Corrosion Inhibition and Adsorption Properties of Some Heterocyclic Derivatives on C-Steel Surface in HCl

5-Amino-3-methyl-1-phenyl-1H-pyrazole-4-carbonitrile (1) was used as a precursor for preparation of 3-methyl-1-phenyl-1,5-dihydro-pyrazolo[3,4-d]pyrimidin-4-one (2) and its derivatives 3–10. The produced compounds were separated, purified, and characterized by FT-IR, 1HNMR, 13C NMR, and mass spectroscopy. The surface properties were studied by measuring the surface tension. The surface tension, critical micelle concentration (CMC), and surface activities were determined. The surface parameters such as surface excess concentration (Γmax), the area per molecule at interface (Amin), and the effectiveness of surface tension reduction (πCMC) were determined from the adsorption isotherms of the prepared compounds. Furthermore, the corrosion inhibition performance of the prepared compounds was evaluated by chemical methods (weight loss) at different inhibitor concentrations and different temperatures. The corrosion inhibition efficiency increased with increase in inhibitor concentration, but decreased with increase in temperature. Thermodynamic activation parameters were computed and discussed to reach the mechanism of the corrosion inhibition process.