Nano NiO catalyst: synthesis, characterization, and their application for the synthesis of substituted imidazoles
Raghavendra,Mahadevaiah,1,3S. P. Vinay,1,2*LalithambaHaraluru Shankraiah,3,
1Department of Chemistry, Govt. First Grade College, Vivekananda nagara,
B.H. road, Tumkuru-572101. Karnataka, India
2Department of Chemistry, Shridevi Institute of Engineering and Technology, TumakuruI-572106. Karnataka, India
3Department of Chemistry, Siddaganga Institute of Technology, B.H. Road,Tumakuru - 572 103, Karnataka, India
*Corresponding author: E mail: s.pvinay143@gmail.com
ABSTRACT
Ongoing advances in nanotechnology research have established a variety of methods to synthesize nanoparticles (NPs) from a diverse range of materials, including metals, semiconductors, ceramics, metal oxides, polymers, etc. Depending upon their origin and synthesis methods, NPs possess unique physicochemical, structural and morphological characteristics, which are important in wide variety of applications concomitant to electronic, optoelectronic, optical, electrochemical, environment and biomedical fields. This work provides ainformation about bio-synthesis method of NiO NPs characterization and its organic application. A highly efficient and new method for the nanoNiOcatalyzed oxidative tandem cyclization of simple vinyl azides and benzylamines has been developed for the synthesis of substituted imidazoles. In this reaction, various substituted groups on vinyl azides and benzylamines proceed the desired imidazoles are obtained in a good yields.
INTRODUCTION
Nanoparticle having at least one measurements of the request of 100nm or less have pulled in significant fascination due to their abnormal and interesting properties, with different applications, over beneficiary mass partners[1,2]. As of now, an expansive number of physical, concoction, natural, and half and half methods are accessible to combine diverse sorts of nanoparticles[3,6]. Though physical and chemical methods are more popular for nanoparticle synthesis, the use of toxic compounds limits their applications. The development of safe eco-friendly methods for biogenetic production is now of more interest due to simplicity of the procedures and versatility [7,8]. Traditionally nanoparticles were produced only by physical and chemical methods. Some of the commonly used physical and chemical methods are ion sputtering, solvothermal synthesis, reduction and sol gel technique. Basically there are two approaches for nanoparticles synthesis namely the Bottom up approach and the Top down approach. Current research in biosynthesis of nanoparticles using plant extracts has opened a new era in fast and nontoxic methods for production of nanoparticles. Utilising plant extracts in the synthesis of nanoparticles has drawn more interest of researchers since it is single step biosynthesis. Plants are a superior option for synthesis of nanoparticle since natural capping agents are readily supplied by the plants .The production of gold and silver nanoparticles using Geraniumextract [9], Aloe vera plant extracts [10], sundried Cinnamomumcamphora and Azadiractaindica leaf extract has been explained [11-13].Oxide nanoparticles can exhibit unique physical and chemical properties due to their limited size and a high density of corner or edge surface sites. A decrease in the average size of an oxide particle does in fact change the magnitude of the band gap [14] with strong influence in the conductivity and chemical reactivity [15].
In this study, we have used simple nontoxic, ecofriendly method for the synthesis of Nickel oxide nanoparticles from Nickel nitrate using the leaf extracts of Capsicum annum. The leaf extracts act as stabilizing and capping agents in the synthesis of Nickel oxide nanoparticles. The obtained powders were characterised by XRD, SEM and Uv-vis.
Imidazoles and their derivatives are one of the important class of N-heterocyclic compounds broadly found in pharmaceutical compounds and natural products.[16-19] The increasing importance of substituted imidazoles in the current area of organic chemistry research for the development of new synthetic methods. Great progress have been achieved for the synthesis of the imidazole scaffolds in the earlier period[20,21]. There are various reaction systems, such as Lewis acids[22], base[23], and transitionmetalcatalyzed[24], reported for the construction of imidazole structures[25]. However, new and efficient synthetic approaches to substituted imidazoles are of continuous interest. Particularly, synthetic protocols to simple substituted imidazoles with benzyl amines are still limited[26].
The indole nucleus is a well-known heterocyclic moiety widely present in naturally occurring
alkaloid-type products and synthetic molecules of interesting bioactivities[27-29]. While the imidazole, being a core unit in many biological systems[30]viz. Histidine, Histamine and Biotin, an active component in several pesticides[31] and drug molecules[32] and has attracted attention in recent years. Different substituted imidazoles show variable biological activities such as anti-inflammatory activity,[33] analgesic activity,[34] anti-allergic activity,[35] antibacterial,[36] antiepileptic,[37]antirheumatoid arthritis,[38] antiviral,[39] and anticancer activities[40].
2. Experimental Part
For the biosynthesis of Nickel oxide nanoparticles, the collected leaf of Capsicum annumwas washed thoroughly with tap water to remove the dust and dirt particles and then washed with double distilled water. 20 g of each chopped leaves were added to conical flask containing 100 ml of double distilled water and stirred at 60 °C for 20 min on heating mantle. Then, the mixture was cooled for 15 min and the filtrate is separated using Whatman filter paper No. 1. The collected leaf concentrate (green color) was used for the biosynthesis of Nickel oxide nanoparticles.
10 ml of leaf Capsicum annumwas added to the 90 ml of 5 mM NiNO3 solution at ambient temperature and stirred continuously for 20 min using magnetic stirrer. The mixture is allowed for 24 h for bioreduction process. After 24 h green color of the mixture turned to dark brown color due to the formation of NiO NPs. The NiO NPs obtained from the solution was refined by continual centrifugation at 10,000 rotations per minute for 15 min using Remi cooling centrifuge C-24 .The obtained residual portion (NiO NPs) was cleaned using distilled water then dried and stored for further analysis.
General procedure for synthesis of substituted imidazoles from vinyl azides and benzylaminesemploying NiOnano catalyst:
The experiments wereconducted for the reaction of vinyl azides and substitutedbenzylamines under optimized conditions, and the results were shown in Table 1. A series of substituted imidazoles were prepared efficiently by this method. As presented in Table S1, the reaction proceeded more efficiently in the systems of nanoNiO/TBHP. This result promoted us to investigate other oxidants for The scope and generality of this reaction were investigated and the results were illustrated in Table 1. A series of vinyl azides with electron
donating or withdrawing groups could react with benzylamine smoothly in the reaction and the desired substituted imidazoles could be efficiently obtained in moderate yields. As shown in Table 1, the reaction was not significantly affected by the nature of the groups in aromatic ring of vinyl azides. The position of substituents on the benzene ring had a slight impact on the reaction yields.
Table 1.The reaction of substituted vinyl azides and phenylmethanaminea
|
Entry |
|
R1 |
Product |
Yields(%) |
|
1 |
1a |
H |
3aa |
70 |
|
2 |
1c |
4-Me |
3ca |
74 |
|
3 |
1e |
2,5-diMe |
3ea |
45 |
|
4 |
1g |
2-Cl |
3ga |
74 |
|
5 |
1i |
3-CI |
3ia |
78 |
|
6 |
1k |
4-Cl |
3ka |
56 |
|
7 |
1f |
2-F |
3fa |
70 |
Spectral data of the selected compounds
1- benzyl-2-phenyl-4-(p-tolyl)-1H-imidazole (3ca):
Yellow Solid, mp: 136-138 oC.1H NMR (400 MHz, CDCl3, ppm): δ = 7.75-7.70 (m,2 H), 7.60-7.56 (m, 2 H), 7.43-7.38 (m, 3 H), 7.37-7.26 (m, 3 H), 7.20-7.14 (m, 3 H), 7.15-7.14 (m, 2 H), 5.19 (s, 2 H), 2.34 (s, 3 H); 13C NMR (100 MHz, CDCl3, ppm): δ = 148.49, 141.65, 136.97, 136.45, 131.29, 130.50, 129.30, 129.08, 129.00, 128.96, 128.64, 127.97, 126.69, 124.87, 116.44, 50.47, 21.27. HRMS calcd for C23H21N2 [M+H]+ 325.1699; found: 325.1695.
1-benzyl-4-(2-chlorophenyl)-2-phenyl-1H-imidazole (3ga):
Yellow liquid.1H NMR (400 MHz, CDCl3, ppm): δ = 8.36-8.34 (m, 1 H), 7.75 (s, 1 H), 7.61-7.59 (m, 2 H), 7.43-7.38 (m, 4 H), 7.36-7.29 (m, 4 H), 7.19-7.13 (m, 3 H), 5.27 (s, 2 H); 13C NMR (100 MHz, CDCl3, ppm): δ = 147.75, 137.51, 136.86, 132.39, 130.79, 130.30, 130.14, 129.60, 129.04, 128.66, 127.90, 127.50, 126.80, 126.52, 121.65, 50.56. HRMS calcd for C22H18N2 [M+H]+345.1153; found: 345.1147, 347.1113.
1-benzyl-4-(4-chlorophenyl)-2-phenyl-1H-imidazole (3ka):
Yellow Solid, mp: 126-128 oC. 1H NMR (400 MHz, CDCl3, ppm): δ = 7.76-7.74 (m, 2 H), 7.61-7.58 (m, 2 H), 7.42-7.41 (m, 3 H), 7.38-7.31 (m, 5 H), 7.22 (s, 1 H), 7.13-7.12 (m, 2 H), 5.20 (s, 2 H); 13C NMR (100 MHz, CDCl3, ppm): δ = 148.82, 140.49, 136.70, 132.66, 132.31, 130.29, 129.16, 129.08, 129.02, 128.72, 128.68, 128.10, 126.73, 126.19, 116.98, 50.57. HRMS calcd for C22H18N2 [M+H]+ 345.1152; found: 345.1146, 347.1117.
The reduced NiO NPs powder was coated on a glass substrate and the X-ray diffraction measurement were carried out using a powder X-ray instrument (model PAN analytical BV) operating at 40 kV and 30 mA current. The output was recorded in the form of a graph with 2θ on x-axis and intensity on y-axis.
The particle size and their morphological distribution of the NiO NPs were assessed with scanning electron microscopy (SEM). A drop of aqueous solution containing purified Nickel oxide nanoparticles obtained after repetitive centrifugation was placed on the carbon-coated copper grids and dried under infrared lamp for characterization using TESCAN, VEGA3 LMU model scanning electron microscope at accelerating voltage of 30 kV.
Bio-reduction of Ni ions present in the solution of NiNO3 into silver nanoparticles by the phytocompounds present in the Capsicum annumplant leaf extract was studied using UV–visible spectroscopy. UV–visible spectrograph of NiO NPs solution was noted as a function of time by a quartz cuvette and water as reference. Highest absorbance peak was observed at 365 nm for Capsicum annum Fig. 1 [41], which indicates the formation of NiO NPs.
Fig. 1 UV-vis absorption spectra of NiO NPs.
X-ray diffraction pattern was recorded for the synthesized NiO NPs are shown in Fig. 2, which shows a number of Bragg reflections corresponding to (111) and (200) sets of lattice planes are observed. Which may be indexed based on the structure of Ni. The diffraction peaks at 2θ = 38° and 44° were indexed obtained Nickel oxide (NiO) as per the Joint Committee on Powder Diffraction Standards (JCPDS) Card No. 47-1049 was matched with database. The XRD pattern thus clearly shows that the synthesized NiO NPs are crystalline in nature [42].
Fig. 2 XRD spectrum of NiO NPs.
The SEM has shown the uniform distribution of NiO NPs. The SEM images (Fig. 3) has shown separate NiO NPs as well as particle agglomeration. The results indicate that NiO nanoparticles are in spherical shape. We can observe that the particles are highly agglomerated and they are essentially a cluster of nanoparticles, respectively [43].
Fig. 3 SEM image of NiO NPs.
Conclusion
We have developed a effeicient protocol for the construction of substituted imidazoles from vinyl azides and benzylamines under nano NiO catalytic reaction system.The nano NiO catalyst is expected to contribute to the development of environmentally benign methods and forms a part of the nanomaterial chemistry.
REFERENCES