Abstract

The oxo process, also known as hydroformylation, is the reaction of carbon monoxide and hydrogen with an olefinic substrate to form isomeric aldehydes. Oxo aldehyde products range from C₃ to C₁₅ and are used as intermediates to alcohols, acids, polyols, and esters by the appropriate reduction, oxidation, or condensation chemistry.

Hydroformylation occurs most frequently in the liquid phase in the presence of a soluble metal catalyst, most frequently a member of the Co–Rh–Ir triad. The first commercial oxo catalyst was cobalt hydrocarbonyl, which has been largely replaced for both ethylene and propylene hydroformylation by more reactive, more selective ligand-modified rhodium catalysts. Various metal catalysts and ligands, required reaction conditions, and mechanisms are discussed. The most widely employed commercial ligand is triphenylphosphine. Propylene is by far the dominant olefinic substrate subject to the oxo process. Butanals are the largest-volume product. In the United States these aldehydes are converted principally to butanols; in Europe and Japan, n-butanal is converted chiefly into the plasticizer alcohol, 2-ethyl-1-hexanol. Other oxo process products include both linear and branched higher alcohols, propionaldehyde, and valeraldehyde. Vol. 17, pp. 902–919, 36 refs. to April 1995.