Methyl ketones from carboxylic acids as valuable target molecules in the biorefinery

Abstract For the preparation of methyl ketones, cross Ketonic Decarboxylation, i.e., the formation of a ketone from two different carboxylic acids, and the reketonization, i.e., the transformation of a carboxylic acid into a ketone employing a ketone as alkyl transfer agent, may be interesting alternatives to classical pathways involving metal-organic reagents. The fine chemical 2-undecanone was chosen as model compound and ketonic decarboxylation and reketonization evaluated by Green Chemistry matrices, namely the carbon atom efficiency and the e-factor. The e-factor of the reaction of decanoic acid with acetic acid was less than five and, therewith, in the acceptable range for bulk chemicals, when valorizing acetone (e.g., as a solvent) and considering a 90% solvent recycling. The reketonization of decanoic acid with acetone provided a different main product, namely 10-nonadecanone, with a detrimental effect on atom efficiency. By means of labeling experiments it was shown that ketonic decarboxylation is significantly faster than the reketonization reaction. The transformation of acetic acid into acetone was studied by in-situ and operando IR spectroscopy. Thereby it was found that the surface was covered by acetic acid. The lack of adsorption of acetone is a clear drawback for the reketonization of carboxylic acids. To improve the reaction outcome, and therewith, its sustainability a possibility has to be found to stabilize the ketone molecules on the surface in the presence of carboxylic acids.