2.2.6.6- Tetramethylpiperidinyl-1 -oxyl

Foohiotes (a) Data from [9], adjusted to see using data for oxidation of 2,2,6,6-tetramethylpiperidinyl-1 -oxyl. 

Tetramethylpiperidinyl-1 -oxyl. Thallium(III) nitrate. Zinc permanganate. 

Hydroxyimino-2,2,6,6-tetramethylpiperidinyl- 1-oxyl NOH A Reaction of NOH A +H3O3/ EPR/ 65Bril, 64Bril/ 69Karl... 

Table 3 Physical constants of the radicals TEMPO (tetramethylpiperidinyl-iST-oxyl), 1,3,5-triphenylverdazyl (10), and their complexes with the oxidized cation salts...

Table 2 Ruthenium/2,2, 6,6 -tetramethylpiperidinyl-W-oxyl (TEMPO) catalysed oxidation of primary and secondary alcohols to the corresponding aldehyde using molecular oxygen. 15 mmol substrate, 30 ml chlorobenzene, RuCl2(PPh3)3/TEMPO ratio of 1/3, 10 ml mur1 02/N2 (8/92 v/v), P=10 bar, T=100 °C...

Fig. 15 Ruthenium/2,2, 6,6 -tetramethylpiperidinyl-Ar-oxyl catalysed aerobic oxidation of alcohols...

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]. 

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