A clarification of mechanism of inhibition requires full knowl- edge of the interaction between the protective compound and the metal surface. Many of the organic corrosion inhibitors have at least one polar unit with atoms of nitrogen, sulphur, oxygen and phosphorous. It has been reported that the inhibi- tion efficiency decreases in the order to O < N < S < P. Also, iron is well known for its co-ordination affinity to heteroatom bearing ligands