2,2,6,6-tetramethylpiperidine-l-oxyl TEMPO

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... 

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... 

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. 

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. 

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... 

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]. 

The primary alcohol of the diol 309 was selectively oxidized to the corresponding hydroxyaldehyde through a 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO)-catalyzed oxidation. The remaining secondary hydroxyl functionality was protected as an acetoxy group and the aldehyde was further oxidized to the acetate carboxylic acid. Treatment of... 

Electron paramagnetic resonance (EPR) and neutron diffraction can also be used to study molten salts. An example of the former is a study of the motion of large organics [2,2,6,6-tetramethylpiperidine-l-oxyl (tempo) and 4-amino tempo, or tem-pamine] dissolved in room-temperature molten salts, e.g., l-ethyl-3-methylimidazalo-... 

Fig. 19. Different ways to introduce oxyl radical reactivity nature employs metal bound tyrosyl radicals (19) or high-valent metal oxo fragments in many active sites (65,153). Nitroxyl radicals such as 2,2,6,6,-tetramethylpiperidin-l-oxyl (TEMPO, 20) are reactive species used in organocatalysis (154). The excited states of carbonyl functional groups (21) and metal oxo-fragments (22) display a radical pair character, which may become very attractive for biomimetic photoredox processes upon spectral sensitization (3,5).

The self-reactivity of R and their reactivity with oxygen are serious competitive processes for the reaction (Eq. 16). Recombination of R is preferred in PE, disproportionation in PP [186]. Oxidation proceeds in both polymers. The low probability of the reaction (Eq. 16) in the air atmosphere has, unfortunately been, mostly not reported in discussions of the HAS mechanism. Serious doubts arise when analyzing the reaction possibilities of R and NO [177,178,184,185,187]. Aliphatic ] N0 react rapidly with R at ambient and elevated temperatures [65]. The rate constants for the coupling with R are influenced by the resonance stability of alkyls [187]. The five membered NO l,l,3,3-tetramethylisoindoline-2-oxyl (TMIO) was found to be more reactive than 2,2,6,6,-tetramethylpiperidine-l-oxyl (TEMPO). w-Pentyl, Cert-butyl and benzyl radicals were used at 20 2°C in deaerated isooctane (solvent) [178,184,185]. The rate constants for bimolecular reactions of R (disproportionation and recombination) were compared with those of R oxidation and TEMPO scavenging [178,184,185,188] (Scheme 15). At room temperature, the scavenging of R by N0 is, by about one order of magnitude, slower than the self-termination of R [178],... 

Efficient and simple oxygenation procedures using 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) are reported [18-21]. Tin hydride, ditin and silanes have been sue-... 

As mentioned at the beginning of this section, Kirmse and coworkers (Bunse et al., 1992) found the first clear case of a homolytic aliphatic dediazoniation As shown in Scheme 7>24, the aqueous diazotization of 2>amino>2>methylpropane" nitrile (7.59) with two equivalents of NaN02 (or N2O4) yields products that are likely to be formed from the carbocation 7.60, namely 2>hydroxy-2-methylpropane-nitrile (7.62) and 2-methylprop-2-enenitrile (7.61), but also 2-methyl-2-nitropropane-nitrile (7.64), and the 7V,A-disubstituted 2>amino-2>methylpropanenitrile (7.66). The two last-mentioned products are probably formed via the radical 7.63. Direct evidence for this radical was found by experiments conducted in the presence of the radical scavenger 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) to give 7.65 in good yield. In other experiments, dimerization and oxidation products of the radical 7.63 were identified. 

A good method for the direct conversion of alcohols to carboxylic acid uses 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) 51, in conjunction with the co-oxidant sodium chlorite (NaC102) and sodium hypochlorite (NaOCl) as a catalyst. See M. Zhao, J. Li, E. Mano, Z. Song, D. M. Tschaen, E. J. J. Grabowski and P. J. Reider, J. Org. Chem., 64 (1999), 2564. 

Capsule morphologies could also be obtained by applying the biodegradable surfactant lecithin and the eco-friendly hydrophobe Neobee M5 (triglyceride) [68] after copolymerizafion of styrene and divinyl benzene (DVB), controlled by 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) and stabilized by poly(vinyl alcohol) (PVA) [69]. 

It was shown that the NFC may be obtained using an efficient process, where 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) oxidation was utilized as a pretreatment step prior to mechanical treatment (Lavoine et al., 2012 Saito et al.,... 

Since its discovery in 1993 [27], nitroxide-mediated polymerization (NMP) has been the most extensively studied technique from the dissociation-combination dass of LRP mechanisms (Scheme 13.7). This method is also commonly termed stable free radical polymerization (SFRP). NMP reactions are distinguished by the use of stable free radical nitroxide molecules (N ) as the controlling agent [e.g. 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO), (l-diethylphosphono-2,2-dimethyl)propyl nitroxide (DEPN)]. 

The electrochemical behavior of tris(4-bromophenyl)amine (xxiii) and 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO, xxiv) was comparatively studied in [C4mim][CF3S03], [C4mim][BF4], and [C4mim][PF6] [18]. TEMPO showed a... 

The amorphous regions were studied using EPR spectroscopy, which allows the estimation of the molecular mobility in disordered regions [17], A stable nitroxyl radical, 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) was used as a paramagnetic probe. The radical was introduced into the films from vapor at a temperature of 30 C. The rotational mobility of the radical probe was determined by the correlation time The following formula is used to calculate Eq. (2) r ... 

Stable free radicals are frequently employed as inhibitors (436,437). The most commonly used species are nitroxides, eg, 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) 18. They are far too stable to be able to initiate polymerization, but they are reactive enough to imdergo reaction with other free radicals (438). Nitroxides are very efficient inhibitors, being capable of producing induction periods when present in concentrations of less than 10 mol L" Nitroxides, such as TEMPO, react with carbon-centered radicals at close to diffusion controlled reaction rates (439-441). The stoichiometry between the number of the chains... 

Not many initiation events are needed, but the propagation cycle must be fast and efficient to afford a successful process. Radical probes have been used to demonstrate the formation of radicals along the propagation cycle and also as a synthetic tool. Thus, products from ring closure or ring opening or from rearrangement of the radicals were taken as evidence of the presence of these intermediates. Inhibition by radical traps with stable free radicals 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO), di-t-butyl nitroxide (DTBN), etc. has been extensively used to provide mechanistic... 

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