Absorption spectrometric and thermodynamic study of charge transfer complexes of menadione (Vitamin K 3) with a series of phenols

Abstract

The electron donor–acceptor (EDA) interactions between menadione (i.e., 2-methyl-1,4-naphthoquinone, which is also called ‘Vitamin K 3’) and a series of phenols (viz., phenol, resorcinol and p-quinol) have been studied in CCl 4 medium. In all the cases, charge transfer (CT) bands have been located. The CT transition energies ( hν CT) of the complexes are found to change systematically with change in the number and position of the –OH groups in the aromatic ring of the phenol moiety. From the trends in the hν CT values, the Hückel parameters ( h Ö and k C–Ö) for the –OH group have been obtained. The CT transition energies are well correlated with the ionisation potentials of the phenols. From an analysis of this variation the electron affinity of Vitamin K 3 has been found to be 2.28 eV. The stoichiometry of the complexes in each case has been found to be 1(menadione):2 (phenol). Formation constants of the complexes have been determined at four different temperatures from which the enthalpies and entropies of formation of the complexes have been estimated.