Iodoform sample

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negative and positive iodoform sample

The iodoform sample , also known as the Lieben reaction , is used to detect chemical compounds that contain an acetyl group (H 3 C-CO-) or a 1-hydroxyethyl group (H 3 C-CH (OH) -). These compounds include, for example, acetone or ethanol . This sample was discovered by Adolf Lieben in 1870 .

Overview reaction

In the Lieben reaction, an alkaline iodine solution splits methyl ketones into carboxylic acid salt and iodoform.

Overview reaction love reaction

The substance to be tested is mixed with potassium hydroxide and Lugol's solution and briefly heated, whereupon the yellow and water-insoluble iodoform is formed.

The reaction can also be carried out with primary and secondary methyl carbinols. These are oxidized to the respective carbonyl compounds.

Reaction mechanism

This is a haloform reaction . The reaction is a combination of two different reactions.

First reaction phase

In the first reaction phase, the methyl group of the methyl ketone is triply iodinated. Here, the basic aldol reaction forms the enolate form, which attacks the electron- loving particle of the iodine molecule.

First part. Love-response mechanism

The second and third halogenation of the methyl group is completely analogous.

Second reaction phase

In the second reaction phase, the actual cleavage of the triiodo ketone formed is carried out into a carboxylic acid and iodoform.

Second part. Love-response mechanism

The cleavage is initiated by adding a base. The hydroxide ion attacks the carbonyl carbon. A triiodomethyl anion is then split off. This is protonated by adding acid to the iodoform.

Individual evidence

  1. ↑ Entry on Haloform reaction. In: Römpp Online . Georg Thieme Verlag, accessed on June 14, 2014.
  2. ↑ A. Lieben: On the formation of iodoform and the application of this reaction in chemical analysis. In: Justus Liebigs Ann. Chem. 1870 Supp. 7, 218-236.
  3. ↑ A. Lieben: Postscript to the treatise on the formation of iodoform and application of this reaction in chemical analysis. In: Justus Liebigs Ann. Chem. 1870 Supp. 7, 377-378.
  4. ↑ a b c Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, New Jersey 2009, ISBN 978-0-471-70450-8 , pp. 1750-1753 .
  5. ↑ a b Thomas Laue, Andreas Plagens: Name and keyword reactions in organic chemistry . Teuber, Wiesbaden 2006, ISBN 3-8351-0091-2 , pp. 169-171.
  6. ↑ Thomas Laue, Andreas Plagens: Name and catchword reactions of organic chemistry. Teuber, Wiesbaden 2006, ISBN 3-8351-0091-2 , p. 11.