2,2,4,4-Tetramethylpiperidine-l-oxyl

Acetamido-2,2,6,6-tetramethylpiperidine-l-oxyl (acetamidoTEMPO) [14691-89-5] M 213.3, m 144-146, 146-147. Dissolve in CH2CI2. wash with saturated K2CO3, then saturated aqueous NaCl, dry (Na2S04>, filter and evaporate. The red solid is recrystd fi om aqueous MeOH, m 147.5°. [J Org Chem 56 6110 1991 , Bull Acad Sci USSR. Div Chem Set 15 1422 7966.]... 

FIGURE 10.3 The structure of TEMPO. The compound 2,2,6,6-tetramethylpiperidine-l-oxyl is a stable radical. 

Figure 5.9 TEMPO DE is obtained by electrodeposition of a thin layer of orga-nosilica doped with TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) upon application of — 1.1 V (v.v. Ag/AgCl) for 15 min to a solution of suitable organosilanes (left). The electrocatalytic film thereby obtained selectively converts benzyl alcohol dissolved in 0.2 M NaHC03 (right). 

In other cases, organic modification of the sol gel cages markedly protects the entrapped molecular dopant from degradation by external reactants, as shown for instance by the entrapment of the radical 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO). This is a highly active catalyst which in the NaOCl oxidation of alcohols to carbonyls in a CH2CI2-H20 biphasic system becomes highly stabilized upon sol gel entrapment in an ORMOSIL matrix it progressively loses it activity when entrapped at the external surface of commercial silica.25... 

This blend was obtained by polymers mixture extrusion and extraction with the azeotropic mixture of hexane/ethanol, and modifying the obtained polymer surface by coupling of 4-isocyanato butanoic acid methyl ester (as a spacer molecule) to PVA blend, saponification of methyl ester groups and coupling of 4-amino-TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) [229],... 

The formed acyl radicals are reactive towards efficient radical trapping reagents such as 2,2,6,6-tetramethylpiperidine-l-oxyl radical (TEMPO), diphenyl diselenide and diphenyl disulphide, and A-f-butyl-a-phenylnitrone giving the respective adducts. ... 

Reaction of the Ru macrocyclic complex [RuLCy (L= 1,5,9,13-tetramethyl-l,5,9,13-tetraaza-cyclohexadecane) with N02 results in a disproportionation of the initial [Ru °LCl(N02)], the final products being traTO-[Ru L(0)Cl]" " and [Ru L(OH)(NO)] " "." The reaction between [Ru(OEP)Me] (H2OEP = octaethylporphyrin) and 2,2,6,6,-tetramethylpiperidine-l-oxyl (TEMPO) produces [Ru(OEP)CO]. There is clear evidence that the CO ligand is derived from the axially bound CH3 group, making this reaction an important example of CH3 to CO transformation." ... 

Methyl to CO transformation has been observed in the reaction of [Ru(OEP)Me] with 2,2,6, 6-tetramethylpiperidine-l-oxyl (TEMPO). There is clear evidence that the CO ligand in the... 

Three nitroxide derivatives of Ru2 species have been reported. The first contains the [Ru2(//-02C Bu)4L2] ion where L = 2,2,6,6-tetramethylpiperidine-l-oxyl. A relatively large antiferromagnetic coupling is observed between the Ru2 " core and the nitroxide radical. The second example is [Ru2(//-02C Bu)4L ] where L = 2-phenyl-4,4,5,5-tetramethyM,5-dihydro-lH-imidazolyl-l-oxy-3-oxide. 

During the induction periods caused by adding antioxidants, a small contraction in volume occurred because of the formation of dimers of chloroprene (14). This reaction occurs during the oxidation but was most easily studied by dilatometry in the absence of oxygen. A few values of the initial rate of dimerization of chloroprene, inhibited against polymerization with 2,2,6,6-tetramethylpiperidine-l-oxyl, are given in Table III. Their dependence on temperature is given by... 

As peracids react very sluggishly with alcohols, it was apparent that the presence of a nitroxide was playing an important role in the oxidation of the alcohol into a ketone. This seminal serendipitous observation led to the development of the first description of the oxidation of alcohols mediated by catalytic 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) (55), published almost simultaneously by Celia et al and Ganem.3 These authors presented two papers with remarkably similar contents, in which alcohols were oxidized by treatment with MCPBA in CH2CI2 at room temperature in the presence of a catalytic amount of TEMPO (55). In both papers, a plausible mechanism is presented, whereby m-chloroperbenzoic acid oxidizes TEMPO (55) to an oxoammonium salt 56. This oxoammonium salt 56, as detailed in Ganem s paper, can react with the alcohol producing an intermediate 57, which can deliver a carbonyl compound by a Cope-like elimination. 

Certain radicals are especially stable and are of biological consequence or have been used as antioxidants. TEMPO radicals (TEMPO = 2,2,6,6-tetramethylpiperidin-l-oxyl) have been particularly well studied because they are readily prepared and extremely stable. 

The anionic methylruthenium(II) species was autoxidized to a Ru(III) compound, RuMe(OEP). The methyl group of this compound was accidentally transformed into a coordinated carbon monoxide molecule by an excess of 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) [158] on an attempt to use TEMPO as a radical trap for the measurement of the Ru-C bond energy in solution. This was the first transformation of a methyl group to carbon monoxide to be observed in the proximity of a metal. 

The TEMPO moiety (2,2,6,6-tetramethylpiperidine-l-oxyl) has been incorporated into acetoacetic derivatives to achieve E-selective Knoevenagel condensations, exploiting the steric hindrance that it causes.269 In contrast, acylacetoamides (including Weinreb amides) produce Z-adducts. Downstream reductions of carbonyl groups in the products allow access to a variety of useful materials. 

Figure 7.2.12 shows the principal set-up for this experiment. The column, containing the immobilized free radicals consists of an adapted PEEK tube, which fits into the flow probe below the detection cell. Figure 7.2.13 depicts a spectrum of d-n-butylphthalate recorded under the influence of a ( free-radical ) column filled with 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO), immobilized with an aminopropyl spacer on silica. The spectrum is taken from an on-line separation of a two-compound mixture. The line width is of the same order as... 

Stable organic nitroxyl radicals are of relatively recent use as catalysts in the oxidation of alcohols. Nitroxyl radicals are compounds that contain the A ,A -disubstituted NO-group with one unpaired electron, and their uses have been reviewed.124 The most simple radical of this class is 2,2,6,6-tetramethylpiperidin-l-oxyl (43, TEMPO). It is generally assumed that the active oxidizing species, the oxoammonium salt (44), is formed in a catalytic cycle by a one-electron oxidation of the nitroxyl radical by a primary oxidant [two-electron oxidation of the hydroxylamine (45) is also possible, depending on the primary oxidant] (Scheme 21). 

Figure 15.6 Effects of modulation amplitude on cw-EPR line-shape. Spectra shown were obtained on a Bruker EMX spectrometer equipped with a high-sensitive cavity. The sample was an aqueous solution of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-l-oxyl) (12.5 fiM, 5 fil) placed in a round glass capillary (0.6 mm ID, 0.8 mm OD Vitrocom, Inc., Mountain Lakes, NJ) sealed at one end. Acquisition parameters listed in Table 15.1 were used, except that the modulation amplitude (M.A.) was varied as respectively indicated for each spectrum. Note that these spectra have not been normalized, and differences in the amplitude of the spectrum are due to the different modulation amplitudes used.

Our group have developed 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO)-functionalized PEG for biomimetic oxidation of alcohols together with CuCl in compressed C02, through a so-called mono-phase reaction, two-phase separation process to recover the catalyst, thus leading to conducting a homogeneous catalysis in a continuous mode [62]. 

Figure 2.5 Experimental and calculated aN values of TEMPO-choline [4-(N, Ndimethyl-N-(2-hydroxyethyl))ammonium-2/2/6/6-tetramethylpiperidine-l-oxyl chloride] as a function of the solvent dielectric constant.

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