Hydrogenation and transfer hydrogenation of Image-fructose catalyzed by dichlorotris (triphenylphosphine) ruthenium (II)

Abstract

Image-Fructose is hydrogenated to Image-glucitol and Image-mannitol using RuCl2 (PPh3)3 as catalyst at 100°C and atmospheric pressure. Besides hydrogenation, fructose undergoes transfer hydrogenation when propan-2-ol and butan-2-ol are used as solvents. Under an inert atmosphere (nitrogen), only transfer hydrogenation of fructose is observed in these alcohols. The rate of hydrogenation is comparable with transfer hydrogenation under similar reaction conditions. Cyclohexanol, benzyl alcohol, 1-phenylethanol and benzhydrol are also found to be good hydrogen donors for fructose reduction. Both hydrogenation and transfer hydrogenation yield glucitol and mannitol whose ratio is always 1:1. The catalyst is deactivated when hydrogen donors such as 2-methoxyethanol and tetrahydrofurfuryl alcohol are employed. The deactivation is attributed to the formation of an inactive ruthenium carbonyl complex, viz., RuHCl (CO) (PPh3)3. The hydrogen donating ability of these alcohols and their oxidation potentials are compared and the relative degrees of correlation are rationalized.