Roy Lavelle Pruett

The rhodium-promoted guerbet reaction: Part I. Higher alcohols from lower alcohols

Abstract The multiple roles played by both the rhodium and alkoxide catalysts in the efficient and mild condensation of alcohols to higher molecular weight alcohols, the Guerbet reaction, have been clarified. Rhodium promotes alcohol dehydrogenation at the beginning of the reaction sequence, and later assists in the saturation of an allyl alcohol intermediate. The alkoxide catalyst pushes the intermediates through the reaction sequence by serving both as a simple base in the aldol condensation step, and as a hydride reducing agent for the various vinyl and carbonyl moieties found in the reaction intermediates. The investigation also revealed a strong rate dependence upon the initial alkoxide concentration and indicated how the presence of water, a primary Guerbet reaction product, leads to deactivation of the system.

The rhodium-promoted guerbet reaction: Part II. Secondary alcohols and methanol as substrates

Abstract The scope of the low temperature rhodium-promoted Guerbet alcohol condensation reaction has been extended to include methyl secondary alcohol substrates. The condensation proceeds via ketonic intermediates with the new C-C bond forming in an aldol condensation step. Unsymmetrical alcohol substrates gave product distributions which mirrored those expected from methyl ketone self-condensations. The investigation also revealed that methanol could serve both as a solvent for the Guerbet reaction and as a substrate. A cross-condensation between methanol and a primary alcohol gave a β-methyl carbinol.