Introduction: Tetrazoles are important and useful class of heterocycles with wide range of applications in medicinal chemistry, coordination chemistry and material science. Due to the harsh conditions and harmful side products of the acid-catalyzed procedures for the synthesis of 5-substituted-1H-tetrazoles, new metal-based catalysts have been reported. Among them Cu, Cd, Fe, Zn, Ag, and In-based homogeneous catalyst have been investigated for production of tetrazoles via a [3+2] cycloaddition reaction between azide ion and organic nitriles. In this work, new magnetically recoverable lanthanum-based heterogeneous catalyst has been studied for the synthesis of tetrazoles for the first time [1]. Methods / Experimental: The Stöber method was utilized for the synthesis of core-shell Fe3O4@SiO2 MNPs [2]. An aqueous dispersion of Fe3O4 were dissolved into a mixture of ethanol/deionized water. Ammonia solution was then added and tetraethyl orthosilicate was dropped into the mixture. Finally, aqueous solution of LaCl3 was dropped into the suspension of Fe3O4@SiO2 under stirring and were heated at 723K. Catalyst was then separated with an external magnet and washed with ethanol and dried at 80 oC. Results and Discussion: The TEM micrographs and size distributions (70 and 68 nm) of nanocatalyst are shown in Fig. 1a and Fig. 1b. TEM images indicated that the most of the prepared nanoparticles are rod shaped and have sized 60-70 nm (Fig.1a). The energy dispersive spectrum (EDS) indicated the presence of Fe, O, Si and La elements (Fig. 1c). This analysis confirms that La is supported on catalyst. The magnetic saturation value of the Fe3O4 and Fe3O4@SiO2@La is 64.99 and 35.13 emu/g, respectively, demonstrating that the composite particles possess magnetic properties (Fig. 1d). Scheme 1. Synthesis of tetrazoles. Only 40% addition product is obtained when the reaction is carried out without catalyst in DMSO at 100 ºC, despite of prolonged reaction time. At the same reaction condition, 100% conversion was obtained after 30 min in the presence of Fe3O4@SiO2@La. This result highlights the specific role of our catalyst in [3+2] cycloaddition reaction of benzonitrile with sodium azide 2 (Scheme 1). Among the different tested solvents, DMSO was found to be the solvent of choice for the synthesis of tetrazoles. Increasing the catalyst loading than 0.1 mol% did not lead to higher conversion, while lower catalyst loading has lessened the reaction yield even after longer reaction time. Fig. 1. a) TEM image, b) Particle size histogram, c) EDS analyze, d) VSM of Fe3O4@SiO2@La. Conclusion: In conclusion, a simple and effective method for the synthesis of 5-substituted-1H-tetrazoles from nitriles and sodium azide has been developed using Fe3O4@SiO2@La. This nano sized heterogeneous catalyst is easily prepared and stable to air which shows excellent catalytic performance for various nitriles. References: [1] a) L. Bosch and J. Vilarrasa, Angew. Chem., 2007, 46, 3926; b) G. Venkateshwarlu, A. Premalatha, K. C. Rajanna and P. K. Saiprakash, Synth. Commun., 2009, 39, 4479; c) J. Bonnamour and C. Bolm, Chem.–Eur. J., 2009, 15, 4543; d) D. J. Carini, J. V. Duncia, P. E. Aldrich, A. T. Chiu, A. L. Johnson, M. E. Pierce, W. A. Price, J. B. Santella and G. J. Wells, J. Med. Chem., 1991, 34, 2525; e) P. Mani, A. K. Singh and S. K. Awasthi, Tetrahedron Lett., -80 -60 -40 -20 0 20 40 60 80 -10000 -5000 0 5000 10000 Magnetization (emu/g) Applied field (Oe) a b c d 3 2014, 55, 1879; f) V. S. Patil, K. P. Nandre, A. U. Borse and S. V. Bhosale, E-J. Chem., 2012, 9, 1145. [2] S. Shylesh, V. Schünemann, W. R. Thiel, Angew. Chem. Int. Ed. 2010, 49, 3428.

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