A comparative study of pyridine and pyrimidine derivatives based formamidine for copper corrosion inhibition in nitric acid: Experimental and computational exploration

This paper investigates the performances of two synthesized formamidine derivatives, namely: N,N-dimethyl-N'(pyridin-2-yl) formamidine (A) and N,N-dimethyl-N'-(pyrimidin-2-yl) formamidine (B) to inhibit the corrosion of copper in 1.0 M HNO3 solution at fixed temperatures. Different tools, viz. electrochemical, chemical, and microscopic techniques were utilized in this paper. The evaluated inhibition efficiencies (% IEs) of the tested formamidine derivatives increased with their concentrations. Results indicated that the tested compounds acted as mixed-kind inhibitors with anodic seniority. The acquired great% IEs of such compounds were mainly attributed to the strong adsorption of the compounds' molecules on the copper surface. The mode of adsorption was agreed with Langmuir isotherm. The results acquired from all utilized tools agreed with each other which disclosed that the %IE values of inhibitor A were somewhat lesser than those of inhibitor B under analogous circumstances. The influence of temperature was investigated and revealed that the %IE values decreased with rising temperature. Also, thermodynamic parameters were evaluated and discussed herein. The kinetics and mechanisms of the copper corrosion and its inhibition by the tested compounds were investigated. Molecular modeling provided strong evidence for the preference of the molecules A and B for their adsorption on the copper surface, while DFT investigations underlined the importance of N heteroatom as a relevant local site for molecular adsorption.