ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Fe₃O₄@SiO₂ magnetic nanoparticles for bulk scale synthesis of 4′-chloro-2,2′:6′,2″-terpyridine

M. Chandrappa, G. V. Shiva Reddy, Rahaman Fazlur, B. Narasimha Murthy, Phani Kumar Pullela, and S. Girish Kumar

Bigtec Labs Pvt Ltd., Bangalore, India

E-mail: phanikumar.p@cmrit.ac.in

Abstract: Terpyridines are unique class of functional compounds that is extensively spotlighted in diverse fields like synthesis of supramolecular chemistry, nanomaterials, medicinal chemistry intermediates, drugs and active pharmaceutical ingredients and so on. The key challenges for the production of terpyridine lie in the bulk scale synthesis of intermediates. The expansively used synthon for terpyridine synthesis is 4′-chloro-2,2′:6′,2″-terpyridine and their bulk scale synthesis under the ambient conditions using a Fe₃O₄@SiO₂ magnetic nanomaterial catalyst is investigated in the present work. In the protocol stabilized, ethyl-2-pinacolate and acetone were reacted in the presence of NaH to obtain 1,5-bis(2-pyridinyl) pentane-1,3,5-trione. The enolate of acetone is difficult to generate even with NaH and we used Fe₃O₄@SiO₂ to increase the rate of H₂ gas evolution. The triketone is cyclized with CH₃COONH₄ to obtain 2,6-bis(2-pyridinyl)-4-pyridine. This reaction proceeds quantitatively and the off-white solid was easy to isolate from the reaction medium. The subsequent aromatization was observed with PCl₅/POCl₃ and acidic silica gel promoted the product yield to reach ~78%. The crux of the present protocol is that it does not involve any column purification and significant yield of 4′-chloro-2,2′:6′,2″-terpyridine can be conveniently attained. The Fe₃O₄@SiO₂ aids in the stabilization of carbonyl on the solid support and abstraction of hydrogen from methyl group of acetone. The 40 nm sized Fe₃O₄@SiO₂ favored the maximum yield attributed to the density of active sites to promote the reactions. Due to high value nature of 4′-chloro-2,2′:6′,2″-terpyridine, the nominal 30% yield improvement achieved at the bulk scale gauges significant at the industrial scale.

Keywords: Fe₃O₄@SiO₂; Catalytic solid supports; Terpyridine, 4′-chloro-2,2′:6′,2″-terpyridine; Bulk scale synthesis; Reaction mechanisms; Structural elucidation; NMR

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-017-0238-0

Chemical Papers 71 (12) 2445–2453 (2017)