Equilibria of aminoethanols with protons and metal(II) ions. Part 3. L-(+)-threo-2-Amino-1-phenylpropane-1,3-diol with protons and copper-(II) in aqueous solution

Abstract

The equilibria of L-(+)-threo-2-amino-1-phenylpropane-1,3-diol [H₂L = HO·CH(Ph)·CH(NH₂)·CH₂OH] with H⁺ and Cu^II have been determined potentiometrically at 25 °C and I= 0.1 mol dm^–3(K)Cl. The protonation constants are log K₁= 12.01 and log K₂= 13.22 for the two hydroxyl groups, and log K₃= 8.446 for the amine group. With copper(II) the complexes [Cu(H₂L)]²⁺, [Cu(HL)]⁺, [Cu(HL)₂], [Cu(OH)(HL)], and [Cu(HL₂)]^– are formed. They contain, with the exception of [Cu(H₂L)]²⁺, five-membered chelate rings, with amine nitrogen and hydroxyl oxygen as donor atoms. The crystal structure of the compound [Cu(HL)₂(OH₂)]·4H₂O, obtained from alkaline solutions, confirms this interpretation.