Galvinoxyl radical

Figure 14.4 Four examples of the phenolic compounds (ArOH) involved in the equilibrium studies of reaction 14.32. Compound 5 is a-tocopherol, a very important antioxidant. The reactant (Ar O) is the galvinoxyl radical, produced from 1.

Further to its ability to perform allylic and benzylic oxidations,149 /-butylpcroxy-iodane (6) effects radical oxidation of 4-alkylphenols to give 2,5-cyclohexadien-l-ones under mild conditions in good yields.150 o,o-Coupling dimers as side products and inhibition of the reaction by added galvinoxyl radical scavenger support a radical oxidation mechanism. 

In the case of SET addition of R3GeLi to 3,5-di-t-butyl-o-quinone (Scheme 42)198,199, the two radical intermediates were observed by ESR when R = Mes. The dominance of this mechanism was demonstrated by the reaction between R3GeLi and a paramagnetic quinonic species, the galvinoxyl radical, which was almost completely transformed into a diamagnetic anion (Scheme 43)199. 

The behaviour of the galvinoxyl radical as described in the previous section is the result of a redox cycle incorporating features of both CB-A and CB-D antioxidant steps. This is shown in Scheme 1.67. 

The redox reaction also extends to the participation of hydroperoxides, but their efficient decomposition depends on the formation of a non-radical product such as an alcohol. Another example of a redox couple is found in the behaviour of the nitroxyl radical (R NO )- Depending on the structure of R, these are efficient radical scavengers and a redox couple between the mdical and the hydroxyl amine (R NO /R NOH) is formed (which is analogous to the galvinoxyl radical G-/GH). It is noted that the hindered amine stabilizers (e.g. Tinuvin 770 and the monomeric and polymeric analogues) are ineffective as melt antioxidants, possibly because of reaction with hydroperoxides or their sensitivity to acid. 

Scheme 1.67. The redox reaction of galvinoxyl radical, G, and the parent phenol, GH. After Al-Malaika (1989).

In the case of molecular materials, the first evidence of a purely organic compound with ferromagnetic interactions was given in the late 1960s when such interactions were identified in the case of galvinoxyl radicals [52] (Fig. 2). 

Fig. 2 Molecular formula (left) and magnetic susceptibility (right) of galvinoxyl radical. Reprinted from ref 52 [Blundell SJ, Pratt FL, Organic and Molecular Magnets , (2004) J Phys Condens Matter 16 R771] with permission of lOP publishing Ltd...

Fig. 3.3 Simulated ESR spectra of (a) galvinoxyl radical with acH = 0.61 mT, aortho(4H) = 0.144 mT, and of (b) CH3-substituted galvinoxyl radical with acH = 0.595 mT, aortho(4H) = 0.137 mT, acH3(6H) = 0.395 mT, see paper by C. Besev et al. [Acta Chem. Scand. 17, 2281 (1963)] for experiments and analysis...

THERMODYNAMIC PROPERTIES OF GALVINOXYL RADICAL AND ITS PHENOL DERIVATIVE, MECHANISM OF THE PHASE TRANSITION. 

In 2001, Milstein studied the reactivity of Pd(ll) aryl complex 8 with one-electron oxidants galvinoxyl radical and AgOTf (Fig. 5) [66]. Treatment of Pd(ll)... 

Chemiluminescence has been observed in the oxidation of certain disubstituted organobor-anes. The reaction of diisopinocampheylborane or 9-borablcyclo[3.3.1]nonane with O2 in tetrahydrofuran leads to relatively bright chemiluminescence (ca. 2x10 photons s" mL" mol- ). The B-H infrared spectral modes disappear during the process, and 0-H and C=0 modes appear. The introduction of a galvinoxyl radical scavenger leads to a simultaneous drop in chemiluminescence and in O2 absorption [7]. 

Hydrolysis of the starting compound with water produced 2-aminophenol in a side reaction. It was oxidized to 2-aminophenoxazine-3-one. Galvinoxyl radical did not affect the rate of oxidation, therefore no free radical reactions seem to be involved. 

Awaga, K., Sugano, T., and Kinoshita, M., Ferromagnetic intermolecular interactions in a series of organic mixed-crystals of galvinoxyl radical and its precursory closed shell compound, J. Chem. Phys., 85, 2211, 1986. 

H. Nishide, T. Kaneko, R. Gotoh, and E. Tsuchida, Polyacetylene derivatives with chain-sided phenoxy and galvinoxyl radicals. Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A, 233, 89 (1993). 

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