2,2,6,6-Tetramethylpiperidine A -oxide

Figure 13.15 Synthesis of 2,2,6,6-tetramethylpiperidine A-oxide (TEMPO) functionalized dendrimers.

Figure 13.16 Stackplot of electron paramagnetic resonance (EPR) spectra of 2,2,6,6-tetramethylpiperidine A -oxide (TEMPO)-functionalized dendrimers with 5, 10, 25, 50, 75, 90, and 95% TEMPO.

Figure 13.17 Graph of line-broadening effects for 2,2,6,6-tetramethylpiperidine A -oxide (TEMPO) and R-4-isothiocyanato (R-NCS) functionalized dendrimers from Figure 13.15. NCS-TEMPO was added first half of the time and R-NCS was added first half of the time.

Figure 13.19 Affinity chromatography with 2,2,6,6-tetramethylpiperidine A-oxide (TEMPO)-/mannose-functionalized dendrimers. Electron paramagnetic resonance spectra for one TEMPO/mannose experiment are shown.

The iodine atom in a 2-deoxy-2-iodo-gIycoside can be replaced by a hydroxyl group by radical deiodination in the presence of 2,2,6,6-tetramethylpiperidine-A -oxide, resulting in adducts such as 88 and its C-2 epimer, the N-0 bond in which can then be reductively cleaved (Zn, HOAc). ... 

The binding of the spin label 4iV-acetainido-2,2,6,6-tetramethylpiperidine A -oxide (2) with tetragonal lyso me has been studied at 6 A resolution The spin label is rather different from the inhibitor, -acetylglucosamine. 

Spectroscopic techniques such as electron spin resonance (ESR) offer the possibility to "probe" the chemical environment of the interlayer regions. With the ESR technique, an appropriate paramagnetic ion or molecule is allowed to penetrate the interlayer, and chemical information is deduced from the ESR spectrum. Transition metal ions, such as Cu2+, and nitroxide radical cations, such as TEMPAMINE (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) have been used as probes in this manner (6-14). Since ESR is a sensitive and non-destructive method, investigations of small quantities of cations on layer silicate clays at various stages... 

First, one had to check that the mechanism of action was correct. The product of co-ozonlysis of O-methyl-2-adamantanone oxime with 1,4-cyclohexanedione afforded on treatment with ferrous acetate a secondary carbon-centered free radical that was trapped with the usual spin trap, 2,2,6,6-tetramethylpiperidine-Ar-oxide (TEMPO), and involved a /3-scission of the adamantane fragment, thus proving that the attack of the Fe(ll) species occurred on the less-hindered peroxide bond oxygen atom (Scheme 85) <2004NAT900, 2005JOC513>. 

Mukerjee et al. [218] and Wrona et al. [219] have used the highly solvatochromic 71 transition energy of the stable 2,2,6,6-tetramethylpiperidine-l-oxide radical (TMPNO) for the development of a solvent polarity scale. So-called values, as empirical measures of solvent Lewis acidity, have been determined for 53 pure organic solvents and some binary solvent/water mixtures [219]. 

The formation of alternating copolymers through the polymerization of pairs of monomers, one of which is the donor and the other the acceptor of an electron, is well known. We shall mention only a few studies out of a great number of those recently published. First, those dealing with the nature of active centers in such systems will be examined. When radical initiators are used, e.g., benzoyl peroxide as in17), and the reaction is inhibited with different radical polymerization inhibitors, such as stable radicals like 2,2,6,6-tetramethylpiperidine 1-oxide, quinones, fluorene etc., questions concerning the nature of active centers can be regarded as solved. 

Tetramethylpiperidine-N-oxide(Tempo) traps R but not the Co(IT) unit in a Costa-type model B12 system, and has been used by Finke s group to obtain kinetic parameters for reaction (17) for R = PhCH2 and Mc3CH2 (see Table 11.2). (Further data on the saloph, cobalamin, and... 

The hindered secondary amines can be highly effective photostabilizers for various polymers (]+.,5.,.6) Various hindered amines have been shown to retard oxidation, but most share the common feature of being secondary or tertiary amines with the a-carbons fully substituted. The most widely exploited representatives of this class are based on 2,2,6,6-tetramethylpiperidine either in the form of relatively simple low molecular weight compounds, or more recently as backbone or pendant groups on quite high molecular weight additives ( i.,5.,6). The more successful commercial hindered amines contain two or more piperidine groups per molecule. Photo-protection by tetra-methylpiperidines (near UV transparent) must result from the interruption of one or more of the reactions 1 to 3. Relatively recent results from our own laboratories, and in the open literature will be outlined in this context. 

Chakraborty and Scott have reported the detection of N-OH groups in the photo-oxidation of methylcyclohexane containing a bis-piperidine or a nitroxide, based on their observation of an IR absorption at 2765 cm-1(13). However we have found the )>N-0H absorption to occur at 3 60 cm 1 (ll) in 1-hydroxyl-2,2,6,6-tetramethylpiperidines which throws some doubt on their IR detection of >N0H. 

The second synthesis of crystalline 43 was reported by Mori as summarized in Scheme 62 [93]. The building block (4.R,5S)-A was prepared by an enzymatic process, while another building block C was synthesized via Sharpless asymmetric epoxidation. Coupling of A with C gave D, which was cyclized under Op-polzer s conditions to give crystalline E. When E was oxidized with Dess-Martin periodinane or tetra(n-propyl)ammonium perruthenate or Jones chromic acid, crystalline 43 was obtained. Swern oxidation or oxidation with 2,2,6,6-tetramethylpiperidin-1 -oxyl of E afforded only oily materials. Accordingly, oxidation of E to 43 must be executed extremely carefully. A synthesis of oily 43 was reported by Gil [94]. 

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... 

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. 

The oxidation of secondary amines with no a-hydrogen atoms leads to hydroxy-lamines, but excessive dioxirane may further oxidize the hydroxylamines to the corresponding nitroxyl radical. For example, when a slight excess of isolated DMD is employed, 2,2,6,6-tetramethylpiperidin-4-ol (15) is quantitatively transformed into the hydroxylamine... 

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... 

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