Evolution of the Efficiency of Divalent Cobalt and Copper Chelates Based on Isatin Derivatives and Thiosemicarbazide Ligands as Inhibitors for the Corrosion of Sabic Iron in Acidic Medium

Abstract

Divalent cobalt and copper chelates of the two ligands 1-(1- Ethoxycarbonylmethyl-2-oxoindolin-3-ylidene) thiosemicarbazide (EOIT) and 1-(1-Benzyl-2-oxoindolin-3-ylidene) thiosemicarbazide (BOIT) are the target compounds of the current study. Identification of the constitution and geometry of these compounds have been performed using the possible physicochemical and analytical instruments. Elemental analysis, molar conductance and thermal analysis assured the composition of the four chelates to be [Co(POIT)Cl]•1.5H2O, [Cu(POIT)Cl], [Co(BOIT)Cl2(H2O)]•5H2O and [Cu(BOIT)Cl]•Cl which was further confirmed by the measurement of mass spectra. The architecture arrangement of the ligand atoms around Co and Cu centers has been determined depending on the UV-Vis spectral measurements and calculation of µeff values assuring the copper compounds to be square plane whereas the cobalt complexes have tetrahedral or octahedral arrangements. These compounds were examined as corrosion inhibitors for the Sabic steel in 1.0 M HCl utilizing potentiodynamic polarization, electrochemical impedance spectroscopy, mass-loss method and scanning electron microscopy at fixed temperature of 298 K. The acquired outcomes disclosed that the inhibition efficiencies (% IEs) of the examined compounds were set to be dependent on both the concentrations and composition of the compounds. The examined compounds were set to have high % IEs, which were interpreted by strong adsorption of the compounds’ molecules on the iron surface and such adsorption was discovered to follow Langmuir adsorption isotherm. The investigational results obtained from all utilized techniques were set to be in a good accord with each other.