Unraveling Acid–Base Contributions in P-Nitrophenyl Acetate Hydrolysis: Kinetics, Mechanism, And Activation Parameters in Aqueous Media

• Author(s): Ghali Muhammad Rabiu ; Musa Hamisu ; Ladi Lawan ; Mohammed Hussaini ; Abba Haruna Adamu
• Paper ID: 1710748
• Page: 1117-1120
• Published Date: 22-09-2025
• Published In: Iconic Research And Engineering Journals
• Publisher: IRE Journals
• e-ISSN: 2456-8880
• Volume/Issue: Volume 9 Issue 3 September-2025

Abstract

Hydrolysis of p-nitrophenyl acetate (PNPA) serves as a classical model for studying acid–base catalysis in aqueous solution. Despite its widespread use in enzymology and mechanistic chemistry, comprehensive datasets unifying acid- and base-catalyzed pathways remain limited. In this study, PNPA hydrolysis was monitored spectrophotometrically across pH 2–11 and temperatures 20–45 °C. Pseudo-first-order rate constants (kobs) were determined from exponential fits of absorbance–time traces at 400 nm. A characteristic U-shaped pH–rate profile was obtained, confirming contributions from both acid- and base-catalyzed pathways. Arrhenius and Eyring analyses yielded an activation energy (E?) of 54.7 kJ·mol?¹, enthalpy of activation (?H) of 52.2 kJ·mol?¹, and entropy of activation (?S) of ?47.8 J·mol?¹·K?¹, consistent with a bimolecular, ordered transition state. The results bridge existing gaps by integrating acid- and base-mediated hydrolysis within a single mechanistic framework, providing a reference dataset for both physical organic chemistry and enzymatic catalysis.

Keywords

PNPA, Ester Hydrolysis, Acid–Base Catalysis, Activation Parameters, Aqueous Kinetics

Citations

IRE Journals:
Ghali Muhammad Rabiu , Musa Hamisu , Ladi Lawan , Mohammed Hussaini , Abba Haruna Adamu "Unraveling Acid–Base Contributions in P-Nitrophenyl Acetate Hydrolysis: Kinetics, Mechanism, And Activation Parameters in Aqueous Media" Iconic Research And Engineering Journals Volume 9 Issue 3 2025 Page 1117-1120

IEEE:
Ghali Muhammad Rabiu , Musa Hamisu , Ladi Lawan , Mohammed Hussaini , Abba Haruna Adamu "Unraveling Acid–Base Contributions in P-Nitrophenyl Acetate Hydrolysis: Kinetics, Mechanism, And Activation Parameters in Aqueous Media" Iconic Research And Engineering Journals, 9(3)