2,2,6,6-tetramethylpiperidinyl-l-oxyl

This type of chemoselectivity has been observed in the oxidations of alcohols using copper(II) chloride and a catalytic quantity of 2,2,6,6-tetramethylpiperidinyl-l-oxyl (11 equation 11). The oxidizing species which is generated, in fw example the oxidation of (12) to (13), is the cation (14), which may also be produced using electrochemicai oxidation (in the wesence of the weak base 2,6-lutidine). Allylic and ben lic alccAols are easily oxidized by this reagent, whereas secondary alcdiols react slowly. 

More recently, the new photochromic spin probe 74 was synthesized.67 As the paramagnetic unit is provided by a 4-(2,2,6,6,-tetramethylpiperidinyl-l-oxyl) (TEMPO) moiety, it is not unexpected that the spectral parameters of this radical, i.e., aN= 15.5 G and g = 2.0055, did not differ from those of TEMPO itself. 

Great attention has been paid to HAS and their safety application in plastics and coatings. The 4-unsubstituted 2,2,6,6-tetramethylpiperidine is considered as relatively toxic, the acute oral toxicity being about 1 g/kg. The substitution in position 4 (i.e. the general mode in the synthesis of HAS for polymer purposes) dramatically improves the situation. Therefore, commercial HAS like 28 (R = H), 34,35a or 35b were approved for stabilization of packaging materials in contact with food [307]. Some data are available on properties of TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxyl) and its 4-amino or 4-hydroxy derivatives. They were found to act as weak intrinsic direct mutagens in Salmonella typhimurium. TEMPO increases intracellular hydroperoxide concentration. This may indicate its pro-oxidative effect which does not result, however, in cellular toxicity [314]. 

A third type of indirect electrochemical process involves processes in which the mediator is fixed at the electrode, such as 4-amino-2,2,6,6-tetramethylpiperidinyl-l-oxyl (TEMPO) modified graphite felt electrodes. 

NMP can be achieved in either of two ways (1) by adding a stable nitroxyl radical to the polymerization reaction initiated by traditional initiators (peroxides or azo compounds) to generate an alkoxyamine in situ, or (2) by preparing an alkoxyamine to be used as the initiator. Two widely stndied examples of stable nitroxyl radicals are 2,2,6,6-tetramethylpiperidinyl-l-oxyl [2564-83-2] (4, TEMPO) or 4-substitnted derivatives thereof and N-tert-bntyl-iV-[l-(diethylphosphono)-2,2-dimethylpropyl]nitroxide [188526-94-5] (5) (165-172). 

C.,H,4N30,]- 4-(Dimethylaminocarbonylamino)- 2,2,6,6-tetramethylpiperidinyl-l-oxyl NHCON(CH3)j H3C CH3 H3C ljJ CH3 o- -/ Aqueous sodium dodecyl sulfate EPR/ 300 no hyperfine compling constants given 7IG0II 216 ... 

Technical grade, distilled dichloromethane and deionized water were used. The bleach solution used was of technical grade (Stanchem, Poland). 2,2,6,6-Tetramethylpiperidinyl-l-oxyl (TEMPO) and NaBr were purchased from Acros. H NMR (300 MHz) and C NMR (75 MHz) were recorded on BmkerAvance 300 spectrometer in CDCI3 (with solvent residual signal as an internal standard). 

Kim and Jung (2003) oxidized benzylic and allylic alcohols by molecular oxygen in presence of catalytic amounts of 2,2,6,6-tetramethylpiperidinyl-l-oxyl (TEMPO) and CAN (scheme 64). Molecular oxygen is reduced to water by oxidation of Ce + to Ce . The nitroxyl radical of TEMPO is oxidized to the A-oxoammonium cation by Ce +. The N-oxoammonium cation then oxidizes the alcohol to a carbonyl compound. The reactions were carried out in refluxing acetonitrile and molecular oxygen was bubbled through the reaction mixture. The amount of CAN varied between 10 and 20 mol%, and the amount of TEMPO... 

It is noteworthy that the addition of a radical scavenger such as 2,2,6,6-tetramethylpiperidinyl-l-oxyl (TEMPO) completely suppressed the reactivity, showing that a radical mechanism is most likely involved in the transformation. Furthermore, a significant amount of 1,2-diphenylethane was obtained under such standard conditions, which also supports the formation of a benzyl radical 6-D during the reaction (Scheme 4.6). Firstly, ferf-butyl peroxide decomposes to give a tert-butyl peroxide radical and oxidizes Fe(ii) 6-A into Fe(iii) 6-B, which reacts with the 1,3-dicarbonyl derivative leading to an Fe(iii) enolate 6-C. Meanwhile, a benzyl radical 6-D obtained by abstraction of H can then react with 6-C. 

Acidic solvents, and particularly fluorinated alcohols, activate hydrogen peroxide, and even in the absence of a catalyst the rearrangement proceeds faster [308]. Other more uncommon non-metaUic oxidants such as perhydrates [309] and TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxyl) in combination with sodium hypochlorite [309] have also been applied. 

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