Inhibition of mild steel corrosion by some macrocyclic compounds in hot and concentrated hydrochloric acid

Three macrocyclic compounds, namely 2,3,9,10-tetramethyl-6,13-dithia-1,4,5,7,8,11,12,14-octaaza-cyclotetradeca-1,3,6,8,10,13-hexaene (MTAT), 3,4,9,10-tetramethyl-7,12-dithia-1,2,5,6,8,11-hexaazacyclododecane-2,4,7,8,10,12-hexaene (MTAD), 3,4,9,10-tetramethyl-7,12-dioxa-1,2,5,6,8,11-hexaazacyclododecane-2,4,7,8,10,12-hexaene (MOAD) were synthesized to study their corrosion inhibitive effect in 5 N HCl by weight loss and potentiodynamic polarization studies. Inhibition efficiencies (IE) and corrosion rates (CR) of these compounds have been evaluated at three different temperatures ranging from 25 to 70 °C. Enhancement in IE of these compounds was observed on addition of potassium iodide (KI) due to synergism. Potentiodynamic polarization studies showed that MTAT is mixed in nature. Adsorption studies have shown that all of these compounds inhibit corrosion of mild steel in 5 N HCl by adsorption mechanism.