Structural Investigation of N-Arylpyrroles as Iron Corrosion Inhibitors in Hydrochloric Acid Available to Purchase

In previous works, the authors found that substituted N-aryl-2,5-dimethylpyrroles are very effective inhibitors of iron corrosion in acid solutions. The efficiency of an inhibitor in protecting metals from corrosion is often associated with the molecular structure of the inhibitor as well as with the distribution of charge in the molecule. In this paper, the effect of the type and the position of the substituted group of N-arylpyrrole derivatives on corrosion inhibition of iron in strong acid-pickling solution (5 mol dm^–3 hydrochloric acid) has been investigated using electrochemical methods. For this purpose, different substituted N-arylpyrroles were synthesized. The inhibition efficiency of the substituted N-arylpyrroles containing halide ions follows the order: F > Br > I > Cl. The position of the substituent with respect to the benzene ring of the N-arylpyrrole affected the inhibition efficiency as follows: ortho > meta > para. The effect of the temperature on the inhibition process is studied in the temperature range from 20 to 80°C. The activation energy calculated using Arrhenius plot for iron in 5 mol dm^–3 hydrochloric acid is E_a = 14.9 kJ mol^–1, and for iron in 5 mol dm^–3 hydrochloric acid with the addition of 0.01 mol dm^–3 1 – (2-fluorophenyl) - 2,5-dimethylpyrrole, it is E_a = 87.9 kJ mol^–1.