Polarographic Performance of Some Azo Derivatives Derived from 2-amino-4-hydroxy Pyridine and Its Inhibitory Effect on C-steel Corrosion in Hydrochloric acid

Abstract

The polarographic performance of five azo compounds derived from 2-amino-4-hydroxypyridine was studied in BR buffer series of pH 2-12. The polarograms of all azo compounds in strong acidic solutions gave a single irreversible diffusion-controlled 4-electron wave representing the splitting of the N=N group to the amine stage but in alkaline solutions 2-electron irreversible wave is obtained corresponding to the reduction of the azo center to the hydrazo stage. For NO2 substituted derivative, approximately two equal waves were observed in the acidic solutions, , but in the alkali, the rise of the second wave is approximately twice that of the first wave. The effect of substituents on electrode reaction was investigated and the kinetic parameters were calculated. The mechanistic pathway was proposed and interpreted. The dissociation constants of the tested azo compounds were examined by potentiometric methods and the M-L formation constants of their complexes with some transition metal ions were computed. Application of the investigated azo compounds as inhibitors of dissolution of carbon steel in in 1MHCl solutions was inspected using potentiodynamic polarization technique. The results indicated that these compounds inhibit C-steel corrosion in HCl solutions and the inhibition efficiency reached 81% in presence of 1x10-3 M of the inhibitors. The efficiency of the inhibitors follows the following sequence: III> II > I > IV > V This arrangement is consistent with the sequence of the E1/2 and the pka values of these azo compounds.