Homogeneous Hydrogenation of Fatty Acid Methyl Esters and Natural Oils under Neat Conditions

A series of ruthenium- and iron-based pincer catalysts have been tested for the homogeneous hydrogenation of fatty acid methyl esters to fatty alcohols with turnover numbers (TONs) of up to 1860. These catalysts operate under neat conditions (no solvent) from the gram to the kilogram scale. The required temperature (135 degrees C) and H-2 pressure (300-1000 psig) are much lower than those needed for current industrial processes, which rely on heterogeneous copper chromite catalysts. The fatty alcohol products can be purified through distillation, resulting in low levels of Ru (1 ppm) and P (<25 ppm). The five-coordinate Milstein catalyst and Takasagos borane-stabilized catalyst are also effective for the direct hydrogenation of coconut oil to fatty alcohols. These results hold the promise of using homogeneous catalysts for ester hydrogenation in an industrial setting.