KINETIC STUDIES OF THE Fe(III)/DI-2-PYRIDYL KETONE BENZOYLHYDRAZONE COMPLEX REDUCTION BY SULFITE

摘要

The reactions of HSO_3~- with Fe(III) in the presence of di-2-pyridyl ketone benzoylhydrazone (DPKBH) have been investigated at 4.2-7.2 pH. The decomposition reaction of Fe(III)/DPKBH has been studied as a function of total sulfite concentration using spectrophotometric techniques. The kinetics are controlled by the equilibrium [Fe~(III)(DPKBH)(H_2O)]~(2+) <-> [Fe~(III)(DPKBH)(OH)]~+ + H~+, for which the hydrolysis constant was potentiometrically determined as 4.3 X 10~(-5)M, at (25.0+-0.1) deg C and 1.5 X 10~(-3)M ionic strength. Both of those species undergo sulfite substitution and the significantly more labile species is the aqua complex. The formation constants of [Fe~(III)(DPKBH)(SO_3)] are 1.2 X 10~4 at pH 4.2 and 1.9 X 10~2 M~(-1) at pH 6.2. The limiting rate constants, k, at high HSO_3~- concentrations are 3.5 x 10~(-2) s~(-1) and 1.4 X 10~(-2) s~(-1), respectively, at pH 4.2 and 6.2, I= 1.3 X 10~(-2) M. The results are discussed with reference to the available literature data.