HYDROLYSE BASIQUE COMPAREE D'ESTERS ALLOPHANIQUES ET PHOSPHORIQUES EN MILIEU MIXTE ACETONITRILE/EAU FAIBLEMENT AQUEUX; MISE EN EVIDENCE D'UNE ENTITE CATALIQUE, INTERMEDIARE DE LA REACTION ENTRE BASE ET SOLVANT

Article abstract of DOI:10.1016/S0040-4020(01)87351-8

Kinetic study of base catalysed hydrolysis in acetonitrile-water mixtures of allophanic esters (models of carboxybiotine) and phosphoric esters shows in the range of low water content (less than 1 molar) an enhancement in rate (10³) with a maximum at 0.1-0.3 molar in water.This rate enhancement is ascribed to ground state desolvation and the maximum is interpreted by a change in the rate determining step: leaving group departure in the tetrahedral intermediate is indeed the slow step for the reactions in acetonitrile/water mixture less than 0.1 molar in water.For charged phosphoric esters the rate enhancement from an aqueous medium (pH=10) to organic is larger since as high as 10⁶.On the other hand, in such a medium, an additional catalytic effect is observed; it is shown that it is due to the formation of a reactive species which results from reaction of the base on acetamide when accumulated in the medium from base catalysed hydrolysis of the solvent.