Mahtab Yaghubzadeh,
Sedigheh Alavinia and
Ramin Ghorbani-Vaghei*
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan, 6517838683, Iran. E-mail: rgvaghei@yahoo.com; ghorbani@basu.ac.ir; Tel: +98-8138380647
First published on 17th August 2023
The selective oxidation of active and inactive alcohol substrates is a highly versatile conversion that poses a challenge in controlling the functionality and adjustments on MOFs. On the other hand, it offers an attractive opportunity to expand their applications in designing the next generation of catalysts with improved performance. Herein, a novel iron-based MOF containing sulfonamide (MOF-BASU1) has been fabricated by the reaction of 1,3-benzene disulfonylchloride linker and FeCl3·6H2O. Based on the results, the active surface area of the synthesized MOF is large, which highlights its unique catalytic activity. Optimum conditions were reached after 0.5–2 h, with 15 mg loading of the synthesized MOF under optimal conditions. Furthermore, the turnover frequency was 18–77.6 h−1, which is comparable to values previously reported for this process. Overall, the high catalytic activity observed for MOF-BASU1 might be because of the obtained high surface area and the Lewis acidic Fe nodes. Furthermore, the MOF-BASU1 revealed a remarkable chemoselectivity for aldehydes in the presence of aliphatic alcohols. Overall, the high product yields, facile recovery of nanocatalysts, short reaction times, and broad substrate range make this process environmentally friendly, practical, and economically justified.
Recently, various homogeneous catalysts have played an important role owing to their efficiency and all-purpose impact on the many catalytic reactions.7–9 However, despite the high efficiency of homogeneous catalysts, all these reactions suffer from poor catalyst recovery. The benefits of catalyst recovery include the economic and environmentally friendly concept of special transition metals; however, the key challenges are yet to be resolved.10–12 One of the solutions to overcome this limitation in oxidation reactions is the immobilization of homogeneous catalysts on supports that are not chemically active. In this regard, one of the most popular materials for a wide range of applications in oxidation reactions are metal–organic frameworks (MOFs) with tunable chemical and physical properties.13–19
Metal organic frameworks (MOFs) are a new class of organic–inorganic hybrids that, owing to their nature, have many applications in fields, such as gas storage,20 catalytic processes,21,22 encapsulate material, super capacitors, and the absorption of heavy metals.23 MOFs not only have a higher level of activation and stability than other classes of porous materials, but can also change the morphology and size of cavities uncomplicatedly, and this has become an advantage in terms of separation and greater selectivity in their applications.24–27
Designing and synthesizing new molecular scaffolds with unique structural and biological properties that increase their capability and selectivity is an interesting challenge. Nowadays, sulfonamides, with unique features, such as strong chemical/thermal stability, are considered as new ligands by the chemical community.28–30 The use of sulfonamide ligands in the synthesis of metal organic frameworks can create a revolution in the MOFs field and catalysis.
Regarding the points mentioned, this study presents the development and characterization of a new Fe-based MOF (MOF-BASU1) from the reaction of 1,3-benzenedisulfonamide (BDS) and FeCl3·6H2O (Scheme 1). The catalytic activity of the MOF-BASU1 was tested in aerobic alcohol oxidation without over oxidation. In the light of the results obtained, the high efficiency, high surface area, and easy recovery of the catalyst are strong points to justify its use. To the best of our knowledge, there are no reports on the use of a MOF-BASU1 catalyst in the synthesis of aldehyde/ketone compounds. The catalyst can usefully act as both acid and redox active sites platform. This study consistently has advantages, such as the availability of MOF, inexpensive catalyst, mild reaction conditions, reasonable yields, and simple experimental procedures. Such a potential catalytic utility of MOF-BASU1 make it quite attractive for sustainable industrial chemistry.
Materials and equipment | Purity and brand |
---|---|
Iron(III) chloride hexahydrate (FeCl3·6H2O) | Sigma–Aldrich (≥98%) |
Potassium carbonate (K2CO3) | Merck (98%) |
N,N-Dimethylformamide (DMF) | Merck (99.8%) |
n-Hexane | Sigma–Aldrich (95%) |
Ethanol | Sigma–Aldrich (97%) |
Acetonitrile | Merck (98%) |
FT-IR analysis | Shimadzu IR-470 spectrometer |
EDX analysis | Numerix DXP-X10P |
SEM analysis | Sigma-Zeiss microscope |
XRD analysis | JEOL JDX-8030 (30 kV, 20 mA) |
NMR analysis | Varian Unity Inova 500 MHz |
Ultrasound cleaning bath | KQ-250 DE (40 kHz, 250 W) |
Melting point measurement | Electrothermal 9100, made in UK |
XRD analysis was used to check the crystal structures of 1,3-benzenedisulfonamide and MOF-BASU1 samples (Fig. 2). The XRD spectrum of 1,3-benzenedisulfonamide shows diffraction peaks at 2θ = 18°, 23°, 28°, 32°, and 40° (Fig. 2A). Also, the same peaks in the MOF-BASU1 sample were shifted compared to the pure 1,3-benzenedisulfonamide and appeared with less intensity (Fig. 2B). Moreover, the introduction of the iron into the MOF-BASU1 was well defined by the peaks at 52.46°, 58.40°, and 65.61° suggesting the clear growth in the crystal structure. The average distance and crystal size were then calculated by Scherrer and Bragg equations to determine 45 nm.
The energy-dispersive X-ray spectroscopy (EDX) elemental mapping of C, N, O, S, and Fe in MOF-BASU1 is depicted in Fig. 3. The analysis exhibited that all the required elements, including C (31.66%), O (22.10%), N (15.69%), S (8.55%), and Fe (3.46%) are present in the structure of MOF-BASU1. The elemental mapping studies of MOF-BASU1 show a uniform distribution of carbon, oxygen, iron, nitrogen, and sulfur components in the fabricated structure (Fig. 4).
Fig. 5 shows the FE-SEM characterization of the size, shape, and morphology of the synthesized MOF-BASU1 nanocomposite. In the as-synthesized MOF-BASU1, we observed well distributed nearly-spherical uniform nanostructures (Fig. 5–D).
Fig. 6 shows the TGA carried out to study the stability of the prepared catalyst. The first step initiates from 25 to 200 °C. This step is attributed to solvent removal. According to Fig. 6, MOF-BASU1 decomposes at 309.14 °C, and generally loses 37.59% of its weight.
The important parameters associated with the porosity of MOF-BASU1 sample, including the surface area, average diameter of the pores, and total pore volume of the pores, are reported in Table 2. Fig. 7 indicates the N2 adsorption isotherms of the sample. Nitrogen adsorption and desorption curves of the sample show type I isotherm with H2 hysteresis curves, which confirms their microporous structure.
Sample | Surface area (m2 g−1) | Mean pore diameter (nm) | Total pore volume (cm3 g−1) |
---|---|---|---|
MOF-BASU1 | 14.56 | 30.09 | 0.11 |
Entry | Catalyst (mg) | Solvent | Temperature (°C) | Time (h) | TBHP (mmol) | Yieldb (%) |
---|---|---|---|---|---|---|
a Reaction condition: p-chlorobenzyl alcohol (1.0 mmol).b Isolated yields.c The reaction was investigated in the absence of O2. | ||||||
1 | — | H2O:CH3CN (1:1) | r.t. | 12 | — | N.R. |
2 | — | H2O:CH3CN (1:1) | 80 | 12 | — | N.R. |
3 | — | H2O:CH3CN (1:1) | 80 | 12 | 3 | Trace |
4 | IRMOF-3 (15) | H2O:CH3CN (1:1) | 80 | 6 | 3 | 30 |
5 | UiO-66-NH2 (15) | H2O:CH3CN (1:1) | 80 | 6 | 3 | 35 |
6 | Basolite (Fe) (15) | H2O:CH3CN (1:1) | 80 | 6 | 3 | 55 |
7 | MIL (101)Fe (15) | H2O:CH3CN (1:1) | 80 | 6 | 3 | 62 |
8 | MOF-BASU1 (15) | H2O:CH3CN (1:1) | 80 | 1 | 3 | 98 |
9 | MOF-BASU1 (15) | Toluene | 80 | 1 | 3 | N.R. |
10 | MOF-BASU1 (15) | CH3CN | 80 | 1 | 3 | 80 |
11 | MOF-BASU1 (15) | H2O | 80 | 1 | 3 | 40 |
12 | MOF-BASU1 (15) | EtOH | 80 | 1 | 3 | 65 |
13 | MOF-BASU1 (15) | H2O:EtOH (1:1) | 80 | 1 | 3 | 75 |
14 | MOF-BASU1 (15) | Solvent-free | 80 | 1 | 3 | 52 |
15 | MOF-BASU1 (15) | DMF | 80 | 1 | 3 | 39 |
16 | MOF-BASU1 (7.5) | H2O:CH3CN (1:1) | 80 | 1 | 3 | 82 |
17 | MOF-BASU1 (20) | H2O:CH3CN (1:1) | 80 | 1 | 3 | 97 |
18 | MOF-BASU1 (15) | H2O:CH3CN (1:1) | 60 | 1 | 3 | 79 |
19 | MOF-BASU1 (15)c | H2O:CH3CN (1:1) | 80 | 10 | 3 | 80 |
20 | MOF-BASU1 (15) | H2O:CH3CN (1:1) | 80 | 1 | 2 | 80 |
Optimized conditions in hand, the generality and limitations of the catalytic activity of MOF-BASU1 were confirmed by developing the oxidation of benzyl alcohol derivatives. The nanocatalyst carried out the reactions chemoselectively with high yields. A range of functional groups on the phenyl ring of the benzyl alcohol, such as bromo, chloro, nitro, hydroxyl, methyl, and methoxy, were compatible under this procedure, and the products were isolated in good to high yields. Furthermore, when the reaction was performed with substrates bearing meta-substituted aryl rings, the reaction occurred with high selectivity (Table 4). The chemoselectivity of benzyl alcohol was investigated in the presence of aliphatic alcohols (Scheme 3). The results strongly confirmed the chemoselectivity of the present methodology for aldehydes.
Entry | Substrate | Product | Time (h) | Yieldb (%) | TOFc (h−1) | TONd | Melting point–boiling point |
---|---|---|---|---|---|---|---|
a Reaction condition: benzyl alcohol derivatives (1.0 mmol), TBHP (3 mmol).b Isolated yields.c TOF (turnover frequency) = TON per time (h).d TON = yield (%)/catalyst (mol%). | |||||||
1 | 0.5 | 97 | 77.6 | 38.8 | 172 | ||
2 | 1.5 | 97 | 25.86 | 38.8 | 103–104 | ||
3 | 1.5 | 98 | 26.13 | 39.2 | 58–60 | ||
4 | 1 | 98 | 39.2 | 39.2 | 48–50 | ||
5 | 2 | 90 | 18 | 36 | 59 | ||
6 | 0.5 | 85 | 68 | 34 | 200 | ||
7 | 1 | 96 | 38.4 | 38.4 | 244–246 | ||
8 | 1.5 | 90 | 24 | 36 | 113–115 | ||
9 | 1 | 88 | 35.2 | 35.2 | 200 | ||
10 | 1 | 96 | 38.4 | 38.4 | 90–92 |
In addition to catalyst activity, its reusability is a significant point in practical application. To investigate its recovery performance, MOF-BASU1 was examined by successive cycles of catalytic oxidation reactions. In a general experiment, the catalyst was isolated from an as-completed reaction solution and used directly for the next reaction cycle. Results of these studies exhibited that the catalyst could successfully be recycled and reused for 6 sequential runs without diminution in catalytic activity (98, 97, 96, 94, 92, and 90).
According to a literature survey, the catalyst sites are the weak Brønsted acid sites, which may be attributed to uncoordinated sulfonamide groups, the redox-active,31 and Lewis acid iron sites.32 So, this catalyst can act usefully both as acid and redox active sites platform (Fig. 8).
Based on the literature survey and the above argument, we introduce a mechanism for the oxidation process as shown in Scheme 4. At first, the coordination of t-BuOOH to the Fe(III) sites affords t-Bu–OO–Fe(III) species (A) which subsequently produces the active species (t-Bu–O–O˙(II)). Then, the abstraction of a hydrogen-atom from the benzyl alcohol gives a radical intermediate (C). As the proposed mechanism shows, the three pathways: (1), (2), and (3) give the aldehyde product (E). The pathway (1) passes through the carbocation formation with the concomitant reduction of Fe(III) to Fe(II). The pathway (2) proceeds via a gem-diol-like structure formation and dehydration. The third pathway (3) involves a hydrogen-atom abstraction from (C) by the t-BuOO˙ and t-BuO˙ radicals.33 Moreover, H2 can be produced from methanol reforming in four different systems: MD, POM, SRM, and OSRM. Methoxy, formaldehyde, dioxymethylene, formate, and methyl formate are the commonly reported surface species detected on Cu-based catalysts.34
The advantages of the nanocomposites produced are summarized in Table 5 by comparing the results of the present study with the different catalytic systems used to produce aldehyde/ketone derivatives. According to these data, the catalytic system proposed herein, is more efficient in terms of reaction yield and time compared to other systems for this reaction. High yields and easy work-up are some advantages of this procedure (entry 7).
Entry | Reaction condition | T (°C) | Time (h) | Yield (%) | Ref. |
---|---|---|---|---|---|
1 | CuPc nanoparticle 5 mol%, n-Bu4NHSO5 (0.7 g), H2O | 85 | 168 | 79 | 35 |
2 | Fe(II) phthalocyanines/TBHP (500/1) | 70 | 3 | 94 | 36 |
3 | Al-MCM-41(10)-CuPc (0.055 g) | 100 | 4 | 47.5 | 37 |
4 | CoPc@cell (0.05 g), KOH, o-xylene, O2 | r.t. | 8.5 | 83 | 38 |
5 | MIL-101-NH2/CoTSPc (0.42 mol%), p-xylene, KOH, air (300 mL min−1) | 100 | 8 | 95 | 39 |
6 | TACoPc/Si–Cl (20 mg), H2O2, CH3CN, visible light | r.t. | 6 | 60 | 40 |
7 | MOF-BASU1 (20 mg), TBHP (3 mmol), CH3CN:H2O | 80 | 1 | 98 | This work |
Footnote |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3ra03058j |
This journal is © The Royal Society of Chemistry 2023 |