Riley oxidation

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The Riley oxidation is a name reaction in organic chemistry and named after the chemist Harry Lister Riley (1899–1986). It is a selective, gentle oxidation method of ketones and alkenes , whereby the carbon atom in the α-position to the carbonyl group or C = C double bond is oxidized with the highly toxic selenium dioxide to form aldehyde , ketone or alkene. Suitable solvents are dioxane , a mixture of acetic acid and acetic anhydride or water.

Response overview

  • an allylic methyl group (or methylene group or methine group) can be oxidized to alcohol by Riley oxidation if a solvent is used. A ketone or aldehyde is formed when working in the gas phase.
Riley oxidation 1.svg
  • an α- methyl group (or methylene group) of carbonyl compounds can be oxidized with selenium dioxide to form the 1,2-dicarbonyl compound:
Riley oxidation 2.svg
  • 1,4-diketones can be oxidized with selenium dioxide to unsaturated 1,4-diketones:
Riley oxidation 5.svg

Reaction mechanism

This section describes the first two mechanisms of the overview reactions. If an alkene 1 is reacted with selenium dioxide, the double bond initially undergoes a nucleophilic attack on the selenium of the selenium dioxide. A proton is transferred in the process. This can be classified as an ene reaction. After a [2,3] rearrangement, intermediate 3 , which is oxidized in the allyl position and which, after splitting off selenium oxide, yields the desired allyl alcohol 4 , then arises .

Mechanism 1 of the Riley oxidation

If the ketone 5 is reacted with selenium dioxide, the first reaction step is determined by a nucleophilic attack on the selenium of the selenium dioxide by the carbonyl group of the ketone. A proton is transferred and, after further electron pair rearrangements, ketone 7 is obtained as an intermediate. In the last step, elemental selenium and water are split off, so that the desired 1,2-dicarbonyl compound 8 is formed.

Mechanism 2 of the Riley oxidation

advantages and disadvantages

  • A particular advantage of the reaction is that no further oxidation of aldehydes to carboxylic acids occurs , which is often observed with other oxidizing agents.
  • The reaction is very specific for oxo compounds and alkenes.
  • The high toxicity of the selenium dioxide used is a disadvantage.

Individual evidence

  1. ^ Harry Lister Riley, John Frederick Morley, Norman Alfred Child Friend: 255. Selenium dioxide, a new oxidizing agent. Part I. Its reaction with aldehydes and ketones. In: Journal of the Chemical Society. 1932, p. 1875, doi : 10.1039 / jr9320001875 .
  2. a b Dr. Thummel: Organic Synthesis & Reactions ( Memento of May 14, 2006 on the Internet Archive ), University of Houston.
  3. a b c Zerong Wang: Comprehensive Organic Name Reactions and Reagents , Volume 3, Wiley Verlag, 2009, p. 2395, ISBN 978-0-471-70450-8 , (3-Volume Set).
  4. a b c László Kürti , Barbara Czakó: Strategic Applications of Named Reactions in Organic Synthesis ; Elsevier Academic Press, Burlington-San Diego-London 2005, 1st edition; ISBN 0-12-369483-3 .
  5. GR Waitkins, CW Clark, Chem. Rev. 1945 , 36 , pp. 235-289.