Decarbonylation

In chemistry, decarbonylation is a type of organic reaction that involves the loss of carbon monoxide (CO). It is often an undesirable reaction, since it represents a degradation. In the chemistry of metal carbonyls, decarbonylation describes a substitution process, whereby a CO ligand is replaced by another ligand. In the absence of metal catalysts, decarbonylation (vs decarboxylation) is rarely observed in organic chemistry. One exception is the decarbonylation of formic acid: The reaction is induced by sulfuric acid, which functions as both a catalyst and a dehydrating agent. Via this reaction, formic acid is occasionally employed as a source of CO in the laboratory in lieu of cylinders of this toxic gas. With strong heating, formic acid and some of its derivatives may undergo decarbonylation, even without adding a catalyst. For instance, dimethylformamide () slowly decomposes to give dimethylamine and carbon monoxide when heated to its boiling point (154 °C). Some derivatives of formic acid, like formyl chloride (), undergo spontaneous decarbonylation at room temperature (or below). Reactions involving oxalyl chloride (e.g., hydrolysis, reaction with carboxylic acids, Swern oxidation, etc.) often liberate both carbon dioxide and carbon monoxide via a fragmentation process. α-Hydroxy acids, e.g. (lactic acid and glycolic acid) undergo decarbonylation when treated with catalytic concentrated sulfuric acid, by the following mechanism: Silacarboxylic acids () undergo decarbonylation upon heating or treatment with base and have been investigated as carbon monoxide-generating molecules. A common transformation involves the conversion of aldehydes to alkanes. Decarbonylation can be catalyzed by soluble metal complexes. These reactions proceed via the intermediacy of metal acyl hydrides. An example of this is the Tsuji–Wilkinson decarbonylation reaction using Wilkinson's catalyst. (Strictly speaking, the noncatalytic version of this reaction results in the formation of a rhodium carbonyl complex rather than free carbon monoxide.