Synthesis and anticorrosive effects of epoxy-allylpulegols on steel in molar hydrochloric acid

Allylpulegols (2-4) and epoxy-allylpulegols (5-7) are synthesised from R-(+)pulegone, the major compound of Mentha pulegium oil. The compounds (2-7) are tested as corrosion inhibitors of steel in 1M HCl using weight loss measurements. The addition of allylpulegols decreases weakly the corrosion rate, but in the presence of epoxy-allylpulegols the corrosiveness of acid is reduced. Epoxy-allylpulegols tested adsorb on the steel surface according to Langmuir isotherm. The negative values of free enthalpy indicate that these compounds act spontaneously on the metal surface. The higher inhibition efficiency (79 %) is obtained for 5 at 0.8 g/L at one hour of immersion. The corrosion rate decreases with rise of temperature in the presence and absence of inhibitors. The corresponding efficiency decreases with the temperature. The corresponding activation energies are determined.