The Chemistry of Stable Phenoxy Radicals

Altwicker, Elmer R.

doi:10.1021/cr60249a001

Cited by 265 publications

(197 citation statements)

References 204 publications

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“…13,47 The mechanism 48 The initially reported unreactivity of galvinoxyl against oxygen 1 was shown to stem from the inhibition of the oxidation reaction by hydrogalvinoxyl. 2,49 On the other hand, rapid reduction of galvinoxyl to the galvinoxylate anion in basic media is well documented. 47 Despite this, it seems justified to consider galvinoxyl to have an extraordinary stability.…”

Section: Resultsmentioning

confidence: 99%

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Photophysics of the galvinoxyl free radical revisited

Grilj

Zonca

Daku

et al. 2012

Phys. Chem. Chem. Phys.

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The photophysical properties of the free neutral radical galvinoxyl were studied by a combination of femtosecond time-resolved spectroscopy and quantum chemical calculations. The electronic absorption spectrum is dominated by an intense band at 430 nm that is ascribed to the D 9,10 ' D 0 transitions. Upon photoexcitation at 400 nm, the population of the D 9,10 states decays within less than 200 fs to the electronic ground state. This ultrafast internal conversion does not involve intramolecular modes with large amplitude motion as the measured dynamics does not show any significant dependence on the environment, but is most probably facilitated by a high density of electronic states of different character. Depending on the solvent, a weak transient band due to the galvinoxylate anion is also observed. This closed-shell species, which is fluorescent although its deactivation is also dominated by non-radiative decay, is generated upon biphotonic ionization of the solvent and electron capture. The ultrashort excited-state lifetime of the galvinoxyl radical precludes photoinduced disproportionation previously claimed to be at the origin of the formation of both anion and cation.

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Section: Resultsmentioning

confidence: 99%

“…1,2 This stability stems from both steric hindrance induced by the bulky tert-butyl groups and efficient delocalization of the unpaired electron all along the conjugated system. It is widely used as an EPR standard and serves as a radical scavenger/antioxidant, and, as such, it has numerous biological applications.…”

Section: Introductionmentioning

confidence: 99%

Photophysics of the galvinoxyl free radical revisited

Grilj

Zonca

Daku

et al. 2012

Phys. Chem. Chem. Phys.

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“…35269 in some ortho-substituted derivatives (see, for example, ref. 6). In solution, its vibrational structure is poorly resolved, but in an early vapour-phase experiment, Ward (7) was able t o observe four distinct maxima with spacings of about 5 0 0 cm-I.…”

Section: Introductionmentioning

confidence: 99%

Assignment and vibrational analysis of the 600 nm absorption band in the phenoxyl radical and some of its derivatives

Johnston¹,

Mathivanan²,

Negri³

et al. 1993

Can. J. Chem.

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. 71, 1655 (1993).An experimental and theoretical study is reported of the 600 nm band system of phenoxyl and several methoxy substituted phenoxyls. These radicals, generated in freon, show a diffuse band in this region with a vibrational structure that is incompletely resolved but consistent with the 500 cm-I "progression" observed earlier for phenoxyl in the vapour and in a rigid matrix. The low intensity of this band is considerably enhanced by ortho-methoxy substitution. To establish its assignment and analyze its structure, semi-empirical and nb initio quantum chemical calculations have been performed. It is found that, on the basis of the ordering of the states and the magnitude of their transition moments, all calculations favour a TT* ('B~ + 'A~) rather than the earlier proposed nn* assignment for this band. Of the methods used, only the (nb initio) CASSCF method is found to be able to simulate the observed vibrational structure adequately. This simulation is based on optimized structures and vibrational force fields calculated for the lB, and 1A2 states of phenoxyl. It identifies the dominant mode of about 500 cm-' as vki, the characteristic deformation mode of phenyl rings, but shows that higher members of the "progression" receive large intensity contributions from higher frequency modes. The chosen assignment and the assignments of higher-energy transitions reported in the literature are compared with those for the better known benzyl radical. It is shown that some of the phenoxyl assignments reported in the literature contain errors. Une etude experimentale et theorique est presentee concernant le systeme de bandes pres de 600 nm du phenoxyle et de plusieurs phenoxyles comportant un ou deux groupes methoxy. Ces radicaux, produit dans Ie frCon, montrent une bande diffuse dans cette region; la structure vibrationelle n'est pas completement resolue mais est en accord avec la "progression" de bandes de 500 cm-' observCe plus tat pour le phCnoxyle dans la vapeur et dans une matrice rigide. L'intensitC de cette bande faible est hausste considCrablement par des substituants ortho-methoxy. Pour etablir l'attribution de cette bande et pour analyser sa structure, on a fait des calculs avec des mCthodes de chimie quantique, non seulement semi-empirique mais aussi nb initio. On a trouve que, selon l'ordre des Ctats et la magnitude des moments de transition, tous ces calculs favorisent l'attribution de la bande a une transition TT* ('B, + 'A?) au lieu de l'attribution t z~" proposee prCcCdemment. De toutes les methodes utilisees, seule la methode (ab initio) CASSCF peut simuler d'une fason acceptable la structure vibrationnelle observCe. Cette simulation est basee sur les structures optimisCes et les champs de force vibrationnels calcults pour les Ctats 1B2 et 1A, du phCnoxyle. Elle mene l'identification du mode normal de 500 cm-I, qui domine le spectre, avec le mode v6,, c'est-a-dire le mode caracteristique pour la deformation des noyaux benzeniques; cependant, des modes normaux d'une frequence plus ClevCe cont...

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“…Electrooxidation of syringaldehyde produces its corresponding acid as well as dimers. These dimers, although present in smaller quantities, provide evidence for the polymerisation of the lignin monomer, which is known to occur in reactions based on radical formation (Pearl, 1952;Pardini et al, 1991;Pearl, 1957;Altwicker, 1967). Electro-oxidation reactions of the extracted organic component of the effluent, a concentrated form of the effluent and a solution in water of lignosulphonate powder obtained from Lignotech, all showed the formation of syringaldehyde and a smaller amount of vanillin.…”

Section: Discussionmentioning

confidence: 99%

The electro-oxidation of lignin in Sappi Saiccor dissolving pulp mill effluent

Moodley¹,

Mulholland²,

Brookes³

2011

WSA

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Electro-oxidation reactions using a nickel anode were carried out on the calcium-spent liquor effluent obtained from Sappi Saiccor (formerly South African Industrial Cellulose Corporation) dissolving pulp mill as well as on lignin-and lignan-type compounds previously identified in the effluent. Voltammograms were obtained for each solution in order to identify the oxidation potentials of the compounds to be electro-oxidised. Value-added products such as vanillin and syringaldehyde were identified in the electro-oxidised reaction mixtures using gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Profiles of the changes in concentration of these compounds were determined as a function of time with maximum concentrations reached within the first half hour. These findings are significant in that few electro-oxidation reactions have been carried out on the effluent of a pulp mill which uses the acid bisulphite pulping process and no results have previously been reported on the electro-oxidation of syringaldehyde. This study contributes to a further understanding of the electro-oxidation of lignin and is of value to the paper and pulp industry at large. Reduction of the organic content of the effluent by electro-oxidation was shown to be possible.

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The Chemistry of Stable Phenoxy Radicals

Cited by 265 publications

References 204 publications

Photophysics of the galvinoxyl free radical revisited

Photophysics of the galvinoxyl free radical revisited

Assignment and vibrational analysis of the 600 nm absorption band in the phenoxyl radical and some of its derivatives

The electro-oxidation of lignin in Sappi Saiccor dissolving pulp mill effluent

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