Solvent-free synthesis of amidoalkyl naphthols in the presence of MWCNTs@SiO2/SO3H as effective solid acid catalyst

Multiwalled carbon nanotubes (MWCNTs) were modified with sulfonic acid groups through a new method. In the first step, MWCNTs' surfaces were hydroxylated using KMNO4 as oxidating agent and a surfactant (TPABr). Second, SiO2-coated MWCNTs were prepared through the reaction of hydroxylated CNTs with tetraethyl orthosilicate, and in last step, MWCNTs@SiO2/SO3H was prepared using the reaction of MWCNTs@SiO2 with ClSO3H. Obtained catalyst was used as efficient solid acid catalyst for one-pot three-component condensation reaction of 2-naphthol, benzaldehyde, and amide derivatives to afford the corresponding amidoalkyl naphthols. The reaction was performed under solvent-free conditions and products were obtained in high to excellent yields (80-98%). Prepared solid acid catalyst was characterized using FT-IR, BET, TGA, SEM, and EDX techniques. Presented methodology has several advantages such as simple procedure, excellent yields of products, effective reusable solid acid catalyst, and eco-friendly reaction conditions.