2,2, 6,6-Tetramethylpiperidine structure

FIGURE 10.3 The structure of TEMPO. The compound 2,2,6,6-tetramethylpiperidine-l-oxyl is a stable radical. 

Normal-phase TLC has been employed for the control of the synthesis of some new reactive azo dyes containing the tetramethylpiperidine fragment. The chemical structure of the basic molecule and the substituents of the new derivatives are shown in Fig. 3.16. The new derivatives were characterized by their RF values determined in different mobile phases. Compositions of mobile phases were n-propanol-ammonia (1 1, v/v) for dye 1.2 (Rp = 0.84) n-propanol-ammonia (2 1, v/v) for dyes 1.3 (RF = 0.50) and 1.4 (RF = 0.80) and n-heptane-diethyl ether (1 1, v/v) for dyes 1.5 (RF = 0.80) and 1.6 (RF = 0.76). The results indicated that together with other physicochemical methods such as IR and H NMR, normal-phase TLC is a valuable tool for the purity control and identification of new synthetic dyes [96],... 

Some new benzanthrone dyes were synthesized and applied for the one-step colouration and stabilization of polystyrene. The chemical structures of monomeric benzanthrone dye (formula 1), the stabilizer TTMP 2,2-(2,2,6,6-tetramethylpiperidine-l-yl)-4,6-dichloro-l,3,5-triazine (formula 2) and the new synthetic product showing both colouration and stabillizer capacity (formula 3) are shown in Fig. 3.135. The synthesis process was controlled by TLC using a silica stationary phase and an n-heptane-acetone (1 1, v/v)... 

The mixed metal alkyl-amido base [BuNa(TMEDA)][TMP2Mg] (TMP = 2,2,6,6-tetramethylpiperidine) is capable of deprotonating furan selectively at its 2-position in THF as a solvent. The product obtained is a complex tris-furylmagnesiate, with the empirical formula [Na2(THF)3][2-furyl6Mg2(TMEDA)] (15) . An X-ray crystal-structure determination showed that in the solid state this compound exists as a coordination polymer of [Na2(THF)3][2-furyl6Mg2] units linked by bridging TMEDA molecules (Figure 16). 

Several examples are known of N—O coordination of iV-hydroxypiperidines resulting in three-membered chelate rings on deprotonation (14). The crystal structures and Mo NMR studies of some complexes of MoVI containing this grouping have appeared.46"4 A similar coordination mode was observed in the crystal structure of a Pdn complex of the 2,2,4,4-tetramethylpiperidine derivative.49... 

Since malonate (Structure I) is able to fulfill the role of the anion in transferrin, it seemed reasonable to see whether spin-labeled derivatives of malonate could serve as probes of the active sites. Two such spin-labled derivatives were prepared and tentatively identified as having structures II (N-4-(2,2,6,6-tetramethylpiperidin-l-oxyl)malonamide) and III (N-4-(2,2,6,6-tetramethylpiperidin-l-oxyl)malonate). Similar results were obtained with each (Figure 3). Upon mixing Fe(III), transferrin, and II at low pH, and then raising the pH to near-neutrality with C02-free ammonia, the characteristic orange-red color of the ternary Fe-transferrin-anion complex is promptly displayed. However, the anticipated EPR signal of the nitroxide spin-label is not observed, presumably because it is broadened beyond detectability by its proximity... 

In Scheme 5 are given the structures of some 2,2,6,6-tetramethylpiperidine derivatives which are effective polymer stabilizers. The analysis of the structures of these compounds allows the formulation of the design principles of polymer stabilizers based on hindered amines in general and hindered piperidines in particular (38,51). 

Suggest structures for the compounds in the following sequence 2-methyl-5-hydroxy-4-pyrone reacted with MeOTf —> CvHpOsTfO (a salt), then this with 2,2,6,6-tetramethylpiperidine (a hindered base) —> CvHgOs, a dipolar substance, and this then with acrylonitrile —> C10H11NO3. 

Heat and light stability has been attributed to sec- and terl-piperidines, derived O-alkylhydroxylamines or hydroxylamines containing hydrolysis resistant phosphite moieties, e.g. [bis(2,2,6,6-tetramethylpiperidin-4-yl)2,6-di-fm-butyl-4-methylphenyl)]phosphite 176 [276]. The light/heat stabilizing effect was confirmed in PP films [277]. The bifunctional piperidine stabilizers were superior to mixtures of structurally analogous aromatic phosphites and HAS in the both thermooxidized (110°C) and photo-oxidized (30 °C) PP. Features of synergism were observed. 

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. 

Fig. 2 Chemical structures of common nitroxide spin probes Fremy s salt (potassium nitrosodi-sulfonate) TEMPO and derivatives (2,2,6,6-tetramethylpiperidine-l-oxyl), DOXYL (4,4-dimethyl-oxazolidine-l-oxyl) PROXYL (2,2,5,5-tetramethylpyrrolidine-l-oxyl) Dehydro-PROXYL (2,2,5,5-tetramethylpyrroline-l-oxyl) 5-DSA (5-DOXYL stearic acid) 16-DSA (16-DOXYL stearic...

In THF, (53) with tetraphenylcyclopentadienone and with tetramethylpiperidine, as base, gave the imexpected dithiin (86) in low yield (Equation (2)) together with the product of reaction of the aryne with the very hindered amine used. The dithiin structure (86) is interesting since the aryne appears to have been incorporated twice. A possible pathway for its formation is proposed in <89PS(43)261,91JCS(P1)317>. 

Further splittings of the main resonance line, due to hyperfine interactions, are (to first order) independent of the microwave frequency. Measurements at different frequencies can therefore clarify if an observed spectrum is split by Zeeman interactions (different g-factors) or other reasons. The example reported in Fig. 4.6 due to Tempone (2,2,6,6- tetramethylpiperidine-N-oxyl) spin label illustrates how spectral features caused by hyperfine structure and g-anisotropy can be differentiated by measurements at X and W-bands [16]. 

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