Experimental and quantum chemical studies on the corrosion inhibition effect of synthesized pyrazole derivatives on mild steel in hydrochloric acid

Two heterocyclic compounds of the pyrazole family were synthesized by cyclocondensation reaction of chalcone derivatives with thiosemicarbazide. The structures of the synthesized pyrazoles, namely, 3,5-diphenyl-4,5-dihydro-1H-pyrazole-1-carbothioamide (DPC) and 5-(3-methoxyphenyl)-3-phenyl-4,5 dihydro-1H-pyrazole-1-carbothioamide (DPCM), were confirmed by infrared IR, H-1 NMR and C-13 NMR spectra. The surface activity of these compounds showed their tendency towards adsorption at the interfaces. The prepared compounds were evaluated as corrosion inhibitors for mild steel in 1 M HCl solution using the gravimetric method. These measurements indicate that the inhibition efficiency of the pyrazole derivatives increased with concentration inhibitor, whereas the latter decreased with temperature. The adsorption of the inhibitors on the mild steel surface obeyed the Langmuir adsorption isotherm, and the calculated Delta G(ads)(0) values of the synthesized inhibitors suggested that the adsorption of these compounds involves two types of interaction, chemisorption and physisorption. The results of the corrosion inhibition using two different heterocyclic compounds showed that the DPCM is more effective than the PCM in 1 MHCl medium.