Understanding functional group effect on corrosion inhibition efficiency of selected organic compounds

Organic compounds exhibit notable efficiency towards inhibition of corrosion on numerous metals and alloys. Because of its vast uses in counteracting material deterioration, the use of organic chemicals to inhibit corrosion has taken on immense relevance. Organic complexes comprising different heteroatoms like Nitrogen(N), Oxygen(O), Sulphur(S), Phosphorus(P), etc. are known as heterocycles. Besides, having very important theoretical and practical applications these compounds have been demonstrated to be particularly effective at suppressing aqueous corrosion, owing to the creation of a coating on the metal surface due to adsorption. Based on the occurrence of lone pair of electrons and the electronegativity of the heteroatoms, there subsists an empirical rule that the accustomed development in the inhibition efficacy of molecules comprising heteroatoms follows the sequence as O < N < S < P. Organic heterocyclic molecules with "polar functional groups like -OH, -OR, -SH, -SR, -CONH2, -COOH, -COOR, -COR, -COCl, -COBr, -COI, -S-S-, -SOR, -PO3, -PO4," etc. exhibit good inhibition efficiency by providing heavy bonding with metallic surface This review mainly emphasizes, how the substitution to the heterocycles effects and brings about an obvious change in corrosion inhibition propensity based on their electron-donating and withdrawing capacity on the external layer of metallic compounds. According to a simplified model for predicting the relative efficiency of organic chemisorbed complexes as corrosion inhibitors, electron giving substituents improve corrosion inhibition efficacy, while electron-withdrawing substituents reduce inhibition capacity. Just a few published works have found exceptions to this generalization. This review article compiles findings and conclusions from previous studies that looked into the influence of substituent factions on corrosion inhibitory abilities of seven different classes of organic compounds. (C) 2021 Elsevier B.V. All rights reserved.