Inhibition of Steel Corrosion in HCI by Derivatives of Cinnamaldehyde

Singly substituted derivatives of cinnamaldehyde were tested as corrosion inhibitors for API J55 steel in static experiments conducted in 75% HCI at 65°C for 24 h. Four substituent sites were examined. Corrosion rates measured with added surfactants were correlated with physicochemical properties of the inhibitors, including electronic, steric, and solubility parameters. The best-fitting simple relations were three- or four-term power-law expressions that incorporate a solvent interaction parameter and, to a lesser extent, a parameter related to electron affinity or electronegativity. These expressions are consistent with a proposed corrosion inhibition model and with the quantitative structure-activity relationship (OSAR) proposed by Hansch. However, no single OSAR was found that would satisfactorily accommodate the data from all four substituent groups, a result attributable to site-specific variability in the nature of the π-electron system and in the molecular geometry.