TEMPO nitroxides

Oxidations Using Oxoammonium Ions. Another oxidation procedure uses an oxoammonium ion, usually derived from the stable nitroxide tetramethylpiperidine nitroxide, TEMPO, as the active reagent.31 It is regenerated in a catalytic cycle using hypochlorite ion32 or NCS33 as the stoichiometric oxidant. These reactions involve an intermediate adduct of the alcohol and the oxoammonium ion. 

Organosiliconboranes having bulky substituents on the boron, e.g. R3SiB[N(CHMe)2]2, exhibit UV absorption at wavelengths longer than 300 nm. Photolysis of this band afforded a pair of silyl and boryl radicals that can be trapped quantitatively by nitroxide (TEMPO) as shown in Reaction (1.4) [10]. 

ESR spectra have been used to study interaction of the free radical base 2,2,6,6-tetramethylpiperidine nitroxide (tempo), a weak Lewis base, with GaCl3.586 This system reveals the expected 1 1 complex GaCl3-tempo. Only one bridging Cl bond in the Ga2Cl6 molecule has... 

Narrow distribution in the backbone length as well as in the chemical composition or the branch frequency may be expected from a living-type copolymerization between a macromonomer and a comonomer provided the reactivity ratios are close to unity. This appears to have been accomplished to some extent with anionic copolymerizations with MMA of methacrylate-ended PMMA, 29, and poly(dimethylsiloxane) macromonomers, 30, which were prepared by living GTP and anionic polymerization, respectively [50,51]. Recent application [8] of nitroxide (TEMPO)-mediated living free radical process to copolymerizations of styrene with some macromonomers such as PE-acrylate, la, PEO-methacr-ylate, 27b, polylactide-methacrylate, 28, and poly(e-caprolactone)-methacrylate, 31, may be a promising approach to this end. 

Scheme 2 Dissociation of a typical alkoxyamine into a carbon-centered radical (ethylbenzene radical) and a nitroxide (TEMPO)...

From a study of fluorescence and triplet quenching of a series of aromatic hydrocarbons by tetramethylpiperidine nitroxide (TEMPO) in methylcyclohexane it has been concluded that both quenching processes (10) and (11) are the result of... 

Nitroxide-mediated polymerization (NMP) is one of the CRP methodologies to which ESR spectroscopy was successfully apphed to study reaction mechanisms and kinetics [134-136]. Thus, MacLeod and coworkers [134] have monitored by ESR the free niiroxide level for styrene polymerization at 135 C, initiated by TEMPO-BPO, with a large excess of initiator used relative to nitroxide (TEMPO/BPO=0.5 1). 

The stable free radical polymerization technique is characterized by the growing polymer chains that are reversibly capped by a stable free radical [e.g., 2,2-tetramethyl-l-piperidynyloxy nitroxide (TEMPO)]. For example, stable polystyrene dispersions were prepared by the stable free radical polymerization of styrene conducted in miniemulsion polymerization at 135 C [62]. Sodium dodecylbenzene sulfonate, hexadecane, and potassium persulfate/ TEMPO were used as the surfactant, costabihzer, and initiator system, respectively. Prodpran et al. [63] studied the styrene miniemulsion polymerization stabilized by Dowfax 8390 and hexadecane and initiated by benzoyl peroxide at 125 °C. A molar ratio of TEMPO to benzoyl peroxide equal to 3 to 1 resulted in polystyrene with the lowest polydispersity index (1.3) of polymer molecular weight distribution. 

Figure 15 Structure of the nitroxides TEMPO (left) and SG1 (right).

The possibility of exploiting enhanced paramagnetic relaxation as an effective source of structural constraints was explored by JarOTiiec and coworkers on microcrystalline samples of a model protein, the B1 immunoglobulin-binding domain of protein G (GBl). Here a solvent-exposed cysteine residue was used to incorporate a thiol-specific paramagnetic nitroxide (TEMPO) or a thiol-specific EDTA-metal reagent bound to Cu and Mn° ions [99-101]. 

Hodges et al. [152] and Bian and Cunningham [153] reported the grafting of PS, poly(acetoxystyrene), poly[styrene-b-(methyl methacrylate-co-styrene)], poly(acetoxystyrene-co-styrene), and poly(styrene-co-2-HEMA) copolymers onto 2,2,6,6-tetramethyl-l-piperidinyloxy nitroxide (TEMPO) bound Merrilield resin. Merrifield resin is a PS resin based on a copolymer of styrene and chloromethylstyrene cross-linked with divinylbenzene. In these works, a pronounced increase of particle size was observed, which was attributed to the formation of chains both at the surface and within the microspheres. The polymerization control was enhanced both on the surface and in solution by the addition of sacrificial nitroxide. 

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