Dithiazolidines—A New Class of Heterocyclic Inhibitors for Prevention of Mild Steel Corrosion in Hydrochloric Acid Solution

Heterocyclic compounds, namely 3,5-diphenyl-imino-1,2,4-dithiazolidine (DPID); 3-phenyl-imino-5-chlorophenyl-imino-1,2,4-dithiazolidine (PCID); 3-phenyl-imino-5-tolyl-imino-1,2,4-dithiazolidine (PTID); and 3-phenyl-imino-5-anisidyl-imino-1,2,4-dithiazolidine (PAID), were synthesized in the laboratory. Their influence on the inhibition of corrosion of mild steel in 1 N hydrochloric acid (HCl) was investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency of these compounds was found to vary with concentration, temperature, and immersion time. Good inhibition efficiency (>90%) was evidenced even at a concentration of 25 ppm. Potentiodynamic polarization results revealed that three of the inhibitors, DPID, PCID, and PAID, are cathodic inhibitors while PTID is a mixed-type inhibitor. Adsorption on the metal surface obeyed Temkin’s adsorption isotherm.