Equilibrium constants K and
rate constants kf have been measured, at 25°C and ionic strength of
1.0, for the substitution of the labile water molecule in trans-[aquabis(ethylenediamine)sulphito-cobalt(III)]
ion by thiosulphate ion (K = 1.8×102 mol-1 1., kf
= 1.27×103 mol-1 1. s-1), thiocyanate ion (2.5×103,
2.75×102), nitrite ion (1.0×103, 2.06×102),
azide ion (2.9×102, 2.4×102) ferricyanide ion (-, 1.72×103),
hydrogen azide (< 1.2,1.4×10), ammonia (3.0, 6.7) and imidazole (2.6×102,
5.2). ��� The correlation of these rate constants
with charge on the incoming ligand, as well as a decrease in the apparent
second-order rate constants observed at high concentrations of the anionic
ligands, requires a rapid outer-sphere pre-equilibrium step followed by a rate-
determining dissociative interchange of the incoming ligand with the bound
water molecule. The activation energy of the thiocyanate substitution was found
to be 48 kJ mol-1. Aquation of cis-
[azidobis(ethylenediamine)-sulphitocobalt(III)] ion, in the range of hydrogen
ion concentration between 10-2 and 0.2 M, was found to give the
trans-aquasulphito complex with a first-order rate constant consistent with the
equation
��������������������������� k = 4.9×10-4[H+]+1.0×10-5
s-1
at 25°C and ionic strength
1.0.
Quantitative Analysis of Membrane Fouling Mechanisms Involved in Microfiltration of Humic Acid–Protein Mixtures at Different Solution Conditions
