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 corrosio n behaviour of iron in 1M HCl has been investigated by gravimetric and electrochemical polarization methods. Both techniques gave the same o rder of inhibition efficiencies. Polarization data indicate that all o f the compounds tested act as mixed-type inhibitors, without changing the mechanism of the cathodic hydrogen evolution reaction. The inhibit ion efficiency of the compounds tested has been found to decrease as f ollows: 7-methyl 4-phenyl 1,5-benzodiazepin 2-one > 4-phenyl 1,5-benzo diazepin 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 h ave been explained on the basis of nature of substituents and stabilit y 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 temperatur e increases. Apparent activation energies were determined.