Alcohol oxidation is a class of
organic reactions
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemi ...
in which the alcohol functional group is converted into another functional group (e.g.,
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 gro ...
,
ketone,
carboxylic acid) in which carbon carries a higher
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
.
Through a variety of mechanisms, the removal of a hydride equivalent converts a primary or secondary alcohol to an aldehyde or ketone, respectively. The oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate (''gem''-diol, R-CH(OH)
2) by reaction with water. Thus, the oxidation of a primary alcohol at the aldehyde level without further oxidation to the carboxylic acid is possible by performing the reaction in absence of water, so that no aldehyde hydrate can be formed.
Oxidation to aldehydes
Oxidation of alcohols to aldehydes is partial oxidation; aldehydes are further oxidized to carboxylic acids. Conditions required for making aldehydes are heat and distillation. In aldehyde formation, the temperature of the reaction should be kept above the boiling point of the aldehyde and below the boiling point of the alcohol.
Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones. These include:
*
Chromium-based reagents, such as
Collins reagent (CrO
3·Py
2),
PDC or
PCC.
*
Sulfonium species known as "activated
DMSO" which can result from reaction of DMSO with
electrophiles, such as
oxalyl chloride (
Swern oxidation), a
carbodiimide (
Pfitzner-Moffatt oxidation) or the complex SO
3·Py (
Parikh-Doering oxidation).
*Hypervalent iodine compounds, such as
Dess-Martin periodinane or
2-Iodoxybenzoic acid.
*Catalytic
TPAP in presence of excess of
NMO (
Ley oxidation
Ley may refer to:
Toponyms
* Ley (landform), name for a crag, rock or cliff in the north German language area
* Ley (crater), crater on the Moon
* Ley, Moselle, commune in France
* Ley Hill, hill in England
People
* Ley Matampi (born 19 ...
).
*Catalytic
TEMPO in presence of excess
bleach (
NaOCl
Sodium hypochlorite (commonly known in a dilute solution as bleach) is an inorganic chemical compound with the formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may also be viewed as the sodium salt of hy ...
) (
Oxoammonium-catalyzed oxidation).
*Catalytic transition metal complex in the presence of dioxygen or another terminal oxidant.
Allylic and benzylic alcohols can be oxidized in presence of other alcohols using certain selective oxidants such as
manganese dioxide (MnO
2).
Oxidation to ketones
Reagents useful for the oxidation of secondary alcohols to ketones, but normally inefficient for oxidation of primary alcohols to aldehydes, include
chromium trioxide
Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.
This compound is a dark-purple s ...
(CrO
3) in a mixture of sulfuric acid and
acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour.
Acetone is miscibl ...
(
Jones oxidation) and certain ketones, such as
cyclohexanone, in the presence of
aluminium isopropoxide
Aluminium isopropoxide is the chemical compound usually described with the formula Al(O-''i''-Pr)3, where ''i''-Pr is the isopropyl group (–CH(CH3)2). This colourless solid is a useful reagent in organic synthesis.
Structure
A tetrameric st ...
(
Oppenauer oxidation
Oppenauer oxidation, named after , is a gentle method for selectively oxidizing secondary alcohols to ketones.
The reaction is the opposite Meerwein–Ponndorf–Verley reduction. The alcohol is oxidized with aluminium isopropoxide in excess ac ...
). Another method is
oxoammonium-catalyzed oxidation. Additionally,
sodium hypochlorite (or household bleach) in acetone has been reported for efficient conversion of secondary alcohols in the presence of primary alcohols (Stevens oxidation).
Oxidation to carboxylic acids
The direct oxidation of primary alcohols to carboxylic acids can be carried out using
*
Potassium permanganate (KMnO
4);
*
Jones oxidation;
*
PDC in
DMF;
*
Heyns oxidation;
*
NaOCl
Sodium hypochlorite (commonly known in a dilute solution as bleach) is an inorganic chemical compound with the formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may also be viewed as the sodium salt of hy ...
;
*
Ruthenium tetroxide (RuO
4);
*or
TEMPO.
Diol oxidation
Alcohols possessing two
hydroxy groups located on adjacent carbons —that is, vicinal diols/ 1,2-
diols — suffer oxidative breakage at a carbon-carbon bond with some oxidants such as
sodium periodate (NaIO
4),
(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)
or
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 st ...
(Pb(OAc)
4), resulting in generation of two
carbonyl groups. The reaction is also known as
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 substitutio ...
.
References
{{Organic reactions
Organic redox reactions