How to bring alcohols out of the Guerbet’s labyrinth: an efficient homogeneous catalytic approach

Bio-ethanol refining is conceived to develop new strategies to second-generation biofuels production. Among others, the Guerbet reaction is an attractive route for the catalytic upgrading of ethanol to linear and branched higher alcohols, which possess greater energy density and miscibility with conventional fuel compared to their lighter analogue. While simple in principle, this is difficult in application due to several concerns encountered in selectivity and conversion. These drawbacks can be partially avoided exploiting homogeneous catalysts as recently reviewed by Wass and co-workers.1 Here we report on unprecedented catalytic activity (up to 88%) and selectivity (up to 97% in C4-C10 alcohols) gained by the synergistic role of ruthenium-cyclopentadienone complexes [Ru], base and benzoquinone (Figure 1) under mild conditions (T = 150 °C, t = 4h, [Ru] = 0.2 mol%, BQ = 1.5 mol%, NaOEt = 20 mol%).The catalytic system, at first studied on absolute ethanol, shows comparable efficiency on a real matrix (head and tail waste from alcohol distillation) even in presence of a significant amount of water.