Catalytic transformation of alcohols to carboxylic acid salts and H2 using water as the oxygen atom source

ARTICLES

PUBLISHED ONLINE: 6 JANUARY 2013 | http://www.nature.com/doifinder/10.1038/nchem.1536

Web End =DOI: 10.1038/NCHEM.1536

Catalytic transformation of alcohols to carboxylic acid salts and H2 using water as the oxygen atom source

Ekambaram Balaraman1, Eugene Khaskin1, Gregory Leitus2 and David Milstein1*

The oxidation of alcohols to carboxylic acids is an important industrial reaction used in the synthesis of bulk and ne chemicals. Most current processes are performed by making use of either stoichiometric amounts of toxic oxidizing agents or the use of pressurized dioxygen. Here, we describe an alternative dehydrogenative pathway effected by water and base with the concomitant generation of hydrogen gas. A homogeneous ruthenium complex catalyses the transformation of primary alcohols to carboxylic acid salts at low catalyst loadings (0.2 mol%) in basic aqueous solution. A consequence of this nding could be a safer and cleaner process for the synthesis of carboxylic acids and their derivatives at both laboratory and industrial scales.

Selective catalytic oxidation of alcohols is an important process for the synthesis of intermediates and chemicals of industrial interest19. Traditionally, chlorinated solvents and stoichio-

metric oxidants are often used to accomplish this transformation1.

However, recent reports present catalytic systems that operate with water as the solvent and use molecular oxygen as an oxidant. The role of O2 during oxidation in water is not always straightforward, with a recent computational report suggesting that the oxygen incorporated into the substrate originates from water7. Within these examples, direct catalytic oxidation of primary alcohols to carboxylic acids or their salts is rare7,8. Acids are still produced from primary alcohols in one step by the use of toxic strong oxidants such as iodate or chlorite with catalytic ruthenium and chromium oxides, resulting in copious waste10. Even recent literature examples of primary alcohol oxidation to acids involve expensive and non-atom-economic stoichiometric reagents11. According to Fernandez and Tojo10, 40% of all oxidations to carboxylic acids are carried out by a two-step procedure via the aldehyde, leading them to conclude that the transformation of primary alcohols to carboxylic acids is [undoubtedly not a mature technology].

Recently, Grtzmacher and co-workers reported a homogeneous rhodium-catalysed oxidation of alcohol to an acid salt1214 that occurs under mild conditions at high pH and is driven by a sacricial hydrogen acceptor ketone as an oxidant12. A variant...