CaFe2O4@SiO2-Cu as a novel and highly efficient nanocatalyst for direct conversion of epoxides to β-acetoxy esters | Scientific Reports

Scientific Reports volume 14, Article number: 26606 (2024) Cite this article

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Direct conversion of structurally various epoxides to the related β-acetoxy esters was investigated using catalytic amounts of CaFe2O4@SiO2-Cu. The reactions were accomplished in the presence of acetic anhydride under solvent-free conditions within 0.5–2 h to give desired products in high yields. Initially, the CaFe2O4 nanoparticles were manufactured through a chemical coprecipitation reaction of calcium nitrate and hydrated iron (III) nitrate in the presence of ammonium hydroxide solution, and then calcined at 800 ºC. Next, to protect the prepared CaFe2O4 from oxidation and aggregation, its surface was covered with a silica layer to give CaFe2O4@SiO2. Eventually, by adding copper chloride solution followed by potassium borohydride solid powder, Cu nanoparticles were successfully immobilized on the silica surface and the new CaFe2O4@SiO2-Cu nanocomposite was obtained. FT-IR, SEM, EDX, VSM, ICP-OES, TGA, TEM and XRD techniques were employed to characterize the newly synthesized nanostructure. In addition, durability of the catalyst was considered for several sequential reaction cycles without the notable loss of catalytic activity. The absence of hazardous organic solvents, high product yields, short reaction times and recoverability of the magnetic catalyst are among the remarkable advantages of the introduced procedure.

In organic syntheses and reactions, increasing attention is being focused on green chemistry, using environmentally benign reagents and conditions, particularly solvent-free procedures1, which often lead to clean, eco-friendly, and highly efficient methods involving simplified workups2. Reactions under dry conditions were originally developed in the late 1980s3 and offer several advantages4. The absence of solvent reduces the risk of hazardous explosion when the reaction takes place in a closed vessel. Moreover, aprotic dipolar solvents with high boiling points are expensive and are difficult to remove from reaction mixtures.

In recent years, one-pot reactions have received special attention in different areas such as pharmaceutical and chemical industry, synthesis of organic compounds, biomedical and production of biological reagents5,6. The advantages such as simplicity of the procedure, environment-friendliness, excellent product yields, perfect regioselectivity and short reaction times have increased the efficiency of these types of reactions7,8,9,10,11. These reactions introduce unique opportunities for synthesis of a great variety of organic compounds including bioactive structures which present advantages such as high economic efficiency, no need to go through the tedious protection-deprotection process, making them assuredly more preferable than multistage synthetic methods12,13,14,15. These procedures are helpful because many synthetic conversions can be performed in a single vessel, while simultaneously bypassing time-consuming purification process. A one-pot reaction can therefore minimize the generation of harmful chemical waste, optimize the use of resources, save time, and make plainer experimental features16,17,18. In addition, organocatalysis represents one of the most exciting and rapidly developing research fields in one-pot reactions. This issue can be proven by the significant increase of syntheses in the presence of organocatalysts over the past decade19,20,21,22,23.

Epoxides have been identified as one of the most convertible intermediates in organic synthesis24. Epoxides are easily prepared and because of their ring strain they are able to react with numerous nucleophiles to afford 1,2-difunctional derivatives25,26,27,28,29. Among these products, β-acetoxy esters (1,2-diacetates) have very valuable synthetic applications. Because of the valuable applications of 1,2- diacetates as building blocks and synthetic intermediates in the synthesis of natural products, especially carbohydrates and steroids, and also for the protection of 1,2-diols30, direct conversion of epoxides into 1,2-diacetoxy esters is of special importance. A review of the literature reveals a number of reagents that have been reported for the preparation of 1,2-diacetates from epoxides31,32,33,34,35,36,37,38,39,40,41,42,43,44,45. But, some of reported methods suffer from using inaccessible, costly or dangerous reagents, extremely acidic/basic reaction conditions, long reaction times and the laborious process of separating the catalyst from the reaction medium.

In recent years, the various synthetic reactions have been simplified and expedited using heterogeneous catalysts. Among them, magnetic nano-ferrites have attracted considerable attention as green catalysts in organic transformations due to their simple synthesis, effortless separation, high durability, excellent catalytic ability, environmental friendliness, and recyclability utilizing just a simple magnet without any need to filtrate of the catalyst46,47,48,49,50.

Nevertheless, nano-ferrites due to their high surface to volume ratio are usually subject to adsorption anomalies, as they can generate powerful magnetic attractions which is the reason for the self-aggregation of their particles and subsequently reducing the number of functional groups on their surface51. Therefore, in order to improve the performance of nano-ferrites and prevent them from accumulation, their surfaces are modified using various coating materials such as silica, alumina, metal particles, polymers, surfactants and oxides52.

The covering of ferrite surfaces with an active layer containing functional groups, increases their catalytic ability through increasing the number of reaction sites. Moreover, recently, the nanoparticles covered with metal, metal oxides and silica have been broadly utilized as specific detector of biological substances53, recoverable catalysts in organic synthesis, and smart nanomaterials used in the field of biomedicine to increase the capacity of biologically synthesized nanoparticles for improving human health through vast usage in the medical implants, drug delivery with controlled release, drug targeting, tissue scaffolds, and wound dressing54,55,56,57.

Generally, nucleophilic ring opening of epoxides with water in the presence of Lewis or Brönested acids leads to the production of 1,2-diols, and in the next step, 1,2-diacetates are created as a result of acetylation by acetyl halides (Fig. 1). But, in an effortless procedure, epoxides could be directly transformed to 1,2-diacetoxy esters with acetic anhydride in the presence of a catalyst. This process is much straightforward and favorable, because it can avoid laborious isolation steps and purification of the chemical intermediates. Herein, as a part of our research program on the synthesis of magnetic nanoparticles and ongoing commitment to advancing one-pot organic synthesis reactions58,59,60,61,62,63,64,65, we have investigated the efficacy of immobilized copper nanoparticles on magnetic silica supported calcium ferrite (CaFe2O4@SiO2-Cu) as a new nanocatalyst for direct synthesis of β-acetoxy esters from epoxides under solvent-free conditions (Fig. 2).

Multi-step synthesis of β-acetoxy esters from epoxides.

Direct conversion of epoxides to β-acetoxy esters catalyzed by CaFe2O4@SiO2-Cu.

CaFe2O4@SiO2-Cu was synthesized through a three-step procedure: (1) preparation of CaFe2O4 magnetic nanoparticles by a chemical co-precipitation of Ca(NO3)2 and Fe(NO3)3·9H2O in the presence of NH4OH, (2) coating of silica layer on the surface of magnetite nanocores by tetraethyl orthosilicate (TEOS) at room temperature, and (3) addition of copper nanoparticles on the surface of CaFe2O4@SiO2 via an in situ growth procedure by an aqueous solution of Cu2+ salt (Fig. 3).

Three-step synthesis of CaFe2O4@SiO2-Cu.

CaFe2O4@SiO2−Cu as a novel catalyst was characterized by various techniques such as FT-IR, vibration sample magnetometer (VSM), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and inductively coupled plasma optical emission spectrometry (ICP-OES).

Magnetic properties of CaFe2O4, CaFe2O4@SiO2 and CaFe2O4@SiO2-Cu nanoparticles were studied using VSM technique. The narrow cycles with low coercivity exhibit ferromagnetic property of the soft magnetic materials at room temperature. The saturation magnetization (Ms) values of CaFe2O4, CaFe2O4@SiO2 and CaFe2O4@SiO2-Cu nanoparticles were around 28, 11 and 7 emu g−1, respectively. As expected, the nonmagnetic layers of silica and copper led to the reduction of the magnetic properties of the new synthesized nanocomposite (Fig. 4).

Magnetization curves of (a) CaFe2O4, (b) CaFe2O4@SiO2 and (c) CaFe2O4@SiO2-Cu.

The presence of functional groups in CaFe2O4, CaFe2O4@SiO2 and CaFe2O4@SiO2-Cu nanostructures were confirmed utilizing the FT-IR spectroscopy (Fig. 5). The absorption band at 517 cm−1 is assigned to the stretching mode of metal oxide bonds (Fe-O and Ca-O) which proves the successful formation of CaFe2O4 nanoparticles66. The spectrum shows broad absorption peak around 3446 cm−1, corresponding to the stretching mode of O–H group which adsorbed on the surface of nanostructures67. The absorption band at 1625 cm−1 is attributed to the hydroxyl bending mode. The absorption peaks at 1109 and 883 cm−1 belong to the asymmetrical and symmetrical stretching vibrations of Si–O–Si, respectively, which indicate the presence of silica layers in the structure of nanocomposite64. Two characteristic peaks at 1164 and 1390 cm−1 are related to Cu–OH vibration of orthorhombic phase. The band corresponding to Cu-O stretching vibrations of monoclinic CuO also appears at 505 cm−1, which probably overlaps with the absorption band at 517 cm–168.

FT-IR (KBr) spectra of (a) CaFe2O4, (b) CaFe2O4@SiO2 and (c) CaFe2O4@SiO2-Cu.

The X-ray diffraction patterns of CaFe2O4, CaFe2O4@SiO2 and CaFe2O4@SiO2-Cu are shown in Fig. 6. XRD analysis was performed after a calcination at 800 °C. As shown, all the peaks of CaFe2O4, SiO2 and Cu particles are observable. The diffraction peaks at 2Ө = 30.11°, 31.20°, 36.66°, 39.82, 43.49°, 47.80°, 53.92°, 57.46° and 63.10° belong to (311), (011), (320), (400), (510), (421), (600), (533) and (440) crystal planes of CaFe2O4, which verify the presence of calcium ferrite nanoparticles. These peaks indexed to the orthorhombic structure diffraction peak are well matched with the standard CaFe2O4(JCPDS 78-4321)69. Also, the broad band near 2Ө~15–20 corresponds to the amorphous silica surrounding the magnetite cores of calcium ferrite. CaFe2O4@SiO2shows a similar pattern of characteristic peaks, which indicates the preservation of its crystalline phase after anchoring the silica layer on the surface of the magnetic cores. The diffraction peaks of copper nanoparticles located at 2Ө = 43.07°, 50.67°, and 74.51° are related to the (111), (200), and (220) planes of the fcc structure, respectively and they are accordant with Cu standard (JCPDS 04-0836)70. The average crystallite size of nanoparticles was calculated using the Scherer equations (38.8 nm).

XRD patterns of (a) CaFe2O4, (b) CaFe2O4@SiO2 and (c) CaFe2O4@SiO2-Cu.

The morphology, surface microstructure and size distribution of CaFe2O4@SiO2-Cu were investigated by TEM and FESEM techniques. TEM images of CaFe2O4@SiO2-Cu exhibit the black cores of calcium ferrite which are successfully coated with gray silica layers. In some images, the orthorhombic structure of calcium ferrite particles is clearly visible. The Cu nanoparticles are also observable as small dark grains anchored on the surface of silica (Fig. 7).

TEM images of CaFe2O4@SiO2-Cu in two different magnifications.

FESEM images reveal that the calcined CaFe2O4@SiO2-Cu shows a sponge-like, porous architecture of the interconnected grains. These images offer more accurate data on the morphology and size of the as-prepared magnetic nanoparticles. As it is clear, the presence of particles with diameters ranging from 37 to 46 nm is acknowledged by FESEM images. The results are fully compatible with TEM and XRD data (Fig. 8).

FESEM images of CaFe2O4@SiO2-Cu.

The elemental mapping patterns and chemical composition of CaFe2O4@SiO2-Cu with weight and atomic percentages of the elements were revealed through the EDS technique (Fig. 9). This analysis shows that the Fe, O, Cu, Si and Ca elements are present in the sample of nanocomposite. The exact concentration of Ca, Fe and Cu was determined by ICP-OES and the resulting amounts were 1.62, 2.75 and 1.79% respectively, which are completely compatible with the information obtained from the EDS analysis.

EDS of CaFe2O4@SiO2-Cu and elemental mapping of Fe, O, Cu, Si, Ca.

In order to examine the thermal stability of CaFe2O4@SiO2-Cu, thermal gravimetric analysis (TGA) was carried out in the temperature range of 20–800 ºC under nitrogen atmosphere (Fig. 10). The weight loss at 250 ºC was attributed to the loss of the adsorbed water species from the catalyst surface and dehydroxylation of internal -OH groups. Thus, TGA profile indicated reasonable stability of the catalyst up to 800ºC and it is safe to carry out the reaction even at high temperatures under heterogeneous conditions.

TGA of CaFe2O4@SiO2-Cu.

The reaction conditions of the one-pot synthesis of 1,2-diacetoxy-1-phenylethane from styrene oxide and acetic anhydride was optimized utilizing various conditions. The different factors such as temperature, catalyst and reactant quantities, reaction time and solvent were studied. Table 1 illustrates the summarized results. The optimization experiments showed that the reaction of styrene oxide (1 mmol) and acetic anhydride (2 mmol, 0.2 mL) in the presence of CaFe2O4@SiO2-Cu (0.05 g) was performed efficiently in an oil bath (70 °C) under solvent-free conditions (Table 1, entry 3). It is notable that the presence of catalyst is necessary to perform the reaction, and in the absence of CaFe2O4@SiO2-Cu, the reaction did not progress even after 4 h (entry 4). The catalyst quantity was optimized using different amounts of CaFe2O4@SiO2-Cu (0.03, 0.05, 0.06 and 0.07 g) in the model reaction, and the favorite result was achieved utilizing 0.05 g. Increasing the amount of catalyst from 0.03 to 0.05 g improved the reaction rate and product yield dramatically (entries 3 and 5). Using more than 0.05 g of the catalyst (0.06 and 0.07 g) did not affect the product yield (entries 6 and 7). The turn over number (TON) and turn over frequency (TOF) of the catalyst were calculated for the model reaction based on the amount of the active metal and they were found to be 1234 and 369 h−1 respectively.

In addition, the mentioned reaction was examined in the presence of different amounts of acetic anhydride (1, 2 and 3 mmol) and the best outcome was obtained with 2 mmol (entries 1–3). The effect of temperature on the reaction was also investigated by comparing the information obtained from conducting the reaction at different temperatures (25, 60, 85, 70 and 100 °C). The results revealed that the obtained values ​​for the product yield and reaction time at lower temperatures were not satisfactory (entries 8 and 9). On the other hand, the higher temperature led to a decrease in the reaction time but did not increase the product yield (entries 10 and 11). To study the effect of solvent, the model reaction was carried out in various solvents such as ethanol, ethyl acetate and water. Although the conversion of styrene oxide to the corresponding β-acetoxy ester was successful in the presence of these solvents, it required more reaction time, and the product yield was lower compared to the solvent-free conditions (entries 12–14). The catalytic activity of the catalyst components was also evaluated by performing the model reaction in the presence of CaFe2O4, CaFe2O4@SiO2 and Cu separately under the optimal conditions (entries 15–17). As can be seen, the synergistic effect between catalyst components significantly increased the catalytic activity, and the highest efficiency was achieved in the presence of CaFe2O4@SiO2-Cu.

The suitability of this procedure was studied by the reaction of structurally different epoxides bearing either electron-donating or withdrawing groups as well as the cyclic epoxides in the presence of Ac2O and CaFe2O4@SiO2-Cu nanocatalyst under the optimized conditions. All reactions were carried out successfully within 0.5–2 h to give 1,2-diacetoxy esters in 80–98% yields (Table 2).

In the case of cyclic epoxides (Table 2, entries 10–12), trans-1,2-diacetoxy esters were manufactured as the products in which two acetoxy groups were anti to each other. This assignment was carried out by: (i) comparison of their 1HNMR spectra with reported authentic samples71, and (ii) the hydrolysis of the produced trans-1,2-diacetoxy esters to the corresponding trans-1,2-diols and confirming their structures by comparing the physical and chemical properties with the samples presented in reliable sources72,73.

Recoverability of the CaFe2O4@SiO2-Cu nano-catalyst was evaluated in the conversion of styrene oxide to 1,2-diacetoxy-1-phenylethane in the presence of Ac2O under optimized reaction conditions. The magnetic catalyst was easily separated and collected utilizing a simple external magnet, washed with ethyl acetate, and after drying reused several times without the significant loss of catalytic activity (Fig. 11). Experimental errors are mainly caused by not completely drying a product before massing it or losing some products during separation process, especially for the recycling process. The error bars in Fig. 11 indicate that the standard deviation of product yield is 1%.

Recycling of CaFe2O4@SiO2-Cu in the synthesis of 1,2-diacetoxy-1-phenylethane. The number of each experiment replicates is displayed at the bottom of the corresponding column. The yield for each species is shown as the average of the replicates ± 1σ.

The magnetic property and structure of the recycled catalyst were confirmed using different techniques. The results revealed that the structure of nano-catalyst was almost unchanged even after five runs. For better comparison, the results obtained from FT-IR, XRD, FESEM, TEM and VSM analyzes of the pristine and recycled CaFe2O4@SiO2-Cu catalyst were located close to each other in Fig. 12. The XRD analysis showed that the crystalline structure of the catalyst did not change after 5 runs. The comparison of VSM curves disclosed that the magnetic property of the recovered catalyst was not much different from the pristine one, and it was sufficient for magnetically separation from the reaction mixture. The amount of Ca, Fe and Cu leaching during catalytic reactions was examined by ICPOES analysis of the supernatant liquid after removing the catalyst. The results showed no presence of metals in the supernatant liquid.

(i) FT-IR, (ii) XRD, (iii) FESEM, (iv) TEM and (v) VSM of CaFe2O4@SiO2-Cu (a) before using (b) after five runs.

The hot filtration test was performed to confirm the heterogeneity of CaFe2O4@SiO2-Cu nano-catalyst. In this regard, the catalyst was filtered after 15 min in the model reaction at 70 ºC, and then the filtrate was permitted to react for further 3 h. But in the absence of catalyst, there was no progress in the reaction. Stopping the reaction at this stage indicated that the catalyst did not leak into the reaction mixture. Therefore, the test results proved that the CaFe2O4@SiO2-Cu is a heterogeneous catalyst and its presence is necessary to carry out the model reaction.

The advantages of the presented procedure were manifested by comparing the conversion of styrene oxide to 1,2-diacetoxy-1-phenylethane in the presence of CaFe2O4@SiO2-Cu with the other catalysts (Table 3). In terms of temperature, reaction time, product yield, conducting the reaction under solvent-free conditions and recyclability of the catalyst, the present method is more appropriate. The reaction is catalyzed by CaFe2O4@SiO2-Cu as an eco-friendly catalyst in the absence of hazardous organic solvents, and 1,2-diacetoxy-1-phenylethane is produced with higher yield.

Although the exact mechanism for this transformation is not clear and we never studied a complete mechanistic pathway on this conversion, a possible mechanism is illustrated in Fig. 13. Probably, the catalytic cycle of this mechanism includes the following steps: First, a non-covalent interaction is established between the oxygen of epoxide and the metal of catalyst, which leads to activate the epoxide ring through the Lewis acid property. The complexation of the epoxide ring with metal generates (I) species. Then, the reaction of (I) with the produced anion acetate forms alkoxy acetate (II), and eventually, the reaction of alkoxy acetate (II) with acetic anhydride gives 1,2-diacetate (II)41.

The mechanism proposed for the synthesis of 1,2-diacetoxy esters catalyzed by CaFe2O4@SiO2-Cu.

According to the information obtained from Table 1 (entries 15–17), the catalytic activity of the CaFe2O4@SiO2-Cu nanocomposite is mainly due to the presence of copper nanoparticles. However, the iron and calcium metallic ions in the ferrite structure as well as the hydroxyl groups dispersed on the silica layer could be partially responsible for the catalytic activity. When the epoxide molecules are adsorbed on the surface of the composite, the acidic sites of the catalyst are activated, followed by a non-covalent interaction between metal and oxygen74,75,76,77. The epoxide ring-opening reaction in the presence of the prepared catalyst gives two possible products regarding the nature of the substituent group. Epoxides bearing aryl substituents prefer to be opened from the more hindered position as the benzyl carbocation resulting from SN1 type of mechanism (α-cleavage) is more stable; however, the regioselective ring opening of epoxides with alkyl and allyl groups is carried out from the less hindered carbon via SN2 type of mechanism (β-cleavage).

In summary, the CaFe2O4@SiO2-Cu nanocomposite as a novel magnetic catalyst was prepared and then characterized through different techniques such as XRD, EDS, FT-IR, FESEM, TEM, TGA, VSM and ICP-OES. Its efficiency in organic synthesis was studied through a one-pot conversion of various epoxides to 1,2-diacetoxy esters. A broad scope of 1,2-diacetates, which are considered as valuable intermediates in the pharmaceutical field, can be synthesized through this method. Moreover, the new nano-catalyst provided perfect recoverability, as it was easily separated from the reaction mixture using just a simple magnet and reused for several consecutive cycles. In general, the significant privileges of this procedure such as easy preparation of pure products with high yields, short reaction times, using the recyclable green catalyst, the benefits of one-pot and solvent-free conditions, easily accessible and low-cost starting reactants, as well as simple workup and convenient separation of product and catalyst make this approach a useful addition to the present methodologies.

All materials were prepared from the Merck and Aldrich Chemical Companies and were utilized without further purification. 1H/13C NMR spectra were recorded on 300 MHz Bruker Avance spectrometer and FT-IR spectra were obtained by Thermo Nicolet Nexus 670 FT-IR. Magnetic properties of nanoparticles were measured by a VSM (Meghnatis Daghigh Kavir Co., Kashan Kavir, Iran) at room temperature. FESEM images were recorded on FESEM-TESCAN. The energy dispersive X-ray spectrometer (EDS) analysis was taken on a MIRA3 FE-SEM microscope (TESCAN, Czech Republic) equipped with an EDS detector (Oxford Instruments, UK). Morphology of the catalyst was investigated with with a Zeiss (EM10C-Germany) transmission electron microscope (TEM) operating at 100 kV. The crystalline structure of the catalyst was examined by X-ray diffraction on a Bruker D8-Advanced diffractometer with graphite-monochromatized Cu Kα radiation (λ = 1.54056 A°) at room temperature. Thermogravimetric analysis (TGA) was determined on Perkin Elmer, Diamond TG/DTA. The Cu content on the catalyst was measured by Perkin Elmer Optima 7300DV ICP-OES analyzer.

The CaFe2O4 nanoparticles were synthesized via a chemical coprecipitation procedure78. First, Ca(NO3)2 (16 mmol, 2.63 g) and Fe(NO3)3·9H2O (10 mmol, 4.04 g) were dissolved in 50 mL of deionized water. Next, 40 mL of 25% ammonium hydroxide solution was diluted to 200 mL and then added dropwise to the mixture with vigorous stirring. The mixture was then allowed to react for 30 min at room temperature to produce a dark brown precipitate which was subsequently separated using a magnet. The recovered substance was rinsed and centrifuged at 8000 rpm several times until the pH of the solution reached about 7. The wet product was dried at 80 ˚C in an oven for 2 h. The obtained product was calcined at 700 °C for 2 h to obtain the pure CaFe2O4 nanoparticles as a dark powder.

The surface of CaFe2O4 nanoparticles was coated with silica through a modified sol-gel method79. Initially, calcium ferrite (0.5 g) was added to a solution of ethanol (50 mL), distilled water (10 mL) and ammonium hydroxide (2.5 mL, 25%) and then dispersed under ultrasonication for 2 h. Next, 1.5 mL of tetraethyl orthosilicate (TEOS) was added dropwise to the produced mixture and sonicated for another 30 min. The mixture was stirred for an additional 24 h at room temperature. Finally, the product was isolated, washed several times with distilled water and then dried in an oven at 100 °C for 10 h to generate the pure silica supported calcium ferrite (CaFe2O4@SiO2) particles as a dark brown powder.

First, the prepared nanoparticles of CaFe2O4@SiO2 (1 g) were added to a solution of CuCl2⋅2H2O (0.68 g, 4 mmol) in water (50 mL). After the addition, the mixture was vigorously stirred for 30 min, and then 0.1 g of KBH4 powder was added little by little to reduce Cu2+ cations to copper nanoparticles on the silica surface, and the stirring of the mixture was continued for one more hour at room temperature. Eventually, the dark orange CaFe2O4@SiO2-Cu nanocomposite was produced and separated utilizing an external magnet, washed with distilled water and dried in an oven at 70 °C.

In a round-bottomed flask (25 mL) equipped with a magnetic stirrer, a mixture of an epoxide (1 mmol), acetic anhydride (2 mmol, 0.2 mL) and CaFe2O4@SiO2-Cu (0.05 g) was prepared. The resulting mixture was placed in an oil bath 70 °C and stirred for an appropriate time. The completion of the reaction was evaluated by TLC using n-hexane: ethyl acetate (10:2) as an eluent. After completion of the reaction, aqueous solution of NaHCO3 (5%, 10 mL) was added and the mixture was stirred for 15 min. Then, the nano-catalyst was separated using an external magnet and collected for the next run. The mixture was extracted with diethyl ether and then dried over anhydrous sodium sulfate (Na2SO4). After filtration and solvent evaporation, 1,2-diacetates were obtained as pure and viscous liquids. The produced 1,2-diacetoxy esters were characterized by FT-IR1, H NMR and 13C NMR spectra. All products are known compounds and their structures were confirmed by comparing their spectra with authentic sample36,39. These data are provided in the supplementary information.

To evaluate the recoverability of the catalyst, after the reaction, the catalyst was recovered via simple magnetic decantation. The recovered catalyst was washed with ethyl acetate three times, dried, and finally weighed to measure the amount recovered. The collected nanoparticles were reused in the next run without any significant loss of magnetic property or catalytic activity.

In a round-bottomed flask (10 mL) equipped with a magnetic stirrer, a solution of trans-1,2-diacetate (1 mmol) in aqueous MeOH (50%, 3 mL) was prepared. K2CO3 (0.2 g, 1.5 mmol) was then added and the reaction mixture was stirred for 0.5 h at room temperature. After completion of the reaction, the mixture was acidified with HCl (1 N). The methanol was evaporated and the mixture was extracted with diethyl ether. The combined ether phases were dried over anhydrous Na2SO4 and evaporated to give the corresponding trans-1,2-diol.

All data from this study are included in the article and the Supplementary Information File.

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The financial support of this work by the Research Council of Payame Noor University is gratefully acknowledged.

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

Ronak Eisavi

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Ronak Eisavi designed the research framework, conducted experiments, carried out the data analysis and wrote the final manuscript.

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Supplementary Material 1. The FT-IR, 1H NMR and 13C NMR spectral information of β-acetoxy esters are given in the supplementary section.

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Eisavi, R. CaFe2O4@SiO2-Cu as a novel and highly efficient nanocatalyst for direct conversion of epoxides to β-acetoxy esters. Sci Rep 14, 26606 (2024). https://doi.org/10.1038/s41598-024-77281-1

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Received: 13 August 2024

Accepted: 21 October 2024

Published: 04 November 2024

DOI: https://doi.org/10.1038/s41598-024-77281-1

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