H-1-NMR spectroscopic investigations were performed on aqueous solutions of carbon dioxide and piperazine at temperatures ranging from (283 to 333) K to determine quantitatively the speciation. The experimental results were used to determine the chemical equilibrium constants for the formation of piperazine carbamate, piperazine, dicarbamate and protonated piperazine carbamate. (C) 2003 Elsevier Science Ltd. All rights reserved.