An environmentally friendly synthesis of 2,4-dihydroxybenzophenone by the single-step O-mono-benzoylation of 1,3-dihydroxybenzene (resorcinol) and Fries rearrangement of intermediate resorcinol monobenzoate: the activity of acid-treated montmorillonite clay catalysts

Abstract

Acid-treated montmorillonites belonging to the K series (supplied by Süd-Chemie) were tested as heterogeneous catalysts for the liquid-phase acylation of 1,3-dihydroxybenzene with benzoic acid; this reaction may represent an environmentally friendly alternative to the use of benzyltrichloride as the acylating agent. It was found that conversion was proportional to the Al content in samples; the catalytic activity was associated to the Brønsted acidity generated by the interaction of water molecules in hydrated clays with Al. The removal of water from samples by preliminary thermal treatment indeed led to the decrease of the catalytic activity. The reaction mechanism was found to consist of the direct O-benzoylation with formation of resorcinol monobenzoate, while no primary formation of the product of C-benzoylation (2,4-dihydroxybenzophenone) occurred. The latter product formed exclusively by consecutive Fries rearrangement upon the benzoate.