Catalytic effect of a dinuclear image complex in the hydrolysis of bis(2,4-dinitrophenyl) phosphate

The kinetics of the hydrolysis of bis(2,4-dinitrophenyl) phosphate (BDNPP) has been studied in the presence of a dinuclear Fe(III) complex that acts as a catalyst in the hydrolytic reaction. One equivalent of the 2,4-dinitrophenolate ion (DNP) and one equivalent of 2,4-dinitrophenylphosphate (DNPP) were liberated for each equivalent of BDNPP, and the reaction showed first-order kinetics in relation to both BDNPP and the metal ion complex. Potentiometric titrations of the dinuclear complex are consistent with two deprotonation constants of the metal coordinated water molecules, with pKa values of 4.88 and 6.33 and the reactions show a pH dependence which is consistent with a Fe2(OH)(OH2) form as the reactive species during the hydrolytic reaction. The kinetics of the reaction show an inverse solvent isotope effect of 0.44, which is consistent with a pre-equilibrium proton transfer before the hydrolysis reaction of the BDNPP.