KINETICS AND MECHANISM OF VILSMEIER-HAACK SYNTHESIS OF 3-FORMYL CHROMONES DERIVED FROM O-HYDROXY ARYL ALKYL KETONES - A STRUCTURE-REACTIVITY STUDY

Kinetics of Vilsmeier-Haack reaction with o-hydroxy acetophenones (OHA P) have been investigated in different solvent systems comprising eith er a single component viz., dichloromethane (DCM), dichloroethane (DCE ), acetonitrile (ACN), benzene or binary solvent mixtures of benzene a nd acetonitrile. The study revealed a total second order kinetics with a first order dependence on each of the [reactant] namely, [VH adduct ] and [OHAP]. Increase in the dielectric constant (D) of the medium al tered the rate of the reaction non linearly. The data did not fit into either Amis or Kirkwood's theories. These results were interpreted in terms of solvent-solute and solvent-cosolvent interactions. Structure -reactivity correlations have been explained by Hammett's equation.