Catalytic hydrogenation of arabinonic acid and lactones to arabitol

Aqueous solutions (20 wt%) of arabinonic acid in equilibrium with arabinonolactones were hydrogenated on ruthenium catalysts at 100degreesC or lower temperatures in a batch reactor. The highest selectivity to arabitol was 98.9% at 98% conversion, with a reaction rate of 73 mmol h(-1) g(Ru)(-1) at 80degreesC. Reaction modeling was achieved by a detailed kinetic analysis of reaction data under various reaction conditions. The conversion of substrate follows a rate equation established with the Horiuti-Polanyi mechanism. The selectivity was higher on small particles supported on carbon supports because of an electron-donating effect of the support on the ruthenium particles, which decreases the rate of dehydroxylation reactions leading to unwanted deoxy products. The most important factor enhancing the selectivity was the presence of anthraquinone-2-sulfonate (A2S), which decreased the formation of deoxy products. With an optimum amount of A2S the selectivity at 100degreesC was improved from 93.6 to 96.7%. The molecule acted as a permanent surface modifier since the catalyst was recycled with the same selectivity without further addition of A2S. The molecule could act as an electron-donating surface ligand decreasing the rate of dehydroxylation reactions. (C) 2002 Elsevier Science (USA).