Limits and developments in ecofriendly corrosion inhibitors of mild steel: a critical review. Part 1: Coumarins

This review summarizes the possibility of using coumarin-derived organic compounds as green environmentally friendly corrosion inhibitors for mild steel alloys in hydrochloric acid environments.These corrosion inhibitors are usually synthesized from coumarin as a basic unit, usually substituted by heterocyclics, double and/or triple bonds, and various other functional groups such as amine, hydroxy and sulfur groups.Due to the presence of multiple functional groups and heterogeneous atoms, coumarins are readily adsorbed as eco-friendly organic compounds on the surface of mild steel alloys, which effectively reduces the degradation of mild steel.In the current review article, the literature based on the inhibition of corrosion of steels by green coumarin-derived inhibitors was evaluated, and the significant results and performance of these inhibitors in acid solutions were confirmed.The application and role of theoretical studies, especially the density function theory (DFT), in predicting the inhibition efficiency of the utilized green inhibitors, as well as the roles and effects of substitution groups in coumarin rings in raising the inhibition efficiency and reducing the corrosion rate were discussed.In addition, the literature dealing with understanding the role of coumarins as anticorrosive materials by codifying the potential mechanism of corrosion inhibition is covered.Coumarins were chosen for this review as they are natural materials in origin, which makes them suitable environmentally friendly candidates as corrosion inhibitors for mild steels.