Combined dehydration/(transfer)-hydrogenation of C6-sugars (D-glucose and D-fructose) to γ-valerolactone using ruthenium catalysts

Abstract

γ-Valerolactone (GVL) is considered a very interesting green, bio-based platform chemical with high application potential. We here describe research activities on the one-pot catalytic synthesis of GVL from C6-sugar sources (D-glucose, D-fructose, sucrose and cellulose) using an acid catalyst in combination with a hydrogenation catalyst (Ru/C) and either molecular hydrogen or formic acid as the hydrogen donor. When using formic acid, the highest yield of GVL (52 mol%) was obtained at 180 °C, 16 h reaction time and D-fructose as the C6-sugar source. The major by-products were insoluble solids, known as humins, formed during the acid catalysed conversion of D-fructose to the intermediate levulinic acid (LA). When using molecular hydrogen as the hydrogen source, the highest yield of GVL (62 mol%) was obtained using D-fructose in combination with TFA and Ru/C in water (180 °C, 94 bar H₂, 8 h). Complete conversion of D-fructose was observed at these conditions. The major by-products were formic acid and insoluble solid materials (humins). The use of a pre-formed homogeneous water soluble ruthenium catalysts from RuCl₃ and tris(3-sulfonatophenyl)phosphane (TPPTS) in combination with TFA gave quantitative C6-sugar conversions but a lower GVL yield (23 mol%) compared to the heterogeneous Ru catalyst.