Stopped‐flow determination of carbon dioxide–diethanolamine reaction mechanism: Kinetics of carbamate formation

The reaction mechanism of carbon dioxide with diethanolamine (DEA) is investigated using the stopped‐flow method with optical detection in the ranges of concentration [DEA] = 0.111–8.4 × 10 −2 M and [CO 2 ] = 2.94–5.6 × 10 −3 M . The comparison of the fast time‐dependent light transmission change of a pH indicator with theoretical simulations of integrated rate equations requires a kinetic model in which a simple carbamate formation takes place simultaneously with hydration reactions, whose contributions are far from being negligible. A first‐order reaction relative to DEA is thus found with a rate constant for carbamate formation smaller than usually predicted (110 ± 15 M −1 s −1 at 25°C). The equilibrium constant for the same reaction is also determined giving p K R = 5.3 at 25°C, in satisfactory agreement with values assumed so far.