LAUSR

Abstract The structural and electronic characteristics of some phosphoramide derivatives with the general formula 4-X-C6H4-C(O)-NH-P(O)(OCH3)2 where X = H, F, Cl, Br, CH3, CF3, CCl3 and CBr3 as well as their H-bonded structures with HCl were investigated for application as corrosion inhibitors using density functional theory (DFT) computations accomplished at both B3LYP-D3 and B3PW91-D3 levels of theory using 6-31+G(d,p) basis set in water. A comparison of the ΔEbinding values using the two B3LYP-D3 and B3PW91-D3 methods established that the B3LYP-D3 provided more negative binding energies. The H…N bond distances in the H-bonded structures 9–16 were varied in the range of 2.179–2.272 A and 2.109–2.255 A using the B3LYP-D3 and B3PW91-D3 methods, respectively, indicating the phosphoramides 1–8 formed strong hydrogen bonds with the HCl molecule which was favorable for the inhibition of the corrosion using these compounds. The compounds 8 and 16 (both containing CBr3 substituent) illustrated the lowest band gap and hardness whereas the greatest electrophilicity index among structures 1–8 and 9–16, respectively, approving they had the most reactivity to attach the metal surface and afford the most efficient corrosion inhibition. Consequently, compounds 8 and 16 were proposed as the most appropriate corrosion inhibitors. The molecular dynamics (MD) simulations were performed on PA-Fe and PA-Fe-W systems (where PA = compound 16, Fe = iron and W=H2O) at four temperatures (298.15, 308.15, 318.15 and 328.15 K) and it was found that the strongest PA-Fe interactions were occurred at the lowest temperature confirming the most effective anticorrosion capacity was happened at 298.15 K. For an efficient anticorrosion application, the 3PA-Fe-W was selected as the most suitable anticorrosion system because it exhibited desirable strong interactions between the Fe atoms and PA species as well as moderate diffusion rate of the PA molecules and good anticorrosion loading.