Corrosion inhibition of carbon steel in sulfuric acid by bicyclic isoxazolidines

The cycloaddition of cyclic nitrone1-pyrroline-1-oxide with 1-dodecene and 1-hexadecene afford a bicydic (isoxazolidines). These isoxazolidines were tested for corrosion inhibition of carbon steel in 1N H₂SO₄ in the 30-60°C temperature range by gravimetric and electrochemical methods. The compound isoxazolidines exhibited excellent inhibition efficiency in the acidic corrosion environment. The presence of heteroatoms such as N and O induce greater adsorption of the inhibitor molecules onto the surface of carbon steel and the long hydrocarbon chains ensure coverage of the metal surface. The values of activation energy and free energy of adsorption indicated the physical nature of the adsorption on the surface of the carbon steel. Thermodynamic parameters were determined for the adsorption process (ΔG _ads⁰, ΔH_ads⁰, ΔS _ads⁰), and kinetic parameters for the metal dissolution (or hydrogen evolution) reaction in the presence of the isoxazolidines. The adsorption of inhibitors on the metal surface was found to obey the Langmuir adsorption isotherm. The isoxazolidines were found to be mixed-type inhibitors. The isoxazolidine which had a tetradecyl hydrophobe was found to be a better inhibitor than was the decyl analogue.