The Catalysis of the Ruff Oxidative Degradation of Aldonic Acids by Copper(II)-Containing Solids

The catalysis of the Ruff oxidative degradation of calcium D-gluconate to D-arabinose by aqueous diluted hydrogen peroxide was investigated using copper(II)-containing solids: zeolites and resins. Among zeolites, copper(II)-exchanged Y faujasite has given good results, similar to homogeneous copper catalysts. Only minute amounts of soluble copper were detected at the end of the reaction and the recovered solid was recycled twice without diminution of efficiency. However, it was not true heterogeneous catalysis because the chelating gluconate anion leached copper right from the beginning of the reaction. So, the catalysis occurred in solution but the metal precipitated again at the end of the reaction, when all the gluconate was consumed. Copper (II) iminodiacetic resin, in which the metal cation is more strongly bound than in the gluconate complex, was not active. This demonstrates that copper(II) must be in solution in order to be active.