Solvolyses of Phosphoric Acid Derivatives

Solvolyses of Phosphoric Acid Derivatives.— There has been relatively little work reported on the solvolysis of simple phosphate esters. Instead, attention has been given to situations where intramolecular participation or other special features are likely to be important. 

Using a phosphodiesterase, it has been possible to measure directly the enthalpies of hydrolysis of ethylene phosphate, trimethylene phosphate, and diethyl phosphate (all as their sodium salts). As expected, that of the first was found to be appreciably more negative than the latter two. 

From a detailed comparison of the rates of aqueous hydrolysis of a very wide range of phosphate monoester monoanions it was found that there exists 

Kolodyazhnyi, G. A. Kalyagin, and Y. G. Gololobov, Zhur. obshchei Khim., 1973, 

Catalysis of the hydrolysis of O-phosphoryl threonine in the presence of pyridoxal is observed with Cu and but not with other transition-metal ions there is further rate enhancement when an organic base is added.It seems clear that these two metal ions form a 1 1 complex (21) with the 

Solvolyses of Phosphoric Acid Derivatives.—The solvolysis of organic phosphates has been reviewed. A significant 0 isotope effect was observed in the solvolysis of the dianion of 2,4-dinitrophenyl phosphate, and since no such isotope effect is observed in the alkaline solvolysis of the dibenzyl ester this has been adduced as evidence for a monomeric metaphosphate elimination in the former case. The nucleophilic attack of hydroxide ion on bis-(2,4-dinitrophenyl) phosphate is inhibited by micelles of non-anionic detergents and this is attributed to binding of the substrate. Hydrolysis of 3,4-dimethoxyphenyl phosphate proceeds by way of the monoanion, the neutral molecule, and the conjugate acid, and is thus in accord with earlier results on other methoxyphenyl phosphates.  

Rates of solvolysis of phenyl and methyl polyphosphates in water and alcohols have been measured and the reasons for the enhanced reactivity of the former relative to the phenyl phosphorochloridate discussed. From studies on a series of substituted aryl sulphatophosphates (19) it was 

Several studies on intramolecular catalysis of the solvolysis of phosphate esters have been reported. The larger hydrolysis rate of the zwitterion of 8-hydroxyquinoline phosphate (20) compared with that of pyridyl 3-phosphate (21) was attributed, on the basis of the kinetic isotope effect, to intramolecular general acid catalysis. A similar general acid catalysis by the hydroxy-group seems to operate in the (3-hydroxy-2-pyridyl)methyl phosphate dianion (22), which hydrolyses faster than either the monoanion or the neutral molecule. From a study of 4- and 5-substituted derivatives of salicyl phosphate (23) it is suggested that the negligible solvent isotope effect is inconsistent with preliminary proton transfer, and that here also intramolecular general acid catalysis by the 

Tagaki, T. Eiki, and I. Tana, Bull. Chem. Soc. Japan, 1971, 44, 1139. 

The role of zinc ions as catalysts for phosphoryl transfer between phosphorimidazole and pyridine-2-carboxaldoxime is attributed to a lowering of the electrostatic barrier for attack of the anion of (26) on phosphorus it may also act as a template for the proper alignment of the entering and leaving groups. With amine nucleophiles it was found that zinc, in common with several bivalent cations, inhibited attack on phosphorimidazole. 

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