Alkenyl peroxides

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General structure of an alkenyl peroxide

Alkenyl peroxides are chemical compounds that have an alkenyl group attached to the peroxide group . They are generally characterized by a significantly greater instability compared to other peroxides.

properties

Peroxides with an adjacent alkenyl group decompose very easily by homolytic cleavage of the OO bond into two radicals , an oxyl radical and an alkenyloxyl or α-oxo-alkyl radical.

Decomposition of alkenyl peroxides by homolytic breaking of the OO bond

The weak OO bond can be justified by the resonance stabilization of the alkenyloxyl radical, which can also be understood as an oxy-allyl radical, or the formation of the strong carbonyl bond . Correspondingly, this also applies to the structurally related aryl peroxides. The OO bond is therefore much weaker than with other peroxides. Due to their easy decomposition, alkenyl and aryl peroxides are generally postulated only as reactive intermediates. As an exception, few heteroaryl peroxides are known that were long enough for characterization.

Occurrence and manufacture

In the atmosphere

Alkenyl hydroperoxides (R1 = H) have been postulated as reactive intermediates in atmospheric chemistry. They are formed by ozonolysis of alkenes in the atmosphere and, as a result of their decay, form hydroxyl radicals , which play an important role in the breakdown of organic compounds in the atmosphere. During the day, hydroxyl radicals are primarily formed photochemically ; at night, alkenyl peroxides are believed to be the main source of their formation.

In solution

In solution, alkenyl peroxides can be produced by the acid-catalyzed condensation of ketones with organic hydroperoxides or hydrogen peroxide . This is suspected based on the characterization of the corresponding decay products. It is assumed that alkenyl peroxides occur in Baeyer-Villiger oxidations with hydrogen peroxide as undesirable by-products which, through their decomposition and subsequent reactions, reduce the effectiveness of these reactions.

use

Alkenyl peroxides can be used in radical reactions. The resulting radicals can mediate the functionalization of CH bonds through H abstraction reactions, and the alkenyloxyl radicals can also be used to introduce keto groups in organic synthesis through addition to alkenes.

Individual evidence

  1. ↑ M. Klussmann: Alkenyl and Aryl Peroxides . In: Chemistry - A European Journal . tape 24 , no. 18 , 2017, p. 4480-4496 , doi : 10.1002 / chem . 201703775 .
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  8. ↑ M. Klussmann, B. Schweitzer-Chaput, Synlett 2016, 27, 190–202. doi: 10.1055 / s-0035-1560706 .
  9. ↑ B. Schweitzer-Chaput, J. Demaerel, H. Engler, M. Klussmann, Angew. Chem. Int. Ed. 2014, 53, 8737-8740, doi: 10.1002 / anie.201401062 .
  10. ↑ E. Boess, S. Karanestora, A.-E. Bosnidou, B. Schweitzer-Chaput, M. Hasenbeck, M. Klussmann, Synlett 2015, 26, 1973–1976. doi: 10.1055 / s-0034-1381052 .
  11. ↑ X.-F. Xia, S.-L. Zhu, M. Zeng, Z. Gu, H. Wang, W. Li, Tetrahedron 2015, 71, 6099-6103, doi: 10.1016 / j.tet.2015.06.106 .