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Journal of Chemistry
Volume 2013, Article ID 418969, 7 pages
http://dx.doi.org/10.1155/2013/418969
Research Article

A Clean, Simple, and Efficient Synthesis of 2-Substituted Aryl (Indolyl) Kojic Acid Derivatives by Kaolin/Ag Nanocomposite as a Reusable Catalyst: A Green Protocol

Department of Chemistry, Islamic Azad University, Yazd Branch, P.O. Box 89195-155, Yazd 8916871967, Iran

Received 20 May 2013; Revised 23 July 2013; Accepted 24 July 2013

Academic Editor: Mallikarjuna Nadagouda

Copyright © 2013 Bahareh Sadeghi and Mohammad Reza Shahedi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Kaolin/Ag nanocomposite (kaolin/Ag nanocomposite) was synthesized in a nanoreactor by the calcination of the precursor at high temperature and was shown to efficiently catalyze the one-pot, three-component reaction of an aromatic aldehyde, kojic acid, and indole derivatives under solvent-free conditions to afford the corresponding 2-substituted aryl (indolyl) kojic acid derivatives in high yield.

1. Introduction

Nanocomposite is a new class of composites in which the dimensions of the material are in the order of nanometers. Because of this nanometer size characteristic, nanocomposites possess superior properties than the conventional composites such as thermal stability, high surface areas, and mechanical and catalytic properties [13]. Up to now, various nanocomposites were synthesized on the basis of Ag nanoparticles with antibacterial and catalytic activities, including silver-hydroxyapatite, dendrimer-silver complexes, hollow Pt/Ag, and silver-silica nanocomposite [47]. In this paper, we used the adsorption layer on the surface of kaolin as reactor to prepare Kaolin/Ag nanocomposite material which had a small average grain size and was well distributed. The prepared composite was characterized using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM) instruments.

The 3-substituted indole moieties are included in numerous natural products and they are dominant molecules in medicinal chemistry [8, 9]. On the other hand, kojic acid is also known as an attractive molecule in pharmaceutical chemistry due to its accessibility, potential biological activity, and high reactivity [10, 11]. Due to the vast medicinal utility of kojic acid and 3-substituted indole derivatives, the introduction of a mild, efficient, and selective method to synthesize these compounds is still needed. In continuation of our investigations of the application of solid acids in organic synthesis [1216], we have investigated the synthesis of Kaolin/Ag nanocomposite as a catalyst and applied for the synthesis of 2-substituted aryl (indolyl) kojic acid derivatives.

2. Experimental

2.1. General

Melting points were determined with an Electro thermal 9100 apparatus. IR spectra were recorded on a Shimadzu IR-470 spectrometer. 1H and 13C NMR spectra were recorded on Bruker DRX-400 Avance Spectrometer for solutions in CDCl3 using TMS as an internal standard. Mass spectra were recorded on a FINNIGAN-MAT 8430 mass spectrometer operating at an ionization potential of 70 eV. Elemental analyses were performed using a Costech ECS 4010 CHNS-O analyzer at the analytical laboratory of Science and Research Unit of Islamic Azad University, Iran. The morphologies of the products were observed using SEM of VEGA/TESCAN microscope with an accelerating voltage of 15 kV. X-ray diffraction (XRD) patterns were taken on a Rigaku instrument with Cu Ka radiation (40 kV, 100 mA) to analyze crystalline structure. The chemicals for this work were purchased from Fluka (Buchs, Switzerland) and were used without further purification.

2.2. General Procedure for the Preparation of Kaolin/Ag Nanocomposite Material

1.5 g Kaolin was dried at 90°C for 2 h and cooled at room temperature. Then, 600 mL of absolute ethyl alcohol was added and well mixed. After 2 h, water (3 mL) and NaOH (0.162 g) were added into the reaction system under stirring and room temperature conditions. After the adsorption equilibrium was attained (24 h), silver nitrate in water (100 mL and 2.28 g) was added at a constant rate, react with NaOH, and reduced by ethanol. After reacting for a definite time, the product was gained by centrifugation and dried at room temperature.

2.3. General Procedure for the Preparation of Compounds 4a–m

A mixture of aryl aldehyde (1 mmol), kojic acid (1 mmol), and Kaolin/Ag NPs (0.001 g) was stirred at 90°C. After 5–15 min, indole (1 mmol) was added and the reaction was continued for appropriate time. After the completion of the reaction (as monitored by TLC), water was added with reaction mixture (15 mL) and extracted with ethyl acetate (3 × 10 mL). The organic layer was dried over sodium sulfate and concentrated under vacuum. The crude product was chromatographed in silica gel (70 : 30 -hexane/ethyl acetate) and appropriate isolated yield.

3. Results and Discussion

Herein, we attempted to synthesize Kaolin/Ag nanocomposite in a nanoreactor, which was shown to efficiently catalyse the synthesis of 2-substituted aryl (indolyl) kojic acid derivatives, by the three-component condensation of an aromatic aldehyde 1, kojic acid 2, and indole derivatives 3 (Scheme 1).

418969.sch.001
Scheme 1: Synthesis of 2-substituted aryl (indolyl) kojic acid derivatives in the presence of Kaolin/Ag nanocomposite as catalyst.

The stable catalyst is easily prepared and used for preparation of 2-substituted aryl (indolyl) kojic acid derivatives. The Kaolin/Ag nanocomposite is made using nanotechnique and the mechanism of adsorption. Silver ion is reduced by methanol in an alkaline solution while the temperature was fixed to 25°C during the reaction. These are the differences and advantages of this method compared with previous article [17].

In the experiment, we first studied IR spectra of Kaolin and Kaolin/Ag nanocomposite (Figure 1). In both of them, OH stretching bond is observed at ~3621 cm−1. Comparison of the infrared spectra of Kaolin and Kaolin/Ag show that, in both of them, the asymmetric stretching vibrations for Al2O3 and SiO2 appeared at ~914 cm−1 and ~1114 cm−1, respectively. Also, the symmetric stretching vibrations for Al2O3 and SiO2 appeared at ~694 cm−1 and ~789 cm−1, respectively. In Kaolin/Ag spectrum, the absorption of nitrate is observed at 1369 and 1444 cm−1. It is detected that Ag nanoparticles are distributed over the surface of Kaolin in the form of massive agglomeration.

418969.fig.001
Figure 1: FT-IR spectrum of (a) Kaolin and (b) Kaolin/Ag nanocomposite.

The results of XRD are shown in Figure 2. In both XRD patterns, peaks that appeared at and 25° are quartz crystals. The pattern of Kaolin (a) shows that at no characteristic peaks come out, but pattern of Kaolin/Ag nanocomposite (b) shows that at intensities of peaks increase, which demonstrates that Kaolin/Ag nanocomposite is produced.

418969.fig.002
Figure 2: XRD patterns of (a) Kaolin and (b) Kaolin/Ag nanocomposite.

As reported in the article for silver nanoparticle/kaolinite composites [17], silver is placed in the space between the layers of kaolinite and that explains why the XRD of kaolinite and silver nanoparticle/kaolinite composites are identical.

The dimensions of nanoparticles were observed with SEM. The size of commercial Kaolin/Ag nanocomposite is about 36–53 nm, and SEM images of Kaolin/Ag nanocomposite showed that the Ag nanoparticles were homogeneously dispersed in Kaolin matrices (Figure 3).

fig3
Figure 3: SEM images of Kaolin/Ag nanocomposite.

It is clearly seen on the TEM images of Kaolin that the crystals’ size is 170–400 nm, but TEM images of Kaolin/Ag nanocomposite show crystals’ size decrease of 50 nm, and it is detected that Ag nanoparticles are distributed over the surface of Kaolin in the form of massive agglomeration (Figures 4 and 5).

fig4
Figure 4: TEM images of (a) Kaolin 400 nm and (b) Kaolin 170 nm.
418969.fig.005
Figure 5: TEM image of Kaolin/Ag NPs 50 nm.

BET results are given in Table 1. This information includes the measurement of surface area, total pore volume, and the average pore diameter of Kaolin/Ag nanocomposite and Kaolin. According to the obtained data, weight, surface area, and the average pore diameter of Kaolin/Ag nanocomposite were increased than those of Kaolin and the total pore volume was decreased.

tab1
Table 1: Study of BET tests of Kaolin and Kaolin/Ag nanocomposite.

To optimize the reaction conditions, the reaction of benzaldehyde, kojic acid, and indole was used as a model reaction. In order to establish the better catalytic activity of Kaolin/Ag nanocomposite, we have compared the reaction using other catalysts at solvent-free conditions and for 75 min. The results are listed in Table 2. The problems in the reported protocols such as prolonged reaction time and poor yields prompted us to develop a new rapid method affording excellent yield for the synthesis of 2-substituted aryl (indolyl) kojic acid derivatives.

tab2
Table 2: Evaluation of the activity of different catalysts for the synthesis of 4a.

In order to determine the optimum quantity of Kaolin/Ag nanocomposite, the reaction of benzaldehyde, kojic acid, and indole was carried out at solvent-free conditions using different quantities of Kaolin/Ag nanocomposite (Table 3). Kaolin/Ag nanocomposite of 0.001 g gave an excellent yield in 75 min (Table 3, entry 4).

tab3
Table 3: Optimization amount of Kaolin/Ag nanocomposite catalyst for the synthesis of 4a.

The above reaction was also examined in various solvents (Table 4). The results indicated that different solvents affected the efficiency of the reaction. Most of these solvents required a longer time and gave moderate yields, and the best results were obtained when solvent-free was used (Table 4, entry 6).

tab4
Table 4: Effect of the solvent on the synthesis of 4a by Kaolin/Ag nanocomposite catalyst.

To study the scope of the reaction, a series of aromatic aldehydes, indoles, and kojic acid catalysed by Kaolin/Ag nanocomposite as catalyst were examined. The results are shown in Table 5. In all cases, aromatic aldehyde substituted with either electron-donating or electron-withdrawing groups underwent the reaction smoothly and gave products in good yields.

tab5
Table 5: Condensation of aromatic aldehyde, kojic acid, and indole derivatives in the presence of Kaolin/Ag nanocomposite catalyst.

The compounds 4a–f were characterized by their 1H-NMR and IR spectroscopy and elemental analyses. Spectral data were compared with the literature data [18].

Compounds 4g–m was new and their structures were deduced by elemental and spectral analyses. The mass spectrum of compound 4h showed the molecular ion peak at 361. The 1H NMR spectrum of 4h exhibits three sharp lines at , 6.29, and 6.63 ppm for the proton of methine and olefinic protons, respectively. The 1H-NMR spectrum of compound 4h exhibited protons of methylene at 4.21 ppm and protons of methyl group at . Three single signals are observed at 10.19, 7.43, and 5.92 ppm that disappeared after the addition of a few drops of D2O to CDCl3 solution of compound 4h. These signals are related to OH and NH protons. Multiplets are observed between 6.70 and 7.35 ppm which are related to aromatic protons. The 13C-NMR spectrum of compound 4h showed 20 signals in agreement with the proposed structure. The IR spectrum of compound 4h also supported the suggested structure.

An interesting feature of this method is that the reagent can be regenerated at the end of the reaction and can be used several times without losing its activity. To recover the catalyst, after completion of the reaction, the mixture was filtered, catalyst (Kaolin/Ag nanocomposite) was washed with CHCl3, and then the solid residue was dried. This process repeated for three cycles, and the yield of product 4a did not change significantly (Table 6).

tab6
Table 6: Recycling studies of reaction between benzaldehyde, kojic acid, and indole in the presence of Kaolin/Ag nanocomposite to give product 4a.

A mechanistic route is suggested for the generation of 2-substituted aryl (indolyl) kojic acid derivatives from the reaction of an aromatic aldehyde, kojic acid, and indole derivatives in the presence of Kaolin/Ag nanocomposite and role of Kaolin/Ag nanocomposite shown as the catalyst in this proposed mechanism (Scheme 2). The initiation step of this chain process begins with the interaction of aldehyde and Kaolin/Ag nanocomposite. The subsequent reaction between the activated aldehyde and kojic acid takes place with the formation of the enone. The resulting enone may undergo Michael’s addition with indole to give the desired product as depicted in Scheme 2.

418969.sch.002
Scheme 2: Proposed mechanism for 2-substituted aryl (indolyl) kojic acid synthesis.

4. Conclusion

In summary, by adsorption phase nanoreactor technique, Kaolin/Ag nanocomposite material is synthesized and has shown that it has advantages in the preparation of 2-substituted aryl (indolyl) kojic acid derivatives such as shorter reaction times and simple workup and affords excellent yield. The present method does not involve any hazardous organic solvent. Therefore, this procedure could be classified as green chemistry.

Acknowledgments

The authors gratefully acknowledge the financial support from the Research Council of Islamic Azad University of Yazd, University of Mazandaran, Razi Metallurgical Research Center, and Fluka Company.

References

  1. F. G. Ramos Filho, T. J. A. Mélo, M. S. Rabello, and S. M. L. Silva, “Thermal stability of nanocomposites based on polypropylene and bentonite,” Polymer Degradation and Stability, vol. 89, no. 3, pp. 383–392, 2005. View at Publisher · View at Google Scholar · View at Scopus
  2. K. Wang, L. Chen, J. Wu, M. L. Toh, C. He, and A. F. Yee, “Epoxy nanocomposites with highly exfoliated clay: mechanical properties and fracture mechanisms,” Macromolecules, vol. 38, no. 3, pp. 788–800, 2005. View at Publisher · View at Google Scholar · View at Scopus
  3. J. B. Silva, C. F. Diniz, R. M. Lago, and N. D. S. Mohallem, “Catalytic properties of nanocomposites based on cobalt ferrites dispersed in sol-gel silica,” Journal of Non-Crystalline Solids, vol. 348, pp. 201–204, 2004. View at Publisher · View at Google Scholar · View at Scopus
  4. M. Díaz, F. Barba, M. Miranda, F. Guitián, R. Torrecillas, and J. S. Moya, “Synthesis and antimicrobial activity of a silver-hydroxyapatite nanocomposite,” Journal of Nanomaterials, vol. 2009, Article ID 498505, 6 pages, 2009. View at Publisher · View at Google Scholar · View at Scopus
  5. L. Balogh, D. R. Swanson, D. A. Tomalia, G. L. Hagnauer, and A. T. McManus, “Dendrimer-silver complexes and nanocomposites as antimicrobial agents,” Nano Letters, vol. 1, no. 1, pp. 18–21, 2001. View at Publisher · View at Google Scholar · View at Scopus
  6. M. R. Kim, D. K. Lee, and D.-J. Jang, “Facile fabrication of hollow Pt/Ag nanocomposites having enhanced catalytic properties,” Applied Catalysis B, vol. 103, no. 1-2, pp. 253–260, 2011. View at Publisher · View at Google Scholar · View at Scopus
  7. S. Egger, R. P. Lehmann, M. J. Height, M. J. Loessner, and M. Schuppler, “Antimicrobial properties of a novel silver-silica nanocomposite material,” Applied and Environmental Microbiology, vol. 75, no. 9, pp. 2973–2976, 2009. View at Publisher · View at Google Scholar · View at Scopus
  8. G. W. Gribble, “Recent developments in indole ring synthesis—methodology and applications,” Journal of the Chemical Society, Perkin Transactions 1, no. 7, pp. 1045–1075, 2000. View at Publisher · View at Google Scholar · View at Scopus
  9. W.-N. Xiong, C.-G. Yang, and B. Jiang, “Synthesis of novel analogues of marine indole alkaloids: mono(indolyl)-4-trifluoromethylpyridines and bis(indolyl)-4-trifluoromethylpyridines as potential anticancer agents,” Bioorganic and Medicinal Chemistry, vol. 9, no. 7, pp. 1773–1780, 2001. View at Publisher · View at Google Scholar · View at Scopus
  10. M.-Z. Piao and K. Imafuku, “Convenient synthesis of amino-substituted pyranopyranones,” Tetrahedron Letters, vol. 38, no. 30, pp. 5301–5302, 1997. View at Publisher · View at Google Scholar · View at Scopus
  11. X. Xiong and M. C. Pirrung, “Modular synthesis of candidate indole-based insulin mimics by claisen rearrangement,” Organic Letters, vol. 10, no. 6, pp. 1151–1154, 2008. View at Publisher · View at Google Scholar · View at Scopus
  12. B. Sadeghi, A. Hassanabadi, and S. Bidaki, “Synthesis of nanoparticles silica supported sulfuric acid (NPs SiO2–H2SO4): a solid phase acidic catalyst for one-pot synthesis of 4H-chromene derivatives,” Journal of Chemical Research, vol. 35, no. 11, pp. 666–668, 2011. View at Publisher · View at Google Scholar · View at Scopus
  13. M. Khazaei, M. Anary-Abbasinejad, A. Hassanabadi, and B. Sadeghi, “ZnO nanoparticles: an efficient reagent, simple and one-pot procedure for synthesis of highly functionalized dihydropyridine derivatives,” E-Journal of Chemistry, vol. 9, no. 2, pp. 615–620, 2012. View at Publisher · View at Google Scholar · View at Scopus
  14. B. Sadeghi, A. Namakkoubi, and A. Hassanabadi, “BF3·SiO2 nanoparticles: a solid phase acidic catalyst for efficient one-pot Hantzsch synthesis of 1, 4-dihydropyridines,” Journal of Chemical Research, vol. 37, no. 1, pp. 11–13, 2013. View at Publisher · View at Google Scholar
  15. B. Sadeghi, S. Zavar, and A. Hassanabadi, “Monolayer-protected silver nanoparticles: an efficient and versatile reagent for the synthesis of 3, 4-dihydropyrimidine-2-(1H)-ones (thiones),” Journal of Chemical Research, vol. 36, no. 6, pp. 343–346, 2012. View at Publisher · View at Google Scholar
  16. B. Sadeghi and M. Ghasemi Nejad, “Silica sulfuric acid: an eco-friendly and reusable catalyst for synthesis of benzimidazole derivatives,” Journal of Chemistry, vol. 2013, Article ID 581465, 5 pages, 2013. View at Publisher · View at Google Scholar
  17. R. Patakfalvi, A. Oszkó, and I. Dékány, “Synthesis and characterization of silver nanoparticle/kaolinite composites,” Colloids and Surfaces A, vol. 220, no. 1–3, pp. 45–50, 2003. View at Publisher · View at Google Scholar · View at Scopus
  18. B. V. S. Reddy, M. R. Reddy, C. Madan, K. P. Kumar, and M. S. Rao, “Indium(III) chloride catalyzed three-component coupling reaction: a novel synthesis of 2-substituted aryl(indolyl)kojic acid derivatives as potent antifungal and antibacterial agents,” Bioorganic and Medicinal Chemistry Letters, vol. 20, no. 24, pp. 7507–7511, 2010. View at Publisher · View at Google Scholar · View at Scopus