The Criegee oxidation is a

glycol cleavage Glycol cleavage is a specific type of organic chemistry oxidation. The carbon–carbon bond in a vicinal diol (glycol) is cleaved and instead the two oxygen atoms become double-bonded to their respective carbon atoms. Depending on the substituti ...

reaction in which vicinal

diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. The most common industrial diol is e ...

s are oxidized to form

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...

s and aldehydes using lead tetraacetate. It is analogous to the

Malaprade reaction In organic chemistry, the Malaprade reaction or Malaprade oxidation is a glycol cleavage reaction in which a vicinal diol is oxidized by periodic acid or a periodate salt to give the corresponding carbonyl functional groups. The reaction was first ...

, but uses a milder oxidant. This oxidation was discovered by

Rudolf Criegee Rudolf Criegee (* May 23, 1902 in Düsseldorf; † November 7, 1975 in Karlsruhe) was a German organic chemist. Early life Criegee's family was wealthy. His father worked as a court director. The family was national liberal, Prussian and Prot ...

and coworkers and first reported in 1931 using ethylene glycol as the substrate. Glycol Criegee

The rate of the reaction is highly dependent on the relative geometric position of the two

hydroxyl group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy g ...

s, so much so that diols that are '' cis'' on certain rings can be reacted selectively as opposed to those that are ''trans'' on them. It was heavily stressed by Criegee that the reaction must be run in

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

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. For example, glucose, glycerol, mannitol, and xylose can all undergo a Criegee oxidation in aqueous solutions, but

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

cannot.

Mechanism

There are two mechanisms proposed for the Criegee oxidation which depend on the configuration of the diol. 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. ''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. Criegee Mechansim

Modifications

Although the classic substrate for the Criegee oxidation are 1,2-diols, the oxidation can be employed with β-amino alcohols, α-hydroxy carbonyls, and α-keto acids, In the case of β-amino alcohols, a free radical mechanism is proposed. The Criegee oxidation can also be employed with 2,3-

epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...

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. Criegee epoxide mech

Criegee oxidations are commonly used in carbohydrate chemistry to cleave 1,2-glycols and differentiate between different kinds of glycol groups.

References

{{Reflist Name reactions Organic oxidation reactions