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

4,6-Bis(3,5-dimethyl- 1H -pyrazol-1-yl)- N -phenyl-1,3,5-triazin-2-amine ( PTA-1 ), N -(4-bromophenyl)-4,6-bis(3,5-dimethyl- 1H -pyrazol-1-yl)-1,3,5-triazin-2-amine ( PTA-2 ) and 4,6-bis(3,5-dimethyl- 1H -pyrazol-1-yl)- N -(4-methoxyphenyl)-1,3,5-triazin-2-amine ( PTA-3 ) were synthesized and characterized. Their corrosion inhibition of carbon C-steel in 0.25 M H 2 SO 4 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 s -triazine derivatives behave as mixed type inhibitors. The IE% values were 96.5% and 93.4% at 120 ppm for inhibitor PTA-2 and PTA-3 bearing -Br and -OCH 3 groups on aniline, respectively. While PTA-1 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 K ° ads and free energy change Δ G ° ads 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 E ads /d N i , for both forms of PTA-2 and PTA-3 with electron donating groups (-439.73 and -436.62 kcal mol -1 ) is higher than that of PTA-1 molecule (-428.73 kcal mol -1 ). This aligned with experimental inhibition efficiency results.