Solution Equilibria and Kinetic Studies of the Copper(II) Promoted Hydrolysis of 8-Quinolyl Phosphate. A Large Rate Enhancement for the Hydrolysis of a Phosphate Monoester Dianion

The dissociation constants of 8-quinolyl phosphate (H3L+) at 10°C and I = 0.1 mol dm-3 (NaC104) have been determined (pKa values < 1.5, 4.12 and 6.46). At a 1:1 ligand to metal ratio, the interaction of copper(II) with 8-quinolyl phosphate can be described by the equilibria given below. [image omitted]The pKa values for the ionisation processes [CuHL]+ ⇄ [CuL] + H+ and [CuL(OH2)] ⇄ [CuL(OH)]- + H+ are 3.75 and 5.71, respectively. Kinetic studies establish that in the copper(II)-promoted hydrolysis the complex [CuL] is the active species with kCuL = 2.7 × 10-3 s_1 at 30°C and I = 0.1 moldm-3. Copper(II) ions promote the hydrolysis of the normally unreactive dianion L2- of the phosphate monoester by a factor of ca 106.