What is hydroformylation?

The process of synthesizing aldehydes and alcohols from olefins and synthesis gas using a cobalt or rhodium catalyst at high pressures and temperatures was first reported in the 1930s by Smith and Roelen. This reaction is commonly known as hydroformylation, oxo reaction, oxo process, oxo synthesis, and is widely used in the field of organometallic chemistry, producing millions of metric tons of aldehydes and alcohols annually.

Hydroformylation - general reaction scheme - oxo reaction - oxo process - oxo synthesis
  • R1 = H, alkyl, vinyl, aryl
  • R2 = H, alkyl
  • R3 = CHO, CH2OH

Under specific conditions, aldehydes dominate at lower temperatures, while alcohols are the primary products at higher temperatures. In some cases, the process is conducted in two stages to produce both aldehydes and alcohols. Straight-chain terminal olefins typically lead to isomeric aldehydes or alcohols, while ethylene produces ketones.

α,β-unsaturated aldehydes and ketones can undergo direct reduction to saturated aldehydes and ketones without hydroformylation, but under similar pressure and higher temperatures, they are fully reduced. Conjugated dienes and furans undergo both types of reactions, while benzene is inert under hydroformylation conditions.

Rhodium-catalyzed hydroformylation adds hydrogen and formyl groups to both cis and trans internal olefins with high stereospecificity. However, due to the high cost of rhodium catalyst, the process has been modified using a VIB group metal complex in combination with trace amounts of cobalt or rhodium carbonyl. This modification allows for adjustments in catalytic activity and selectivity.