Anionic ruthenium iodocarbonyl complexes as selective dehydroxylation catalysts in acqueous solution

The selective dehydroxylation in aqueous solution of C3-C5 polyols and C6 sugars in the presence of homogeneous ruthenium iodocarbonyl catalysts, [Ru(CO)3I3]- species, has been studied. Glycerol, pure or in dilute aqueous solution, is dehydroxylated to give n-propanol and its ethers with selectivities of up to 90%. Xylitol and C6 sugars, glucose and fructose, are dehydrated and hydrogenated through initial formation of levulinic acid to give gamma-valerolactone with high yields. The dehydroxylation of these polyhydroxylic substrates is made possible in water solution by the bifunctional nature (acidity and hydrogenating ability) of the ruthenium catalytic system. The requirements necessary for the catalytic system to be active and stable in water have been studied, and the mechanism of the reaction discussed.