NMR studies of mixed amines

1H and quantitative 13C NMR spectroscopy was used to study the reaction of CO2 with mixed aqueous amines. This technique permits the measurement of carbamates of each amine and bicarbonate concentrations as a function of time (and loading). The ratio of the amount of each carbamate formed (for primary and secondary amines) is shown to be thermodynamically rather than kinetically controlled, due a rapid exchange reaction between amine and carbamate. This exchange reaction is the likely basis of the “shuttle” mechanism of rate enhancement in mixed amines.