.025Search in Google Scholar

[72] Otokesh S, Kolvari E, Amoozadeh A, Koukabi N. Magnetic nanoparticle-supported imidazole tribromide: a green, mild, recyclable and metal-free catalyst for the oxidation of sulfides to sulfoxides in the presence of aqueous hydrogen peroxide. RSC Adv. 2015, 5, 53749–53756.10.1039/C5RA07530KSearch in Google Scholar

[73] Shiri L, Tahmasbi B. Tribromide ion immobilized on magnetic nanoparticles as an efficient catalyst for the rapid and chemoselective oxidation of sulfides to sulfoxides. Phosphorus Sulfur Silicon Relat. Elem. 2016, 192, 53–57.10.1080/10426507.2016.1224878Search in Google Scholar

[74] Shiri L, Ghorbani-Choghamarani A, Kazemi M. Synthesis and characterization of tribenzyl ammonium-tribromide supported on magnetic Fe3O4 nanoparticles: a robust magnetically recoverable catalyst for the oxidative coupling of thiols and oxidation of sulfides. Res. Chem. Intermed. 2017, 43, 2707–2724.10.1007/s11164-016-2790-6Search in Google Scholar

[75] Atashin H, Malakooti R. Magnetic iron oxide nanoparticles embedded in SBA-15 silica wall as a green and recoverable catalyst for the oxidation of alcohols and sulfides. J. Saud. Chem. Soc. 2017, 21, S17–S24.10.1016/j.jscs.2013.09.007Search in Google Scholar

Received: 2016-12-29
Accepted: 2017-8-9
Published Online: 2017-9-19
Published in Print: 2017-11-27

©2017 Walter de Gruyter GmbH, Berlin/Boston

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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