Abstract

An electrochemical study related to the redox characteristics of 2-arylaldehydehydrazono-3-phenyl-5-substituted-2,3-dihydro-1,3,4-thiadiazoles (1a-h)  in nonaqueous solvents such as 1,2-dichloroethane (DCE), dichloromethane (DCM), acetonitrile (AN),dimethylsulphoxide (DMSO) and tetrahydrofurane (THF) using 0.1 mol dm^-3 tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte at platinum electrode, has been performed using cyclic voltammetry (CV). Controlled potential electrolysis (CPE) is also carried out to elucidate the course of different electrochemical reactions through the separation and identification of the intermediates and final electrolysis products. The redox mechanism is suggested and proved. It was found that all the investigated compounds in all solvents are oxidized in two irreversible one-electron processes following the well known pattern of EC-mechanism; the first electron loss gives the corresponding cation – radical which is followed by a proton removal from the ortho-position in the N-phenyl ring forming the radical. The obtained radical undergoes a second electron uptake from the nitrogen in the N=C group forming the unstable intermediate (di-radical cation) which undergoes a ring closer forming the corresponding cation. The formed cation can be stabilized in solution through its combination with a perchlorate anion from the medium. On the other hand, these compounds are reduced in a single two electron or in a successive two irreversible one electron processes following the well known pattern of EEC-mechanism according to the nature of the substituent; the first one gives the anion-radical followed by a second electron reduction to give the dianion which is basic enough to abstract protons from the media to saturate the (C = O) bond.

Key words: Redox characteristics, non-aqueous solvents, thiadiazoles, cyclic voltammetry.

Abbreviation

DCE, 1,2-Dichloroethane; DCM, dichloromethane; AN, acetonitrile; THF, tetrahydrofuran; DMSO, dimethylsulfoxide; CPE, controlled potential electrolysis