Co3O4/NiO@GQDs@SO3H nanocomposite as high performance catalyst for the preparation of pyrimidines
Hossein Shahbazi-Alavi
1
(
Young Researchers and Elite Club, Kashan Branch, Islamic Azad University, Kashan, Iran, E-mail addresses: hossien_shahbazi@yahoo.com
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Iran
)
Javad Safaei-Ghomi
2
(
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Iran
)
Ali Kareem Abbas
3
(
College of applied medical sciences, University of Kerbala, Iraq
)
Keywords: nanocomposite, One-pot, Heterogeneous catalysts, pyrimidine, nanoanalysis,
Abstract :
Co3O4 / NiO @ GQDs @ SO3H nanocatalyst has been used as an effective catalyst for the preparation of 2,4-diamino-6-arylpyrimidine-5-carbonitrile derivatives through a three-component reaction of malononitrile, aromatic aldehydes and guanidine hydrochloride under reflux conditions in ethanol. The catalyst has been characterized by FT-IR, XRD, SEM, EDS, BET, TGA, XPS and VSM. Atom economy, reusable catalyst, low catalyst loading, applicability to a wide range of substrates and high yields of products are some of the notable features of this protocol.The best results were gained in EtOH and we found that the reaction gave convincing results in the presence of Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) under reflux conditions. This green nanocatalyst could be used for other significant organic reactions and transformations. Further explorations of similar protocols are underway in our laboratory. This recoverable catalyst will provide a regular platform for heterogeneous catalysis, green chemistry, and environmentally benign protocols in the near future.
Journal of Nanoanalysis
Abstract Co3O4/NiO@GQDs@SO3H nanocatalyst has been used as an effective catalyst for the preparation of 2,4-diamino-6-arylpyrimidine-5-carbonitrile derivatives through a three-component reaction of malononitrile, aromatic aldehydes and guanidine hydrochloride under reflux conditions in ethanol. The catalyst has been characterized by FT-IR, XRD, SEM, EDS, BET, TGA, XPS and VSM. Atom economy, reusable catalyst, low catalyst loading, applicability to a wide range of substrates and high yields of products are some of the notable features of this protocol.
Keywords; nanocomposite; one-pot; Heterogeneous catalysts; pyrimidine; nanoanalysis
Introduction
Pyrimidines show biological activities including anticancer [1], anti-inflammatory [2], anti-proliferative [3], anti-HIV [4] anti-bacterial [5], antihypertensive [6], antimalarial [7], antioxidant [8] and protein Kinase inhibitors [9]. These attributes make pyrimidines notable targets in organic synthesis for future consideration. A number of procedures have been developed for the preparation of pyrimidines using bismuth (III) nitrate pentahydrate [10], sodium hydroxide [11], potassium carbonate [12] and sodium acetate [13]. Despite the use of these ways, there remains a need for further new methods for the synthesis of pyrimidines. Graphene quantum dots (GQDs) are a novel member of carbon nanostructures that have quasi-spherical structures. GQDs have gained intensive attention owing to the remarkable features containing biological [14], biomedical [15], therapeutic applications [16], as a new class of photocatalysts [17], surfactants [18], electrochemical biosensing [19], electrocatalytic activity [20], lithium battery application [21], optical properties and photovoltaic applications [22], photoluminescence [23-24]. bioimaging properties [25], and catalytic activity [26]. Potential applications of N-graphene quantum dots were recently reviewed on the basis of experimental and theoretical studies [27-30]. Synthesis of highly efficient nanocomposite catalysts for the synthesis of organic compounds is still a big challenge. To obtain larger surface area and more active sites, nanocatalysts are functionalized by active groups [31-33]. It has been demonstrated that the decoration of the nanocatalyst with GQDs prevents the aggregation of fine particles and thus increases the effective surface area and number of reactive sites for an efficient catalytic reaction. The chemical groups on a GQD are able to catalyze chemical reactions. The -COOH and -SO3H groups can serve as acid catalysts for many reactions [26-34]. Nano catalyst/nanosorbents such as nano azido-selenenylation, nanomontmorillonite , MOF, MSN, nanocarbon structure(GO/G/MWCNTs) with different groups such as HS, NH2, COOH and SO3H, Cysteine and …, help for extraction cancer genic metals such as Cr, Pb, Hg from human body and use for drug delivery in cancer cells [35-38]. Herein, we reported the use of Co3O4/NiO@GQDs@SO3H nanocomposite as a new efficient catalyst for the preparation of pyrimidines through a three-component reaction of malononitrile, aromatic aldehydes and guanidine hydrochloride (Scheme 1).
Scheme 1. The preparation of pyrimidines using Co3O4/NiO@GQDs@SO3H nanocatalyst
Experimental
Materials and characterization
Powder X-ray diffraction was taken on a Philips diffractometer of X’pert Company with monochromatized Cu Kα radiation (λ = 1.5406 Å). X-ray photoelectron spectroscopy (XPS) spectra were determined on an ESCA-3000 electron spectrometer. Microscopic morphology of nanocatalyst was performed by SEM (MIRA3). The thermogravimetric analysis (TGA) curves are gained by V5.1A DUPONT 2000. The magnetic measurement of samples was registered in a vibrating sample magnetometer (VSM) (Iran, Kashan Kavir). Surface area was carried out using nitrogen adsorption measurement (Micrometrics ASAP-2000).
Preparation of Co3O4/NiO nanoparticles: Co(NO3)3 and of NiCl2 with 3:1 molar ratio were dissolved in ethylene glycol. Afterward, the appropriate amount of aqueous ammonia solution (28 wt%) was added to the above solution until the pH value reached 10. Then, transparent solution was placed in autoclave at 150 °C for 4h. The obtained precipitate was washed twice with methanol and dry at 60 °C for 8h. Finally, the product was calcined at 500 °C for 2h.
Preparation of Co3O4/NiO@N-GQDs nanocomposite: 1 g citric acid and was dissolved into 20 mL deionized water, and stirred to form a clear solution. After that, 0.3 mL ethylenediamine was added to the above solution and mixed to obtain a clear solution. Then, 0.1 g Co3O4/NiO nanoparticles were added to mixture. The mixture was stirred at room temperature within 5 minutes. Then the solution was transferred into a 50 ml Teflon lined stainless autoclave. The sealed autoclave was heated to 180°C for 12 hours in an electric oven. Finally, as-prepared nanostructured Co3O4/NiO@GQDs was obtained, washed several times with deionized water and ethanol, and then dried in an oven until constant weight was achieved.
Preparation of Co3O4/NiO@GQDs@SO3H nanocomposite: 1g of Co3O4/NiO@N-GQDs nanocomposite was dispersed in dry CH2Cl2 (10 mL) and sonicated for 5 min. Then, chlorosulfonic acid (0.8 mL in dry CH2Cl2) was added drop-wise to a cooled (ice-bath) mixture of Co3O4/NiO@N-GQDs, during a period of 30 min under N2 with vigorous stirring. The mixture was stirred for 120 min, while the residual HCl was removed by suction with trapping. The resulted Co3O4/NiO@GQDs@SO3H nanocomposite was separated, washed several times with dried CH2Cl2 before being dried under vacuum at 60 °C.
General procedure for the synthesis of pyrimidines:
A mixture of malononitrile (1 mmol), aldehydes (1 mmol), guanidine hydrochloride (1 mmol) and Co3O4/NiO@GQDs@SO3H nanocatalyst were stirred in 5 mL ethanol under reflux condition. The reaction was monitored by TLC. After completion of the reaction, the solution was filtered and the heterogeneous catalyst was recovered. Water was added, and the precipitate was collected by filtration and washed with water. The crude product was recrystallized or washed with ethanol to give the pure product. Spectra data 4c and 4d compounds are presented:
2,4-diamino-6-(4-bromophenyl)pyrimidine - 5-carbonitrile (4c): M. p. 261-263 °C. – IR (KBr): 
= 3423, 3298 (NH2), 2187 (CN), 1635, 1602, 1484 cm-1. – 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 6.84-6.90 (4H, 2 NH2), 7.03-7.05 (2 H, J = 8 Hz, ArH), 7.11-7.14 (2 H, J = 8 Hz, ArH). – 13C NMR(100 MHz, DMSO-d6): δ (ppm) = 76.10, 118.37, 128.72, 130.42, 135.58, 136.20, 163.15, 165.30, 168.54. – Analysis for C11H8BrN5: calcd. C 45.54, H 2.78, N 24.14; found: C 45.42, H 2.69, N 24.08.
2,4-diamino-6-(4-methoxyphenyl)pyrimidine- 5 -carbonitrile (4d): M. p. 236-238 °C. – IR (KBr): = 3385, 3325, 3284, 3205 (NH2), 2202 (CN), 1646, 1482 cm-1. – 1H NMR (400 MHz, DMSO-d6): δ (ppm) = 3.55 (3H, s, OCH3), 7.57-7.64 (4H, 2 NH2), 7.32 (2 H, m, ArH), 8.34 (2H, m, ArH). – 13C NMR (100 MHz, DMSO-d6): δ (ppm) = 54.32, 79.16, 113.42, 117.90, 125.64, 128.10, 160.22, 164.92, 167.44, 169.32. – Analysis for C12H11N5O: calcd. C 59.74, H 4.60, N 29.03; found C 59.64, H 4.43, N 28.94.
In the beginning, we prepared Co3O4/NiO nanoparticles by easy techniques. A facile hydrothermal method was used for the preparation of N-GQDs [39]. Sulfonated graphene quantum dots were prepared using chlorosulfonic acid [40]. XRD pattern of Co3O4/NiO, Co3O4/NiO@N-GQDs and Co3O4/NiO@GQDs @ SO3H nanocomposite, is shown in Fig. 1. XRD pattern confirms presence of both NiO (JCPDS No.22-1189) and Co3O4 (JCPDS No 65-3103).
Fig 1. XRD pattern of (a) Co3O4/NiO, (b) Co3O4/NiO@GQDs and (c) Co3O4/NiO@GQDs @ SO3H
In order to investigate the particle size and morphology of nanoparticles, SEM image of Co3O4/NiO and Co3O4/NiO@ GQDs@SO3H nanocomposite is indicated in Fig. 2. SEM images of the Co3O4/NiO@GQDs@SO3H nanocomposite showed the formation of uniform particles, and the energy-dispersive X-ray spectrum (EDS) confirmed the presence of Co, Ni, O, S and C species in the structure of the nanocomposite (Fig. 3).
Fig 2. SEM image of (a) Co3O4/NiO, (b) Co3O4/NiO@GQDs @SO3H
Fig 3. EDS spectrum of (a) Co3O4/NiO, (b) Co3O4/NiO@GQDs @SO3H
Magnetic properties of nanocomposites before and after their being decorated with GQDs were tested by vibrating-sample magnetometer (VSM) (Fig 4). The lower magnetism of the as-synthesized Co3O4/NiO@GQDs@SO3H compared with the Co3O4/NiO was ascribed to the antiferromagnetic behavior of GQDs as a dopant. These results demonstrate that the magnetization property decreases by coating and functionalization [41-42].
Fig 4. VSM of (a) Co3O4/NiO, (b) Co3O4/NiO@GQDs and (c) Co3O4/NiO@GQDs @SO3H
FT-IR spectra of Co3O4/NiO, Co3O4/NiO@N-GQDs and Co3O4/NiO@GQDs @ SO3H nanocomposite are shown in Fig. 5. The absorption peak at 3335 cm-1 related to the stretching vibrational absorptions of OH. The peaks at 461.4, 568.4, 657.1 cm-1 corresponded to the Ni-O, Co+2-O and Co3+-O respectively. The characteristic peaks at 3440 cm-1 (O-H stretching vibration), 1705 cm-1 (C=O stretching vibration), 1125 cm-1 (C-O-C stretching vibration) appear in the spectrum of Figure 5b. The peak at approximately 1475-1580 cm-1 is attributed to C=C bonds. The presence of sulfonyl group is also verified by the peaks appeared at 1215 and 1120 cm−1. The broad peak at 3350cm-1 related to the stretching vibrational absorptions of OH (SO3H) (Fig 5c).
Fig 5. FT-IR of (a) Co3O4/NiO, (b) Co3O4/NiO@GQDs and (c) Co3O4/NiO@GQDs @SO3H
The BET specific surface area of Co3O4/NiO and Co3O4/NiO@GQDs@SO3H nanocomposites was determined by the nitrogen gas adsorption-desorption isotherms (Fig. 6). The results presented that the BET specific surface area of Co3O4/NiO was improved from 12.25 to 32.43 m2/g after modification with GQDs, therefore more active sites were introduced on Co3O4/NiO@GQDs@SO3H surface.
Fig 6. The BET specific surface area of (a) Co3O4/NiO, (b) Co3O4/NiO@GQDs @SO3H
Fig 7. TGA of Co3O4/NiO@GQDs @SO3H nanocomposit
X-ray photoelectron spectroscopy (XPS) analysis of Co3O4/NiO@GQDs@SO3H nanocomposite was indicated in Figure 8. In the wide-scan spectrum of nanocatalyst, the predominant components are Ni 2p1/2 (873.4 eV), Ni 2p3/2 (854.4 eV), Co 2p1/2 (792.6 eV), Co 2p3/2 (780.4 eV), O 1s (529.8 eV), N 1s (400 eV), C 1s (284.5 eV) and S 2p (164.3 eV).
Fig. 8. X-ray photoelectron spectroscopy (XPS) analysis of Co3O4/NiO@GQDs@SO3H nanocomposite
The concentration of sulfonic acid groups was quantitatively estimated by back titration using HCl (0.01 N). 2 mL of KOH (0.01 N) was added to 0.02 g of the nanoparticles and the mixture was stirred for 30 min. The catalyst was filtered and washed with deionized water. The excess amount of KOH was titrated with HCl (0.01 N) in the presence of phenolphthalein as indicator. Averages of 3 separate titrations were performed to obtain an average value for the acid amount of Co3O4/NiO@GQDs@SO3H nanocomposite. The results revealed that the samples of Co3O4/NiO@GQDs@SO3H nanocomposite possessed 0.82 mmol g-1 acid amount.
Initially, we carried out three-component reaction of malononitrile, benzaldehyde and guanidine hydrochloride as a model reaction. The model reaction was performed by Et3N, NaHSO4, ZrO2, p-TSA, NiO, Co3O4, Co3O4/NiO, Co3O4/NiO@GQDs and Co3O4/NiO@GQDs@SO3H nanocomposite. The reactions were tested using diverse solvents containing ethanol, acetonitrile, water and dimethylformamide. The best results were gained in EtOH and we found that the reaction gave convincing results in the presence of Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) under reflux conditions (Tables 1).
A series of aromatic aldehydes were studied under optimum conditions (Table 2). The results were good in yields using aromatic aldehydes, either bearing electron-withdrawing substituents or electron-donating substituents. The influence of electron-withdrawing and electron-donating substituents on the aromatic ring of aldehydes upon the reaction yields was investigated. Aromatic aldehydes having NO2 and halogen groups reacted at faster rate compared with aromatic aldehydes substituted with other groups.
Table1: Optimization of reaction condition using different catalysts a
Entry | Catalyst (amount) | Solvent (reflux) | Time (min) | Yield % |
1 | none | EtOH | 300 | NR |
2 | Et3N (5 mol%) | EtOH | 300 | 38 |
3 | NaHSO4 (4 mol%) | EtOH | 250 | 42 |
4 | ZrO2 (4 mol%) | EtOH | 150 | 50 |
5 | pTSA (5 mol%) | EtOH | 150 | 55 |
6 | Nano-Co3O4 | EtOH | 150 | 48 |
7 | Nano-NiO | EtOH | 150 | 58 |
8 | Co3O4/NiO nanocomposite | EtOH | 150 | 64 |
9 | Co3O4/NiO@GQDs nanocomposite | EtOH | 150 | 74 |
10 | Co3O4/NiO@GQDs@SO3H nanocomposite (2 mg) | EtOH | 30 | 85 |
11 | Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) | EtOH | 30 | 92 |
12 | Co3O4/NiO@GQDs@SO3H nanocomposite (6 mg) | EtOH | 30 | 92 |
13 | Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) | H2O | 50 | 68 |
14 | Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) | DMF | 50 | 73 |
15 | Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) | CH3CN | 50 | 80 |
a Reaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol), and guanidine hydrochloride (1 mmol);
b isolated yield
Table 2: Synthesis of pyrimidines using Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg)
m.p. (°C) |
yield (%)
|
Time (min)
|
Ar |
Product |
Entry |
237-239 | 92 | 30 | C6H5 | 4a | 1 |
265-267 | 93 | 25 | 4-Cl-C6H4 | 4b | 2 |
260-262 | 94 | 25 | 4-Br-C6H4 | 4c | 3 |
236-238 | 84 | 40 | 4-OMe-C6H4 | 4d | 4 |
255-257 | 86 | 40 | 4-Me-C6H4 | 4e | 5 |
275-276 | 94 | 25 | 2,6-di-Cl-C6H4 | 4f | 6 |
232-235 | 93 | 30 | 2-Cl-C6H4 | 4g | 7 |
225-227 | 88 | 40 | 3-Me- C6H4 | 4h | 8 |
252-254 | 96 | 25 | NO2 | 4i | 9 |
242-244 | 94 | 25 | CN | 4j | 10 |
a isolated yield
To compare the efficiency of Co3O4/NiO@GQDs@SO3H nanocomposite with the reported catalysts for the synthesis of pyrimidines, we have tabulated the results in Table 3. As Table 3 indicates, Co3O4/NiO@GQDs@SO3H nanocomposite is superior with respect to the reported catalysts in terms of reaction time, yield and conditions. Atom economy, reusable catalyst, low catalyst loading, applicability to a wide range of substrates and high yields of products are some of the notable features of this protocol.
Table 3. Comparison of catalytic activity of Co3O4/NiO@GQDs@SO3H nanocomposite with other reported catalysts
Entry | catalyst | Time (min) | Yield,a % | [Ref] |
1 | Sodium acetate (20 mol%) | 300 | 78 | [9] |
2 | Potassium carbonate (10 mol%) | 180 | 75 | [8] |
3 | Sodium hydroxide (20 mol%) | 30 | 88 | [7] |
4 | Co3O4/NiO@GQDs@SO3H nanocomposite (4 mg) | 30 | 92 | This work |
a Isolated yield
We also determined recycling of Co3O4/NiO@GQDs@SO3H nanocomposite as catalyst for the model reaction under reflux conditions in ethanol. The results showed that nanocomposite can be reused several times without noticeable loss of catalytic activity (Yields 92 to 90%) (Fig. 9).
Fig. 9. Recycling of Co3O4/NiO@GQDs @SO3H nanocomposite as catalyst for the model reaction
A plausible mechanism for the preparation of pyrimidines using Co3O4/NiO@GQDs@SO3H nanocomposites is indicated in Scheme 2. Firstly, the reaction occurs by formation of the cyano olefin A from the condensation of malononitrile and aryl aldehyde. The second step is followed by Michael addition, cycloaddition, isomerization, aromatization to afford the pyrimidines. The SO3H groups distributed on the surface of Co3O4/NiO@GQDs activate the C=O and C≡N groups for better reaction with nucleophiles.
Scheme 2: Possible mechanism for the synthesis of pyrimidines using Co3O4/NiO@GQDs@SO3H nanocatalyst
Conclusion
In this study, we described the preparation of pyrimidines using Co3O4/NiO@GQDs@SO3H nanocomposite as a superior catalyst under reflux conditions. The SO3H groups distributed on the surface of Co3O4/NiO@GQDs activate the C=O and C≡N groups for better reaction with nucleophiles. The current method provides obvious positive points containing environmental friendliness, significantly shorter reaction time, reusability of the catalyst, low catalyst loading and simple workup procedure.
Acknowledgment
The authors are grateful to the University of Kashan for supporting this work under grant no. 159148/XII.
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