Dicarboxylic acids are chemicals of high value and with many applications. Adipic acid that is produced in large scales, e.g. for polyamide production, is just one example for an important representative of this class of chemicals. However, unlike their shorter chain congeners, long-chain linear dicarboxylic acids have been difficult to access in a direct way to date.<br/>In this contribution, we present the direct generation of long-chain α,ω-dicarboxylic acids by catalytic isomerizing functionalization of unsaturated fatty acids and plant oils. The double bond deep in the fatty acid chain is selectively carbonylated with water as a nucleophile to a terminal carboxy group. Identified key elements of this reaction are a homogeneous reaction mixture that ensures sufficient contact between all reactants and a catalyst system that allows for activation of the Pd-precursor under aqueous reaction conditions. The unique specific activation pathway for the Pd(II)-precursor proceeds via a reductive elimination forming an intermediate Pd(0)-species and oxidative addition of protonated diphosphine ligand generating the catalytically active Pd-hydride species. A relatively small nucleophile concentration and an incomplete formation of the Pd-hydride species limit the potential of the reaction. Additionally, the rates are limited by a high energetic barrier for the hydrolysis, as identified by DFT calculations. Nevertheless, the isomerizing hydroxycarbonylation of unsaturated fatty acids ranks as one of the most active isomerizing functionalization reactions in combination with remarkable selectivities above 90% toward the desired linear product.

Single step access to long-chain α,ω-dicarboxylic acids by catalytic isomerizing hydroxycarbonylation

253rd National Meeting (2017)

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