Glycol cleavage is a specific type of organic chemistry

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

. The carbon–carbon bond in a 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 ...

(glycol) is cleaved and instead the two oxygen atoms become double-bonded to their respective carbon atoms. Depending on the substitution pattern in the diol, these

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...

s can be either

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 or

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

s. Glycol cleavage is an important reaction in the laboratory because it is useful for determining the structures of sugars. After cleavage takes place the ketone and aldehyde fragments can be inspected and the location of the former hydroxyl groups ascertained.

Reagents

Periodic acid Periodic acid ( ) is the highest oxoacid of iodine, in which the iodine exists in oxidation state +7. Like all periodates it can exist in two forms: orthoperiodic acid, with the chemical formula , and metaperiodic acid, which has the formula . ...

(HIO₄),

(diacetoxyiodo)benzene (Diacetoxyiodo)benzene, also known as phenyliodine(III) diacetate (PIDA) is a hypervalent iodine chemical with the formula . It is used as an oxidizing agent in organic chemistry. Preparation This reagent was originally prepared by Conrad Willg ...

(PhI(OAc)₂) and

lead tetraacetate Lead(IV) acetate or lead tetraacetate is an organometallic compound with chemical formula . It is a colorless solid that is soluble in nonpolar, organic solvents, indicating that it is not a salt. It is degraded by moisture and is typically store ...

(Pb(OAc)₄) are the most common reagents used for glycol cleavage, processes called 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 ...

and

Criegee oxidation 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 Malaprade reaction, but uses a milder oxidant. This oxidation was discovere ...

, respectively. These reactions are most efficient when a cyclic intermediate can form, with the iodine or lead atom linking both oxygen atoms. The ring then fragments, with breakage of the carbon–carbon bond and formation of carbonyl groups. If an R group is a hydrogen atom, an aldehyde is formed at that site. If the R group is a chain that begins with a carbon atom, a ketone is formed. : Glycol cleavage

Warm concentrated

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

(KMnO₄) will react with an alkene to form a glycol. Following this

dihydroxylation Dihydroxylation is the process by which an alkene is converted into a vicinal diol. Although there are many routes to accomplish this oxidation, the most common and direct processes use a high-oxidation-state transition metal (typically osmium or ...

, the KMnO₄ can then easily cleave the glycol to give aldehydes or ketones. The aldehydes will react further with (KMnO₄), being oxidized to become

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

s. Controlling the temperature and concentration of the reagent can keep the reaction from continuing past the formation of the glycol.

Reagents

References

External links