CATALYTIC CONVERSIONS IN WATER .4. CARBONYLATION OF 5-HYDROXYMETHYLFURFURAL (HMF) AND BENZYL ALCOHOL CATALYZED BY PALLADIUM TRISULFONATED TRIPHENYLPHOSPHINE COMPLEXES

Carbonylation of renewable 5-hydroxymethylfurfural (HMF) under aqueous phase catalytic conditions using the water soluble catalyst Pd(TPPTS) (3) (TPPTS = sodium salt of trisulfonated triphenylphosphine, P(C6H4-m -SO3Na)(3)) was investigated. Pd(TPPTS)(3) was easily prepared in situ via complexation of PdCl2 in an aqueous TPPTS solution and reduction with carbon monoxide, Using the Pd(TPPTS)(3) catalyst at 70 degrees C, 5 bar CO pressure and [Pd] = 150 ppm chemoselective carbonylation of HMF was observed to yield 5-formylfuran-2-acetic acid (FFA) as the sol e carbonylation product; the only by-product was 5-methylfurfural (MF) . The formation of MF under these conditions amounts to a new type of catalytic and very selective reduction with CO, formally equivalent to hydrogenolysis of an alcohol group without using H-2. This is surpris ing since one would expect the water gas shift reaction, Both the acti vity and selectivity of HMF carbonylation were strongly influenced by the TPPTS/Pd molar ratio; maximum efficiency being observed for TPPTS/ Pd = 6. The nature of the anion of the added acid markedly influenced the selectivity. Acids of weakly or non-coordinating anions, such as H 3PO4, CF3COOH, p-CH3C6H4SO3H, H2SO4, and HPF6 afforded mainly carbonyl ation. The selectivity decreased dramatically with acids of strongly c oordinating anions such as HBr and HI. With the latter the only produc t observed was MF. Replacement of TPPTS by ligands containing less-SO3 Na groups such as disulfonated triphenylphosphine (TPPDS) or disulfona ted tris(p-fluorophenyl)phosphine (TFPPDS) gives rise to a dramatic dr op in the catalytic activity. Using palladium catalysts modified with monosulfonated triphenylphosphine (TPPMS) only traces of FFA and MF we re obtained. Pd(TPPTS)(3) in aqueous media similarly catalyses the sel ective carbonylation of benzyl alcohol to phenylacetic acid. In sharp contrast, classical hydrophobic Pd/PPh(3) catalysts are inactive in th is carbonylation reaction in organic solvents. A catalytic cycle is pr oposed to explain the observed results.