Inhibition of copper corrosion in aerated hydrochloric acid solution by heterocyclic compounds containing a mercapto group

Inhibition of copper corrosion by benzotriazole (BTA), 2-mercapto benzoxazole (MBO) and 2-mercapto benzimidazole (MBI) in 0.5 mol L⁻¹ HCl was investigated by weight-loss measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy. MBI was shown to be the most effective inhibitor among those tested. Potentiodynamic polarization results revealed that the three compounds acted as anodic inhibitors, particularly MBI strongly suppressed anodic current densities. Molecular structure parameters of BTA, MBO and MBI were obtained by using an MM2 forcefield program and PPP–SCF quantum chemical calculation. It was found that MBI has higher levels of HOMO and LUMO energy and the larger π-electron density.