Mercaptopyrimidines as inhibitors of carbon dioxide corrosion of iron

The inhibition activity of 2-mercaptopyrimidine (I), 2-mercipto-4-methylpyrimidine hydrochloride (II), 2-mercapto-4,6-dimethylpyrimidine (III) and its hydrochloride (IV) upon carbon dioxide corrosion of iron has been studied in a wide range of concentrations at 40-90 degrees C using electrochemical and mass-spectrometry methods. High activity has been found for all compounds (P = 80-99%) at very low concentrations (0.02-5 mg/l). Adsorption of inhibitor by metal not only blocks its surface but changes the reaction mechanism as well. Charge transfer is the limiting stage of both cathode and anode reactions. The title compounds can be considered as inhibitors of what is a mixed type with prevailing effect on the anode reaction. (C) 2007 Elsevier Ltd. All rights reserved.