TEMPO 2,2 ,6,6 -tetramethylpiperidine

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). 

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],... 

Shorthand notations such as ET (electron transfer), HAT (hydrogen atom transfer), BDE (bond dissociation energy), NHE (normal hydrogen electrode), CV (cyclic voltammetry), LFP (laser flash photolysis), EPR (electron paramagnetic resonance) and KIE (kinetic isotope effect) will be used throughout the chapter. In addition, recurring chemical compounds such as TEMPO (2,2,6,6-tetramethylpiperidine-Ai-oxyl), HBT (1-hydroxyben-zotriazole), BTNO (benzotriazole-A-oxyl), HPI (iV-hydroxyphthalimide), PINO (phthal-imide-iV-oxyl), NHA (A-hydroxyacetanilide) and a few others will be referred to by means of the capital-letter acronym. 

TEMPO (2,2,6,6-tetramethylpiperidine-Af-oxyl) and its cognates (4-OH, 4-oxo, 4-OMe substituted derivatives TMIO etc.) belong to a group of stericaUy hindered aminoxyl radicals (Chart 1) and, in view of the long hfetimes, are said to be persistent and... 

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. 

TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl TBACI = tetrabutyl ammonium chloride NCS = A/-chlorosuccinimide... 

MFEs on reaction yields had only been observed in the reactions through radical pairs and biradicals for long years after the discovery of the MFEs on luminescence due to the T-T quenching and T-D one in solid and liquid phases. On the other hand, the MFEs of radical pairs and biradicals are due to the spin conversion between their singlet -triplet (S-T) states. As shown in Section 13.2, CFDEP induced by the T-D quenching were also found in many reactions in solution at room temperature. Thus, the author s group tried to find MFEs on the yields of such reactions with our ns-laser photolysis apparatus. At first, we studied the electron transfer reaction of triplet 10-methylphenothiazine ( D ) with 4-(4-cyanobenzoyloxy)TEMPO ( A-Ri") in 2-propanol at 293 K [14]. Here, Ri is the TEMPO (2,2,6,6-tetramethylpiperidin-l-oxyl) radical. The reaction scheme is shown in Fig. 13-5(a). 

PFOB perfluoro-n-octyl bromide TEMPO 2,2,6,6 -tetramethylpiperidine- N-... 

The use of TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) as an oxidant for the oxidation of primary and secondary alcohols to the corresponding aldehyde or ketone in combination with primary oxidants has also received significant attention in the past few years [18]. It is, therefore, not surprising to see the amount of effort that has been devoted to the synthesis of immobilized versions of this family of reagents (Figure 4.3) [19], on a wide variety of supports (e.g. silica-supported... 

TABLE 10.2 Addition Rate Constants kj of Various Radicals to Monomers Reaction Rate Constants kr of These Radicals with Oxygen, an Amine, a Stabilizer (HQME Hydroquinone-Methyl Ether) and a Spin Trap (TEMPO 2,2,6,6 Tetramethylpiperidine N-Oxyl). 

The polymerization of VAc by NMP was reported by Matyjaszewski group in 1996. To reduce the bimolecular radical termination dnring the polymerization, the authors attached the stable nitroxyl radical (TEMPO 2,2,6,6-tetramethylpiperidine-l-oxyl radical) to the interior of a dendrimer and used this modified TEMPO ([G-3]-TEMPO) as a scavenger combined with 2,2 -azobis(2-methyl-propionitrile) (AIBN) to polymerize VAc. Fignre 5 shows the kinetic plot and the dependence of molecular weight on monomer conversion for the bnlk polymerization of VAc at 80 °C in the presence of [G-3]-TEMPO/AIBN. 

The nitroxyls (a.k.a. nitroxides) are remarkably stable free radicals. Nitroxyls have two major resonance structures, one N-centered and one O-centered the lone electron may also be considered to be in the tt orbital of an N—O tt bond. Nitroxyls are thermodynamically stable because dimerization would give a very weak N—N, N—O, or O—N bond. TEMPO (2,2,6,6-tetramethylpiperidin-l-oxyl), a commercially available nitroxyl, is further stabilized by steric shielding, as shown here. Other thermodynamically stable free radicals include the small molecules O2 (a 1,2-diradical, best represented as -O—O ) and nitric oxide (NO), a messenger molecule in mammals that mediates smooth muscle contraction. 

It has been reported that living radical polymerization of 4-acetoxystyrene with a TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) adduct as the initiator, followed by base hydrolysis produces PHOSTs with narrow polydispersity, 1.1-1.4, which tend to have a 10-20°C higher 7g than their conventional PHOST counterparts (with polydispersity of 2.0-2.4), whose 7g ranges from 140 to 180°C. Hirao et al. have demonstrated the synthetic route to monodisperse PHOST, involving the living anionic polymerization of 4-tert-butyl(dimethyl)siloxystyrene... 

The starting point for every kind of EPR study is the choice of the radical that is best suited to deliver valuable information on the systems that are investigated. In this chapter only three types of radicals are used for this purpose. Nitroxide radicals such as TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl Pig. 2), its derivatives, and its five-ring analogs (Fig. 2) are the by far most widely used spin probes and spin labels and they are the spin probes of choice for the majority of EPR spectroscopic applications in naturally diamagnetic systems [2, 19]. 

Abbreviations used in this review APL, acute promyelocytic leukaemia CEF, chick embryo fibroblasts CRABP, cellular retinoic acid-binding protein ODC, ornithine decarboxylase RA, retinoic acid RARE, retinoic acid responsive element RAR, retinoic acid receptor RXR, retinoid X receptor TEMPO, 2,2,6,6-tetramethylpiperidine Y-oxide TOC, tracheal organ culture TPA, 12-<2-tetradecanoylphorbol-13-acetate TTNN, 6-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-2-naphthanoic acid TTNPB, 4-((.Q-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthyl)propenyl)benzoic acid. 

TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) as an important reagent in alcohol oxidation and its application in synthesis of natural products between 2000 and 2004 06MRO155. 

The Ru-catalyzed epoxidation of tran -stilbene in the presence of NaI04 was carried out using a bipyridyl ligand with a fluorous ponytail at the 4 and 4 positions. As illustrated by the first equation in Scheme 8, a triphasic system comprising water, dichloromethane and perfluorooctane was employed in the reaction. The reaction was complete in 15 min at 0°C and tran -stilbene oxide 5 was obtained from the dichloromethane layer in a 92% yield. The fluorous layer, containing the catalyst, could be recycled for four further runs without any addition of RuCls. The same perfluoroalkyl-substituted bipyridyl ligand was used successfully in the copper(i)-catalyzed TEMPO (2,2, 6,6 -tetramethylpiperidine (V-oxyl)-oxidation of primary and secondary alcohols under aerobic conditions (Scheme 8, second equation). ... 

Li and coworkers developed an effective system for the oxidation of alcohols under an atmosphere of oxygen, without the need for any additional solvent or transition metal catalyst, by using catalytic amounts of (diacetoxyiodo)benzene, TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) and potassium nitrate (Scheme 4.56) [88]. A tentative mechanism for this catalytic oxidation involves the oxoammonium cation 109, which... 

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