Electrochemical investigations of some newly synthesized arylazapyrazole derivatives

Abstract

Three derivatives of arylazapyrazole ((E)-4-(phenyldiazenyl)-3,5-dimethyl-1H-pyrazole, (E)-4-[(4-fluorophenyl)diazenyl]-3,5-dimethyl-1H-pyrazole, and (E)-4-[(4-iodophenyl)diazenyl]-3,5-dimethyl-1H-pyrazole) were synthesized, characterized, and further investigated for their electrochemical behavior at glassy carbon electrode using cyclic voltammetry. All compounds were reduced following E i C i mechanism giving single cathodic peak in potential range 0 to −2 V vs. Ag/AgCl. The plots of log i P vs. log ν showed that the electrode process is mixed adsorption-diffusion controlled. The kinetic parameters such as transfer coefficient (αn), diffusion coefficients (D o), and standard heterogeneous rate constants (k s ) were determined from the electrochemical data. The values of D o were determined and found greater for the smallest among the three compounds. k s values were calculated by Laviron formalism which lies in the order of 10−2 s−1. Temperature and pH effects were studied and thermodynamic parameters such as change in free energy of activation (ΔG # ), apparent activation energy (E a ), enthalpy (ΔH # ), and entropy (ΔS # ) of activation were determined. Negative values of E a , ΔH # , and ΔS # imply that the electrode process needs lesser over potential with temperature rise, pre-adsorption of the analyte onto the electrode surface and the activated complex has a more organized structure than the reactants, respectively.