Protective effect of substituted isoxazole and isoxazoline compounds on the dissolution of iron in hydrochloric acid

Inhibitive efficiency of solutions of substituted isoxazole and isoxazoline organic compounds on Fe dissolution in deaerated solutions of 4M HCL using nitrogen gas was studied at 15°C using the steady‐state potentiostatic current‐potential method at a sweep rate of 1 mV/S. Inhibitive efficiencies were calculated at constant time of immersion of the working electrode from the measurement of current densities, icorr µA cm‐2, in the presence and absence of the organic compounds at the corrosion potentials, Ecorr. Inhibitive efficiency, ?, increases as the concentration of the organic compound increases to a certain limit then decreases again. This may be due to stimulation effect in which the solubility of the adsorbate increase with concentration of the organic compounds. In the region, where the organic compounds act as inhibitors, substituted oxazole compounds showing better inhibitive efficiencies, this maybe due to the fact that the presence of double bond between the two carbon atoms in the oxazole unit enhance the adsorption via ?‐electrons and/or to decrease in steric effect. Other factors that have been found to affect the inhibition efficiencies of these substrates are the size and the relative strength of the electron releasing group of R‐substituents on the isoxazole or isoxazoline unit.