Inhibitive effect of some 1,5-benzodiazepin 2-one derivatives on the corrosion of iron in 1M HCl

The effect of some 1,5-benzodiazepin 2-one derivatives on the corrosion behaviour of iron in 1M HCl has been investigated by gravimetric and electrochemical polarization methods. Both techniques gave the same order of inhibition efficiencies. Polarization data indicate that all of the compounds tested act as mixed-type inhibitors, without changing the mechanism of the cathodic hydrogen evolution reaction. The inhibition efficiency of the compounds tested has been found to decrease as follows: 7-methyl 4-phenyl 1,5-benzodiazepin 2-one > 4-phenyl 1,5-benzodiazepin 2-one > 3,7-dimethyl 1,5-benzodiazepin 2-one. These compounds are adsorbed on the iron surface according to a Frumkin isotherm. The inhibition efficiency and the mode of adsorption of these compounds have been explained on the basis of nature of substituents and stability of conformers in the seven-membered ring of 1,5-benzodiazepin 2-one. The effect of temperature in the range 18-50 degrees C indicates that the protection efficiency decreases very slightly when the temperature increases. Apparent activation energies were determined.