HYDROGENATION AND TRANSFER HYDROGENATION OF D-FRUCTOSE CATALYZED BY DICHLOROTRIS (TRIPHENYLPHOSPHINE) RUTHENIUM (II)

D-Fructose is hydrogenated to D-glucitol arid D-mannitol using RuCl2(P Ph3), as catalyst at 100-degrees-C and atmospheric pressure. Besides h ydrogenation, fructose undergoes transfer hydrogenation when propan-2- ol and butan-2-ol are used as solvents. Under an inert atmosphere (nit rogen), only transfer hydrogenation of fructose is observed in these a lcohols. The rate of hydrogenation is comparable with transfer hydroge nation under similar reaction conditions. Cyclohexanol, benzyl alcohol , 1-phenylethanol and benzhydrol are also found to be good hydrogen do nors for fructose reduction. Both hydrogenation and transfer hydrogena tion yield glucitol and mannitol whose ratio is always 1:1. The cataly st is deactivated when hydrogen donors such as 2-methoxy-ethanol and t etrahydrofurfuryl alcohol are employed. The deactivation is attributed to the formation of an inactive ruthenium carbonyl complex, viz., RuH Cl(CO)(PPh3)3. The hydrogen donating ability of these alcohols and the ir oxidation potentials are compared and the relative degrees of corre lation are rationalized.