Corrosion inhibitor activity of 1,3-diketone malonates for mild steel in aqueous hydrochloric acid solution

Four 1,3-diketone malonates compounds were synthesized and tested as corrosion inhibitors for mild steel in 1.0 M aqueous hydrochloric acid. Gravimetric and polarization tests showed that inhibitor efficiencies were related to molecular moiety and depended on tautomer concentration, i.e. enol–keto and diketo. Both tautomers displayed relatively high corrosion inhibition efficiency (75–96%) at 100 mg L−1, which increased with temperature (25–55 °C) and dependent on diketo population. Improvement in corrosion resistance was related to the presence of different substituent groups, from which hydrogen substituent contributed the most, apparently due to easiness of electron acceptance as confirmed by quantum chemical calculations.

► 1,3-Diketone malonates displayed relatively high corrosion inhibition efficiency.
► Inhibition efficiency is improved when temperature is increased within 25–55 °C.
► Corrosion inhibitor efficiency of diketone malonates is dependent on diketo population tautomer.
► Diketone malonates act as mixed corrosion inhibitors with a Langmuir isotherm.