TEMPO

Description

TEMPO, like DABCO, the Molecule of the Week for August 29, 2022, is one of those molecules best known by its acronym. TEMPO’s full name is 2,2,6,6-tetramethyl-1-piperidinyloxy.
TEMPO is also unusual in that it is a stable free radical. Because of its unpaired electron, its color is a bright red-orange, in contrast to similar molecular structures, which do not absorb light in the visible region.
TEMPO was first synthesized in 1959 by USSR chemists O. L. Lebedev and S. N. Kazarnovskii. They oxidized 2,2,6,6-tetramethylpiperidine1 with hydrogen peroxide in the presence of pertungstate ion (WO42–). The authors called the resulting product an “intermediate”; it is not clear whether they realized that it was a free radical. Three years later, another Soviet researcher, A. V. Il’yasov, published data on the effect of solvents on the electron paramagnetic resonance2 (EPR) spectra of some stable free radicals, including TEMPO, so its status had been established by then.
TEMPO has multiple uses in organic chemistry: as a catalyst in oxidation reactions and radical-mediated polymerizations and as an EPR marker or probe in chemical and biochemical systems. In a recent example, Abudureheman Wusiman and co-workers at Xingjiang Normal University (Urumqi, China) used it to promote the mono- and bisimidation of tertiary anilines. The purpose of the reaction was to create a straightforward route to symmetric and unsymmetric N-Mannich bases3 under mild conditions.
1. CAS Reg. No. 768-66-1. 2. Also known as electron spin resonance (ESR). 3. A Mannich base is a β-amino ketone; an N-Mannich base has a nitrogen atom in place of the intermediate carbon atom, e.g., R2NCH2NHC(O)R.

Description

2,2,6,6-Tetramethylpiperidine is a product that is used for the most diverse purposes because of its strong basicity, for example, as a light stabilizer for polyolefins, as a cocatalyst in olefin polymerizations (Ziegler catalysts), as a building block for the synthesis of pharmaceuticals and crop protection products, as a cocatalyst in the synthesis of dichloroacetyl chloride. The 4-unsubstituted 2.2.6,6-tetramethylpiperidine is generally prepared from the corresponding 4-oxo compound. It is known that triacetonamine can be converted by hydrazine to the hydrazone, which is then cleaved in the presence of alkali into 2,26,6-tetramethylpiperidine and nitrogen.

Chemical properties

orange crystals or powder

Characteristics

2,2,6,6-Tetramethylpiperidinooxy(TEMPO) has the characteristics of high yield, good selectivity, good stability, and recyclable use.

The Uses of TEMPO

TEMPO(2,2,6,6-Tetramethylpiperidinooxy) is a stable radical prepared through the oxidation of 2,2,6,6-tetramethylpiperidine. TEMPO has a wide range of applications including use as a free radical scavenger, a reagent in organic synthe sis and as a structural probe in electron spin resonance spectroscopy. TEMPO can also be used as a mediator in free radical polymerization.

The Uses of TEMPO

In organic chemistry as a radical trap, 2,2,6,6-Tetramethylpiperidinooxy can be used as a catalyst and in polymerization mediation.

The Uses of TEMPO

TEMPO can be used:

• As a catalytic oxidant for copper-catalyzed, greener oxidation of alcohols under aerobic conditions.
• As a catalytic oxidant in the iodobenzene diacetae oxidation of nerol to neral.
• For trapping the styrenyl radical generated from benzoyl peroxide during nitroxide-mediated radical polymerization of styrene.
• In the carboxylation of water-resistant nanofibrillated cellulose (NFC) films.

What are the applications of Application

TEMPO is a catalyst employed in the oxidation of primary alcohols to aldehydes with NaOCl

General Description

For a synthetic protocol using NMP initiators, contributed by Prof. Karen Wooley, please visit our technology spotlight.

Purification Methods

Purify TEMPO by sublimation (33o, water aspirator) [Hay & Fincke J Am Chem Soc 109 8012 1987, Keana Chem Rev 78 37 1978].