Inhibition of Steel Corrosion in HCl by Derivatives of Cinnamaldehyde:Part II. Structure–Activity Correlations

Singly substituted derivatives of cinnamaldehyde were tested as corrosion inhibitors for APl J55 steel in static experiments conducted in 75% HCl 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 (QSAR) proposed by Hansch. However, no single QSAR 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.