Phosphoric acid supported on alumina: A useful and effective heterogeneous catalyst in the preparation of α-amidoalkyl-β-naphthols, α-carbamato-alkyl-β-naphthols, and 2-arylbenzothiazoles

Phosphoric acid supported on alumina (H3PO4/Al2O3) is found to be an efficient catalyst for the three-component condensation reaction of β-naphthol, aromatic aldehydes and amides or carbamates to afford the corresponding α-amidoalkyl-β-naphthols, α-carbamato-alkyl-β-naphthols under solvent-free conditions. In addition, the preparation of 2-arylbenzothiazoles from the reaction of aromatic aldehydes and 2-aminothiophenol was described under mild and solvent-free conditions. The remarkable features of these catalytic procedures are high conversions, shorter reaction times, cleaner reaction, simple experimental, and work-up procedures. Phosphoric acid supported on alumina as catalyst can be reused several times without significant loss of its catalytic activity.