Stability Studies of Lysine Acetylsalicylate (Aspirin Derivative): Mechanisms of Hydrolysis

Oussama Kamal, Abderazzak Benlyamani, Farid Serdaoui, Mohammed Riri, Abdelmjid Cherif, Miloudi Hlaïbi

Laboratoire d’Interface Matériaux d’Electrochimie et Chimie de l’Environnement (LIME), Université Hassan II Faculté des Sciences A?n Chock, Casablanca, Morocco.

DOI: 10.4236/ojpc.2012.22011                

Abstract

To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in water solutions have been carried out. The pH-rate profile (log k_obs = f(pH)), shows that the hydrolysis reaction of the LAS, is conducted by a catalysis acid-base mechanism, with multiple reaction pathways. The rate constants, k_H, k_OH and k₀ to the reaction pathways catalyzed by H₃O⁺, HO^– ions and to the spontaneous reaction, for the hydrolysis reaction of the reagent LAS, were determined. The results show that the studied compound LAS is unstable in basic medium and the hydrolysis reaction catalyzed by HO^– ions is predominant.For a known acidity (pH ≈ 10), studies conducted for different temperatures of the medium, clearly indicate, that the experimental rate constant k_obs,depends on the temperature according to the Arrhenius equation. The activation parameters: activation energy (E_a), enthalpy (ΔH^≠) and entropy (ΔS^≠), for the transition state were determined, The very negative value obtained for the activation parameter ΔS*, first indicates that in the transition state there is gain in order, then this late state, resembles the products and that probably for the mechanism of the LAS hydrolysis reaction catalyzed by HO^– ions, the rate-determining step is a bimolecular reaction. Finally from all these results, the mechanism for the reaction pathway catalyzed by HO^– ions has been elucidated.

Keywords

Lysine Acetylsalicylate; Hydronium Ions Hydroxide Catalyzed; Catalysis Acid-Base Mechanism; Multiple Reaction Pathways; Activation Parameters

Conflicts of Interest

The authors declare no conflicts of interest.

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