The Co-ordinate Compounds of Iron with Some Hydroxycarboxylic Acids

Chelating action of salicylic, sulphosalicylic and 2-hydroxy-3-naphthoic acids towards iron was investigated quantitatively, and it was found that they combine with one-to-one molecular ratio with iron. In order for these substances to be used as colorimetric reagents for the determination of iron, it is desirable that the reagents as well as their complexes be well soluble in water, and that the equilibrium contants of the complexes be sufficiently large so that the proportionality between the absorbance caused by complex and the concentration of iron or chelating agent may hold in a wide range. In this respect sulphosalicylic acid may be regarded as most suitable, among the three hydroxycarboxylic acids studied, as a reagent for iron determination. In view of the fact that the introduction of sulphonyl group into salicylic acid caused the increase of K, it may be expected that a more suitable iron reagents would be obtained by further introduction of sulphonyl group in salicylic acid.