KINETIC AND MECHANISTIC STUDIES OF THE REACTION OF A RANGE OF BASES AND METAL-HYDROXO COMPLEXES WITH THE PHOSPHONATE ESTER 2,4-DINITROPHENYL ETHYL METHYLPHOSPHONATE IN AQUEOUS-SOLUTION

The base hydrolysis and spontaneous water hydrolysis of the phosphonat e ester 2,4-dinitrophenyl ethyl methylphosphonate (DNPEMP) has been st udied in detail and the activation parameters for these processes dete rmined. The catalytic effect of a series of 19 oxygen and nitrogen bas es and metal hydroxo complexes has been studied. The Bronsted plot of pK versus log k(N) has a slope (beta) of 0.47, which is fairly typical for phosphate and phosphonate esters. alpha-Effect nucleophiles such as 2-iodosobenzoate, hypochlorite and the hydroperoxide ion. (HO2-) ex hibit enhanced reactivity, as does fluoride ion and the bifunctional m etal complex [Cu(tmen) (OH2)(OH)](+) (tmen = N,N,N',N',-tetramethyleth ylenediamine). Reactions involving these species appear to take place by a nucleophilic pathway, while the other oxygen and nitrogen bases a ct as general base catalysts. The solvent deuterium isotope effect for Et3N catalysis, k(H2O)/k(D2O) = 1.3, is consistent with general base catalysis. The mechanisms of these reactions are discussed in detail.