Manganese Oxide / Silica catalysed Decarboxylative Ketonization of Aliphatic Carboxylic Acids in a Continuous Flow Reactor

The sustainable synthesis of long carbon chain molecules from carbon dioxide, water and electricity relies on the development of waste‐free, highly selective C–C bond forming reactions. An example for such a power‐to‐chemicals process is the industrial‐scale fermentation for the production of hexanoic acid. Herein, we describe how this product is transformed into 6‐undecanone via decarboxylative ketonization using a heterogeneous manganese oxide / silica catalyst. The reaction reaches full conversion with near‐complete selectivity when carried out in a continuous flow reactor, requires no solvent or carrier gas, and releases carbon dioxide and water as the only by‐products. The reactor was operated for several weeks with no loss of reactivity, producing 7 kg of 6‐undecanone from 10 g of catalyst and achieving a productivity of 1.135 kg per litre of reactor volume per hour. 6‐Undecanone and other long‐chain ketones accessible this way can be hydrogenated to industrially meaningful alkanes, or converted into valuable fatty acids via a hydrogenation / elimination / isomerizing hydrocarboxylation sequence.