Mutual determination of iron (III) and tropolone, and the formation constant of their complex

Abstract

Iron (III) reacts with tropolone to give green and brownish-red complexes. The green complex is formed in the presence of an excess of iron. When a large excess of tropolone is allowed to react, the brownish-red one is formed. Both complexes can be utilized for the determination of tropolone and iron respectively.
The green complex shows absorption maxima at 435 and 582 mμ. It is stable over an acidity range from 0.05 to 1 N. The brownish-red one is stable over a pH range from 1.3 to 8.5, and has peaks at 425, 550, and 595 mμ, the first of them being very sharp.
The composition of the green complex is 1:1, and that of the brownish-red one is considered to be 1:3. Formation constant of the green complex is evaluated to be 1.0×10¹¹.
Both complexes obey Beer's law, and with them iron and tropolone can be determined up to 3.9 γ/ml and 5.3×10^-5 M/l respectively.