Carboxylate-assisted formation of alkylcarbonate species from CO(2) and tetramethylammonium salts with a ß-amino acid anion.

Tetramethylammonium-based molten salts bearing a ß-amino acid anion (TMAAs) are synthesized through Michael addition reactions of amines with methyl acrylate followed by hydrolysis and subsequent neutralization by using aqueous tetramethylammonium hydroxide. The CO(2) capture performances of the TMAAs are evaluated and are shown to interact with CO(2) in a 1:1 mode in both water and alcohol. FTIR and (13)C NMR spectroscopic studies on the interactions of TMAAs with CO(2) indicate that the type of CO(2) adduct varies with the solvent used. When water is used as the solvent, a bicarbonate species is produced, whereas hydroxyethylcarbonate and methylcarbonate species are generated in ethylene glycol and methanol, respectively. Computational calculations show that the carboxylate groups of TMAAs contribute towards the formation and stabilization of 1:1 CO(2) adducts through hydrogen bonding interactions with the hydrogen atoms of the amino groups.

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 (CO(2)) 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 CO(2). The formation of carbonate rather than carbamate species, which contribute to the unusual high working capacity of ∼1 mole CO(2) 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 ν(CO(2)), 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 CO(2) absorbents.