Green synthesis of novel bis structure of (Carbamothioyl) oxalamide derivatives as corrosion inhibitors for copper in 3.5% NaCl; experimental and theoretical investigation

•Synthesis of soluble oxalamide derivatives and it application as anti-corrosion.•Correlation between quantum chemical calculation and the actual results.•Electrochemical apllication. Carbamothiol oxalamide derivatives as new compounds are synthesized and named N1, N2-bis (2- ((2-hydroxyethyl) amino) ethanethiol) oxalamide (bis 1), and N1, N2- bis(2-(bis(2-hydroxyethyl) amino) ethanethiol) oxalamide (bis 2). The noteworthy highlights of this method are eco-friendly, excellent yields, economic, catalyst-free, and solvent-free. Their chemical structures are clarified and validated using elemental analysis and spectroscopic techniques such as Fourier-transform infrared spectroscopy (IR), 1H, and 13C- nuclear magnetic resonance. Then, Weight loss (WL), electrochemical impedance spectroscopic (EIS), and potentiodynamic polarization (PDP) techniques are applied to examine the inhibition impact of these new derivatives on copper in 3.5% NaCl. The density functional theory is used to apply theoretical computations. The results of the experiments indicate that these substances are effective corrosion inhibitors, and their inhibition efficiencies rise with concentration. The bis 2 compound having four OH groups, give the highest efficiency compared to bis 1. There was good agreement on the outcomes of the various procedures. Utilizing 0.01 M of bis 2 to examine the surface under the SEM reveals the existence of an adsorbed layer. All organic molecules, including nitrogen, sulfur, and oxygen, block the metal surface as shown by the electronic parameters highest occupied and lowest unoccupied molecular orbital energy, and ΔEg. The results from theoretical calculations and those from experimental measurements correspond well.