Hydrolysis of phosphate monoester monoanions

Converging lines of evidence have led to a general acceptance of the monomeric metaphosphate mechanism for the hydrolysis of phosphate monoester monoanions. The pH rate profile for aryl and alkyl phosphate monoester hydrolyses commonly exhibits a rate maximum near pH 4. where the concentration of the monoanion is at a maximum. The proposed mechanism is based on these principal points of evidence (a) a general observation of P-O bond cleavage (b) the entropies of activation for a series of monoester monoanions are all close to zero, which is consistent with a unimolecular rather than a bi-molecular solvolysis where entropies of activation are usually more negative by 20 eu7 (c) the molar product composition (methyl phosphate inorganic phosphate) arising from the solvolysis of the monoester monoanion in a mixed methanol-water solvent usually approximates the molar ratio of methanol ... 

Taken together, the data indicate direct phosphoryl transfer to a metal-bound water molecule without a phosphoenzyme intermediate. A Bronsted analysis found a value of (j of -0.3 for V/K,137 similar to the value for the uncatalyzed hydrolysis of phosphate monoester monoanions, which could be indicative of charge neutralization on the leaving group in the transition state via protonation. 

The spontaneous hydrolysis of 2-pyridyl phosphate (PP) is a good model for the special mechanism (Scheme 15) for the hydrolysis of phosphate monoester monoanions (M ), which are believed to react via an initial proton transfer equilibrium to form the highly reactive species the proton transfer occurring from a hydroxyl group attached... 

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