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 beta-naphthol, aromatic aldehydes and amides or carbamates to afford the corresponding alpha-amidoalkyl-beta-naphthols, alpha-carbamato-alkyl-beta-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. (C) 2012 Production and hosting by Elsevier B.V. on behalf of King Saud University.