Formation of carbamic acid in organic solvents and in supercritical carbon dioxide

The behavior of amines in various CO2-rich solvents is described. 1H and 13C NMR spectra in DMSO, chloroform, and benzene show that the amines are completely converted into carbamic acid by just bubbling atmospheric CO2 through the solution. However, the chemical shifts of several protons and the carbonyl 13C in the newly formed compounds strongly depend on the organic solvent used. FT-IR measurements confirm the observation that carbamic acid formation occurs. Changing the solvent to supercritical CO2 shows a temperature- and pressure-dependent equilibrium between the amine and the carbamic acid; higher pressures shift the equilibrium towards the carbamic acid, whereas higher temperatures favor the free amine.