Hydrolysis of phosphate mono ester of 2-methoxy-4-nitro aniline proceeds Via p-n bond fission

Study Kinetic study of the hydrolysis of mono-2-methoxy-4-nitroaniline phosphate has been carried out both in acid (0.1 to 6.0 mol. dm-.3 HCl) as well as in buffer medium (1.24 to 7.46 pH) in aqueous solution at 97 ± 0.5oC. The rate of hydrolysis was determined by measuring the rate of appearance of inorganic phosphate by colorimetric method1 (Allen’s modified method). The concentration of the monoester in all the kinetic runs was maintained 5.0 × 10–4 mol. dm–3. Reactive species of monoester are conjugate acid species, neutral, mono-negative and dinegative species, but for the sake of convenience only conjugate acid species has been given in this discussion. Effect of factors such as hydrogen ion concentration, ionic strength, temperature, substrate concentration. etc. have been studied on the rate of hydrolysis to estimate the participation of water molecules, bond fission and molecularity of the reaction Presumption of pH values and ionic strength data were used to estimate the rates in various zones of pH log rate profile. Molecularity of the reaction was determined by empolying concepts such as Zucker-Hammett hypothesis2, Bunnett parameters3 and Hammett acidity function4. The probable mechanism of the hydrolysis of mono 2-methoxy, 4-nitroaniline phosphate via conjugate acid species have been studied by using the comparative rate date and isokinetie relationship of other similarly substituted phosphate mono-esters.