2-Amino-5-nitro-4,6-diarylcyclohex-1-ene-1,3,3-tricarbonitriles as new and effective corrosion inhibitors for mild steel in 1 M HCl: Experimental and theoretical studies

The influence of three 2-amino-5-nitro-4,6-diarylcyclohex-2-ene-1,3,3-tricarbonitrile (ANDT) derivatives namely, 2-amino-5-nitro-4,6-diphenylcyclohex-1-ene-1,3,3-tricarbonitrile (ANDT-1), 2-amino-4,6-bis-(4-methoxy-phenyl)-5-nitro-cyclohex-2-ene-1,3,3-tricarbonitrile (ANDT-2) and 2-amino-4,6-bis-(3-hydroxy-4-methoxy-phenyl)-5-nitro-cyclohex-2-ene-1,3,3-tricarbonitrile (ANDT-3) on mild steel corrosion in 1 M HCl has been investigated using experimental and theoretical techniques. Among the all studied inhibitors the ANDT-3 showed maximum inhibition efficiency of 98.96% at 25 mg L^{- 1}. Adsorption of the ANDTs on mild steel surface follows the Langmuir adsorption isotherm. Polarization studies show that ANDTs act as mixed type inhibitors. SEM, EDX and AFM techniques were used to confirm the existence of adherent protective film of inhibitors on the mild steel surface. A quantum chemical calculation based on the DFT-theory was used to further corroborate the mechanism of inhibition.