Tempo
Encyclopedia : T : TE : TEM : Tempo
| TEMPO | |
|---|---|
| Chemical name | 2,2,6,6-Tetramethylpiperidine 1-oxyl |
| Chemical formula | C9H18NO |
| Molecular mass | 156.25 g/mol |
| Melting point | 36-38 °C |
| Boiling point | ? °C |
| Density | ? g/cm3 |
| CAS number | [2564-83-2] |
| SMILES | ? |
| |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
2,2,6,6-Tetramethylpiperidine 1-oxyl or TEMPO is a remarkably stable radical with many applications in organic synthesis. TEMPO was discovered by chemists Lebelev and Kazarnowskii in 1960. It is prepared by oxidation of 2,2,6,6-tetramethylpiperidine. TEMPO is widely used in electron spin resonance spectroscopy as a probe for biological systems and also as a radical trap [#endnote_1] [#endnote_4] . TEMPO is called a hindered amine. 4 bulky methyl groups surround the nitroxyl amine group and drive selectivity in reactions.
TEMPO is employed in organic synthesis as a very efficient oxidizing agent for alcohol groups to carbonyl groups.The actual oxidant is the N-oxoammonium salt. In a catalytic cycle with sodium hypochlorite, Hypochlorous acid makes sure that the N-oxoammonium salt is generated from the nitroxyl radical. In the oxidation step the oxoammonium salt is regenerated. In this reaction TEMPO is present is catalytic amounts and it is the sodium hypochlorite that is consumed.
One typical reaction example is the oxidation of (S)-(−)-2-methyl-1-butanol to (S)-(+)-2-methylbutanal [#endnote_2]. 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. [#endnote_3] TEMPO oxidations also show great chemoselectivity being able to react exclusively with a primary alcohol group and being inert towards a secondary alcohol group in the same molecule.
When secondary oxidizing agents cause side reactions it is also possible to stoichiometric convert TEMPO to the oxoammonium salt in a separate step. For example in the oxidation of geraniol to geranial 4-acetamido-TEMPO is first oxidized to the oxoammonium tetrafluoroborate [#endnote_5].
External links
References
- ↑ Barriga, Susana Synlett; 04, 2001 [Article]
- ↑ Pier Lucio Anelli, Fernando Montanari, Silvio Quici Organic Syntheses Annual Volume 69, page 212 [Article]
- ↑ Matthew M. Zhao, Jing Li, Eiichi Mano, Zhiguo J. Song, and David M. Tschaen Organic Syntheses Annual Volume 81, page 195 [Article]
- ↑ Zanocco, Antonio L., Canetem., Alvaro Y Melendez, Monica X. a kinetic study of the reaction between 2-p- methoxyphenyl-4-phenyl-2-oxazolin-5-one and 2,2,6,6-tetramethyl-1-piperidinyl-n-oxide Bol. Soc. Chil. Quím. 2000 vol.45, no.1, p.123-129.ISSN 0366-1644 [Article] open access publication
- ↑ 2,6-Octadienal, 3,7-dimethyl-, (2E)- James M. Bobbitt, Nabyl Merbouh Organic Syntheses, Vol. 82, p.80 [Online Article]
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