Nucleophile isotope effects phosphate hydrolysis

A review (91 references) on electrophilic and nucleophilic reactions of trivalent phosphorus acid derivatives, reactions of two-coordinate phosphorus compounds, and miscellaneous reactions has appeared.228 Earlier in this review we looked at the heavy-atom isotope effects on reactions of Co(III)-bound /vnitrophenyl phosphate,186 the uranyl ion hydrolysis of /vnitrophcnyl phosphodiesters (218)-(220),190 and the Th(IV) hydrolysis of these.191... 

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. ... 

Brensted p for bases whose conjugate acids have > 7 is 0.95 and represents nucleophilic catalysed hydrolysis (Proctor and Page, 1979). Evidence for an intermediate ester formed during the reaction has been obtained with alkoxide ions and phosphate dianion (Proctor and Page, 1979 Bundgaard and Hansen, 1981). Weakly basic catalysts probably act as general base catalysts. The reaction with acetate exhibits a solvent isotope effect of 2.1, as expected for general base catalysis but not for a... 

Recent theoretical studies employing quantum mechanics/molecular mechanics (QM/MM) potentials have confirmed that alkaline hydrolysis of 0,0,-diethyl p-nitrophenyl phosphate (paraoxon) takes place through an associative mechanism wherein the bond order of the leaving group is larger than the bond order of the phosphoms atom to the nucleophile. Moreover, the theoretical estimations of the free energy barriers and kinetic isotope effects agreed very well with the experimental values, more so than those by previous theoretical estimations. ... 

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