Criegee oxidation
{{distinguish|Criegee rearrangement|Criegee intermediate|Criegee mechanism}}
{{Reactionbox
| Name = Criegee oxidation
| Type = Organic redox reaction
| NamedAfter = Rudolf Criegee
| Section3 = {{Reactionbox Identifiers
| RSC_ontology_id = 0000257
}}
}}
The Criegee oxidation is a glycol cleavage reaction in which vicinal diols are oxidized to form ketones and aldehydes using lead tetraacetate. It is analogous to the use of periodate (Malaprade reaction) but uses a milder oxidant. This oxidation was discovered by Rudolf Criegee and coworkers and first reported in 1931 using ethylene glycol as the substrate.{{cite journal|last1=Criegee|first1=R.|title=Eine oxydative Spaltung von Glykolen|journal=Berichte der Deutschen Chemischen Gesellschaft|date=1931|volume=64|pages=260–266|doi=10.1002/cber.19310640212}}
The rate of the reaction is highly dependent on the relative geometric position of the two hydroxyl groups, so much so that diols that are cis on certain rings can be reacted selectively as opposed to those that are trans on them.{{cite journal|last1=Reeves|first1=Richard E.|title=Direct Titration of cis-Glycols with Lead Tetraacetate|journal=Analytical Chemistry|date=1949|volume=21|issue=6|pages=751|doi=10.1021/ac60030a035}} It was heavily stressed by Criegee that the reaction must be run in anhydrous solvents, as any water present would hydrolyze the lead tetraacetate; however, subsequent publications have reported that if the rate of oxidation is faster than the rate of hydrolysis, the cleavage can be run in wet solvents or even aqueous solutions.{{cite journal|first1=Erich|last1=Baer|first2=J. M.|last2=Grosheintz|first3=Hermann O. L.|last3=Fischer|title=Oxidation of 1,2-Glycols or 1,2,3-Polyalcohols by Means of Lead Tetraacetate in Aqueous Solution|journal=Journal of the American Chemical Society|date=1939|volume=61|issue=10|pages=2607–2609|doi=10.1021/ja01265a010}} For example, glucose, glycerol, mannitol, and xylose can all undergo a Criegee oxidation in aqueous solutions, but sucrose cannot.{{cite journal|first1=Robert C.|last1=Hockett|first2=Morris|last2=Zief|title=Lead Tetraacetate Oxidations in the Sugar Group. XI. The Oxidation of Sucrose and Preparation of Glycerol and Glycol|journal=Journal of the American Chemical Society|date=1950|volume=72|pages=2130–2132|doi=10.1021/ja01161a073}}{{cite journal|last1=Abraham|first1=Samuel|title=The Quantitative Recovery of Carbon Dioxide in Lead Tetraacetate Oxidations of Sugars and Sugar Derivatives|journal=Journal of the American Chemical Society|date=1950|volume=72|issue=9|pages=4050–4053|doi=10.1021/ja01165a058}}
Mechanism
Two mechanisms are proposed for the Criegee oxidation, depending on the configuration of the diol.{{March6th|page=1732-1734}}{{cite journal|first1=Rudolf|last1=Criegee|first2=Eberhard|last2=Büchner|first3=Werner|last3=Walther|title=Die Geschwindigkeit der Glykolspaltung mit BleiIV-acetat in Abhängigkeit von der Konstitution des Glykols|journal=Berichte der Deutschen Chemischen Gesellschaft|date=1940|volume=73|issue=6|pages=571–575|doi=10.1002/cber.19400730603}} If the oxygen atoms of the two hydroxy groups are conformationally close enough to form a five-membered ring with the lead atom, the reaction occurs via a cyclic intermediate. If the structure cannot adopt such a conformation, an alternate mechanism is possible, but is slower.{{cite encyclopedia|first1=Mihailo Lj.|last1=Mihailović|first2=Živorad|last2=Čeković|first3=Brian M.|last3=Mathes|title=Lead(IV) Acetate|encyclopedia=e-EROS Encyclopedia of Reagents for Organic Synthesis|date=2005|pages=114–115|publisher=Elsevier|doi=10.1002/047084289X.rl006.pub2|isbn=0471936235}} Trans-fused five member rings are heavily strained, thus trans-diols that are on a five-membered ring will react slower than cis-alcohols on such a structure.{{cite book|last1=László, Barbara|first1=Kürti, Czakó|title=Strategic Applications of Named Reactions in Organic Synthesis|date=2005|publisher=Elsevier Academic Press|location=Murlington, MA|isbn=978-0-12-429785-2|pages=114–115}}
Modifications
Although the classic substrate for the Criegee oxidation are 1,2-diols, the oxidation can be employed with β-amino alcohols,{{cite journal|first1=Nelson J.|last1=Leonard|first2=Melvin A.|last2=Rebenstorf|title=Lead Tetraacetate Oxidation of Aminoalcohols|journal=Journal of the American Chemical Society|date=1945|volume=67|pages=49–51|doi=10.1021/ja01217a016}} α-hydroxy carbonyls,{{cite journal|first1=David A.|last1=Evans|author1-link=David A. Evans|first2=Steven L.|last2=Bender|first3=Joel|last3=Morris|title=The total synthesis of the polyether antibiotic X-206|journal=Journal of the American Chemical Society|date=1988|volume=110|issue=8|pages=2506–2526|doi=10.1021/ja00216a026}} and α-keto acids,{{cite journal|last1=Baer|first1=Erich|title=Oxidative Cleavage of Cyclic α-Keto Alcohols by Means of Lead Tetraacetate|journal=Journal of the American Chemical Society|date=1942|volume=64|issue=6|pages=1416–1421|doi= 10.1021/ja01258a049}} In the case of β-amino alcohols, a free radical mechanism is proposed.
The Criegee oxidation can also be employed with 2,3-epoxy alcohols forms α-acetoxy carbonyls. Because the substrates can be produced with specific stereochemistry, such as by Sharpless epoxidation of allylic alcohols, this process can yield chiral molecules.{{cite journal|first1=Enrique|last1=Alvarez-Manzaneda|first2=Rachid|last2=Chahboun|first3=Esteban|last3=Alvarez|first4=Ramón|last4=Alvarez-Manzaneda|first5=Pedro E.|last5=Muñoz|first6=Fermín|last6=Jiménez|first7=Hanane|last7=Bouanou|title=Lead(IV) acetate oxidative ring-opening of 2,3-epoxy primary alcohols: a new entry to optically active α-hydroxy carbonyl compounds|journal=Tetrahedron Letters|date=2011|volume=52|issue=31|pages=4017–4020|doi=10.1016/j.tetlet.2011.05.116}}
Criegee oxidations are commonly used in carbohydrate chemistry to cleave 1,2-glycols and differentiate between different kinds of glycol groups.{{cite book|last1=Perlin|first1=A. S.|chapter=Action of Lead Tetraacetate on the Sugars|title=Advances in Carbohydrate Chemistry|date=1959|volume=14|pages=9–61|doi=10.1016/S0096-5332(08)60222-2|pmid=14431883|isbn=9780120072149}}