The Mechanism of the Hydrolysis of Condensed Phosphates. I. The Solvent Effect on the Hydrolysis of Pyro- and Tripolyphosphates

Abstract

Abstract The hydrolysis of pyro- and tripolyphosphates was run in formic acid–water, acetic acid–water, dioxane–water, and water solvents with an initial concentration of 0.025 mol/l. The hydrolysis of both the phosphates followed first-order kinetics with respect to the concentration of the phosphate under all the conditions studied. The rate of the hydrolysis of both the phosphates in the formic acid–water and acetic acid–water solvents is slower, and that in dioxane–water solvent is faster, than in water. From the results, it has been concluded that, in the formic acid–water and acetic acid–water solvents, the nucleophilicity of the water molecule may decrease on account of the hydrogen bond of the water molecule with these acids, while, in the dioxane–water solvent, since the scission of the hydrogen bond between water molecules may occur by the interaction of the dioxane and the water molecules, the nucleophilicity of the water molecule may increase. The activation energy of the hydrolysis of the phosphates was 19–28 kcal/mol and increased with an increase in the pH value of a solution. The hydrolysis of pyro- and tripolyphosphates has been concluded to be a SN2 reaction; the rate-determining step may be the nucleophilic attack of a water molecule on the phosphorus atom of the phosphates.