Über die thermolyse von p-substituierten α-phenyl-N-t-butylnitronen.

Sommermeyer, K.; Seiffert, W.; Wilker, W.

doi:10.1016/s0040-4039(01)93143-0

Cited by 15 publications

(5 citation statements)

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“…The hyperfine coupling constants measured from these spectra are as follows: a N = 13.9 G and a H = 2.0 G, with a g -factor of 2.0064 and a line width of 12.1 G. On the basis of these constants and spectral simulation experiments, the gas-phase radicals seem to be alkoxyl radicals. These hyperfine coupling constants agree very well with previous determinations of the parameters for the alkoxyl spin adduct of PBN in benzene. , In some experiments, di- tert -butyl-nitroxide was detected as a result of the oxidation of PBN by NO 2 38 or the thermal decomposition of PBN at >100 °C, which yielded an EPR spectrum that exhibited three lines, with a N = 15.2 G…”

Section: Resultsmentioning

confidence: 99%

“…These hyperfine coupling constants agree very well with previous determinations of the parameters for the alkoxyl spin adduct of PBN in benzene. 15,37 some experiments, di-tert-butyl-nitroxide was detected as a result of the oxidation of PBN by NO 2 38 or the thermal decomposition of PBN at >100 °C, 39 which yielded an EPR spectrum that exhibited three lines, with a N ) 15.2 G. 40 The amplitude of spectrum A in Figure 7 was compared with the amplitudes of spectra obtained during control experiments performed without tobacco (spectrum B in Figure 7) and with that obtained during the combustion (oxidation) of tobacco in air (spectrum C in Figure 7). The integrated intensity of the spectrum allows quantification of the yields of trapped radicals.…”

Section: Radicals In Tpmmentioning

confidence: 99%

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Radicals from the Pyrolysis of Tobacco

et al. 2005

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The fractional pyrolysis of Bright tobacco was studied in an inert nitrogen environment at atmospheric pressure over a temperature range of 200-700 °C, using a continuous-flow reactor system. The effect of pyrolysis conditions on the generation of free radicals and their distribution among total particulate matter (TPM), char residue, and the gas phase was characterized using electron paramagnetic resonance (EPR) and EPR spin-trapping techniques. It was found that the fractional pyrolysis of tobacco led to the generation of free radicals with g-factors of 2.0035-2.0040. They were formed during pyrolysis at temperatures of >380 °C and were present in both char and TPM. The concentration of these radicals in TPM varied from 0 spins/g at 240 °C to 11 × 10 16 spins/g of TPM at 620 °C. The concentration of these radicals in the char residue increased as the pyrolysis temperature increased; a maximum concentration of 1.2 × 10 19 spins/g of char at 480 °C was obtained, and then the value declined. The g-values of 2.0035-2.0040 are consistent with (i) surface-associated, carbon-centered radicals, where the unpaired electron is vicinal to an oxygen-containing functional group, or (ii) partially delocalized, polymeric, phenoxyl-type radicals. The analysis of the gas phase of tobacco smoke revealed the formation of alkoxyl radicals. The N-tert-butyl-R-phenylnitrone (PBN) adduct of the alkoxyl radicals is characterized by hyperfine coupling constants of a N ) 13.9 G and a H ) 2.0 G and a g-factor of 2.0064. The concentration of these radicals in the gas phase was insignificant ((5 ( 1) × 10 14 spins/g of tobacco) and was not dependent on the pyrolysis temperature. After exposure to air, the concentration of TPM radicals increased, because of the production of "new" radicals, in addition to the "old" radicals, with the increasing time of storage, reaching a maximum value and then declining. The g-factor of these new radicals is 2.0053 ( 0.0003, and their TPM concentration achieved a maximum for a pyrolysis temperature of 280 °C. At this temperature, the concentration of these new radicals is 8.1 × 10 15 spins/g of tobacco, which is 25 times greater than the concentration of radicals measured immediately after collection. The EPR spectra of the new radicals are consistent with oxygen-centered, semiquinone-type radicals. These results suggest that hydroquinone/ catechol-type species, which are free or chemically bound to TPM and do not produce EPR signals, are converted to semiquinone-type radicals by atmospheric oxidation.

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Section: Resultsmentioning

confidence: 99%

Section: Radicals In Tpmmentioning

confidence: 99%

Radicals from the Pyrolysis of Tobacco

et al. 2005

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“…The rate constants for the elementary processes of the spin trapping reaction in the Barton's reagents system were determined by using eqn. (9). The concentrations of the RCO,' spin adducts produced were estimated from the peak intensities of EPR spectra as described above.…”

Section: Methodsmentioning

confidence: 99%

“…Assuming that carbon radical concentration [R'] is almost zero at the initial stage, eqn. (9) could be derived from eqns. ( 4), ( 5) and (6).…”

Section: S 'Smentioning

confidence: 99%

Spin trapping of oxygen-centred radicals by substituted N-benzylidene-tert-butylamine N-oxides

Abe¹,

Seno²,

Sakakibara³

et al. 1991

J. Chem. Soc., Perkin Trans. 2

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Spin-trapping of oxygen-centred radicals (tert-butoxyl and carboxyl) by substituted Nbenzylidene-tertbutylamine N-oxides (X-PBN) has been studied and the rates have been measured by means of EPR experiments. The experimental results revealed a substituent effect [X-PBN with an electrondonating substituent favours spin trapping (p < O)] and are rationalized by an electron-transfer mechanism between the frontier orbitals of the reactants. The reaction pathway has been deduced from molecular-orbital and molecular-mechanics calculations.

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“…It is known that spin adducts with PBN tend to fragment thermally according to reactions of the type shown above (28). It is also known that methylnitrosopropane (2) (MNP) is photolyzed by visible light into nitric oxide and t-butyl radicals (16).…”

Section: (Npbn) Adduct Reactivitymentioning

confidence: 99%

An electron spin resonance spin trapping investigation of azide oxidation on TiO₂ powder suspensions

Maldotti¹,

Амаделли²,

Carassiti³

1988

Can. J. Chem.

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The oxidation of azide has been studied on Ti02 powder suspensions in water. methanol, and mixtures of the two solvents. The esr spin trapping technique has been employed to provide evidence for the formation of azidyl radicals N; . The results show that an aqueous alkaline medium is necessary to obtain a high production of N; radicals. A mechanism is proposed whereby the oxidation of N; is mainly due to reaction with OH' radicals which are in turn generated upon capture of holes by OH-groups adsorbed on TiOz. Azidyl anions adsorb weakly on TiOz and do not displace adsorbed OH-from the surface.ANDREA MALDOTTI, ROSSANO AMADELLI et V~TTORIO CARASSITI. Can. J. Chem. 66,76 (1988).On a CtudiC I'oxydation de l'azoture sur des poudres de TiO-, en suspension dans I'eau, le mCthanol et des mClanges des deux solvants. On a utilise la technique du pitgeage de spin par rpe pour obtenir des indications relatives i i la formation des radicaux azidyles N;. Les rCsultats dCmontrent qu'il est necessaire d'opCrer dans un milieu aqueux alcalin pour obtenir une production ClevCe de radicaux N; . On propose un mtcanisme selon lequel l'oxydation des ions N;-provient principalement d'une reaction avec des radicaux OH' qui sont 2 leur tour gentrts par la capture de trous par les groupements OH-adsorbes sur le TiOz. Les anions azidyles ne s'adsorbent que faiblement sur le Ti02 et ils ne deplacement pas les OH-qui sont adsorbes sur la surface.[Traduit par la revue]

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Über die thermolyse von p-substituierten α-phenyl-N-t-butylnitronen.

Cited by 15 publications

References 5 publications

Radicals from the Pyrolysis of Tobacco

Radicals from the Pyrolysis of Tobacco

Spin trapping of oxygen-centred radicals by substituted N-benzylidene-tert-butylamine N-oxides

An electron spin resonance spin trapping investigation of azide oxidation on TiO₂ powder suspensions

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Über die thermolyse von p-substituierten α-phenyl-N-t-butylnitronen.

Cited by 15 publications

References 5 publications

Radicals from the Pyrolysis of Tobacco

Radicals from the Pyrolysis of Tobacco

Spin trapping of oxygen-centred radicals by substituted N-benzylidene-tert-butylamine N-oxides

An electron spin resonance spin trapping investigation of azide oxidation on TiO2 powder suspensions

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An electron spin resonance spin trapping investigation of azide oxidation on TiO₂ powder suspensions