PLATINUM-CATALYZED OXIDATION OF ALDOPENTOSES TO ALDARIC ACIDS

The liquid-phase oxidation of xylose, arabinose, lyxose and ribose using platinum-on-alumina catalysts is described. The aldopentoses have equal rates of oxidation to the corresponding aldonic acids, whereas the rates of the consecutive oxidation to the aldaric acids follow the order xylo, arabino > lyxo, ribo. The differences are attributed to leaching of active platinum sites from the catalyst by lyxose and ribose, which provide a favourable coordination site for metal ions. This is supported by the oxidation rates of the corresponding pentitols and the pentonic acids. Analysis of the side-products provided insight into selective cleavage reactions accompanying the oxidation.