Acid dependence and ion pairing in the anation reactions yielding iron(III) monosulfate

Abstract

Stopped-flow studies of the kinetics of the a nation reaction yielding iron(III) monosulfate indicate a significant dependence of rate constant on acidity and also a dependence on iron concentrations. This is consistent with association constants for outer ion pair formation between the reactants which have about three times the Fuoss values.

Peculiar kinetics of the complex formation in the iron(III)–sulfate system

“…The nonzero intercept and the pH‐dependent lines suggest two equilibrium processes: If the correct approximations of [SO] ≫ T and [Fe(OH) 2+ ] ≫ [Fe 3+ ] are applied, then the equation could be derived from these two reactions. The rate constants calculated from this relation, however, are meaningless; log β 101 = 1.4 and 0.9 can be derived from the calculated k 10 / k −10 and from the k 11 / k −11 ratios, respectively, instead of about log β 101 = 2.3 determined by many authors 9–12 and in our present work. More interestingly, the parameter estimation with steps (R10) and (R11) gives an average deviation of 0.0036 AU, which is only slightly worse than the best fit with our suggested model (0.0028 AU).…”

“…Cavasino 11 found two values: k 3 f = 3.0 × 10 3 M −1 s −1 and k 4 f = 1.1 × 10 5 M −1 s −1 . Baker and Smith 12 determined the k 3 f = 5.6 × 10 3 M −1 s −1 and k 4 f = 1.1 × 10 5 M −1 s −1 . Taking the slightly different experimental conditions into account, the k 3 f and k 4 f values are in good agreement.…”

“…The kinetic of the complexation was also studied intensively by the pressure surge relaxation method 10, continuous‐flow method with spectrometry 4, temperature jump investigation 11, stopped‐flow method 12, and combined stopped‐flow temperature jump techniques 5. Most of these works were carried out in large iron(III) excess to avoid the formation of Fe(SO 4 ) 2 (OH) ( x +1)− x ( x = −1, …, 2) species, so a comprehensive investigation of the kinetics is still missing.…”

Sulfur Allocation and Vanadium−Sulfate Interactions in Whole Blood Cells from the Tunicate Ascidia ceratodes, Investigated Using X-ray Absorption Spectroscopy

“…The solvent cage of water molecules and the attendant hydrogen-bonding network surrounding sulfate ion is likewise dynamic on the picosecond time scale. 82 Thus a more approximately tetrahedral symmetry may be restored to bisulfate in acidic aqueous solution by virtue of a position-averaged hydrogen-bonding and solvent cage. In acidic aqueous solution these dynamics may lift much of the unique length found in the solid state -O 3 S-OH bond by averaging the -O 3 SO-H interactions over all four sulfate oxygens.…”

“…, the end-over-end rotation) of nitrate and carbonate, for example, are in the range of a few picoseconds in water solution. , From X-ray scattering experiments, sulfate is known to be hydrogen bonded to about eight water molecules 79-81 in both neutral and acidic aqueous solution. The solvent cage of water molecules and the attendant hydrogen-bonding network surrounding sulfate ion is likewise dynamic on the picosecond time scale . Thus a more approximately tetrahedral symmetry may be restored to bisulfate in acidic aqueous solution by virtue of a position-averaged hydrogen-bonding and solvent cage.…”