Phosphorus-32 tracer
experiments have demonstrated that the phosphato
ligand in [Co en2PO4]0
[Co(NH3)4PO4]O, [CO(NH3)4OH2HPO4]+,
and [Co en2OH2.HPO4]+
undergoes slow substitution in acid and alkaline media at 40-60� and that a
reversible hydrolysis equilibrium is established from pH 3 to 11. Outside this
pH range, acid and base hydrolysis of all these phosphato
complexes to diaquo or dihydroxo
complexes is complete. The infrared spectra of [Co en2PO4]0
and [Co(NH3)4PO4]0 are consistent
with a bidentate phosphato structure and with a
monodentate phosphato ligand in CO(NH3)5PO4
and probably [Co(NH3)4OH2HPO4]+I-.
The bidentate and monodentate complexes may be rapidly and reversibly interconverted but significant concentrations of the
bidentate complexes only persist in the range pH 5.5-7.5.
P.m.r, studies have established the predominantly cis configuration of the aquophosphato complexes. These complexes exhibit four
acidity constants, one due to the aquo ligand, and
three due to the monodentate phosphato ligand. The
bidentate [Co en2PO4]0 exhibits a single
acidity constant above pH 2. The aquophosphato
complexes undergo both acid and base hydrolysis entirely by Co-O bond rupture.
Acid hydrolysis of [Co en2PO4]0
also proceeds entirely by Co-O bond rupture but at pH 6.8 and in 0.25M NaOH hydrolysis proceeds by 60-65% Co-O bond rupture and by
30-35% P-O bond rupture.
Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners
