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

The behavior of amines in various CO(2)-rich solvents is described. (1)H and (13)C NMR spectra in DMSO, chloroform, and benzene show that the amines are completely converted into carbamic acid by just bubbling atmospheric CO(2) through the solution. However, the chemical shifts of several protons and the carbonyl (13)C 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 CO(2) 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. (c) 2006 Elsevier B.V. All rights reserved.