Corrosion inhibiting properties of some polyaza macrocyclic compounds on mild steel in acid environments

Macrocyclic compounds constitute a potential class of corrosion inhibitors. In an attempt to develop effective corrosion inhibitors we have synthesized four macrocyclic compounds by condensing o-ethylene diamine and o-phenylene diamine with ethylacetoacetate and succinic acid. Their inhibiting action was evaluated on corrosion of mild steel in HCl and H2SO4 by weight loss and potentiodynamic polarization methods. A Macrocyclic compound derived by condensing o-phenylene diamine with ethylacetoacetate exhibited best performance by giving IE of 98 percent at 500 ppm concentration. The potentiodynamic polarization studies revealed that the tested compounds are either mixed type or predominantly cathodic inhibitors. IE of all the investigated compounds increased significantly on addition of a small concentration KI in both acids due to synergism.