Efficient inhibition of mild steel corrosion in acidic medium by novel pyrimidine derivatives: Inhibitive effect evaluation and interface adsorption mechanism

In the pickling, oil well acidification, and other industrial processes, mild steel would suffer from severe corrosion in the acidic environment. In this work, two novel pyrimidine derivatives, 2-Benzylthio-6-methylpyrimidin-4(3H)-one (BMPO) and 4-Benzyloxy-2-benzylthio-6-methylpyrimidine (BBMP), were synthesized through nucleophilic substitution reaction, and used as eco-friendly corrosion inhibitors for mild steel in HCl medium. The corrosion inhibition properties of BMPO and BBMP were investigated using electrochemical tests, surface analyses, and theoretical calculations. The experimental results indicate that BMPO and BBMP have superior inhibition effect, with high inhibition efficiency (99.28% and 99.69% at 0.6 mM) and good corrosion inhibition stability. Theoretical calculations reveal that the interface adsorption of BMPO and BBMP is achieved by the bonding of N, S, O atoms and the benzene ring to steel surface. The protonation of BMPO and BBMP molecules could further promote their adsorption. Compared to BMPO, the modification with more benzyl groups lowers the polarity and increases the hydrophobicity of BBMP. Then BBMP molecules could adsorb on steel surface to create a hydrophobic film with a large coverage, which accounts for the better corrosion inhibition effect of BBMP.