In this work, we studied the effect of inhibition of 4-amino-2,6-dihydro-2-(4-nitrophenyl)-6-oxo-8-ptolylpyrimido[ 2,1-b][1,3]thiazine-3,7-dicarbonitrile (AOTP) against corrosion of the carbon steel in phosphoric acid 2.0 M H3PO4. For this, we used the electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results obtained revealed that AOTP performed excellently as a corrosion inhibitor for carbon steel in phosphoric acid solution. Inhibition efficiency increases with increase in concentration of AOTP. The efficiency reaches a maximum value of 95% at 5×10-4 M. Electrochemical methods show that it acts as mixed-type inhibitor with predominant cathodic action. The AOTP admits as the Langmuir adsorption. Attempt to correlate the molecular structure to quantum chemical indices was made using density functional theory (DFT).
