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 C-5-C-9 alkanes (n-pentane, n-hexane, n-heptane, n-octane, n-nonane and 3-methylhexane) into the branched monocarboxylic C-5-C-10 acids bearing one more carbon atom. This method is characterized by a direct, selective and low-temperature (60 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.