Pyridine and some of its derivatives have been evaluated as inhibitors for the corrosion of API‐45 steel in NACE sour solution. Amongst the various methyl and halogen substituted pyridine compounds, 2,4,6‐trimethyl pyridine is found to afford maximum protection followed by 2,6‐dimethyl pyridine, >2,4‐dimethyl pyridine, >3‐bromopyridine, >2‐methyl pyridine, 4‐methyl pyridine, 3,5‐dimethyl pyridine, >2 and 3‐chloropyridine>pyridine. These results have been discussed in the light of availability of the electron densities with the nitrogen atom of the pyridine ring. The inhibitive periormance of all the inhibitors is found to deteriorate with increase in temperature from 30 to 60°C and with passage of time. The values of heat of absorption and free energy of absorption indicates that the inhibitors have a chemical type of absorption at the metal/electrolyte interface. Polarization diagrams and shift in open circuit potential in the presence of inhibitors indicate that these compounds retard the cathodic as well as anodic reaction process.
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