Toward rational design of amine solutions for PCC applications: the kinetics of the reaction of CO2(aq) with cyclic and secondary amines in aqueous solution.

The kinetics of the fast reversible carbamate formation reaction of CO2(aq) with a series of substituted cyclic secondary amines as well as the noncyclic secondary amine diethanolamine (DEA) has been investigated using the stopped-flow spectrophotometric technique at 25.0 °C. The kinetics of the slow parallel reversible reaction between HCO3– and amine has also been determined for a number of the amines by 1H NMR spectroscopy at 25.0 °C. The rate of the reversible reactions and the equilibrium constants for the formation of carbamic acid/carbamate from the reactions of CO2 and HCO3– with the amines are reported. In terms of the forward reaction of CO2(aq) with amine, the order with increasing rate constants is as follows: diethanolamine (DEA) < morpholine (MORP) ∼ thiomorpholine (TMORP) < N-methylpiperazine (N-MPIPZ) < 4-piperidinemethanol (4-PIPDM) ∼ piperidine (PIPD) < pyrrolidine (PYR). Both 2-piperidinemethanol (2-PIPDM) and 2-piperidineethanol (2-PIPDE) do not form carbamates. For the carbamate formi...