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Calixarenes CA1-CA4 containing one to four 4-imidazolylethylamidocarbonyl groups were synthesized and tested as inhibitors for the corrosion of mild steel in 1 M HCl at 308 K. The study was made using Tafel polarisation and weight-loss methods. In contrast to CA1, calixarenes CA2-CA4 were good inhibitors, reaching inhibition efficiencies (E%) of 94 to 100% at 10 -4 M. The values of the inhibition efficiency calculated by the two techniques were in acceptable agreement. E% increased with the number of 4-imidazolylethylamidocarbonyl groups attached to the calixarene. Polarisation curves showed that CA2-CA4 act as mixed-type inhibitors. Their adsorption on the steel surface followed a Langmuir isotherm. Thermodynamic parameters of adsorption were also deduced.

Some bipyrazole derivatives {N,N'-bis-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-N,N'-dimethylethane-1,2-diamine (M1) and N,N'-bis[(3-ethylcarboxylate-5-methyl-1H-pyrazol-1-yl)methyl]-N,N'-dimethyl ethane-1,2-diamine (M2)} have been studied as corrosion reduction for mild steel in 1 M HCl acid. Influence of inhibitors concentration as well as the temperature was investigated using chemical (weight loss) and electrochemical techniques. All the techniques employed are in good agreement. The protection efficiency rise with increasing inhibitors concentration and with rise temperature. Weight loss data used for determining the thermodynamic parameters of dissolution and adsorption processes and the interpretation of the results are given. Adsorption of inhibitor on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Quantum chemical parameters calculation such as the energies of highest occupied molecular orbital (EHOMO) and the lowest unoccupied molecular orbital (ELUMO), energy gap (∆Eg) between EHOMO and ELUMO, dipole moment (µ), ionization potential (I), electron affinity (A), global hardness (η), global electrophilicity index (χ), softness (S), back donation energy (∆Eback donation) total energy and effective atomic charges were calculated. In addition, Monte Carlo (molecular dynamics) simulation was used to simulate the adsorption of bipyrazole derivatives on the iron surface in 1 M HCl acid.