Aliphatic Hydroxamic Acids as Chelating Agents; the Stability of Their Proton and Metal Complexes

Three kinds of aliphatic hydroxamic acids, i.e., acetohydroxamic acid, n-butyrohydrozamic acid, and sorbohydroxamic acid have been prepared as free acids and potassium salts. Their acid dissociation constants and the formation constants of complexes formed by some bivalent metal ions of the first transition element (Mn, Co, Ni, Cu, Zn) with these three chelating agents in aqueous solution have been determined by using potentiometric titration technique at ionic strength of 0.1M by sodium perchlorate and at a temperature of 25°C±0.1°. The stability of the transition metal ion complexes with these aliphatic hydroxamic acids is in the order Mn<Co<Ni<Cu>Zn, which is in agreement with the Irving and William's rule. The chelating forming properties and the comparison of quality as analytical reagent of these three hydroxamic acids were discussed in terms of the proton displacement constant. Sorbohydroxamic acid is superior in its reactivity and the other respects among the three reagents.