Synthesis, single crystal structural studies and anticorrosion screening of 2,21 disulfane-diyl-dianiline (DDD) and its iron complex for mild steel in hydrochloric acid

2,21-disulfanediyldianiline (DDD) was synthesized and characterized by analytical methods including single crystal XRD studies. Iron complex of DDD was also synthesized and characterized by standard procedure. Both of them have been screened as corrosion inhibitors for mild steel in hydrochloric acid. Different concentrations of the inhibitors in 0.5 and 1 M HCl at different temperatures (303 K, 313 K) have been studied using weight loss method, potentiodynamic polarization, electrochemical impedance spectroscopic techniques and computational methods. The adsorption equilibrium constant (Kads) and standard free energy of adsorption (ΔGads0) were also calculated. Results indicate that the compounds are efficient, mixed type inhibitors which adsorb on metal surface obeying Langmuir adsorption isotherm at 303 K and Temkin isotherm at 313 K respectively. Basic quantum chemical parameters like EHOMO, ELUMO, energy gap between HOMO and LUMO (ΔE) etc were calculated by DFT method using B3LYP/6-311+G(d,p) under Gaussian 09 and are found correlating with the experimental findings. Results indicated that corrosion resistance of mild steel in the presence of DDD is greater than its iron complex [FeC12H12N2S2(OC2H5)2].