Electrochemical Evaluation and DFT Studies of 2-(4-chlorophenyl)-3-hydroxy-4,6-dioxo-8-phenyl-4,6-dihydropyrimido[2,1-b][1,3]thiazine-7-carbonitrile of Carbon Steel Corrosion in Hydrochloric Acid

In present study corrosion inhibition property of 2-(4-chlorophenyl)-3-hydroxy-4,6-dioxo-8-phenyl-4,6-dihydropyrimido[2,1-b][1,3]thiazine-7-carbonitrile (CHPPC) in 1.0 M HCl was investigated using electrochemical impedance spectroscopy, potentiodynamic polarization and DFT studies. From electrochemical measurements it is observed that inhibition efficiency increases with CHPPC concentration and maximum efficiency (98.9) was obtained at 1.0 mM. The potentiodynamic study reveals that pyrimidothiazine derivative is a mixed type inhibitor with predominant cathodic action. EIS plot indicates that the addition of inhibitor increases the charge-transfer resistance (Rct) and decreases the double-layer capacitance (Cdl) of the corrosion process, these observation reveal that investigated pyrimidothiazine derivative inhibits carbon steel corrosion by adsorption mechanism. Adsorption of pyrimidothiazine derivative on carbon steel surface obeys the Langmuir adsorption isotherm. The effect of temperature on the corrosion rate was investigated and some thermodynamic parameters were also calculated in order to explain the mechanism of adsorption. A theoretical study of the corrosion inhibition efficiency of this pyrimidothiazine derivative, was carried out using density functional theory (DFT) at the B3LYP/6-31G(d) level of theory.