Hydrogenation of d-glucose catalysed by ruthenium complexes containing triarylphosphine ligands in homogeneous and biphasic-aqueous medium

Abstract

In this investigation the hydrogenation of D-glucose to sorbitol (D-glucitol), a sweetener for industrial use, was carried out using as catalytic precursors ruthenium systems containing triarylphosphine ligands, such as triphenylphosphine (PPh 3), tri (p-) toluyl) phosphine [P (p-tol) 3], triphenylphosphine monosulfonated (TFFMS) and trisulfonated triphenylphosphine (TFFTS), both in homogeneous (water) and biphasic-aqueous medium.  The precatalysts with sulfonated ligands were prepared in situ in the reaction medium by adding the respective sulphonated phosphine (TFFMS and TFFTS) to the aqueous solution of RuCl 3 .3H 2 O, it being found that both systems were found to be active, under moderate conditions of reaction (96% conversion at 10 bar H 2 and 100 ° C with Ru / TFFTS and 100% conversion at 5 bar H 2 and 100 ° C with the Ru / TFFMS system) in a reaction time of 8 h. The complexes RuCl 2 (PPh 3) 3 and RuCl 2 (Pp-tol 3) 3 were found to be poorly active catalysts (<10%) for the biphasic-aqueous hydrogenation of D-glucose, under the same reaction conditions. However, the triphenylphosphine catalyst was active for this reaction in the presence of a phase transfer agent such as cetyltrimethylammonium chloride (CTAC), achieving a conversion of 62% in a period of 24 h, under the same conditions as the Ru system. / TFFTS. It should be noted that in the literature there is no report of hydrogenation of saccharides by biphasic-aqueous catalysis.