Abstract
Several alkanolamines (1A2P, 2A1P, AMP, MAE, EAE, and IPAE) were selected to study the steric hindrance effect on reaction kinetics between amine and CO2 in ethanol and aqueous solutions. Pseudo first-order reaction rate constant k0 was measured by the stopped-flow apparatus. Zwitterion mechanism was applied to describe the reaction and the k0 was well fitted by the corresponding kinetic model with average absolute relative deviation (AARD) in a range of 1.08%-3.89%. Apparent second-order reaction rate constant KA revealed that the reaction rate is simultaneously controlled by steric hindrance and pKa of amines. Additional alkyl groups increase the steric hindrance of amines and accelerate the decomposition of zwitterions. As a result, the reaction rate decreases with stronger steric hindrance effect. The larger pKa is conducive to a better proton receiving of amine. This leads to an acceleration of the deprotonation reaction of zwitterion intermediate. In addition, the relative influence of steric hindrance and pKa on the reaction kinetics is also related to the solvent environment.
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