Homogeneous and heterogeneous catalytic (dehydrogenative) oxidation of oleochemical 1,2-diols to α-hydroxyketones†
Herein, the preparation of methyl oleate α-hydroxyketone from the corresponding 1,2-diol was investigated using both homogeneous and heterogeneous systems. Homogeneous conditions using a Pd(OAc)2/neocuproine complex were first developed using oxygen as a sole oxidant under mild conditions (MeOH, 50 °C). Under these conditions, the conversion of diol reached 95%, and α-hydroxyketone was obtained with 97% selectivity. The access to α-hydroxyketone has also been studied by dehydrogenation using a range of heterogeneous catalysts under solvent-free conditions at high temperatures (160–180 °C). Dehydrogenation using activated Ru/C under vacuum provided α-hydroxyketone with 93% conversion and 82% GC yield. The optimized conditions were applied to a range of oleochemical diols, including a vegetable oil derivative, to obtain the corresponding α-hydroxyketones with up to 74% isolated yields.