Lieben iodoform reaction

What is Lieben iodoform reaction?

Lieben reported in 1870 an alkaline degradation reaction that involves the use of iodine treatment to convert compounds containing acetyl or methylcarbinol groups into volatile iodoform. This reaction, which is widely known as the Lieben iodoform reaction, has been utilized as a means to test for the presence of these groups in compounds.

The Lieben iodoform reaction is also referred to as the Lieben reactioniodoform test of Lieben, or simply the Lieben test.

Lieben iodoform reaction - general reaction scheme - Lieben reaction - iodoform test of Lieben - Lieben test
Lieben iodoform reaction

R = H, alkyl, aryl

The positive test results for the methylcarbinol group are thought to be due to the oxidation of such groups by hypoiodite generated in situ from the alkaline disproportionation of iodine.

The Lieben test has been found to give a positive result for compounds that generate the acetyl group under test conditions, such as through the retro aldol condensation of α,β-unsaturated compounds.

Compounds with groups that exhibit excessive steric hindrance have also been shown to yield positive results. However, some ketones, including α-chloroacetophenone, acetomesitylene, propiophenone, pinacolone, and similar compounds with steric hindrance, have been found to yield negative results.

While the original procedure involves the use of iodine and excess base and can detect compounds at concentrations as low as 1 part in 2000, it often yields ambiguous results because of the anesthetic effect of iodoform on the olfactory nerve.

Before the advent of modern spectroscopy, the reaction described above had significant utility in the determination of the structures of organic compounds. Furthermore, it has also been utilized to synthesize α-monoiodo and α-diiodoketones using less than the theoretical amount of iodine.

References

  • M. Serullas, Ann. Chim., 1822, 20, 165
  • A. Lieben, Liebigs Ann. Chem. (Suppl. binding) 1870, 7, 218
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