Corrosion inhibitors part 3: quantum chemical studies on the efficiencies of some aromatic hydrazides and Schiff bases as corrosion inhibitors of steel in acidic medium

A quantum chemical study of the efficiency of some o-, m-, and p-substituted benzohydrazides, cinnamohydrazide, and Schiff bases derived from salcylaldehyde with o- substituted anilines, p-substituted benzaldehydes with 2-aminopyridine and 2-aminopyrimidine, benzaldehyde and cinnamaldehyde with p-phenylenediamine as corrosion inhibitors of steel in the presence of 1M HCl is presented. The AM1, PM3, MINDO/3 and MNDO semi-empirical SCF molecular orbital methods were used. A possible correlation between corrosion inhibition efficiencies and structural properties was searched to reduce the number of compounds to be selected for testing from a library of compounds. Quantum parameters, total negative charge (TNC) on the molecule, energy of highest occupied molecular orbital (E-HOMO), energy of lowest unoccupied molecular orbital (E-LUMO), dipole moment (mu), total energy (TE), and linear solvation energy terms, molecular volume (Vi) and dipolar-polarization (pi*) were correlated to corrosion inhibition efficiency of the studied compounds. The results were used to predict the corrosion inhibition of some related aromatic hydrazide derivatives with correlation coefficient r > 0.96.