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

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 k 0 to the reaction pathways catalyzed by H 3 O + , 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.

Facilitated Transport of Lysine Acetylsalicylate Through Supported Liquid Membrane Using Methyl Cholate as Carrier: Parameters and Mechanism

“…These samples were diluted in an excess of sodium hydroxide solution to perform the complete hydrolysis of LAS into salicylate ions which has a maximum band of absorption at a wavelength of 300 nm [18]. A standard Helios γ UV-visible spectrometer was used to analyze the LAS samples concentrations and a Hanna 210 microprocessor pH-meter, equipped with a combined glass electrode and calibrated with commercial buffers (pH 4.00 and 7.00) was used for pH measurements.…”