Abstract
The inhibitory activity of new synthesized and characterised bipyrazol derivatives: methyl 2- (bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]amino)-4-methylpentanoate (BT39), methyl 2- (bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]amino)-3-meyhylbutanoate (BT40) and methyl 2-(bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]amino)propanoate (BT45) towards corrosion of C38 steel in molar HCl medium by weight loss and electrochemical technique shows that these compounds were very effective inhibitors, their protection percentage exceeded 88% for (BT40) at low concentrations as much as 10-2M. A cathodic type of inhibition from polarization and a charge transfer mechanism from impedance study in absence and presence of these compounds were found. Langmuir adsorption isotherm is obtained. Relation between inhibition efficiency and molecular structure of (BT36), (BT43) and (BT45) is discussed by considering quantum chemical parameters. The study is completed by the density functional approach B3LYP/6-31G calculations. The quantum chemical parameters calculated show a good correlation to the inhibition efficiency. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), the separation energy (ΔE) and the dipole moment (μ), explain well experimental data.