Recent progresses in Schiff bases as aqueous phase corrosion inhibitors: Design and applications

Schiff bases (SBs) possess the basic feature of compounds that are primarily qualified to test as corrosion inhibitors for different metal/electrolyte systems. SBs adsorb and form corrosion mitigating surface film through their electron rich centers including > C = N– (imine) moiety. The > C = N– (imine) moiety offers strong bonding with the metallic ions because of its π-acceptor properties. It is important to mention that SBs containing polar substituents at suitable positions can form chelates with the central metal ions therefore such SBs are expected to act as superior corrosion inhibitors as compared to the non-substituted SBs. Generally, electron donating substituents such as –OH (hydroxyl), –CH3 (methyl), –NH2 (amino) and –OCH3 (methoxy) are expected to increase the corrosion inhibition potentials of SBs. Halogens are also known to increase electron density at donor sites through their + R-effect. The present review article describes the collection on SBs as corrosion inhibitors for different metal/electrolyte systems. Electronic and molecular structural effects on the corrosion inhibition potential of SBs are discussed in relation to Hammett substituent constants. Interactions of SBs with metallic surfaces at molecular level are discussed in this report. A balanced level of hydrophilicity and hydrophobicity is indispensable for efficient corrosion inhibition activity. Extremely high hydrophobicity has a reducing effect corrosion inhibition performance by decreasing the solubility of the compounds in polar electrolytes.