Kinetics of intramolecular acylation of 3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one in concentrated acids

Abstract

Acid-catalysed intramolecular acylation of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one was studied kinetically in 5–11.5M-HCl, 2–8.8M-HBr, and 5-18M-H₂SO₄ solutions at 70–105, 70–120, and 80° respectively. The rate dependence on acidity is discussed on the basis of hydration parameter treatments. A kinetic scheme is proposed, visualizing the transition state as leading from the protonated substrate through its cis-form to the products. This scheme is consistent with the hydration parameters and acyl– or alkyl–oxygen fission concerted with acylation, the second being the operative mechanism in halogen acid solutions.