Study of the proton transfer during acidification of sodium salicylate based on ReaxFF molecular dynamics simulation

Abstract

Salicylic acid(SA) is known for its pain-relieving and fever-reducing abilities and has a very broad range of applications, being an important ingredient in a wide variety of products such as pharmaceuticals, skin care products, agrochemicals, dyes, colorants, preservatives, and more. SA is mainly synthesized by the Kolbe-Schmitt method in industrial production, but there is still no standardized description of the mechanism of this reaction. The Kolbe-Schmitt reaction mechanism is divided into three steps, and the reaction mechanism of the first two steps has been fully investigated, while the reaction mechanism of Sodium salicylate (SS) acidification, as the last step in the synthesis of SA by the Kolbe-Schmitt process, has not been investigated, so we used the Reactive force-field molecular dynamics simulation (ReaxFF MD) method to simulate and reveal the reaction mechanism of the mixed solution of SS and sulfuric acid, followed by an orthogonal design to explore the effects of different factors on the yield of SA. Through the investigation, it was found that the reaction of SS with sulfuric acid mixed solution was divided into the following four stages in total: hydration reaction, proton transfer reaction, association reaction and dissociation reaction, respectively. It is concluded that the SA yield in SS acidification reaction is affected by the factors in the following order: concentration > pressure > time > temperature, where concentration and pressure significantly affect the SA yield. It is hoped that the present study can supplement the relevant understanding of the reaction mechanism of the Kolbe-Schmitt process, and at the same time have some practical significance and application value for the improvement and optimization of the synthetic SA process.