TEMPO
Names | |
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Preferred IUPAC name
(2,2,6,6-Tetramethylpiperidin-1-yl)oxyl | |
Other names
(2,2,6,6-Tetramethylpiperidin-1-yl)oxidanyl
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Identifiers | |
3D model (
JSmol ) |
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ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard
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100.018.081 |
EC Number |
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PubChem CID
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RTECS number
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
C9H18NO | |
Molar mass | 156.25 g/mol |
Melting point | 36 to 38 °C (97 to 100 °F; 309 to 311 K) |
Boiling point | sublimes under vacuum |
Hazards | |
GHS labelling: | |
Danger | |
H314 | |
P260, P264, P273, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501 | |
Safety data sheet (SDS) | External MSDS |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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(2,2,6,6-Tetramethylpiperidin-1-yl)oxyl or (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl, commonly known as TEMPO, is a
Preparation
TEMPO was discovered by Lebedev and Kazarnowskii in 1960.[3] It is prepared by oxidation of 2,2,6,6-tetramethylpiperidine.
Structure and bonding
The structure has been confirmed by X-ray crystallography. The reactive radical is well shielded by the four methyl groups.
The stability of this radical can be attributed to the delocalization of the radical to form a
Regardless of the reasons for the stability of the radical, the O–H bond in the hydrogenated derivative (the
Application in organic synthesis
TEMPO is employed in
One typical reaction example is the oxidation of (S)-(−)-2-methyl-1-butanol to (S)-(+)-2-methylbutanal:[7] 4-Methoxyphenethyl alcohol is oxidized to the corresponding carboxylic acid in a system of catalytic TEMPO and sodium hypochlorite and a stoichiometric amount of sodium chlorite.[8] TEMPO oxidations also exhibit chemoselectivity, being inert towards secondary alcohols, but the reagent will convert aldehydes to carboxylic acids.
The oxidation of TEMPO can be highly selective. It has been proven that secondary alcohols are more likely to be oxidized by TEMPO under an acidic environment. The reason is when in this condition, secondary alcohols are more easily able to provide an H− ion.[9]
In cases where secondary oxidizing agents cause side reactions, it is possible to stoichiometrically convert TEMPO to the oxoammonium salt in a separate step. For example, in the oxidation of
TEMPO can also be employed in nitroxide-mediated radical polymerization (NMP), a controlled free radical polymerization technique that allows better control over the final molecular weight distribution. The TEMPO free radical can be added to the end of a growing polymer chain, creating a "dormant" chain that stops polymerizing. However, the linkage between the polymer chain and TEMPO is weak, and can be broken upon heating, which then allows the polymerization to continue. Thus, the chemist can control the extent of polymerization and also synthesize narrowly distributed polymer chains.
Industrial applications and analogues
TEMPO is sufficiently inexpensive for use on a laboratory scale.
Industrial-scale examples of TEMPO-like compounds include hindered amine light stabilizers and polymerisation inhibitors.
See also
- 1-Hydroxy-2,2,6,6-tetramethylpiperidine, the reduced derivative of TEMPO
- TEMPOL
- N-Hydroxyphthalimide
References
- .
- ISBN 0471936235.
- ^ Lebedev, O. L.; Kazarnovskii, S. N. (1960). "[Catalytic oxidation of aliphatic amines with hydrogen peroxide]". Zhur. Obshch. Khim. 30 (5): 1631–1635. CAN 55:7792.
- doi:10.1246/cl.2007.866.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - .
- LCCN 2008046989.
- ^ Anelli, P. L.; Montanari, F.; Quici, S. (1990). "A General Synthetic Method for the Oxidation of Primary Alcohols to Aldehydes: (S)-(+)-2-Methylbutanal". Organic Syntheses. 69: 212
{{cite journal}}
: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 8, p. 367. - ^ Zhao, M. M.; Li, J.; Mano, E.; Song, Z. J.; Tschaen, D. M. (2005). "Oxidation of Primary Alcohols to Carboxylic Acids with Sodium Chlorite catalyzed by TEMPO and Bleach: 4-Methoxyphenylacetic Acid". Organic Syntheses. 81: 195
{{cite journal}}
: CS1 maint: multiple names: authors list (link). - ^ "Detailed study about TEMPO oxidation". LISKON-CHEM.
- ^ Bobbitt, J. M.; Merbouh, N. (2005). "2,6-Octadienal, 3,7-dimethyl-, (2E)-". Organic Syntheses. 82: 80
{{cite journal}}
: CS1 maint: multiple names: authors list (link). - ^ "TEMPO". Sigma-Aldrich.
- ^ "TEMPO-LISKON industrial-scale".
- .