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 cpa3– 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 cpa3– makes seven bonds to copper. Channels of disordered solvent occupy 40% of the cell volume and pass completely through the crystals.