Synthesis of 1,6-Naphthyridine Derivatives and Exploration of their Corrosive Effects on 316 L Stainless Steel in Acidic Media

Three derivatives of 1,6-naphthyridine namely (E)-5,7-diamino-2-(dicyanomethyl)-4-styryl-1,2,3,4-tetrahydro-1,6-naphthyridine-3,8-dicarbonitrile (NP1), (E)-5,7-diamino-4-(3-chlorostyryl)-2-(dicyanomethyl)-1,2,3,4-tetrahydro-1,6-naphthyridine-3,8-dicarbonitrile (NP2) and (E)-5,7-diamino-4-(3-bromostyryl)-2-(dicyanomethyl)-1,2,3,4-tetrahydro-1,6-naphthyridine-3,8-dicarbonitrile (NP3) were synthesized through a one pot cascade reaction of aromatic aldehydes and malononitrile dimer in the presence of ethanol as a solvent under reflux mode for 4-6 h and characterized by 1H, 13C NMR, FT-IR and UV-Vis spectroscopies. Since naphthyridine derivatives possess a wide range of biological activities and the synthesized naphthyridine derivatives then subjected to antimicrobial activities. Furthermore, studies on the corrosion inhibition activity of novel naphthyridine derivatives (NP1, NP2 and NP3) was performed in 20% HCl on 316 L stainless steel and show very good corrosion inhibition activity. The corrosion study was carried out via electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), weight loss method and scanning electron microscopy (SEM). The results show that derivative NP2 has a maximum inhibition efficiency of 83.7% at 40 ppm. The potentiodynamic polarization curves demonstrated that all the three naphthyridine derivatives (NP1, NP2 and NP3) act as mixed-type. SEM revealed that all the three naphthyridine inhibitors were adsorbed on the surface of 316 L SS and acted as a protective layer.