Butyl nitroxide

Nitroxides are iV, iV-disubsdnited nitric oxide radicals, the unpaired electron being delocalized between the nitrogen and oxygen The reduction of 2-methyl-2-nitropropane with sodium or electrochemically yields di-r-butyl nitroxide as the final product " Such nitroxide radicals are important for the snidy of a organic ferromagnet... 

In a study directed to the analysis of the role of Fe and the generation of H2O2 in Escherichia coli (McCormick et al. 1998), hydroxyl radicals were specihcally trapped by reaction with ethanol to give the a-hydroxyethyl radical. This formed a stable adduct with a-(4-pyridyl-l-oxide)-iV-t-butyl nitroxide that was not formed either by superoxide or hydroxyl radicals. The role of redox-reactive iron is to use EPR to analyze the EPR-detectable ascorbyl radicals. 

The pot temperature should not exceed 100° until the did-butyl nitroxide fraction is collected. 

The procedure described is that of Hoffmann, Feldman, Gelblum, and Hodgson 4 and is the only one known at this time for the preparation of substantial amounts of di-f-butyl nitroxide. 

The method is specific for the preparation of di-/-butyl nitroxide, a liquid member of a group of stable free radicals useful for the inhibition of a variety of reactions proceeding by radical chain mechanisms as well as for providing standards for e.s.r. measurements. 

The pentane solution is dried over anhydrous magnesium sulfate and fractionated with an efficient spinning-band column (Note 10). After foreruns of pentane and glyme containing f-nitrosobutane are removed (Note 11), 26-27 g. (42-43%) of red di-/-butyl nitroxide, b.p. 59-60° (11 mm.), is obtained. 

The formation R-CO radicals from glucose is verified by spintrapping experiments with tert-butyl-nitroxide and recorded ESR spectra for the resulting compound. Ring-closed vicinal diols indicate fast bond cleavage by Mn + oxidation and efficient initiation of vinyl polymerization., ... 

Scheme 6.24 Formation of the enolether 86 and of oligomers from 5-methyl-l,2-cyclohexadiene (81) and trapping of the diradical 84 by di-tert-butyl nitroxide, according to Bottini and co-workers.

The disappearance of nitroxides may also occur by unimolecular reactions. A good example is found with t-butoxy t-butyl nitroxide, known to be a relatively short-lived species, for which three fragmentation pathways are possible (1 la,b,c). Loss of butoxyl radicals (path a) was shown to be reversible (Perkins and Roberts, 1974), and, in the absence of any substrate which... 

Fig. 1 Esr spectrum of di-t-butyl nitroxide in benzene. Note 13C-satellite lines...

It is important to emphasize the solvent dependence of nitroxide esr spectra. The aN-value may increase by nearly 20% on transferring a given radical from a hydrocarbon solvent to water, and the use of, for example, di-t-butyl nitroxide as a probe for solvent properties has been advocated (Knauer and Napier, 1976 Lim et ah, 1976). The magnitudes of splittings from atoms in substituent groups are also solvent-dependent. 

On occasion, nitrones may lead to unexpected nitroxides. Thus PBN is oxidized to benzoyl t-butyl nitroxide by NOz (Janzen and Blackburn, 1969 ... 

When t-butoxy t-butyl nitroxide was generated in the presence of cumene as a hydrogen donor, its disappearance was much more rapid that in the absence of cumene. This was attributed to rapid fragmentation to t-butoxyl radicals and nitrosobutane (11a) which, in the absence of a hydrogen donor, is reversible. 

Experiments designed to utilize spin trapping to monitor free-radical chemistry in the gas phase were first reported by Janzen and Gerlock (1969). In these, radicals generated by photolysis in a stream of carrier gas were passed over solid PBN. The PBN was then dissolved in benzene, and the solution was found to contain spin adducts of radicals present in the gas stream. Photolysis of t-butyl hypochlorite vapour in this way leads to a nitroxide whose spectrum reveals splitting from two chlorine atoms. This proved to be due to butyl nitroxide (Janzen, 1971 Janzen et al., 1970), and recalls the observation of other nitroxides which apparently result from further reaction of the initial spin adducts. 

Eberson and Nilsson (1990). The benzoyl t-butyl nitroxide [9], often detected in spin trapping experiments under oxidizing conditions. 

The joint action of di-/-butyl nitroxide radicals and tetranitromethane on the hydrazine 371 in ether at room temperature yielded 75% of the A-nitroso compound 372, together with 10% of the dinitrohydrazone 373413. 

The photochemistry of di-terf-butyl nitroxide was studied149. When di-tert-butylnitroxide (DTBN) is excited at 254 nm to the rnt state in pentane solution, it is cleaved to terf-butyl radical and 2-methyl-2-nitrosopropane (with quantum yield of 0.21). The tert-butyl radical is scavenged by DTBN to give di-ferf-butyl-terf-butoxyamine150 (equation 129). 

If di(tcrt-butyl)nitroxide (a radical trap) is present, the reaction with phenylacetonitrile-potassium does not proceed entirely. Acetonitrile-potassium (which is in equilibrium with potassium amide) forms only aminopyridine in the presence of the trap (Moon et al. 1983). Consequently, amination is a classical nucleophile reaction, and the formation of pyridyl acetonitrile is a reaction of the typs- These two reactions are quite different. A stronger CH acid leads to a well-defined synthesis. 

The results obtained in the photostimulated Sj l reaction between carbanions from 2,4,4-trimethyl-2-oxazoline or 2,4-dimethylthiazole and 2-bromopyridine are also consistent with the incomplete formation of the carbanions in KNH2-NH3(ii ) system. In these cases, 2-aminopyri-dine is formed alongside the corresponding pyridyl-2-methylene oxazolinyl or thiazolyl substitution products (Wong et al. 1997). When the Sr I pathway is impeded by conducting the reaction in the dark or in the presence of di(tert-butyl) nitroxide, the ionic amination reaction dominates. 

The photoirradiation effect can be replaced by copper salt catalysis. The catalyzed reactions proceed rapidly and result in a high degree of transformation. Interestingly, ESR method reveals no organic paramagnetic particles in the course of the reaction between haloaryls and phenyl thiolates. The addition of oxidants (oxygen and DNB) or radical acceptors (di(tert-butyl)nitroxide) does not inhibit the substitution. These facts are understandable from Scheme 7.68 (Bowman et al. 1984, Liedholm 1984). 

The Sjjf.fl character of the reaction was ascertained by the effect of light irradiation and addition of a radical trap. Namely, under light irradiation, the half-reaction time was considerably shortened (3 instead of 41 min). Addition of di(tert-butyl)nitroxide completely quenched the reaction—neither C- nor 0-substitution was observed after 4 h. The radical trap may only react with the R radicals that escaped the solvent cage where R, Nu, and X have been formed. This means that, in the... 

Among chain-breaking antioxidants the stable dialkyl nitroxides such as di-f erf-butyl nitroxide (I) and 2,2,6,6-tetramethyl-4-pyridone nitroxide (II) inhibit oxidation by the simplest mechanism and therefore exhibit... 

A radical ipso substitution at the 3-position of 2,3-disubstituted indoles has also been reported in their reaction with benzoyl-r-butyl nitroxide leading to (227) or, with the 2-substituted indole, the dimer (228) (cf. Section 3.05.1.4) (81CC694). In contrast with the benzoyloxylation reactions the nitroxide radical initially abstracts the hydrogen atom at the 1-position to form the indolyl radical. This mechanism is supported by the failure of the corresponding 1 -methylindole to undergo an analogous oxidation. 

Butyl hypochlorite, 55 of phenols to quinones Benzoyl /-butyl nitroxide, 28 2,3-Dichloro-5,6-dicyano-l, 4-benzoqui-none, 104 Periodic acid, 238 of phosphorus compounds Dimethyldioxirane, 120 of selenium compounds Potassium permanganate, 258 of sulfides to sulfoxides and sulfones /-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 ra-Chloroperbenzoic acid, 76, 112 Dimethyldioxirane, 120 of thiols to sulfur compounds Trimethylsilyl chlorochromate, 327... 

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