Kinetics and mechanism of the reaction between carbon dioxide and amines in aqueous solution

Abstract

Rate constants, ΔH^‡ and ΔS^‡ have been measured by the conductimetric stopped-flow technique for the reaction of carbon dioxide in aqueous solution with the primary amines 2-methoxyethylamine, 2-aminoethanol, 3-aminopropan-1-ol, 2-aminopropan-2-ol, DL-aminopropan-2-ol and the secondary amines 1,1′-iminodipropan-2-ol, 2-amino-2-(hydroxymethyl) propane-1,3-diol, 2,2′-iminodiethanol, 2,2,6,6-tetramethylpiperidin-4-ol, and morpholine. The observed first-order rate constants fit the equation k_obs=k_AM[R₂NH]²+k_W[R₂NH][H₂O]. The much-quoted Danckwerts mechanism is shown to be unlikely.