Polymeric sulfonated phenylamine as an efficient solid catalyst for the production of photochromic naphthopyrans

Abstract

Naphthopyran (NP) compounds, known for their photochromic properties, hold considerable promise for various applications. Nevertheless, their synthesis remains a significant challenge. In this research, sulfonated aniline was reacted with 1,4-bis(chloromethyl)benzene via Friedel–Crafts alkylation polymerization to create a novel polymeric sulfonated phenylamine (PSP) solid acid catalyst. This catalyst was employed in the condensation reaction between naphthols (methyl- or methoxy-substituted and unsubstituted) and bisphenyl-2-propynyl-1-alcohol, resulting in high yields of NPs. Remarkably, the catalyst can be easily recovered and reused without significant loss of performance. The study revealed that the appropriate acid strength of PSP is crucial for producing NPs with high activity and selectivity. A possible mechanism explaining the enhanced catalytic activity of this novel PSP has been proposed.