Degradation of a schiff-base corrosion inhibitor by hydrolysis, and its effects on the inhibition efficiency for steel in hydrochloric acid

A Schiff base, known in the literature as a corrosion inhibitor for steel in acidic solution, is shown to hydrolyse in aqueous solution. It appears that the imine group present in this class of molecules is an unstable linkage and the hydrolysis reaction is both acid-catalysed and base-catalysed and is the reverse of the condensation reaction required to synthesize the Schiff base. Measurement of the rate of corrosion of carbon steel in 1 M hydrochloric acid shows that the Schiff base, and its hydrolysis products have similar inhibition efficiency when at similar molar concentration. This suggests that the inhibition imparted by Schiff base may be entirely due to the products of its hydrolysis under acid conditions. We also report here that a derivative of the Schiff base obtained by reduction shows higher corrosion inhibition efficiency and is not degraded by hydrolysis and provides a much more efficient corrosion inhibitor in 1 M HCl solution relative to the Schiff base itself.