Di-/-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 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. 

Di-/-butyl-4-methylpyridine, 160 Di-/-butyl nitroxide, 160-161 Di-r-butyl peroxide, 131... 

The mechanism of triplet quenching by di-/-butyl nitroxide has been discussed by Schwerzel and Caldwell. ... 

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

The monomers used in anaerobic adhesives and sealants generally contain at least one free-radical stabilizer, such as hydroquinone or />-methoxyphenol. It was found that ben-zoquinone, naphthoquinone, and similar compounds provided improved shelf stability without retarding the anaerobic cure [56]. It was also found that anaerobic formulations could be stabilized with a stable nitroxide free radical such as di-/-butyl nitroxide (LIV) [57]. The use of a soluble metal chelating agent such as tetrasodium EDTA (V) was found to be an effective method of stabilizing an anaerobic formulation against small amounts of metal contamination [58]. 

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... 

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. 

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.

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. 

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... 

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