Experimental and theoretical approach to the corrosion inhibition of mild steel in acid medium by a newly synthesized pyrazole carbothioamide heterocycle

Abstract

Heterocyclic compound such as 3,5-disubstitued pyrazole carbothioamide was synthesized by cyclocondensation reaction between chalcone derivative and thiosemicarbazide as nucleophile substrate in ethanolic sodium hydroxide solution. The structure of synthesized compound namely, (E)-5-(4- (dimethylamino)phenyl)-3-(4-(dimethylamino)styryl)-2,3-dihydro-1H-pyrazole-1-carbothioamide (DDP) was confirmed by infrared FT-IR, 1H NMR and 13C NMR spectra. The inhibitory action was investigated using the gravimetric and electrochemical methods. The results show the strong adsorption of target molecule on the surface of mild steel. The adsorption of (DDP) molecules on the steel surface follows the Langmuir adsorption isotherm and the calculated (ΔG°ads) values of the synthesized inhibitor suggested that the adsorption of this compound involves two types of interaction, chemisorption and physisorption. The polarization curves showed that the (DDP) act as mixed type inhibitor. The SEM analysis reveals that the corrosion inhibition is due to the formation of a protective film on the metal surface. DFT calculations were performed to illustrate the relationship between the molecular structure of (DDP) and their inhibitory properties.