Kinetics of the reversible reaction of CO2(aq) and HCO3(-) with sarcosine salt in aqueous solution.

Aqueous sarcosine salts are fast carbon dioxide (CO(2)) absorbents suitable for use in postcombustion CO(2) capture in coal-fired power plants. We have developed a detailed reaction scheme including all the reactions in the sarcosine-CO(2)-water system. All unknown rate and equilibrium constants were obtained by global data fitting. We investigated the temperature-dependent rate and equilibrium constants of the reaction between aqueous CO(2) and sarcosine using stopped-flow spectrophotometry, by following the pH changes over the wavelength range 400-700 nm via coupling to pH indicators. The corresponding rate and equilibrium constants ranged from 15.0 to 45.0 °C and were analyzed in terms of Arrhenius, Eyring, and van't Hoff relationships. The rate constant for the reaction between CO(2) and sarcosine to form the carbamate at 25.0 °C is 18.6(6) × 10(3) M(-1) s(-1), which is very high for an acyclic amine; its activation enthalpy is 59(1) kJ mol(-1) and the entropy is 33(4) J mol(-1) K(-1). In addition, we investigated the slow reaction between bicarbonate and sarcosine using (1)H nuclear magnetic resonance spectroscopy and report the corresponding rate and equilibrium constants at 25.0 °C. This rate constant is 5.9 × 10(-3) M(-1) s(-1).