Glycol cleavage

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The glycol cleavage is the oxidative cleavage of vicinal cis - and trans - diols to carbonyl compounds .

Overview reaction

Lead (IV) acetate or meta - periodic acid are usually used as oxidizing agents . Both methods are name reactions of organic chemistry . If the glycol is split with lead (IV) acetate, it is known as the Criegee reaction . The reaction was named after the German chemist Rudolf Criegee (1902–1975) . The cleavage with periodic acid was discovered by Léon Malaprade (1903–1982) and is therefore called the Malaprade reaction .

Glycol splitting, overview reaction

Reaction mechanisms

The reaction mechanisms of both reactions are not fully understood. The following mechanisms are believed by several authors to be the most likely.

Criegee reaction

First of all, the vicinal cis diol 1 should be cleaved by lead (IV) acetate. For this purpose, an acetate residue is protonated by the diol in an equilibrium reaction , whereby an acetic acid molecule and the alcoholate 2 are formed. Through the formation of a covalent bond to the positively charged lead (IV) acetate cation, compound 3 is formed in an addition reaction .

Reaction mechanism of glycol cleavage, cis-diols, Criegee, a

In the next step, another acetate anion of the lead (IV) acetate is protonated by the second hydroxyl group . The resulting alcoholate also forms a covalent bond with the lead atom. With renewed elimination of an acetic acid molecule, the five-membered, cyclic intermediate 4 is formed . Through ring opening and with elimination of lead (II) acetate , ketone 5 and aldehyde 6 are formed . Depending on which radicals are chosen, two ketones or aldehydes can also be obtained.

Reaction mechanism of glycol cleavage, cis-diols, Criegee, b

For the cleavage of a vicinal trans diol 7 , an acid-catalyzed mechanism is proposed that does not proceed via a cyclic intermediate. The reaction initially proceeds analogously to the cleavage of a cis diol.

Reaction mechanism of glycol cleavage, trans-diols, Criegee

Here, however, the oxygen atom of the acetate residue bound to the carbon atom with a double bond is protonated. Here, too, an acetic acid molecule and lead (II) acetate are split off. The products 5 and 6 obtained remain the same.

Malaprade reaction

The following mechanism applies only to cis diols. Here, too, the periodic acid is added to one of the two hydroxyl groups.

Reaction mechanism of glycol cleavage, cis-trans-diols, Malaprade, a

The five-membered, cyclic diester of iodine (VII) acid 9 is formed by the protonation of individual oxygen atoms in periodic acid .

Reaction mechanism of glycol cleavage, cis-trans-diols, Malaprade, b

H 3 IO 4 is eliminated by ring opening , whereby the carbonyl compounds 5 and 6 are formed. H 3 IO 4 breaks down into water and iodic acid .

Practical meaning

The importance of the reactions lies primarily in the preparative, analytical and theoretical areas. Aliphatic aldehydes with a particularly complex structure are more easily accessible. Sugar chemistry benefits from the reaction because it can be used to analyze vicinal and geminal diols. Thus, the determination of the constitution is facilitated by the glycol cleavage. The Malaprade reaction brought forth the acidometric titration of polyols as a new analytical tool . The splitting of the glycol was of theoretical importance for the final clarification of the first stage of alcoholic fermentation, which was previously difficult to access . Splitting with water-soluble periodic acid is a good alternative to split saccharides because they are difficult to dissolve in organic solvents. Sodium periodate can also be used for acid-sensitive substances . If the glycol cleavage is carried out on dextrans , high molecular weight polyaldehydes are obtained. These are able to bind amino groups of proteins as imines and thereby form adjuvants . Adjuvants are auxiliary substances that enhance the effect of drugs or reagents. That is why glycol cleavage also plays an important role in medicine .

literature

  • Jie Jack Li: Name reactions, a collection of detailed reaction mechanism. Vol 1. Springer 2002 , p. 85. ISBN 3-540-43024-5 .
  • Z. Wang: Comprehensive Organic Name Reactions and Reagents , Vol 1. John Wiley & Sons, Hoboken, New Jersey 2009 , pp. 761-764, ISBN 978-0-471-70450-8 .
  • Z. Wang: Comprehensive Organic Name Reactions and Reagents , Vol 2. John Wiley & Sons, Hoboken, New Jersey 2009 , pp. 1807-1810, ISBN 978-0-471-70450-8 .
  • SK Wiberg, SW Trahanovsky: Oxidation in organic chemistry , Vol 5 (D). Academic Press, New York 1982 , pp. 27-37, ISBN 0-12-697253-2 (Pt. D).
  • HG Maier: Food and Environmental Analysis: Methods and Applications , Vol 1. Steinkopf Verlag, Darmstadt 1990 , p. 51, ISBN 3-7985-0789-9 .
  • T. Laue, A. Plagens: Name and keyword reactions of organic chemistry , Vol 5. Teubner Verlag, Wiesbaden 2006 , pp. 155–157, ISBN 3-8351-0091-2 .

Individual evidence

  1. ^ R. Criegee, E. Höger, G. Huber, P. Kruck, F. Marktscheffel, H. Schellenberger: The speed of glycol splitting with lead tetraacetate as a function of the constitution and configuration of the glycol. ( Part III) , Justus Liebigs Annalen der Chemie 1956 , 599 , pp. 82-124, doi : 10.1002 / jlac.19565990202 .
  2. ↑ R. Criegee: An oxidative cleavage of glycols (second part. On oxidations with lead (IV) salts) , reports of the German chemical society 1930 , 64 , pp. 260–266, doi : 10.1002 / cber.19310640212 .
  3. ↑ B. Sklarz: Organic chemistry of periodates , Royal Society of Chemistry 1967 , 21 , pp. 3-28, doi : 10.1039 / QR9672100003 .
  4. ^ EL Jackson, CS Hudson: The Structure of the Products of the Periodic Acid Oxidation of Starch and Cellulose , Journal of the American Chemical Society 1938 , 60 , pp. 989-991, doi : 10.1021 / ja01272a001 .
  5. ↑ M. Abdel-Akher, F. Smith: Oxidation of Glycogen with Periodic Acid , Journal of the American Chemical Society 1958 , 81 , pp. 1718-1721, doi : 10.1021 / ja01516a049 .
  6. ↑ E. Baer, ​​JM Grosheintz, HOL Fischer: Oxidation of 1,2-Glycols or 1,2,3-Polyalcohols by Means of Lead Tetraacetate in Aqueous Solution , Journal of the American Chemical Society 1939 , pp. 2607-2609, doi : 10.1021 / ja01265a010 .
  7. ↑ RC Hockett, M. Zief: Lead Tetraacetate Oxidations in the Sugar Group. XI. The Oxidation of Sucrose and Preparation of Glycerol and Glycol , Journal of the American Chemical Society 1949 , 72 , pp. 2130-2132, doi : 10.1021 / ja01161a073 .
  8. ↑ WA Krotoski, HE Weimer: Peptide-associated and antigenic changes accompanying periodic acid oxidation of human plasma orosomucoid , Archives of Biochemistry and Biophysics 1966 , 115 , pp. 337-344, doi : 10.1016 / 0003-9861 (66) 90284-0 .