Barakat oxidation

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The Barakat oxidation , also Barakat dehydration , is a name reaction in organic chemistry. It was first described in 1952 by the chemist Mohamed Zaki Barakat . It is used to oxidize alcohols to aldehydes or ketones .

Overview reaction

In this reaction, primary alcohols (R = alkyl, aryl) are oxidized to aldehydes by N -bromosuccinimide :

Barakat oxidation / aldehyde formation

From secondary alcohols (R 1 , R 2 = alkyl, aryl), ketones are formed analogously:

Barakat oxidation / ketone formation

Atomic economy

The Barakat dehydrogenation is a reaction of low atomic efficiency , since stoichiometric amounts of two waste materials ( hydrogen bromide and succinimide ) of high molecular weight are produced. Consequently, this reaction is uneconomical for technical applications and a pure laboratory method.

Reaction mechanism

It is assumed that in alcohol the α-hydrogen atom ( marked blue above ) on the carbon atom with the hydroxyl group is replaced by a bromine atom. Then hydrogen bromide is split off from the resulting molecule , so that the carbonyl compound (aldehyde or ketone) and succinimide are formed.

variants

With the help of N- bromo succinimide, for example, phenols , aromatic amines and aromatic carboxylic acids which contain hydroxyl and amino groups can also be brominated. A multiple bromination is also possible here without changing the original substituents. However, if the original substance contains a functional group of sulfonic acid (–SO 2 OH), these are replaced by bromine. Sulfanyl groups (–SH), on the other hand, are oxidized to disulfide . Under the action of N- bromo succinimide, phenylacetic acid is broken down in aqueous solution to benzaldehyde. Amino acids can be decarboxylated under the influence of N -bromo succinimide. Polyhydric alcohols such as glycerol are completely converted into carbon dioxide and water when they react with N -bromosuccinimide.

Individual evidence

  1. ↑ a b c d Entry on Barakat oxidation. In: Römpp Online . Georg Thieme Verlag, accessed on April 6, 2020.
  2. ↑ a b Eberhard Breitmaier, Günther Jung: Organic Chemistry: Basics, Compound Classes, Reactions, Concepts, Molecular Structure, Natural Products, Synthesis Planning, Sustainability Vol. 7. Georg Thieme Verlag, Stuttgart, 2012, p. 268, ISBN 978-3-13- 541507-9 .
  3. ↑ MF Abdel-Wahab, MZ Barakat: The use of N-bromosuccinimide in bromination and degradation reactions . In: Monthly books for chemistry and related parts of other sciences, 1957, Vol. 88, pages 692-701, doi 10.1007 / BF00901354 .
  4. ^ MZ Barakat, GM Mousa: The action of N-Bromosuccinimide on alcohols and amines . In: Journal of Pharmacy and Pharmacology, 1952, Vol. 4, No. 1, pp. 115-117, https://doi.org/10.1111/j.2042-7158.1952.tb13121.x .