frame|right|Organic redox reactions: the [[Birch reduction]]
Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. In organic chemistry oxidations and reductions are different from ordinary redox reactions, because many reactions carry the name but do not actually involve electron transfer. Instead the relevant criterion for organic oxidation is gain of oxygen and/or loss of hydrogen. Simple functional groups can be arranged in order of increasing oxidation state. The oxidation numbers are only an approximation:
In disproportionation reactions the reactant is both oxidized and reduced in the same chemical reaction forming two separate compounds.
Asymmetric catalytic reductions and asymmetric catalytic oxidations are important in asymmetric synthesis.
Organic oxidations
Most oxidations are conducted with air or oxygen, especially in industry. These oxidation include routes to chemical compounds, remediation of pollutants, and combustion. Some commercially important oxidations are listed:
{| class="wikitable"
|+ Industrial oxidations of organic compounds
|-
! product !! scale (millions of tons/year in 1990's)
|-
| terephthalic acid and esters || 15
|-
| cumylhydroperoxide || 6.5
|-
| benzoic acid || 0.28
|-
| adipic acid || 2.2
|-
| propylene oxide || 4
|-
| adipic acid || 2.2
|}
Many reagents have been invented for organic oxidations. Organic oxidations reagents are usually classified according to the functional group attacked by the oxidant:
- Oxidation of C-H bonds:
:
:
:
:
:
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- Oxidation of C-C, C=C, and bonds
- Oxidation of alcohols and various carbonyls
Often the substrate to be oxidized features more than one functional group. In such cases, selective oxidations become important.
Organic reductions
In organic chemistry, reduction is equivalent to the addition of hydrogen atoms, usually in pairs. The reaction of unsaturated organic compounds with hydrogen gas is called hydrogenation. The reaction of saturated organic compounds with hydrogen gas is called hydrogenolysis. Hydrogenolyses necessarily cleaves C-X bonds (X = C, O, N, etc.). Reductions can also be effected by adding hydride and proton sources, the so-called heterolytic pathway. Such reactions are often effected using stoichiometric hydride reagents such as sodium borohydride or lithium aluminium hydride.
See also
- Oxidizing agent
- Reducing agent
- Transfer hydrogenation
- Electrosynthesis
Functional group oxidations
- Alcohol oxidation
- Oxidation of oximes and primary amines to nitro compounds
- Glycol cleavage
- Oxidative cleavage of α-Hydroxy acids
- Alkene oxidations
- Oxidation of primary amines to nitriles
- Oxidation of thiols to sulfonic acids
- Oxidation of hydrazines to azo compounds
Functional group reductions
- Carbonyl reduction
- Amide reduction
- Nitrile reduction
- Reduction of nitro compounds
- Reduction of imines and Schiff bases
- Reduction of aromatic compounds to saturated rings