Application of Charge Transfer Complexation Reaction for the Spectroscopy Determination of Anticonvulsant Drug Primidone

The interaction of the perimidone drug in solution state with the σ-acceptor iodine, the aliphatic π-acceptor tetracyanoethylene (TCNE) and the aromatic π-acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) have been studied through the initial formation of ionic intermediate to charge transfer (CT) complex in methanol at room temperature. The spectral studies of the complexes were determined by UV-Vis, and Fourier transform infrared (FT-IR). The stoichiometries of the complexes were determined to be 1:2 and 1:1 ratio by the photometric molar ratio between primidone with π-acceptors and σ-acceptor, respectively. The equilibrium constants (KCT), molar extinction coefficient (εCT) and spectroscopic-physical parameters (standard free energy (ΔGo), and ionization potential (Ip)) of the complexes were determined upon the modified Benesi-Hildebrand equation. The most stable mono-protonated form of perimidone is characterized by the formation of +N-H (pyrimidine ring) intramolecular hydrogen bonded. In the high-wavenumber spectral region ∼3400 cm-1, the bands of the +N-H stretching vibrations could be potentially useful to discriminate the investigated forms of perimidone.