Catalysis of Organic..

428Glycerol Hydrogenolysisfundamentally different since the raw materials are hydrocarbons, oxygen free,hydrophobic, volatile and thermally tough.A byproduct of vegetable oil transesterification to make biodiesel fuel, glycerol(GO) has captured our attention for several reasons. In aqueous medium, GO itselfcan be converted to value-added commodity products such as propylene glycol (PG),lactic acid (LA) and ethylene glycol (EG) in the presence of a metal catalyst at mildconditions (2-7). An array of metals deposited on various supports have beenexamined as catalysts for the above reaction (6, 7).But GO is also an archetype for more complex polyols. Catalytic hydrogenolysisof polyols leads to C-C and C-O bond cleavage as well as activation viadehydrogenation of HCOH to C=O sites (8, 9). With its three vicinal hydroxylgroups, and its two types of carbon atoms (all bearing hydroxyl functionalities) GOcan serve as a simple model in which to study the competition between theseprocesses. We aim to gain insight into the individual steps and apply that informationto increase selectivity toward desired products.OHHO OHGOOHOHEG–H 2OH –H 2 OHO O+H 2+H 2 O–H O O2OH + CH+H 2 OH2OOLA+HO –OO+2H 2–2H 2OHOHPGScheme 1Recent isotopic labeling studies of GO hydrogenolysis over Ru/C catalyst atbasic pH found the first step to be C-1 dehydrogenation. The glyceraldehyde analogformed then faces two possible paths (Scheme 1): enolization, water loss, andhydrogenation or base addition and to pyruvaldehyde intermediate isomerization toform PG and LA; or retro aldol cleavage to give, after hydrogenation, EG andformaldehyde (10). In this report we examine GO hydrogenolysis over metalcatalysts at different base concentrations and different solvents. HPLC is used tomonitor the catalyst activity and selectivity toward the products.