Polarographic studies on the formation constants of complexes of indium with aspirin

Abstract

A polarographic study of indium–aspirin complexes has been carried out, with the ionic strength kept constant (µ= 1) by adding requisite amounts of sodium perchlorate. The reduction of indium in various concentrations (0–0·36M) is diffusion-controlled but the process is not reversible. The kinetic parameters α and K_s have been calculated by Gelling's method. The value of K_s was about 2 ± 0·5 × 10^–3 cm./sec., showing that the reduction is a quasi-reversible process. Since the reduction is quasi-reversible, Gelling's method is used to determine the reversible half-wave potential (E_1/2^r). Thus, knowing E_1/2^r, the stability constants of the various complexes in the indium–aspirin anion system have been evaluated by DeFord and Hume's treatment. The values for various complex species present in the solution at 30°, In(Asp)²⁺, In(Asp)₂⁺, In(Asp)₃, In(Asp)₄^–, and In(Aps)₅^2–, are 3 × 10⁴, 5 × 10⁴, 300 × 10⁴, 650 × 10⁴, and 13,500 × 10⁴, respectively. Since the reduction is diffusion-controlled, indium can be determined polarographically in acetylsalicylate solution.