Novel isoquinolinium derivatives as inhibitors of acid corrosion

1-(4-Aminophenyl)-2- (9,10-dimethoxy-13-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)-5,8-dihydro-6H- [1,3]dioxolo [4,5-g]isoquinolino [3,2-a]isoquinolin-8-yl)ethan-1-one (I), 2- (9,10-dimethoxy-13-(7-nitrobenzo[c][1,2,5]ethan-1-one (III) were studied as corrosion inhibitors of steel in 1 M hydrochloric acid at 20-80°C.The efficiency of the compounds was estimated by the gravimetric method, by recording polarization curves and by electrochemical impedance spectroscopy.Quantum-chemical calculations were carried out in the framework of the density functional theory (DFT).It was found that the best inhibitor, i.e., compound III provides steel protection for 98 and 92% at temperatures of 25 and 80°C, respectively.The inhibitors hinder the corrosion process by changing the structure of the electrical double layer, blocking a fraction of the surface, and increasing the effective activation energy.The additives decrease the rates of both partial electrode reactions of the corrosion process.Calculations and optimization of inhibitor structures were carried out within the framework of functional theory.It was found that the best correlation is obtained for linear relationships: inhibition coefficient vs. X, where X is the energy of the highest occupied molecular orbital EHOMO and the lowest unoccupied molecular orbital ELUMO, electronegativity () and the sum of electron densities on heteroatoms (ED).