Karbonylation

Karbonylation is a class of chemical reactions in which a carbonyl group (C=O) is introduced into a molecule, typically through the insertion of carbon monoxide (CO) into a bond or via a CO-containing environment. In many contexts the term refers to catalytic processes that convert simple substrates into aldehydes, acids, esters, or related derivatives under CO pressure.

A central subset is hydroformylation (oxo process), where alkenes react with CO and hydrogen to yield aldehydes. This reaction is commonly catalyzed by rhodium- or cobalt-based systems and is widely used to produce aldehydes that can be further converted to alcohols or acids. Another important industrial example is the carbonylation of methanol to acetic acid, realized in Monsanto and later Cativa processes. These involve CO and methanol under rhodium or iridium catalysis, producing acetic acid with high selectivity under high pressure.

Carbonylation also encompasses reactions where CO inserts into metal–substrate bonds to furnish acyl derivatives. For example, palladium- or nickel-catalyzed carbonylations of aryl halides or olefins can form esters, amides, or acids via carbonyl insertion and subsequent functionalization. Hydroxycarbonylation adds CO and water to unsaturated substrates to give carboxylic acids. Mechanistically, many carbonylations proceed through steps such as oxidative addition of the substrate to a metal center, migratory insertion of CO, and reductive elimination to release the product.

Applications span the synthesis of fine chemicals, polymers, and commodity chemicals. Safety considerations include the toxicity of carbon monoxide and the need for controlled high-pressure equipment and inert handling.