Acceptorless or Transfer Dehydrogenation of Glycerol Catalyzed by Base Metal Salt Cobaltous Chloride – Facile Access to Lactic Acid and Hydrogen or Isopropanol
Himani Narjinari, Sunil Dhole, Akshai Kumar
Abstract
Abstract The dehydrogenation of glycerol to lactic acid (LA) under both acceptorless and transfer dehydrogenation conditions using readily available, inexpensive, environmentally benign and earth‐abundant base metal salt CoCl 2 is reported here. The CoCl 2 (0.5 mol %) catalyzed acceptorless dehydrogenation of glycerol at 160 °C in the presence of 0.75 equiv. of KOH, gave up to 33 % yield of LA in 44 % selectivity apart from hydrogen. Alternatively, with acetone as a sacrificial hydrogen acceptor, the CoCl 2 (0.5 mol %) catalyzed dehydrogenation of glycerol at 160 °C in the presence of 1.1 equiv. of NaO t Bu resulted in up to 93 % LA with 96 % selectivity along with another value‐added product isopropanol. Labelling studies revealed a modest secondary KIE of 1.68 which points to the involvement of C−H bond activation as a part of the catalytic cycle but not as a part of the rate‐determining step. Catalyst poisoning experiments with PPh 3 and CS 2 are indicative of the homogeneous nature of the reaction mixture involving molecular species that are likely to be in‐situ formed octahedral Co(II) as inferred from EPR, HRMS and Evans magnetic moment studies. The net transfer dehydrogenation activity is attributed to exclusive contribution from the alcoholysis step.