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Abstract
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In the present study, six newly synthesized 1,4-dihydropyiridine (DHP) derivatives (isopropyl 2,7,7-trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylates) (DM1-DM6) have been studied in water/ethanol mixture (50/50 v/v) by cyclic voltammetry, choronoamperometry and differential pulse voltammetry techniques at a glassy carbon electrode. A detailed oxidation mechanism is proposed. It involves an irreversible diffusion controlled one electron process followed by a disproportionation reaction resulting in the formation of a pyridine. Kinetic and thermodynamic parameters such as charge transfer coefficient ($\propto $), number of electrons (n), exchange current density (J0) and diffusion coefficient (D) were evaluated. The oxidation process is pH-dependent and the pKa of two protonated DHPs and two protonated pyridines were determined. The effect of the phenyl ring substituents on the diffusion coefficient and oxidation potential of the compounds was also studied. Furthermore, the correlation of the oxidation potentials (Eox) of the DHPs to the highest orbital energy (EHOMO) was investigated.
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