14.3.2: Hydroformylation

Catalytic Olefin Hydroformylation

An important industrial reaction is the catalytic hydroformylation reaction, also known as oxo-process (Figure \(\PageIndex{1}\)). It was discovered in 1938 by Otto Roelen at BASF. In the hydroformylation reaction an H atom and a formyl group are added to an alkene to form aldehydes. The reaction can produce both branched an linear aldehydes from terminal alkenes, CO, and H₂ using a carbonyl hydrides such as HCo(CO)₄ as a catalyst. The reaction is performed at about 100°C at a pressure of up to 100 atm.

Figure \(\PageIndex{1}\): Catalytic olefin hydroformylation

Mechanism of the Catalytic Olefin Hydroformylation by HCo(CO)₄

How does the hydroformylation work mechanistically?

Figure \(\PageIndex{2}\): Mechanism of the catalytic olefin hydroformylation by HCo(CO)₄ (Attribution: A. Vedernikov, U Maryland (modified).)

The mechanism is illustrated for the hydroformylation of propene (Fig. \(\PageIndex{2}\):). The actual catalyst HCo(CO)₄ is first formed from its precatalyst Co₂(CO)₈ in the presence of H₂ in a dinuclear oxidative addition reaction. The catalyst can undergo a substitution reaction in which a CO ligand is replaced by the olefin that binds side-on to the cobalt. This species can then undergo a migratory olefin insertion reaction. This leads to a mixture of linear and branched alkyl groups attached to the Co. A new CO ligand can add to the vacant site. The alkyl group can then insert into a carbonyl group in another migratory insert step, and the vacant site can be reoccupied by a new CO molecule. Then, H₂ is added in an oxidative addition. This is the slowest and rate-limiting step in the catalytic cycle. From the addition product the aldehyde can then be eliminated in a reductive elimination reaction. Addition of CO regenerates the catalyst, and the catalytic cycle can begin again.

Hydrocarbonylations

After the hydroformylation, a number of other hydrocarbonylations were developed, and industrially deployed.

Figure \(\PageIndex{3}\): Hydrocarbonylation reactions

When hydrogen is replaced by H₂O hydrocarboxylations of alkenes lead to carboxylic acids (Fig. \(\PageIndex{3}\):). With an alcohol instead of H₂ hydroalkoxycarbonylcations lead to esters. The employment of amines instead of H₂ leads to amides in hydroamidocarbonylation reactions.