Online ATR-FT-IR for Real-Time Monitoring of the Aspirin Esterification Process in an Acid-Mediated Reaction

Abstract

The process of aspirin synthesis was studied using in situ real-time attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR) from salicylic acid and acetic anhydride accompanied by a sulfuric acid catalyst. The data collected from the IR analysis process showed that there were obvious changes in the position, shape, and intensity of the carbonyl characteristic peaks in the three-dimensional (3D) spectra. Principal component analysis (PCA) followed by target transformation of the resulting factors was used to analyze the spectra and the relationship of the absorbance and time trendlines of raw materials and products in the reaction system. This method would be enough to monitor reaction progress and determine the end point without further separation and purification of the reaction mixture. The results demonstrated that the acetylation of salicylic acid catalyzed by sulfuric acid was a complicated process, and the conversion rate was high. The reaction was a rapid reaction mechanism and could be divided into two stages with different reaction rate. The ATR-FT-IR spectroscopy technique can monitor and analyze the changes of raw materials and products with time, which is more reliable to determine fundamental data for process analysis and optimization using real-time monitoring of the reaction process.