Microwave-assisted synthesis of 4-amino pyrimidine analogues using eco-friendly NiTiO3 nanoparticle supported montmorillonite K30 as a heterogeneous catalyst

Abstract

In this study, NiTiO₃ nanoparticles supported on exfoliated montmorillonite K30 (MK30) were synthesised in an eco-friendly manner using ultrasonication and were used as a benign heterogeneous catalyst for the synthesis of 4-amino pyrimidine analogues in a microwave medium. The nature of the catalyst was investigated using various characterization techniques, including XRD, FT-IR, TGA, BET, FE-SEM, TEM, and XPS. The catalytic activity of the synthesised catalyst was examined, and 20% NiTiO₃/MK30 at 25 wt% showed efficient catalytic activity with high yields compared to other loadings. Non-conventional microwave irradiation was used to carry out the reaction under mild conditions, resulting in a high conversion rate. The reaction was optimised with respect to the type and amount of the catalyst, temperature, solvent, and microwave power. The scope of the reaction was extended using various aldehyde derivatives, which also produced high yields. After 6 cycles, the recovered catalyst showed good catalytic activity, achieving high yields (88–95%) within 5 min. Mechanistic investigation of the reaction hypothesized the 1st step as the synthesis of arylidene malononitrile via Knoevenagel condensation of aldehyde and di-cyanomethane, followed by the Michael addition of acetamidine to arylidene malononitrile and aromatisation to produce 2-methyl-4-amino-pyrimidine-5-carbonitriles. This synthetic approach offers several advantages, including high yield, benign reaction conditions, short reaction time, straightforward work procedure, and catalyst reusability.