TEMPO
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 . 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)-(âˆ')-2-methyl-1-butanol to (S)-(+)-2-methylbutanal . 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. 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 .
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DataSheet*
www.tciamerica.com newsletter# 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. QuÃm. 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
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Online Article
