Kochi reaction

What is Kochi reaction?

In 1965, Kochi reported a reaction that converts carboxylic acids into halides through oxidative degradation by lead tetraacetate (LTA) under free-radical conditions, accompanied by simultaneous replacement with a halogen in the presence of a metal halide. This reaction is known as the Kochi reaction or Kochi oxidative decarboxylation.

Kochi reaction - general reaction scheme
Kochi reaction

Without a metal halide, carboxylic acids will oxidize into various compounds depending on experimental conditions, either thermally or photochemically. The structure of the substrate also affects the oxidation outcome, with tertiary and α-arylalkyl carboxylic acids readily converted into alkenes and esters. Various oxidants, including manganese (III) salt and silver (II) salt, are effective for oxidative decarboxylation.

Pyridine, trialkylamines, and peroxides can enhance the reaction, while a copper salt can catalyze it. In the presence of metal halide, alkyl halides form as major products depending on the reaction conditions, with excellent yields of alkyl chlorides from secondary and tertiary acids if a stoichiometric amount of metal chloride is present. However, alkyl chlorides vanish if an excess amount of metal chlorides are present. Alkyl bromides and iodides can also be formed from oxidative decarboxylation in the presence of corresponding bromide and iodide salts, although relatively low yields are obtained.

The reaction does not work well for benzoic acid, but α,β-unsaturated carboxylic acids can undergo oxidative decarboxylation to afford halogenated olefins using oxidants such as iodosylbenzene or iodosylbenzene diacetate and N-bromo, N-chloro, or N-iodosuccinimide. However, no detectable radical intermediate was found for the oxidative decarboxylations of 2-hydroxycarboxylic acids by lead tetraacetate in anhydrous acetic acid.