KINETICS AND MECHANISM OF FORMATION OF TRISGALLATOIRON(III) COMPLEX FROM MONOGALLATOTETRAAQUO IRON(III) AND BISGALLATO DIAQUO IRON(III) COMPLEXES

Kinetics of formation of 1:3 complexes from 1:1 and 1:2 complexes betw een Fe(III) and gallic acid (3,4,5-trihydroxybennzoic acid) has been s tudied. The rates were measured spectrophotometrically by monitoring t he rise of absorbance at 500 nm (the wave length of maximum absorbance for the tris complex). The reaction was driven by providing a sudden pH jump to 8.0 along with an excess of ligand. Under these conditions, 1:3 complex would completely predominate. The observed pseudo first o rder rate constant increased with increasing ligand concentration init ially, but leveled off at higher ligand concentration. The rate of for mation of 1:3 complex from 1:2 complex was slower than it's formation from 1:1 complex by about an order of magnitude. The mechanistic impli cations of these rate measurements are discussed.