Effect of pressure on product selectivity in an acid-catalyzed reaction: enhancement of β-ionone selectivity during the cyclization of pseudoionone on a solid Brønsted acid catalyst

Abstract Silica-supported methanesulfonic acid, a metal-free solid Brønsted acid catalyst, was studied for the solvent-free acid-catalyzed cyclization of pseudoionone to synthesize β-ionone with high selectivity. The reaction gave poor selectivity to β-ionone owing to the formation of α-ionone, and numerous by-products such as condensation products and oligomeric and polymeric compounds. The pressure was observed to be an effective reaction parameter to enhance the selectivity of β-ionone by reducing the formation of α-ionone and by-products. The lower molar volume of β-ionone as compared with α-ionone and by-products favors the formation of β-ionone under pressure. The study suggests that acid-catalyzed reactions can be made selective by applying pressure to suppress the formation of condensation products and oligomeric and polymeric by-products.