Two-dimensional infrared correlation spectroscopy and principal component analysis on the carbonation of sterically hindered alkanolamines

Despite the academic and industrial importance of the chemical reaction between carbon dioxide (CO₂) and alkanolamine, the delicate and precise monitoring of the reaction dynamics by conventional one-dimensional (1D) spectroscopy is still challenging, due to the overlapped bands and the restricted static information. Herein, we report two-dimensional infrared correlation spectroscopy (2D IR COS) and principal component analysis (PCA) on the reaction dynamics of a sterically hindered amine, 2-[(1,1-dimethylethyl) amino]ethanol (TBAE) and CO₂. The formation of carbonate rather than carbamate species, which contribute to the unusual high working capacity of ∼1 mole CO₂ per mole of TBAE at 40 °C, occurs through deprotonation of the hydroxyl group, protonation on the nitrogen atom of the amino group, and formation of a carbonate species due to the steric hindrance of the tert-butyl group. In particular, PCA captures the chemical transition into a carbonate species and the main contributions of νCO₂, ν_OH, ν_C-N, and ν_C=O bands to the carbonation, while 2D IR COS verifies the interrelation of four bands and their changes. Therefore, these results provide a powerful analytic method to understand the complex and abnormal reaction dynamics as well as the rational design strategy for the CO₂ absorbents.