Electrochemical, molecular dynamics, density functional theory, and corrosion inhibition studies of some chromeno-oxadithiin and chromeno disulfide derivatives for mild steel in 3.5% NaCl

Eight derivatives of chromeno-oxadithiin and chromeno disulfide were greenly synthesized during the reactions of different derivatives of 3-Chloro-3-chlorosulfenylchromanones (2a–d) with potassium iodide. The chemical structure of the newly prepared compounds was confirmed by using different spectroscopic methods (IR, ¹H &¹³C NMR, and MS). The redox properties of the prepared compounds were investigated via cyclic voltammetry where most of the compounds exhibited one quasi-reversible redox couple beside one irreversible reduction peak. The charge transfer process was found to be under diffusion control. Some of these compounds were studied as inhibitors for mild steel corrosion in 0.6 M NaCl by using electrochemical techniques. Both the electrochemical methods and the computational simulations proved that adding 1 × 10^–3 M of Trispiro[cyclohexane-1,2′-chroman-3′,2″-2H-chromeno[3,4-e][1,3,4]oxadithiin-5″,1″′-cyclohexan]-4′-one (3b) to 0.6 M NaCl inhibited mild steel corrosion by an efficiency of 98.8%. The morphology of mild steel surface after 7 days of immersion in this solution studied by scanning electron microscope (SEM) and showed a homogenous surface. The theoretical studies showed that 1,2-Bis (3-chlorospirochroman-2,1′-cyclohexyl-4-one) disulfane (4b) is the most stable one with an electronic energy of − 3101 au. The effects of the methyl and cyclohexane groups, as well as the effects of heterolysis on the corrosion efficiency, were studied.