The kinetics and mechanism of the reaction between carbon dioxide and a series of amines - Observation and interpretation of an isokinetic effect

Kinetics investigations have been made on the reaction of some organic amines with dimethylcarbonate (DMC) in the presence of carbon dioxide. N-alkyl-carbamates were formed and measurements were made for a series of substituents in the amine. Second-order kinetics was used in the analysis. The rate constants have been analyzed and the resulting Arrhenius parameters indicate an isokinetic effect. The stepwise increase of the activation energies and the value of the isokinetic temperature are such that the selective energy transfer (SET) model suggests a delta (COC) vibration mode of the dimethylcarbonate to be activated in the rate determining reaction step. The DMC molecule is hydrogen bonded to the quartenary ammonium cation. The energy source is suggested to be a closely related vibration mode of the dimethylcarbonate serving as solvent. (C) 2001 Elsevier Science B.V. All rights reserved.