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Synthesis and characterization of [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu nanocatalyts and their application in the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile and 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives
⁎Corresponding author. addressa_khazaei@basu.ac.ir (Ardeshir Khazaei)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Abstract
The current study provides a synthetic approach to prepare two novels magnetic Fe3O4@CQDs based catalyst. Accordingly, an ionic-liquid based and copper-based nano-magnetic solid acid catalyst, namely, [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu were synthesized. Carbon quantom dot (CQD), as a green and sustainable support, was used to coating the nano-Fe3O4 instead of conventionl SiO2. Various techniques, in sequence, were used to characterize the as-synthesized catalysts, including infrared (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy (EDX), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and vibrating sample magnetometery (VSM). The activity of the as-prepared catalysts was examined in the synthesis of 5-amino-1,3-diphenyl-1H and (morpholino(phenyl)methyl) derivatives. Interestingly, the pyrazole ring formation is followed by an anomeric effect assisted oxidation reaction even at room temperature. Optimum reaction conditions of morpholino(phenyl)methyl) derivative were determined via design of experiment (DOE).
Keywords
Ionic-liquid based
Copper-based nano-catalyst
5-amino-1
3-diphenyl-1H(morpholino(phenyl)methyl)
One-pot reaction
1 Introduction
In multicomponent reactions (MCRs) more than two starting materials are involved in the reaction, forming a single molecule, in which some parts of the reactants are present in the product. MCRs are more economically viable, highly convergent and have high bond-forming-index (BFI) (Gao et al., 2008) leading structural diversity and molecular complexity in a single step synthesis. The first three component reaction (3CR) traced back to Gerhard and Laurent in 1838, in which cyanohydrin was synthesized from ammonia and bitter almond oil containing benzaldehyde and hydrogen cyanide (Brauch et al., 2013). This method was popularized by Strecker in 1850 (Strecker, 1850) as a route for synthesis of cyano amines, the most important intermediate in the synthesis of amino acids. Following this fundamental work by Strecker, diverse MCRs have been developed for production of value added compounds (Andalibi Salem et al., 2019; Panahi et al., 2019). Examples of these MCRs are Mannich 3CR (Mannich and Krösche, 1912), Strecker 3CR (Strecker, 1850), Ugi 3CR (Ugi, 1962), Pauson-Khand 3CR (Pauson and Khand, 1977), Hantzsch 3CR (Hantzsch, 1881), and Staudinger 3CR (Staudinger, 1907). Other MCRs examples are the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile and 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives that were considered in this research. 1,3-Diphenyl-1H-pyrazol derivatives have shown effects on positive allosteric modulation of the metabotropic glutamate-5 receptor (de Paulis et al., 2006; Lindsley et al., 2004). Not only 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives have biological effect, but also they can be used in non-linear optical (NLO) crystals because of their potential applications in high power lasers (Dennis Raj et al., 2017). To increase the rate of chemical reactions, beside the method of reaction the catalyst usage is a critical factor (Fogler, 1998). Different types of homogeneous and heterogeneous catalysts have so far been developed to achieve the aforementioned objectives. Recently, magnetic catalyst especially nano-magnetic catalysts based on the Fe3O4 have attracted the researcher’s attention (Chen et al., 2014; Nasir Baig and Varma, 2013; Rathi et al., 2016; Roudsari et al., 2019; Ying et al., 2016). Coating and functionalization of Fe3O4 has created more complex and effective structures. Tetramethyl orthosilicate (TMOS) is regularly used to coating the Fe3O4 surface with SiO2 to protect it from harsh acidic and basic media (Rostamnia et al., 2018), which are employed in the following functionalization processes (Meffre et al., 2015; Sharma et al., 2016). Taking this into account, in this study the Fe3O4 surface was coated with the carbon quantum dots (CQDs) for the first time. CQDs were prepared from the cheap, available and sustainable starting material such as glucose, sucrose, and so forth (Liu et al., 2018). The main objective of this study is to coating the Fe3O4 surface with CQDs as linkers, followed by designed functionalizations to prepare recoverable ionic-liquid based and copper based nano-magnetic catalyst to be used in the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile and 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives.
2 Experimental section
2.1 Material and methods
The chemicals used here including FeCl2·4H2O, FeCl3·6H2O, ammonia (28%wt), glucose, oil (palmitic acid 5%, stearic acid 6%, oleic acid 30% and linoleic acid 59%), diethyl ether, 3-(Triethoxysilyl)propylamine, toluene (anhydrous), cyanuric chloride, tetrahydrofuran (THF), ethanol, ethylenediamine, acetone, dichloromethane, chlorosulfonic acid, Cu(OAc)2, phenylhydrazine, benzaldehydes, and malononitrile were purchased from the Merck Company. All chemicals were used as purchased. Melting points were determined with a Barnstead Electrothermal 9200 apparatus, FTIR spectra were recorded on a Perkin-Elmer 1600 spectrometer using KBr disks. The 1H, 13C NMR were measured on a Bruker 250 MHz spectrometer. Various techniques including Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDXA) and Vibrating sample magnetometer (VSM) were used to characterize the as-synthesized catalysts.
2.2 Preparation of Fe3O4 nanoparticles
Fe3O4 nanoparticles were prepared via co-precipitation method, so that 5.6 g of FeCl2·4H2O and 11.3 g of FeCl3·6H2O were dissolved in distilled water (100 mL) and stirred at 80 °C for 30 min (Heidarizadeh et al., 2017). Then 25 mL ammonia (28%wt) was added at once and the resulting mixture was stirred for 2 h under nitrogen atmosphere at 80 °C. Finally the black nano-particles (nano-Fe3O4) were separated with an external super magnet and dried in a vacuum oven at 90 °C for 12 h after washing several times with acetone and water.
2.3 Preparation of carbon quantum dots (CQDs)
CQDs were prepared through bottom-up methods from glucose as small precursor. 20 mL edible oil (palmitic acid 5%, stearic acid 6%, oleic acid 30% and linoleic acid 59%) was gently heated up to 250 °C, then 10 g glucose was added to the oil, and heated for 10 min at 250 °C (to be completely black). Then, by adding 50 mL water and 20 mL diethyl ether, the CQDs were separated by entering into the aqueous phase. This was repeated several times to allow all the CQDs to be completely separated.
2.4 Surface modification of Fe3O4@CQDs
Of the synthesized nano-Fe3O4, 1 g was dispersed in the already prepared CQDs suspension in water using an ultrasonic bath for 24 h at room temperature. The prepared Fe3O4@CQDs were isolated by an external magnet, and then dried using an oven after washing several times with distilled water (Liu et al., 2009).
2.5 Preparation of Fe3O4@CQDs@Si(CH2)3NH2
Of the previous step synthesized Fe3O4@CQDs, 1 g was dispersed in toluene using an ultrasonic bath for 15 min. In sequence, 2 mL 3-(Triethoxysilyl)propylamine was gently added to the dispersed Fe3O4@CQDs solution and was refluxed for 24 h. The obtained nano-Fe3O4@CQDs@Si(CH2)3NH2 was separated using an external magnet, and dried in oven after washing with toluene, and water.
2.6 Preparation of Fe3O4@CQDs@Si(CH2)3NH2@CC
6 g cyanuric chloride was dissolved in 50 mL dry tetrahydrofuran for 3 h at 0 °C under nitrogen atmosphere. Of the previous step synthesized Fe3O4@CQDs@Si(CH2)3NH2, 1 g was added to the solution, and dispersed using an ultrasonic bath for 30 min. The resultant mixture was stirred at 0 °C for 24 h. The obtained nano-Fe3O4@CQDs@Si(CH2)3NH2@CC was separated from the mixture using an external magnet, and dried in an oven after washing with tetrahydrofuran, and ethanol. The reaction between Fe3O4@CQDs@Si(CH2)3NH2 and cyanuric chloride is progressed through nucleophilic substitution (Ahadi et al., 2019). It is assumed that the steric hindrance would prevent the substitution of all three chlorine in cyanuric chloride by the –NH2 of Fe3O4@CQDs@Si(CH2)3NH2. So, based on this judgment, just one chlorine of cyanuric chloride participates in the reaction.
2.7 Preparation of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA
Of the previous step synthesized nano-Fe3O4@CQDs@Si(CH2)3NH2@CC, 2 g was dispersed in toluene using an ultrasonic bath for 15 min. Ethylendiamine (2 mL) was added to the dispersed solution, and then was refluxed for 24 h. The resultant nano-Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA particels were separated using an external magnet, and then dried in an oven after washing with toluene, and acetone.
2.8 Preparation of [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl−
Of the previous step synthesized nano-Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA, 1 g was disprsed in 30 mL dry dichloromethane (using MgSO4, and molecularsieve) using an ultrasonic bath for 15 min (solution A). 24 mmol (2.796 g) chlorosulfonic acid was disolved in 20 mL dry dichloromethane (solution B). In sequence, solution B was dropwise (Doustkhah et al., 2019; Hassankhani et al., 2020) added to the solution A at 0 °C (under hood until degasing all HCl). The resultant mixture was stirred at room temperature for 24 h. The obtained ionic-liquid based nano-magnetic [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− was separaed using an external magnet, and then was dried in an oven after washing with dry 50 mL dichloromethane. It is assumed that ClSO3H only reacts with the most active atom of the as-synthesized catalyst, namely, the nitrogen atom. There are many articles in literature which have proposed such a mechanism (Dashteh et al., 2020; Saffarian et al., 2021).
2.9 Preparation of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu
In the first step, a 5% (w/v) solution of Cu(OAc)2 in methanol was prepared (mixture A) (Andalibi Salem et al., 2019). Next, of the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA, 1 g was added into the 50 mL of methanol and then dispersed in an ultrasonic bath for 15 min (mixture B) (Doustkhah et al., 2018). Then the mixture A was dropwise added to the mixture B by a decanter funnel. After 48 h reflux, the product was separated by an external magnet and was dried in an oven after washing several times with methanol. The total procedures for the synthesis of the introduced ionic-liquid based nano-magnetic solid acid catalyst, namely, [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and copper-based nano-magnetic Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu are given in Fig. 1.![The proposed procedure for the synthesis of [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig1.png)
The proposed procedure for the synthesis of [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.
2.10 General procedure for the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives
Of the synthesized ionic-liquid based catalyst, 0.05 g was added to the 1 mmol (0.14 g) phenylhydrazine, 1 mmol benzaldehydes, and 1.2 mmol (0.66 g) malononitrile. The resultant reaction mixture (model reaction 1) was stirred at room temperature, so that the reaction progress was monitored using a thin layer chromatography (TLC) (n-hexane + ethyl acetate 70:30). 20 mL hot ethanol was added to the reaction mixture after the completion of reaction. The product was purified through crystallization in ethanol (Seyf and Asgari, 2020) after catalyst separation from the reaction medium using an external magnet. Gram scale reaction was performed to demonstrate the industrial application. So, the amount of the starting materials and catalyst were increased 10 times. The reaction was complete after 10 min and the product separation yield (through crystallization) of 85% was obtained.
2.11 General procedure for the synthesis of 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives
β-naphthol (1 mmol), aryl aldehyde (1 mmol), morpholine (1 mmol), with 0.05 g of the copper-based synthesized nanoparticles were added to a test tube and the reaction mixture was stirred at optimal reaction condition (model reaction 2). The reaction progress was followed by TLC (n-hexane + ethyl acetate 70:30). After the reaction was complete, 20 mL of boiling ethanol was added to the reaction mixture, the catalyst was separated by an external magnet, and then the product was purified by crystallization in ethanol. The possibility of industrialization of the reaction was tested by increasing the scale of raw materials up to 10 times. The scaled reaction was complete after 14 min and the product separation yield (through crystallization) of 92% was obtained.
Fig. 2(a) illustrates the total synthesis procedure of the 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile using the as-prepared ionic-liquid based catalyst at room temperature. Fig. 2(b) shows the total synthesis procedure of the 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives using as-prepared copper-based catalyst at optimum condition.
The total synthesis procedure of a) 5-amino-1, 3-diphenyl-1H-pyrazole-4-carbonitrile and b) 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives using the as-preparedcorresponding catalysts.
3 Results and discussion
3.1 Characterization of the catalyst
Various techniques including infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive x-ray analysis (EDXA), EDX elemental mapping, thermal gravimetric analysis (TGA) and vibrating sample magnetometery (VSM) were used to characterize the as-synthesized catalysts.
3.2 Fourier-transform infrared spectroscopy (FTIR)
FTIR technique was qualitatively used to identify different functional groups in the as-synthesized ionic-liquid based and copper-based catalyst. Fig. 3 displays the FTIR spectra of the Fe3O4, Fe3O4@CQD, Fe3O4@CQDs@Si(CH2)3NH2, Fe3O4@CQDs@Si(CH2)3NH2@CC, Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA, [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl−, and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu. In Fig. 3, the bands at 576 cm−1, and 3433 cm−1 are associated to the bending vibration of Fe-O, and stretching vibration of OH in the nano-Fe3O4, respectively (Zhang et al., 2007). The band at 1632 cm−1 is attributed to the stretching vibration of carbonyl groups (C = O) on the CQDs. The broad absorption around 3430 cm−1 is ascribed to stretching of hydroxyl groups (O-H) on the CQDS (Fig. 3). Of the wave numbers in the IR spectrum of Fe3O4@CQDs@Si(CH2)3NH2, 3454 cm−1, and 2922 cm−1 denoting the N-H, and C-H stretching in trimethoxysilyl propylamine, respectively. This implies the loading of trimethoxysilyl propylamine on the surface of Fe3O4@CQD. Of the wave numbers in the IR spectrum of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu, 1620 cm−1 denotes the C = N stretching in cyanuric moiety. This prove loading of cyanuric chloride on the surface of Fe3O4@CQDs@Si(CH2)3NH2. The band at 3261 cm−1 has been assigned to the N-H stretching vibrations of amine group in ethylenediamine. The peaks around 650, 1200, and 3400 cm−1 in the final ionic-liquid based catalyst are associated to the vibrations of S–O (stretching) (Sarmasti et al., 2019), S = O (asymmetric stretching), and OH groups in –SO3H loaded on the catalyst, respectively. Taking together, these IR findings indicate that different layers have been loaded on the Fe3O4 surface, and the ionic-liquid based nano-magnetic solid acid catalyst has been synthesized. In the FTIR of the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu the wave number of C = N in CC was shifted from 1634 cm−1 to 1627 cm−1. This FTIR finding implies the loading of Cu(II) ions on the surface of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA.![IR spectra of Fe3O4, Fe3O4@CQD, Fe3O4@CQDs@Si(CH2)3NH2, Fe3O4@CQDs@Si(CH2)3NH2@CC, Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA, [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig3.png)
IR spectra of Fe3O4, Fe3O4@CQD, Fe3O4@CQDs@Si(CH2)3NH2, Fe3O4@CQDs@Si(CH2)3NH2@CC, Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA, [Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.
3.3 Field emission scanning electron microscopy (FESEM)
By scanning the sample using the focus beam of electrons in FESEM technique, the characteristic three-dimensional of the sample surface is obtained. FESEM generates high-magnification images of the sample morphology (Spiegelberg et al., 2016). Fig. 4 illustrates the FESEM image of the as-prepared nano-magnetic catalysts. As is shown in Fig. 4(a) and (b), the as-prepared ionic-liquid based catalyst agglomerates due to the hydrogen bond formation between catalyst particles. This behavior was also observed in our previous researches, including the synthesis of Fe3O4@SiO2@(CH2)3Cl@Melamine@Picolinealdehyde@SO3H (Khazaei et al., 2018) and sulfonated magnetic carbon quantum dots (Sarmasti et al., 2019). Fig. 4(c) and (d) illustrates the FESEM of the copper-based as-synthesized catalyst. As is shown the copper-based nano-particles are separated unlike the ionic-liquid based catalyst. These findings show the effect of hydrogen bond formation and also prove the formation of the as-prepared ionic-liquid based and copper-based as-synthesized catalysts.![Field Emission Scanning Electron Microscopy (FESEM) of the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− (a and b), and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu (c and d).](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig4.png)
Field Emission Scanning Electron Microscopy (FESEM) of the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− (a and b), and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu (c and d).
3.4 Energy-dispersive X-ray spectroscopy (EDX)
Energy-dispersive X-ray spectroscopy (EDS, EDX, EDXS, or XEDS) is an analytical technique for the chemical characterization of a sample by the interaction of an X-ray source and a sample. The energies of emitted X-rays are characteristic of the atomic structure of the emitting elements; that is, EDX allows the chemical composition of a sample to be measured. Fig. 5(a) illustrates the EDX spectrum of the as-prepared ionic-liquid based nano-magnetic catalyst, and (b) shows the EDX of copper-based nano-magnetic catalyst. EDX shows that the synthesized ionic-liquid based catalyst has O, C, Fe, Si, N and Cl elements with mass percentages of 25.7, 14.6, 50.5, 3.8, 3.8 and 1.6, respectively. The presence of chlorine atom peak in the EDX spectrum implies the formation of the ionic-liquid based structure. Chlorine atom is the negative counter-ion of the as-prepared catalyst. Fig. 5(b) presents the EDX of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu catalyst, so that the mass percentages of C, Fe, O, Cu, N and Si are 14.2, 0.51, 23.7, 2.3, 4.4 and 4.4, respectively. The presence of Cu(II) ions in the EDX spectrum confirms the loading of copper on the as-synthesized catalyst.![The energy-dispersive X-ray spectroscopy (EDX) of the (a) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu (c and d).](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig5.png)
The energy-dispersive X-ray spectroscopy (EDX) of the (a) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu (c and d).
3.5 Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA)
Change of the sample mass owing to the physical or chemical phenomena over the time as the temperature changes is measured in the thermal gravimetric analysis (TGA). TGA provides useful information about the kinetics of pyrolysis reactions (Saddawi et al., 2010). To further characterize the as-synthesized catalysts, TGA and DTA spectra were recorded (Fig. 6(a)), so that seven drops in mass of the ionic-liquid based catalyst are observed. A drop of between 25 and 90 °C is attributable to the loss of solvent and the moisture content of the catalyst (4.5%).![Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) of the (a) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and (b) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig6.png)
Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) of the (a) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and (b) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.
Fig. 6(b) shows the TGA and DTA of the as-synthesized copper-based catalyst. Zones A, B, C, and D would be attributed to fragmentation of the organic units and CQDs. The area above 750 °C is associated to the Fe3O4.
These TGA and DTA multistep patterns confirm the core–shell structure of the ionic-liquid based and copper-based nano-magnetic catalysts with different layers.
3.6 Vibrating sample magnetometery (VSM)
The VSM explains the magnetic properties of a magnetic nanostructure, also explained the shape, and size of the magnetization (Gerber et al.,1 982; Patsula et al., 2016). Accordingly, VSM technique was used to obtain the magnetic saturation pattern of the as-synthesized magnetic nanoparticles. As seen in Fig. 7(a) saturation magnetization of Fe3O4 and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H, are 55 and 7 (emu/g), respectively. The saturation magnetization value of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H is lower than Fe3O4; that is, the insulating organic layers reduce the saturation magnetization. Although the saturation magnetization of the as-synthesized catalyst is low, it is large enough that the catalyst can be easily separated from the reaction medium. This finding further confirms the synthesis of the as-prepared catalyst. Although the same reasoning is valid for the VSM of the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu (Fig. 7(b)), owing to the presence of metallic Cu in the copper-based catalyst the saturation magnetization is higher than the ionic-liquid based catalyst.![Magnetization curves of the (a) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and (b) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig7.png)
Magnetization curves of the (a) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and (b) Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.
4 Evaluation of the catalytic activity of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu
4.1 Effect of solvent
Six separate experiments were performed to investigate the effect of solvents on reaction time and yield, namely model reaction 1 and model reaction 2. Reactions were performed under solvent-free condition and also in the presence of solvents, including ethyl acetate, dichloromethane, water, normal hexane, and ethanol. In all model reactions 1, 0.03 g nano-[Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− catalysts was added to the reaction medium. In model reactions 2, 0.05 g nano-Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu was added to the reacion medium. The effect of solvent-free condition and various solvents on the yield of the model reactions in the presence of the as-synthesized ionic-liquid based and copper-based nano-magnetic catalysts are given in Table 1. The lowest time and maximum efficiency were obtained under solvent-free conditions for both the model reactions, so that the subsequent investigations were done at this condition.
Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl−
Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu
Entry
Solvent
Time (min)
Yielda (%)
Time (min)
Yielda (%)
r.t.b
60 °C
1
---
8
85
15
78
2
EtOAc
20
80
25
75
3
CH2Cl2
35
75
30
77
4
H2O
>30
70
>45
65
5
n-Hexane
>30
80
>45
60
6
EtOH
20
81
22
71
4.2 Effect of catalysts and temperature on the reaction yield
Due to the short reaction time and its high yield at room temperature and no difference in yield compared to when the reaction is carried out at higher temperature, only the amount of the as-catalyst was optimized for the model reaction 1. All reactions were stopped after 4 min. The effect of the as-synthesized catalysts was evaluated in three values of 0.01, 0.03 and 0.05 g. The corresponding yields are equal to 68, 75, and 85%; that is, the solvent free condition at room temperature with 0.05 g of ionic-liquid based catalyst were selected as the optimum operating reaction condition for the model reaction 1.
Temperature and the amount of the copper-based catalyst as the effective factors for model reaction 2 were optimized using the design of experiment (DOE). Details of the DOE are given in the supporting information. Based on the DOE (Design-Expert software) it was found that the optimum condition for model reaction 2 are at 0.05 g of the catalyst and 89.69 °C and the corresponding maximum yield is 85.01%. In Experimental work, the value of proposed temperature by the software is rounded.
4.3 Synthesis of the 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives
It was supposed that the optimum reaction condition for all the 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives are the same as obtained from the model reaction 1. Under optimum model reaction 1 condition, various derivatives of pyrano pyrazoles were synthesized using malononitrile, phenylhydrazine and different benzaldehydes in the presence of the as-synthesized ionic-liquid based catalyst. These derivatives are presented in Table 2 with their corresponding values of time, yield and melting point. As Table 2 represents, these derivatives can be obtained with medium to high yields (75–89%) and short reaction times (3 to 16 min). a: m.p. = melting point (oC), time (min), yield refers to the purified.
Product
Time
yield
m.p.a
Product
time
yield
m.p.a
5
89
160–162
6
85
140–141
7
76
110–114
3
81
140–142
11
81
140–142
12
87
137–138
5
88
115–119
16
80
141–144
5
7
127–129
81
200–204
It is of great importance to state that all reactions are fully completed (100%). Ethanol was used as solvent through crystallization and because of the different solubility of each derivative in ethanol, yields are different. Moderate yields (75%) were most likely related to the derivatives whose solubility in ethanol were higher than the others (Haghtalab and Yousefi Seyf, 2015; Seyf and Asgari, 2020). On the other hand, the minimum crystallization temperature has been set the laboratory temperature. It is well-known that at reduced temperatures the solubility decreases, which in turn, result in increased crystallization efficiency. Benzaldehyde derivatives with halogenated, electron donating and electron withdrawing groups at positions 2, 3 and 4 as well as aldehydes with heterocyclic aromatic ring were successfully used in the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives. These findings demonstrate the effectiveness of the as-synthesized ionic-liquid based nano-magnetic catalyst and can be successfully used in a variety of organic reaction transformations. The characterizations of the synthesized products are given in the Supporting Information.
4.4 Synthesis of the 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives
Table 3 provides the synthesized 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives using the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu at the obtained optimun condition for model reaction 2. As is shown, products are obteined with high yield with different aryl aldehydes containing OMe, Cl, Br substitute. a: m.p. = melting point (oC), time (min), yield refers to the purified.
Product
time
yield
m.p.a
Product
time
yield
m.p.a
12
95
180–184
15
93
129–131
20
88
141–142
27
81
106–107
18
96
177–180
18
95
178–181
22
78
193–196
5 Proposed mechanism
5.1 Proposed mechanism in the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives
The proposed mechanism for the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives in the presence of the as-synthesized ionic-liquid based nano-magnetic catalyst is proposed in the Fig. 8. Supposed that the catalyst acts as an acid to activate carbonyl group of aldehyde derivatives (Khazaei et al.,2015; Khazaei et al., 2018). This interaction would reduce the activation energy between the starting raw materials and activated complex. In sequence the anomeric effect (Akbarpoor et al., 2020; Rakhtshah et al., 2016) leads to the hydride transfer, which in turn led to the gaseous hydrogen formation. This phenomenon is in the favor of Le Chatelier's principle (Levine, 2009) so that the reaction fully proceeds at room temperature. The anomeric effect assisted oxidation mechanism is proposed and proven theoretically by some researchers (Afsar et al., 2020; Ghasemi et al., 2020; Karimi et al., 2020; Torabi et al., 2020; Zolfigol et al., 2016). By similar reasoning, the authors proposed such mechanism.![The proposed mechanism for the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives using the as-synthesized nano-magnetic ionic-liquid based Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl−.](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig8.png)
The proposed mechanism for the synthesis of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile derivatives using the as-synthesized nano-magnetic ionic-liquid based Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl−.
5.2 Proposed mechanism in the synthesis of 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives
The proposed possible mechanism for the synthesis of 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives with the copper-based nano-magnetic catalyst is given in Fig. 9. The Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu interacts with the lone pair electrons of oxygen atom in the aldehyde so that triggered the reaction with induced positive charge on the oxygen atom. The electronic configuration of Cu2+ is 3d9 4S0 3d0; that is, copper atom acts as a lewis acid via its empty orbitals.
The proposed mechanism in the synthesis of 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives using Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.
The mechanistic investigations such as reported by Fallah-Ghasemi Gildeh et al. (2020) is needed to improve the proposed mechanisms.
6 Retrieval of the catalyst
After the completion of the model reaction 1 at the optimum point, the catalyst was separated by an external magnet and used in the next cycle. The decrease in reaction yield compared to the different cycles is shown in Fig. 10(a), so that the catalyst provides 75% efficiency after 4 cycles. Model reaction 1 in all cycles was stopped after 5 min. Fig. 10(b) provides the yield of the model reaction 2 versus different cycles where yield and in other words the activity of the copper-based catalyst does not significantly decrease in the cycles.![(a) Yield of the model reaction 1 versus cycles using Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and (b) yield of the model reaction 2 versus cycles using Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.](/content/184/2021/14/3/img/10.1016_j.arabjc.2021.103026-fig10.png)
(a) Yield of the model reaction 1 versus cycles using Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− and (b) yield of the model reaction 2 versus cycles using Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu.
To find the reason for the decrease in catalytic activity followed by a decrease in the efficiency of the reactions, the acidic surface density of Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@SO3H]+Cl− was measured at the beginning and three stages after catalyst recovery. In light of this, 0.2 g catayst was divided into four parts (0.05 g each part). The acidic surface density of neat atalyst was deermined trough back titration (Akbarpoor et al., 2020; Khazaei et al., 2018; Khazaei et al., 2020; Sarmasti et al., 2019). Then, the second part was back titered after one cylces, the thirs part was back titered after two cylces, the fourth part was back titered after three cylces. 9.2, 8.8, 8.7 and 8.5 mmol/g were obtained for the acidic group of the catalyst. As the catalyst impose itas activity via its surface acidic groups, the decrease in surface density of acidic groups intails the deacrease in catalytic activity. By the similar reasoning, the catalytic activity of the Fe3O4@CQDs@Si(CH2)3NH2@CC@EDA@Cu is reduced with the loss of copper.
7 Conclusion
The current research was found that the priori molecular design can be realized in practice. Accordingly, the ionic-liquid based and copper-based nano-magnetic solid acid catalysts were synthesized. Findings of this study indicate that the as-synthesized catalysts efficiently promote the production of 5-amino-1,3-diphenyl-1H-pyrazole-4-carbonitrile and 1-(morpholino(phenyl)methyl)naphthalen-2-ol derivatives, so that they can be synthesized with medium to high yield. Another important finding was that the heterogeneous as-synthesized Fe3O4@CQDs supported catalysts can be easily recovered from the reaction medium using an external magnet and could be repeatedly used in the next cycles. These main features make the use of these CQDs-coated magnetic nano-particles green and sustainable. Finally, the DOE methodology can be used to find the optimal reaction condition.
Acknowledgments
The authors gratefully acknowledge the Bu-Ali Sina University Research Council and Center of Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS), Iran National Science Foundation (INSF) for providing support to this work.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Appendix A
Supplementary material
Supplementary data to this article can be found online at https://doi.org/10.1016/j.arabjc.2021.103026.
Appendix A
Supplementary material
The following are the Supplementary data to this article:
