The Hydrolysis of p‐Nitrophenylacetate in Water

The hydrolysis of p ‐nitrophenylacetate has been studied between pH 6 and 9 in 3.3% (v/v) dioxane‐0.1 M phosphate or Tris buffer. The results indicate that the hydrolysis is acid‐catalyzed, base‐catalyzed and has a pH‐independent rate component. The observed rate constants for the hydrolysis were determined spectrophotometrically from the initial rate of appearance of p ‐nitrophenol (at 320 nm), p ‐nitrophenoxide (at 400 nm) and the initial rate of disappearance of p ‐nitrophenylacetate (at 270 nm). An equation has been derived permitting the calculation of first and second‐order rate constants from the initial slopes of product appearance or reactant disappearance. The semilog method of first‐order kinetic analyses could not be used since the hydrolysis of p ‐nitrophenylacetate did not go to completion. The apparent incomplete reaction is attributed to the establishment of an equilibrium between p ‐nitrophenol and p ‐nitrophenyl esters. The latter probably includes p ‐nitrophenyl phosphate. The rate constant for the synthesis of p ‐nitrophenyl esters has been determined and it also has acid, base and pH‐independent catalytic components.