Inhibition of the acid corrosion of iron with new pyrazole derivatives

Some new synthetized pyrazole organic-type compounds have been tested as inhibitors for the corrosion of iron in 1M HCl by weight-loss and electrochemical polarization methods. Both techniques gave the same order of inhibition. The compound l,3-bis(3' chloromethyl-5'-methyl-1'-pyrazolyl)propane (Inh.9) was the better inhibitor and its inhibition efficiency increased with increase of concentration and reaching 95% at 4.10-4M. Polarization measurements have shown that the pyrazole substances studied inhibited both the anodic reaction of iron dissolution and the cathodic reaction of hydrogen evolution. These products act without changing the mechanism of the cathodic hydrogen evolution reaction. The corrosion inhibition of pyrazoles studied is regarded by a simple blocked fraction of the electrode surface related to adsorption of inhibitor species according to Langmuir isotherm model on the iron surface. The introduction in the pyrazole ring of a substituent such as -OH, -CO2H, -CO2CH3, and -Cl in the position 3, enhances the inhibiting effect of the pyrazole compounds. The effect of temperature on the corrosion behaviour of iron indicated that inhibition efficiencies of (Inh.9) increased with increasing temperature in the range of 25 - 50 °C. The apparent activation energy for iron corrosion process are modified by addition of (Inh.9)