Crystal structure of a copper complex of 2-carboxypentonic acid; a decomposition product of dehydroascorbic acid

Abstract

In acidic aqueous solution and in the presence of copper(II), ascorbic acid is rapidly oxidized to dehydroascorbic acid, which rearranges to give the branched-chain dicarboxylic acid 2-carboxypentonic acid (1,2,3,4-tetrahydroxybutane-1,1-dicarboxylic acid)(H₃cpa). The ion cpa^3– is sequestered by copper(II) to produce the insoluble crystalline product [Cu₉Cl₂(cpa)₆(H₂O)₃]^2–·xH₂O. Characterization of the crystals by X-ray diffraction indicates that copper exists in two distinct environments, one of which is five-co-ordinate and the other six-co-ordinate, and that cpa^3– makes seven bonds to copper. Channels of disordered solvent occupy 40% of the cell volume and pass completely through the crystals.