Bis(dimethylpyrazolyl)-aniline--triazine derivatives as efficient corrosion inhibitors for C-steel and computational studies.

4,6-Bis(3,5-dimethyl--pyrazol-1-yl)--phenyl-1,3,5-triazin-2-amine (), -(4-bromophenyl)-4,6-bis(3,5-dimethyl--pyrazol-1-yl)-1,3,5-triazin-2-amine () and 4,6-bis(3,5-dimethyl--pyrazol-1-yl)--(4-methoxyphenyl)-1,3,5-triazin-2-amine () were synthesized and characterized. Their corrosion inhibition of carbon C-steel in 0.25 M HSO was studied by electrochemical impedance. The inhibition efficiency (IE%) of triazine was superior due to the cumulative inhibition of triazine core structure and pyrazole motif. Potentiodynamic polarizations suggested that -triazine derivatives behave as mixed type inhibitors. The IE% values were 96.5% and 93.4% at 120 ppm for inhibitor and bearing -Br and -OCH groups on aniline, respectively. While without an electron donating group showed only 79.0% inhibition at 175 ppm. The adsorption of triazine derivatives followed Langmuir and Frumkin models. The values of adsorption equilibrium constant ° and free energy change Δ° revealed that adsorption of inhibitor onto steel surface was favoured. A corrosion inhibition mechanism was proposed suggesting the presence of physical and chemical interactions. Density functional theory computational investigation corroborated nicely with the experimental results. Monte Carlo simulation revealed that the energy associated with the metal/adsorbate arrangement d /d , for both forms of and with electron donating groups (-439.73 and -436.62 kcal mol) is higher than that of molecule (-428.73 kcal mol). This aligned with experimental inhibition efficiency results.