Carboxylate-Assisted Formation of Alkylcarbonate Species from CO2 and Tetramethylammonium Salts with a β-Amino Acid Anion

Abstract

Tetramethylammonium-based molten salts bearing a β-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 CO2 capture performances of the TMAAs are evaluated and are shown to interact with CO2 in a 1:1 mode in both water and alcohol. FTIR and 13C NMR spectroscopic studies on the interactions of TMAAs with CO2 indicate that the type of CO2 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 CO2 adducts through hydrogen bonding interactions with the hydrogen atoms of the amino groups.