Nickel(II) Chromite Nanoparticles: An Eco-Friendly and Reusable Catalyst for Synthesis of 2,4-Diamino-6-aryl-pyrimidine-5-yl Cyanides under Ultrasonic Radiation

Background: One of the principal factors in the field of research in green chemistry is to drive chemical reactions using ultrasonication as a versatile synthetic tool. Moreover, nanostructured metal salts occupy an important position as low cost, efficient, heterogeneous, and green catalysts in chemical reactions. Pyrimidine has also acquired significance because it is a core structure in a variety of natural and non-natural agents, many of which display versatile biological activities and medical applications. Objective: The aim of this study was to explore the role of nickel(II) chromite nanoparticles (NiCr2O4 NPs) as a green and recyclable catalyst for the synthesis of 2,4-diamino-6-arylpyrimidine- 5-yl cyanides under ultrasonic radiation. Methods: A direct cyclocondensation reaction of guanidine nitrate, aromatic aldehydes, and malononitrile was performed using NiCr2O4 NPs as an effective heterogeneous catalyst under ultrasonic radiation at room temperature conditions to prepare 2,4-diamino-6-aryl-pyrimidine-5-yl cyanides in high yields. The described catalyst was prepared successfully according to a simple hydrothermal route and fully characterized by the X-Ray diffraction (XRD) technique, dispersive energy X-Ray (EDS) analysis, scanning electron microscopy (SEM), and dynamic light scattering (DLS). Results: A number of 2,4-diamino-6-aryl-pyrimidine-5-yl cyanides were effectively synthesized in high yields (94-98%) within short reaction times (15 min). All synthesized compounds were well characterized by IR, ¹H and ¹³C NMR spectroscopy, and also by elemental analyses. Conclusion: In conclusion, a simple, efficient, and green synthesis of 2,4-diamino-6-arylpyrimidine- 5-yl cyanides was developed using NiCr2O4 NPs as a green nanocatalyst, and under ultrasound radiation as a green tool. The mild reaction conditions, avoiding the use of toxic solvents or reagents, high atom economy, high yields, and simple workup are the attractive features of this new protocol.