Thermodynamics of protonation and copper(II) complex formation of α-aminomalonic acid
Abstract
The thermodynamic functions (ΔG⊖, ΔH⊖, and ΔS⊖) for the protonation of α-aminomalonic acid were determined in aqueous solution (25 °C, l= 0.1 mol dm–3 NaCl). The basicity constants and enthalpy changes were evaluated from potentiometric and calorimetric data for both the primary amino and the carboxylate groups. On the basis of the thermodynamic changes a closed structure is hypothesized with the protonated amino nitrogen hydrogen-bonded to both the carboxylate groups to form two five-membered rings. The protonation of the CO2– groups provokes opening of the rings. A relatively high stability constant for complexation with Cu2+ was determined, however in a narrow range of low pH. The co-ordination to the copper(II) occurs both with nitrogen and the two oxygen donor atoms, to form two five-membered chelate rings.