Mild, single-pot hydrocarboxylation of linear C5–C9 alkanes into branched monocarboxylic C6–C10 acids in copper-catalyzed aqueous systems

A single-pot method has been developed for the hydrocarboxylation of the liquid C5–C9 alkanes (n-pentane, n-hexane, n-heptane, n-octane, n-nonane and 3-methylhexane) into the branched monocarboxylic C6–C10 acids bearing one more carbon atom. This method is characterized by a direct, selective and low-temperature (60 °C) hydrocarboxylation reaction of the alkane with carbon monoxide, water (which acts as a reagent besides being a solvent component) and potassium peroxodisulfate, in H2O/MeCN medium. The hydrocarboxylations are markedly enhanced in the presence of a tetracopper(II) triethanolaminate complex as a homogeneous catalyst precursor. Total yields (based on alkane) of carboxylic acids up to 46% (with 97–99% overall selectivity) have been achieved, which are remarkable in the field of alkane functionalization under mild conditions, especially for a C–C bond formation reaction in aqueous acid-solvent-free medium. The regio- and bond selectivity parameters have been determined and a free radical mechanism has been proposed.

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► Inert Cn alkanes are directly transformed into branched Cn+1 carboxylic acids.
► Alkane hydrocarboxylations with CO and H2O proceed at low temperature and in H2O/MeCN medium.
► Important features are the mild and acid-solvent-free conditions, high selectivity and efficiency.
► Homogeneous catalysis with an aqua-soluble tetracopper(II) complex.