TEMPO

TEMPO
Chemical name	2,2,6,6-Tetramethyl- piperidine-1-oxyl
Other names	2,2,6,6-Tetramethyl- piperidin-1-oxyl
Chemical formula	C9H18NO
Molecular mass	156.25 g/mol
Melting point	36-38 °C
Boiling point	sublimes under vacuum
Density	? g/cm3
CAS number	[2564-83-2]
IR spectrum (Nujol mull)	1330, 1180, 1060, 975, 950 cm–1
UV spectrum (heptane soln)	470 nm (ε = 10.5)
TEMPO.gif
Risk Statements	34
Safety Statements	26-36/37/39-45
RTECS	TN8991900
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

'2,2,6,6-Tetramethylpiperidine-1-oxyl' or 'TEMPO' is the chemical compound with the formula (CH₂)₃(CMe₂)₂NO. This heterocycle is a red-orange, sublimable solid. As a stable radical, it has applications throughout chemistry and biochemistry.^[1] TEMPO was discovered by Lebelev and Kazarnowskii in 1960.^[2] It is prepared by oxidation of 2,2,6,6-tetramethylpiperidine. TEMPO is widely used as a radical trap, as a structural probe for biological systems in conjunction with electron spin resonance spectroscopy, as a reagent in organic synthesis, and as an initiator in polymer chemistry.^[3] The stability of this radical is attributed to the steric protection provided by the four methyl groups adjacent to the nitroxyl group.^[4]

Contents

Application in organic synthesis

References

External links

Application in organic synthesis

TEMPO is employed in organic synthesis as a catalyst for the oxidation of primary alcohols to aldehydes. The actual oxidant is the N-oxoammonium salt. In a catalytic cycle with sodium hypochlorite as the stoichiometric oxidant, hypochlorous acid generates the N-oxoammonium salt from the TEMPO.
One typical reaction example is the oxidation of (S)-(-)-2-methyl-1-butanol to (S)-(+)-2-methylbutanal.^[5] 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.^[6] TEMPO oxidations also exhibit chemoselectivity, being inert towards a secondary alcohols, but the reagent will convert aldehydes to carboxylic acids.
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 geraniol to geranial 4-acetamido-TEMPO is first oxidized to the oxoammonium tetrafluoroborate.^[7]

References

1. Barriga, S. Synlett; 04, 2001]. http://www.thieme-connect.com/ejournals/pdf/synlett/doi/10.1055/s-2001-12332.pdf
2. Lebelev, O. L.; Kazarnovskii, S. N. Zhur. Obshch. Khim. 1960, volume 30, page 1631ff.
3. Montanari, F.; Quici, S.; Henry-Riyad, H.; Tidwell, T. T. “2,2,6,6-Tetramethylpiperidin-1-oxyl” Encyclopedia of Reagents for Organic Synthesis; John Wiley & Sons, 2005. DOI: 10.1002/047084289X.rt069.pub2
4. Zanocco, A. L.; Canetem., A. Y.; Melendez, M. 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 volume 45, pages 123-129. ISSN 0366-1644.
5. P. L. Anelli, F. Montanari, S. Quici " A General Synthetic Method for the Oxidation of Primary Alcohols to Aldehydes: (S)-(+)-2-Methylbutanal" Organic Syntheses Annual Volume 69, page 212 Article
6. Zhao, M. M.; Li, J.;Mano, E.; Song, Z. J.; Tschaen, D. M. Organic Syntheses Annual Volume 81, page 195. Article
7. 2,6-Octadienal, 3,7-dimethyl-, (2E)- Bobbitt, J. M.; Merbouh, N. Organic Syntheses, Vol. 82, p.80 Online Article

External links

★ DataSheet