**5. Heterocyclic compounds as organic corrosion inhibitor**

Heterocyclic compounds containing N, S, O, and P atoms, as well as compounds containing π-bonds and/or polar group that will provide protection of metals or alloys from corrosion. The heterocyclic compounds such as azoles, indoles, and aromatic rings can be used to provide corrosion protection.

The benzo imidazole [169] derivative, pyridine thiazole [170] compound, imidazole derivatives [171], phenanthroimidazole derivatives [172], and bis-benzothiazoles derivatives [173] can be used as corrosion inhibitor potency for mild steel and others. Pyridine, Indoles, [174–177], and Quinoline [44, 178–181] have shown sufficient potency for inhibition of iron, aluminum, carbon steel, N80 steel, mild steel, and zinc in different acidic media.
