Evaluation of the inhibition effect of novel cyclohepta[b]pyridine derivatives for copper corrosion and theoretical calculations

The inhibiting effect of three prepared derivatives of 4-(4-Hydroxy-3-methoxyphenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridine on the corrosion of copper in 0.6 M NaCl (3.5%) were investigated by different electrochemical techniques and density functional theory (DFT) calculations. The electrochemical results indicated that the inhibition efficiency increased with the increase of the inhibitors concentrations till a certain concentration then nearly became constant. 4-(4-hydroxy-3-methoxyphenyl)-2-mercapto-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridine-3-carbonitrile (C2) represented the best inhibition efficiency of 98.4% at 50 ppm. The polarization measurements revealed that the studied compounds C1-C3 acted as mixed inhibitors. The adsorption of 2-hydroxy-4-(4-hydroxy-3-methoxyphenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridine-3-carbonitrile (C1) on the copper surface obeyed Freundlich isotherm while the other two inhibitors obeyed Langmuir isotherm. Relatively, a good correlation was obtained between the observed inhibition efficiencies from one side, and the electronic and molecular descriptors from another side.