A Bimetallic System for the Catalytic Hydroxylation of Remote Primary C−H Bonds in Functionalized Organics Using Dioxygen

Abstract

In a mixture of trifluoroacetic acid and water, the combination of metallic palladium and copper chloride catalyzes the hydroxylation of remote primary C-H bonds of a variety of acids, alcohols, and aliphatic halides, in the presence of carbon monoxide and dioxygen. Experiments suggest that the principal role of metallic palladium is to generate hydrogen peroxide in situ and that the species responsible for the remote hydroxylation of the substrate by hydrogen peroxide is copper chloride. The unusual preference for the catalytic hydroxylation of primary C-H bonds was also found in an experiment involving competition between ethane and either cumene or p-isopropylbenzoic acid: even though the solution concentration of ethane was significantly lower than the competing substrate, the vast majority of the oxidation product (ethanol) was derived from ethane. In the reactions studied, acetic acid and formic acid were formed through C-C cleavage steps. An examination of the site of C-C cleavage in propionic acid indicated that both C-C bonds were being broken.

Homogeneous Functionalization of Methane

“…Park et al described catalytic copper and vanadium salts for the functionalization of methane to methanol with H 2 O 2 generated in situ from H 2 , O 2 , and Pd/C , at 80 °C . Lower catalyst loadings were required in the systems containing copper salts as they were, in general, more active than vanadium salts.…”

Reactions of C−H Bonds in Water

“…Several remote primary C-H bonds in acids, alcohols (eq 5), and aliphatic halides were hydroxylated by this method. 15 The mechanism of the reaction in these conditions involves formation of hydrogen peroxide by Pd, 16 whereas the role of CuCl 2 is to effect the subsequent oxidation of the substrate by the formed hydrogen peroxide. Increasing the amount of CuCl 2 reduces products resulting from overoxidation and C-C cleavage.…”

Rhodium complexes in homogeneous catalytic systems for oxidative functionalization of alkanes: Experiment and quantum-chemical calculations

“…The formation of intermediate malonic acid is also supported by earlier but unnoticed results [39]. According to [39], during oxidation the C atom of the methylene group in propionic acid may become primary in acetic acid through the reaction (14).…”

“…According to [39], during oxidation the C atom of the methylene group in propionic acid may become primary in acetic acid through the reaction (14). (14) Such a reaction may happen only via the route indicated in Scheme 11.…”