Effect of selected 3-chloromethylcoumarin derivatives on mild steel corrosion in acidic medium: experimental and computational studies

Two 3-chloromethylcoumarins synthesized via the Baylis-Hillman reaction have been investigated for their ability to inhibit corrosion of mild steel in 2.0 M HCl. The inhibition efficiency was evaluated by gravimetric and electrochemical methods. Inhibition efficiency was found to increase with increase in concentration of the 3-chloromethylcoumarins. Kinetics, thermodynamics and adsorption equilibrium of the corrosion of steel in the acid and acid-containing 3-chloromethylcoumarins media were investigated. The results showed that the inhibitive actions of the compounds occurred as a result of adsorption of 3-chloromethylcoumarins molecules on mild steel surface. 3-Chloromethyl-8-ethoxycoumarin 4a showed higher inhibition efficiencies than 6-chloro-3-chloromethylcoumarin 4b, especially at low concentrations and temperatures. Physical adsorption was predicted based on decreasing surface coverage of the inhibitor molecules with increase in temperature. The studied 3-chloromethylcoumarins behaved as mixed-type corrosion inhibitors for mild steel in 2 M HCl. The higher electron-donating ability and lower energy gap of 4a compared to 4b, as derived from computational studies suggest that 4a has higher potentials to inhibit steel corrosion in HCl than 4b. Similar trend was reflected in the Monte Carlo simulations adsorption energies.

Automated summary

Two 3-chloromethylcoumarins synthesized via the Baylis-Hillman reaction were found to effectively inhibit the corrosion of mild steel in concentrated hydrochloric acid. The inhibition efficiency increased with increasing concentration of the 3-chloromethylcoumarins. Among the two compounds, 3-chloromethyl-8-ethoxycoumarin exhibited higher inhibition efficiency than 6-chloro-3-chloromethylcoumarin, especially at low concentrations and temperatures.