New pyrimidothiazine Derivative as Corrosion Inhibitor for Carbon Steel in Acidic Media

Abstract

2,8-bis(4-chlorophenyl)-3-hydroxy-4,6-dioxo-4,6-dihydropyrimido[2,1-b][1,3]thiazine-7-carbonitrile (CHPTC) was tested as corrosion inhibitor for carbon steel in 2.0 M H3PO4 by using polarization, electrochemical impedance spectroscopy (EIS) and computational calculations. Potentiodynamic polarization curves indicated that the pyrimidothiazine derivativeas mixed-type inhibitor. Impedance measurements showed that the double-layer capacitance decreased and charge-transfer resistance increased with increase in the inhibitor concentration and hence increasing in inhibition efficiency. The effect of temperature on the corrosion behavior of carbon steel in 2.0 M H3PO4 with and without addition of CHPTC was studied in the temperature range 313-333 K. The adsorption of the inhibitor molecules was in accordance with the Langmuir adsorption isotherm. Quantum chemical approach used to calculate electronic properties of the molecule to ascertain the relation between inhibitive effect and molecular structure.