LAUSR

The antibiotic para-aminosalicylic acid (PAS) is decomposed into its decarboxylated product, meta-aminophenol, with a series of toxicity symptoms including hemolytic anemia. The present trial investigates the decarboxylation mechanism of PAS, along with an in-detail assessment of the potential energy profiles, geometries, kinetic, and thermodynamic preference of the process. Further, the effects of solvent and pH on the process have been fully investigated. B3LYP-D3(BJ)/G4MP2 calculations have been executed on the para-aminosalicylic acid decomposition with a view to clarify the aqueous thermal decarboxylation and pH influences on the mechanism. The decomposition process can only be described accurately by the inclusion of solvent not only as a reaction medium but also as an active contributor to the chemical process. We further found an optimal preference with respect to energy barriers for the process with decreasing pH. Also, experiments showed the reduction in PAS absorbance with fall in pH. These together suggested the decrease of rate of decarboxylation with pH increase. Finally, we concluded that increasing pH reduces the reaction rate and in the pH around 10, the reaction rate reaches zero and it completely halts. We assume that this experiment can pave the way for advanced experimental and theoretical researches in the drug degradation mechanisms field and the effect of pH and solvent on the process.