Synthesis of Phthalazinones with Amino or Hydrazide Moiety as Corrosion Inhibitors of Low Carbon Steel in 0.5 M H2SO4

[4-(4-methoxy-3-methyl-5 amino phenyl)-1(2H)-phthalazinone (APP), and [4-(4-mehoxy-3-methyl phenyl)-1-oxo-1H-phthalaz-2-yl]acetic acid hydrazide (PPH) were synthesized as a novel independently corrosion inhibitor for carbon steel in 0.5 M H2SO4. Nuclear magnetic resonance, Fourier transform infrared and mass spectroscopy were used to validate the structure of the two anticorrosion compounds. The corrosion rate was studied by electrochemical methods (electrochemical impedance spectroscopy and potentiodynamic polarization) and gravimetric techniques, which clarify that the average corrosion inhibition efficiency of APP and PPH are 86 and 89 %, respectively. Impedance measurements showed that corrosion processes on the surface of LCS are controlled by a charge transfer mechanism. The PPH compound has a greater inhibitory effect on corrosion of low carbon steel. The quantum chemical calculations of APP and PPH were studied using AM1, PM3, and DFT/B3LYP/31G. Moreover, both APP and PPH acted as mixed type corrosion inhibitors. Adsorption of APP and PPH on low carbon steel (LCS) surface was physisorption and best fit to Langmuir isotherm.