Magnetically Recoverable Silica-Decorated Ferromagnetic-Nanoceria Nanocatalysts and Their Use with O- and N-Butyloxycarbonylation Reaction via Solvent-Free Condition.

Silica-decorated ferrite nanoparticles, a new kind, coated with ceric ammonium nitrate (CAN), have been prepared successfully by simple coprecipitation techniques. Powder X-ray diffraction spectroscopy (PXRD), Fourier transform-infrared spectroscopy (FT-IR), field emission-scanning electron microscope (FE-SEM), wavelength-dispersive X-ray spectroscopy (WDX), energy-dispersive spectroscopy (EDS), inductive coupled plasma-optical emission spectroscopy (ICP-OES), and thermogravimetric analysis (TGA) techniques were used to characterize these nanoparticles. The catalysts are further studied for catalytic activity in solvent-free conditions. Importantly, these nanoparticles have been collected from the reaction mixture using an external magnet and recycled up to minimum of 15 cycles with no substantial loss of catalytic characteristics.

Introduction

Scientists nowadays are more inclined toward green chemistry so that reactions are safe and do not pollute the environment. Catalysis has recently developed as a sophisticated field of study with well-established ideas and interpretations. Sustainable synthesis methods that are mostly solvent-free, catalyst-free, and use aqueous media have received a lot of attention. Environmental and ecological pollution prevention methods preserve the environment by decreasing or eliminating the use of harmful substances, as well as preventing the production of byproducts and the production of undesired components.[1,2] Notwithstanding their widespread popularity, many contemporary solvent-free and catalyst-free approaches are less effective for some chemical reactions. For these reactions, effectiveness and a particular catalyst are necessary to achieve the intended results.[3] Unfortunately, relative to their heterogeneous equivalents, homogeneous catalysts frequently suffer from low durability and renewability.

As a result, the development of cost-effective, environmentally friendly, and biodegradable nanoparticles is widely preferred.[4−7] Using eco-friendly ingredients that avert the use of toxic and hazardous substances, utilizing solvent-free reactions circumstances which minimize the treatment and disposal load, mild conditions, shorter reaction speed, the renewability of catalysts, and nanocatalysis is a better route for sustainable and green chemical reactions.[8−10] Such properties of nanoparticles have contributed to their widespread use in a range of synthetic reactions.[11−13] Furthermore, these nanoparticles offer easy and environmentally acceptable ways of achieving high productivity and specificity in chemical synthesis.[14−16]

Nanoparticle development has piqued the interest of researchers in recent decades. Certain functionalized nanoparticles appear to be particularly reactive due based on the evidence of nanomaterial formed by some of the more active centers.[17,76] Ferrite magnetic nanoparticles have been extensively employed in the manufacturing industries and in medical applications such as drug development.[18] The much more common uses for magnetite nanoparticles are in chemical synthesis, including the manufacture of Suzuki coupling reaction,[19] alkynyl chalcogenide,[20] synthesis of quinoxaline,[21] 3,4-dihydropyrimidine-2-(1H),[22] calix-4-resorcinarenes,[23] pyranopyrazoles,[24] α-amino nitriles,[25] synthesis of sulfonamide,[26] α-aminophosphonate,[27] the Sonogashira-Hagihara reaction,[28] propargylic amine synthesis,[29] and acylation reaction,[30] etc. These approaches are becoming increasingly important as a means of reducing byproducts, low costs, and increasing selectivity.[75,77,80]

The protection and deprotection of phenols are used in industrial and academic research for multistep syntheses. The simplicity and fragility of either the protection or deprotection processes are critical to the strategy’s effectiveness. N-Boc compounds are commonly used for the preservation of amino groups.[31] Nonetheless, the synthesizing procedures of many chemical carbonates rely on a basic media or Lewis base, and the employment of hazardous reagents such as phosgene, carbon monoxide, and pyridine.[32−34] As a result, attempts have been made to create environmentally acceptable O-carbonate fabrication methods.[35−37] Because the chemical value of this protection, particularly in terms of carbonates, is more stable than the equivalent esters under primitive conditions.[38] Their usefulness continues to grow in educational and business investigation.[39] The catalyzed forms, on the other hand, appear to be comparatively undiscovered, allowing us to start to design biodegradable nanocatalytic systems for the preservation of phenolic compounds inside the forms of corresponding carbonates.

The N-ter-butyloxycarbonylation of amines prepared via Lewis and Brønsted acid reactions are the past studies that have been reported. Other materials that can be used are guanidine hydrochloride,[40] thioglycouril,[41] thiourea,[42] molecular sieves,[43] succinamide sulfamic acid,[44] saccharin sulfonic acid,[45] sulfamic acid,[46] FeCl3,[47] ZnCl4,[48] InCl3, InBr3,[49] HClO4,[50] LiClO4,[51] Bi(NO3)3·5H2O,[52] La(NO3)3,[53] (CF3)2CHOH,[54] Cu(BF4)2,[55] Zn(ClO4)·6H2O,[56] I2,[57] CsF,[58] and Me2SBr2,[59] etc. Many catalysts have been created such as sulfonic acid supported nanoporous titania, sulfonic acid supported nanoporous Na+ montmorillonite, silica supported sulfonic acid, H3PW12O40 mesoporous silica acid, amberlyst-15, phenyl sulfonic acid, HClO4–SiO2, montmorillonite K10 or KSF, indion-190 resin, poly(4-vinylpyridinium) perchlorate, tungsten phosphoric acid doped mesoporous silica, nano-TiO2–HClO4, and ferrite nanocatalyst.[60] In the same way, ionic liquid used as an acid catalyst including [H-Suc] HSO4, [(HMIm) BF4], [Py] [OTF], [TMG][AC], 1-alkyl-3-methylimidazolium ionic liquid, imidazolium trifluoroacetate, and 1,3-disulfonic acid imidazolium hydrogen sulfate have been used to protect amine analogues against N-Boc attacks.[61] Recent research has found that reactions may occur without the use of catalysts, instead with the use of ethanol,[62] β-cyclodextrin,[63] polyethylene glycol,[64] and water,[65] as well as microwave irradiation both with and without catalyst or in a catalyst-free reaction.[66]

Under this study, the silica-coated ferrite magnetite nanoceria-ceric ammonium nitrate (CAN) has been developed using coprecipitation techniques. In the first step, silica-coated ferrite magnetic nanoparticles (MNPs) are synthesized in an aqueous medium utilizing tetraethyl orthosilicate (TEOS), then the addition of CAN in ethanol under sonication produces magnetite-nanoceria CAN nanocatalyst. The prepared magnetite-nanoceria catalysts were used for O- and N-Boc protection using di-ter-butyl carbonate reagent in an eco-friendly, cost-effective, and simple method. (Scheme )

Scheme 1

Preparation of Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanocatalysts and Its Applications in the N-, O-Boc protection

Results and Discussion

Analysis of Silica-Decorated Ferromagnetic-Nanoceria (CAN) Nanocatalyst

The CAN loaded on silica-coated ferrite nanoparticles was confirmed using FT-IR (Fourier transform infrared) spectroscopy as a preliminary investigation. The infrared spectroscopy of Fe3O4@SiO2@(NH4)2Ce(NO3)6, Fe3O4@SiO2, and Fe3O4 nanocatalysts is shown in Figure , and the distinctive peaks of the FT-IR spectrum are listed in Table . Attributed to the prevalence of water molecules on the surface of the Fe3O4 nanoparticles (Figure A), the signal at 3220.05 cm–1 in the spectrum of Fe3O4 was ascribed to the hydroxyl (O–H) stretching vibrations. Furthermore, the deionized water utilized as a solvent might be attributed to the peaks at 1631.03, 1342.10, and 1017.71 cm–1. The O–Fe vibrational peaks were given at 694.76 cm–1 as well as 450.76 cm–1. Their peak values appeared similar to those reported by Tandon et al.[30] In the FT-IR spectroscopy of Fe3O4@SiO2 (Figure B), a peak at 3211.81 cm–1 matched the O–H bond vibrations of the hydroxyl group stretched in SiO2.[30] Furthermore, the signal at 1631.61 and 1012.31 cm–1 on the surface of SiO2 was ascribed to the H–O–H class. The Fe–O–Si bond was assigned to that same distinctive signal at 690.81 cm–1, confirming the covering of Fe3O4 with SiO2. The Fe–O bonding was responsible for the signal at 445.31 cm–1.[67] The infrared signal at 3339.46 cm–1 in the FT-IR spectroscopy of Fe3O4@SiO2@(NH4)2Ce(NO3)6 (Figure C) was attributed to the Fe–O binding stretching mode of weakly bound ammonium (NH4)+ ions. The distilled water employed as a solvent might be attributed as a signal at 1639.25 cm–1 as well as 1007.34 cm–1. The bending vibration of the Ce–O–Si bond shows an extra signal at 685.66 cm–1 and a signal at 434.20 cm–1 due to the bending vibration of the Fe–O bonding.[78]

Figure 1

Infrared spectra of (A) ferrite, (B) silica-decorated ferrite, (C) (NH4)2Ce(NO3)6 supported silica-ferrite nanocatalysts.

Table 1

Comparative Study of FT-IR Spectrum Peaks of (A) Fe3O4, (B) Fe3O4@SiO2, and (C) Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanocatalysts

nanocatalysts	FT-IR peaks
(A) Fe3O4	3220.05 cm–1, 1631.03 cm–1, 1342.10 cm–1, 694.76 cm–1, 1017.71 cm–1, 450.76 cm–1
(B) Fe3O4@SiO2	3211.81 cm–1, 1631.61 cm–1, 1012.31 cm–1, 690.81 cm–1, 445.31 cm–1
(C) Fe3O4@SiO2@(NH4)2Ce(NO3)6	3339.46 cm–1, 1639.25 cm–1, 1007.34 cm–1, 685.66 cm–1, 434.20 cm–1

Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2@(NH4)2Ce(NO3)6 are depicted in the scanning electron microscopy (SEM) images in Figure . The Fe3O4@SiO2 nanoparticles have been strongly supported on the cerium layer, as evidenced by the acquired morphological pictures. Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2@(NH4)2Ce(NO3)6 all have typical crystallographic sizes of 83, 89, and 92 nm, correspondingly. The presence of distinct intergranular particles has verified the normal development of the crystalline phase.

Figure 2

SEM images of (A) Fe3O4, (B) Fe3O4@SiO2, and (C) Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanocatalysts.

The crystalline structure of the obtained sample was studied using an energy dispersive X-ray spectroscopy (EDX) instrument (make model) in combination with SEM. The Ce, Si, Fe, and O atoms are found in the anticipated ratios of 2.09, 6.08, 70.01, and 21.82%, respectively, in the EDX spectrum of CeO2 silica-coated iron oxide Figure . The analysis confirmed the quantity of elements.

Figure 3

EDX profile data for Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanocatalysts.

In an analysis in conjugation with SEM (scanning electron microscope), WDX (wavelength-dispersive X-ray spectroscopy) has provided a measurable analysis mostly on the predominance of different synthetic materials in catalytic material. Figure displays WDX and SEM pictures of a nanocatalyst developed, revealing that the iron (Fe) atoms remained equally spread throughout the composition. A continuous and homogeneous mixture of Ce, Si, Fe, and O across the components is indicated by the percentage concentration of a substance: 2.09, 6.08, 70.01, and 21.82% of components are present.

Figure 4

SEM images of Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanoparticles depicted as O, Si, Fe, and Ce element in the catalysts.

The produced catalyst was subjected to PXRD investigations with 2θ values ranging from 20 to 80°, and the resulting images are shown in Figure . The appearance of numerous signals inside the powder XRD of at least 3 samples showed that they were polycrystalline. In the powder XRD of iron oxide depicted, the complete development of magnetite Fe3O4 and a tiny residue of Fe2O3 were detected in as an impurity (Figure A). According to the amorphous structure of the material, no extra signal was seen on silicon dioxide (SiO2) loaded on iron oxide (Figure B). However, a rise mostly in the frequency of the 400 bands (2θ, 44.8) in silica-coated iron oxide powder XRD suggests an enhanced crystalline nature and a shift in the crystallite diffraction pattern. Despite the lower ionic radii of Si2+ relative to Fe3+, the maxima shifted somewhat toward a maximum width, indicating the saturation of SiO2 on iron oxide nanoparticles.[30] The remaining single stronger peak at 2θ value of 29.22 was ascribed to the presence of Ce4+ in the powder XRD of ceric ammonium nitrate supported silica-coated iron oxide nanoparticles (CeO2) Figure C.[68] The Fe3O4@SiO2@ceric ammonium nitrate composite diffraction pattern revealed the combination of clean crystallites of Fe3O4@SiO2 and ceric ammonium nitrate.[78] Furthermore, the addition of ceric ammonium nitrate did not affect its diffraction pattern, indicating that metallic ions were present also on the clay’s outermost layer. The average particle size of Fe3O4@SiO2@(NH4)2Ce(NO3)6 and Fe3O4@SiO2, Fe3O4 was determined using Scherrer’s technique, which came out to be 17, 15, 13 nm. The signal for Ce was not noticeable in the XRD pattern, probably due to the low amount of Ce (1.33% by ICP-OES).

Figure 5

Powder XRD spectra of (A) ferrite, (B) silica-decorated ferrite, and (C) silica-decorated ferrite supported with (NH4)2Ce(NO3)6 nanocatalysts

The thermogravimetric analysis (TGA) was studied for Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanocatalysts for temperatures from 30 to 1000 °C under air atmosphere (Figure ). Thermogravimetric analysis (TGA) examination of Fe3O4 and Fe3O4@SiO2 nanoparticles revealed a minor loss in weight below 180 °C, which has been attributed here to the loss of adsorbed water (Figure A,B). Significant weight loss occurs below 180 °C in the thermogravimetric analysis (TGA) curve of Fe3O4@SiO2@(NH4)2Ce(NO3)6, and the subsequent weight loss occurs at 300–600 °C owing to the breakdown of ceric ammonium nitrate (Figure C).

Figure 6

Thermogravimetric analysis of (A) Fe3O4, (B) Fe3O4@SiO2, and (C) Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanocatalysts.

Catalytic Applications of Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanocatalyst

The produced magnetite nanoparticles Fe3O4@SiO2@(NH4)2Ce(NO3)6 were next investigated utilizing a variety of methods. This catalyst was used to create chemoselective protection for amines and phenol derivatives. The chemoselective protection of amines with di-ter-butyl carbonate was utilized as a model reaction to improve the reaction conditions to achieve these objectives. The N-Boc protection was done for the amine leaving hydroxyl group for the reaction (Scheme ). During the study, it was discovered that the reaction of aniline and di-ter-butyl carbonate in the catalyst-free or solvent-free medium does not produce the product. Then aqueous, nonpolar solvent (toluene), polar protic (MeOH, EtOH), polar aprotic (THF, CH3CN), and low polarity (DCM) materials were used to execute various processes, but the results were poor. Remarkable, excellent results were obtained under solvent-free conditions. Significantly, the amine protection advanced well in the presence of 0.08 mg of Fe3O4@SiO2@(NH4)2Ce(NO3)6 at room temperature, producing 80% after 20 min. Similarly, increasing the nanoparticle quantity from 0.08 to 0.09 mg at room temperature raised the reaction yield to 98%, while raising the nanoparticle quantity to 0.10 mg did not affect the process overall productivity (Table ).

Scheme 2

Reaction of Amine with Di-ter-butyl Carbonate Catalyzed by Fe3O4@SiO2@(NH4)2Ce(NO3)6

Table 2

Reaction Optimized Condition for the N-Butyloxycarbonylation Reaction Catalyzed under Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanocatalysta

no.	solvent	catalyst (mg)	time	yieldb (%)
1	none	none	6 h	00
2	H2O	0.09	1 h	10
3	toluene	0.09	1 h	10
4	MeOH	0.09	1 h	25
5	EtOH	0.09	1 h	35
6	THF	0.09	40 min	55
7	CH3CN	0.09	30 min	60
8	DCM	0.09	30 min	75
9	none	0.08	20 min	80
10	none	0.09	10 min	98
11	none	0.10	10 min	98

Reaction condition: aniline (10 mmol), di-ter-butyl carbonate (10 mmol), solvent (5 mL).

Isolated yield.

Under these ideal conditions, chemo-selective N-butyloxycarbonylation of amines was achieved utilizing some cyclic secondary amines, aromatic amines, and aliphatic amine derivatives (Scheme ). In general, aniline and aromatic amines containing electron-donating moieties perform N-Boc protection with good yield in a shorter time (Table , no. 2–7). When compared to the electron-donating substrate, the derivatives with halogens (Br and Cl) and electron-withdrawing substrate had slightly lower yields (Table , no. 8–10). This technique proved extremely effective for cyclic amines or aliphatic primary and secondary amines, yielding N-Boc protected compounds with higher production (Table , no. 11–18). The aliphatic amines interacted more quickly than the aromatic amines, yielding predominantly monoprotected analogues with outstanding yield. It is worth noting that neither side reactions, including the creation of urea or isocyanate, were seen in the case of aliphatic primary amines, nor bis-Boc compounds were found.

Scheme 3

Scope of the Substrate of Amine Derivatives

Table 3

Preparation of N-Boc Protection Catalyzed under Fe3O4@SiO2@(NH4)2Ce(NO3)6a

Reaction condition: amines (10 mmol), di-ter-butyl carbonate (10 mmol), solvent-free at ambient temperature.

Isolated yield.

The model reaction conditions were optimized using the O-Boc protection of phenol as a model reaction (Scheme ). It was discovered during the study that the O-Boc protection did not take place on the reaction of phenol with di-ter-butyl carbonate under solvent-free conditions even at 100 °C. The O-Boc protection reaction performed effectively in the presence of 0.06 mg of Fe3O4@SiO2@(NH4)2Ce(NO3)6 at the same temperature, yielding 61% after 4 h. Furthermore, lowering the temperature from 100 to 70 °C had no discernible effect on the percent yield. Increasing the amount of nanocatalyst from 0.07 to 0.09 mg at 70 °C increased the reaction yield to 96%, whereas increasing the amount of nanocatalyst to 0.10 mg did not affect the total yield of the process. Several processes were performed in the presence of polar protic (EtOH and MeOH), mild polarity (DCM), polar aprotic (CH3CN and THF), and nonpolar solvent (toluene), but results were unsatisfactory (Table ).

Scheme 4

Reaction of Phenol with Di-ter-butyl Carbonate Catalyzed by Fe3O4@SiO2@(NH4)2Ce(NO3)6

Table 4

Reaction Optimized Condition for the O-Butyloxycarbonylation Reaction Catalyzed under Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanocatalysta

no.	solvent	catalyst (mg)	temp (°C)	time (h)	yieldb (%)
1	none	none	100	6	00
2	none	0.06	100	4	61
3	none	0.07	70	4	75
4	none	0.08	70	2	88
5	none	0.09	70	2	96
6	none	0.10	70	2	96
7	ethanol	0.09	100	2	35
8	methanol	0.09	100	2	25
9	DCM	0.09	100	2	43
10	THF	0.09	100	2	50
11	toluene	0.09	100	2	60
12	acetonitrile	0.09	100	2	65

Reaction condition: phenol (10 mmol), di-ter-butyl carbonate (10 mmol), 70 °C temperature, solvent (5 mL).

Isolated yield.

Following the optimization of the circumstances, the substrates’ range for the protection of O-ter-butyloxycarbonylation was investigated (Scheme ). In particular, the hydroxyl group with an electron-deficient group as well as halogens (Br and Cl) provide O-Boc protection with a slightly lower yield as compared to the electron-donating group (Table , no. 1–7). In general, phenols with electron-donating groups provide a better yield of O-Boc protection in less time (Table , no. 8–11). Additional bicyclic aromatic phenol 2-amino-naphthalenes are transformed to O-Boc analogues in good yields (Table , no. 12).

Scheme 5

Scope of the substrate of phenol derivatives

Table 5

Preparation of O-Boc Protection Catalyzed under Fe3O4@SiO2@(NH4)2Ce(NO3)6a

Reaction condition: phenol (10 mmol), di-ter-butyl carbonate (10 mmol), nanocatalyst (0.09 mg), solvent-free, 70 °C.

Isolated yield.

The probable mechanism of N-Boc and O-Boc protection catalyzed by Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanoparticles is depicted in Scheme . The Fe3O4@SiO2@(NH4)2Ce(NO3)6 (I) catalyzed the synthesis of Boc anhydride (II) intermediate. This made a carbonyl group of Boc anhydride very electrophilic, allowing amine or phenol attack via aromatic amines (III) R-XH to give the nucleophilic addition (IV) intermediate. Ultimately, a modification of the (IV) intermediate produced the protected amine and phenol derivatives, as well as ter-butyl alcohol and carbon dioxide as byproducts. Suresh et al.[69] have presented a mechanism that is comparable to this one.

Scheme 6

Probable Mechanism of N-Boc and O-Boc Protection Catalyzed by Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanoparticles

Under optimal reaction conditions, a recyclability study using the nanocatalyst has been carried out for O-Boc protection of phenol with di-ter-butyl carbonate utilizing Fe3O4@SiO2@(NH4)2Ce(NO3)6 MNPs as a nanocatalyst. However, even after 15 cycles (Figure ), the recycling experimental results demonstrated outstanding yields (Table ). The nanocatalyst was magnetically removed after every process, rinsed with ethyl acetate, and dried for 2 h at 60 °C in the oven until being utilized for another process. Veisi et al.[74] also reported a recyclability study similar to this.

Figure 7

Recyclable and reutilization of Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanocatalyst.

Table 6

Recyclable Study of Fe3O4@SiO2@(NH4)2Ce(NO3)6 Nanocatalyst

cycles	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
yield (%)	96	96	96	96	96	96	95	95	95	95	95	94	94	94	94

In comparison to earlier described methodologies depicted in (Table ), the current study has benefits in the form of speed of reaction, solvent-free or mild process, and indeed the avoidance of dangerous and toxic solvents. Furthermore, 15 cycles were successful using the same catalyst.

Table 7

Comparative Study of the Reaction Conditions of the Current Work with Previously Reported Literature for the N-Boc or O-Boc Protection

no.	reaction condition	time	yield (%)	ref
1	iodine, rt, solvent-free	30 min	95	(57)
2	aqueous acetone, rt	7 min	94	(70)
3	FeCl3,rt, solvent-free	1 h	89	(47)
4	InCl2, rt, solvent-free	30 min	90	(49)
5	HClO4, H2O, rt	50 min	95	(50)
6	sulfamic acid, rt solvent-free	30 min	95	(46)
7	β-cyclodextrin, H2O, rt	2.5 h	75	(63)
8	montmorillonite (K10), solvent-free, rt	15 min	98	f
9	ceric ammonium nitrate, rt	24 h	85	(71)
10	Nano-Fe3O4, ethanol, rt	20 min	98	(72)
11	Fe3O4@Co3O4 nanoparticles, 70 °C	3 h	94	(73)
12	Fe3O4@SiO2@(NH4)2Ce(NO3)6, solvent-free, rt	10 min	98	our synthesized catalyst

Experimental Section

Reagents and Chemicals

The chemicals and reagents were obtained from (Sigma-Aldrich, Merck, Spectrochem, and Fluka, etc.) and used without any modifications. The melting points were measured in open capillaries. During thin-layer chromatography (TLC), (Merck Kieselgel 60 F254) precoated aluminum plates (Merck, Kenilworth, NJ, USA) were utilized, and spots were seen under UV light. Numerous analytical approaches were used to characterize the produced nanocatalyst of silica-coating ferrite magnetite-(NH4)2Ce(NO3)6 catalyst. FT-IR spectra (version 10.6.1, PerkinElmer FT-IR), field emission-scanning electron microscopy (JSM-7610F plus, JEOL, FE-SEM), energy-dispersive X-ray spectroscopy (EDS, LN2, Oxford EDS), thermogravimetric analysis (TGA, PerkinElmer 4000), powder X-ray diffraction (PXRD, D8 Advances Bruker), and inductive coupling plasma-optical emission spectrometry (ICP-OES, Agilent model 5110) were utilized for the analysis of the nanoparticles. With the use of tetramethylsilane (TMS) as the internal standard DMSO-d6 and CDCl3 as the solvent, 1H NMR spectra were obtained on an Avance Bruker II 400 FT spectrometer (1H NMR 400 MHz, 13C NMR 100 MHz).

Synthesis of Ferrite Magnetic Nanoparticles

To make ferrite nanoparticles, a simple wet chemical reduction procedure was applied.[30] To generate 0.10 M of the solution, 2.702 g of ferric chloride hexahydrate (FeCl3.6H2O) was prepared in distilled water to ensure that the total quantity was up to mark (100 mL) in a volumetric flask. To create 2.5 M of something like the solution, 9.457 g of sodium borohydride (NaBH4) was mixed in distilled water to form an overall amount of up to the marking (100 mL) in that other volumetric flask. Approximately 40 mL of ferric chloride hexahydrate (FeCl3.6H2O) mixture was added dropwise to 10 mL of sodium borohydride (NaBH4) mixture for around 15 min while stirring. The disappearance of bubbling throughout the working medium and indeed the emergence of dark precipitates signaled the end point of the titration. The ferrite (Fe3O4) nanocatalysts were subsequently isolated from the reaction medium through the use of a magnetic field and then washed with water many times to remove unreacted material. To obtain 1.70 g of Fe3O4 nanoparticles, these nanoparticles were placed in the oven at 60 °C for overnight.

Synthesis of Silica-Coating Ferrite Magnetic Nanoparticles[79]

The simplistic Stober process was used to make fundamental Fe3O4@SiO2 nanoparticles through reacting ferrite nanoparticles using TEOS (tetraethyl orthosilicate). Ferrite nanoparticles (2 g) were distributed in 100 mL of 100% ethanol for all of this experiment, and the mixture was stirred thoroughly for 20 min. Then NH4OH (ammonium hydroxide) 5 mL was added and the mixture was allowed to react to volume after 20 min of ultrasonic treatment, accompanied by the dropwise addition of tetraethyl orthosilicate (TEOS) (2 mL) at 30 °C for 6 h under constant sonication. The resultant silica-coated magnetite nanoparticles (Fe3O4@SiO2) were subsequently isolated again from the process solution using a magnet, rinsed with ethanol and water, afterward dried at 60 °C in vacuum for 12 h. The process yielded 2.17 g of magnetite nanoparticles decorated with silica (Fe3O4@SiO2).

Synthesis of Ceric Ammonium Nitrate Supported Silica-Coated Ferrite Magnetic Nanoparticles

After sonicating a mixture of 2 g of silica-coated nanoparticles in ethanol (100 mL) for around 30 min, 0.54 g of CAN was added to the reaction medium under constant agitation. The pH of the reaction medium was then adjusted to 12 using 1 M sodium hydroxide (NaOH) solution, and also the reaction mixture was agitated for another 24 h at ambient temperature. Eventually, the precipitates were collected, cleaned using double distilled water, and dried overnight at 60 °C to yield 2.32 g of magnetite-CAN.

General Procedure for Protection of Amine (N-Boc) Derivatives

Aniline (1 mmol) was reacted with di-ter-butyl carbonate (1 mmol) in the presence of Fe3O4@SiO2@(NH4)Ce(NO3)6 nanocatalyst (0.09 mg) at ambient temperature while under continuous stirring. TLC was used to track the reaction’s progress in the presence of ethyl acetate and n-hexane (1:9 ratio). The reaction mixture was filtered by adding ethyl acetate (5 mL) solvent, and the nanocatalyst was extracted with an external magnetic field. The nanomaterials were isolated and thoroughly cleaned with water and ethanol several times before being dried in a vacuum. To obtain the required products, the sample solution was rinsed with saturated sodium carbonate (NaHCO3) solution, and the resultant material was extracted with ethyl acetate, dried over Na2SO4. The extract was removed under vacuum.

General Procedure for Protection of Phenol (O-Boc) Derivatives

Phenol (1 mmol) was treated via di-ter-butyloxycarbonate (1 mmol) using Fe3O4@SiO2@(NH4)Ce(NO3)6 nanocatalyst (0.09 mg) at 70 °C temperature under continuous stirring. TLC (thin-layer chromatography) technique was used to track the reaction’s progress in the presence of ethyl acetate and n-hexane (1:9) solvent ratio. Thereafter the mass of the reaction occurred, and the reaction mixture was cooled to room temperature. Then the solution was filtered with the addition of ethyl acetate (5 mL) solvent, and the nanocatalyst was collected with an external magnetic field. The collected nanomaterials were cleaned with aqueous ethanol several times before being dry in a vacuum. After the prepared sample was treated with (NaHCO3) sodium carbonate saturated solution, the resulting residue was isolated into ethyl acetate. The separation was dried under sodium sulfate and collected using suction to generate the desired protected product.

Conclusion

By adding ceric ammonium nitrate on the surface of Fe3O4@SiO2 nanoparticles, we were able to create a unique Fe3O4@SiO2@(NH4)2Ce(NO3)6 nanocatalyst. Furthermore, under di-ter-butyl carbonate, the obtained nanocatalyst was investigated for N-Boc or O-Boc protection of diverse nucleophilic substrates including amine and phenol compounds. This process has huge benefits versus the previously existing techniques of N-Boc or O-Boc protection in terms of superior yields, faster reaction speed, room temperature condition, and a solvent-free environment that encourages green technologies. Moreover, during 15 cycles, there was no loss of catalytic reactivity.