Di-t-butyl nitroxide

Nitroxides are A(./V-disubstituted 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-t-butyl nitroxide as the final product.127 Such nitroxide radicals are important for the study of a organic ferromagnet.128... 

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. 

Two compounds that effectively inhibit electron-transfer reactions are di-t-butyl nitroxide and 1,4-dinitrotoluene ... 

Nitroxides are also used to remove radical anions from a reaction sequence. For example, di-t-butyl nitroxide has often been used to inhibit the SrnI reaction (see Section 10). Apparently, nitroxides remove radicals via coupling reactions (Hoffmann, A. K. Feldman, A. M. Gelblum, E. Hodgson, W. G. /. Am. Chem. Soc. 1964, 86, 639-646). 

In the ketyl radical (63) from hexamethylacetone, C-splittings are observed for both the ketyl-carbon and the six methyl-carbons but not for the remaining two carbons evidently spin is transmitted to the y-carbons by alkyl-hyperconjugation, as represented by (64) (Hirota and Weissman, 1960 Symons, 1962). A similar effect is observed in the isoelectronic di-t-butyl nitroxide (Lemaire et al., 1964). 

Sulfamethoxazole failed to produce any trappable radicals with an array of different spin traps, but naproxen afforded the EPR spectrum shown in Figure 2.11 when irradiated with 330 nm UV-R in the instrument cavity in the presence of 2-methyl-2-nitroso-propane (MNP). The spectrum contains contributions from di-t-butyl nitroxide, a known photoproduct of MNP. The H-atom adduct MNP-H also evident can arise by several different mechanisms, including the trapping of an H atom by MNP the reaction of MNP with an electron followed by protonation and the direct reduction of MNP by an excited state species. In view of the flash photolysis results, it was concluded that photoionization was the major precursor of MNP-H. The third radical corresponded to a C-centered radical carrying a single H atom, leading to the postulate of a decarboxylation reaction as the primary photochemical step. Confirmation of the participation of free radical intermediates came from the initiation of the free radical polymerization of acrylamide with rates as shown in Table 2.1. 

Figure 5 Dependence of the logarithm of the rate constant qT on the energy of the triplet being quenched. A Tetramethylpiperidine nitroxide in methylcyclohexane NO In n-hexane di-t-butyl nitroxide in n-hexane (Reproduced by permission from Chem. Phys. Letters, 1974, 29, 526)...

Synthesis and properties. The intrinsic stability of nitroxide radicals is enhanced by bulky substituents in the immediate vicinity of the NO group, as in di-t-butyl nitroxide radical (Forrester and Thomson, 1964 Rozantsev and Sholle, 1971). Phenyl nitroxide radicals, such as phenyl t-butyl nitroxide and diphenyl nitroxide, are known to decompose readily even in solid form by bimolecular attack of the NO oxygen on the p-carbon of another radical (Forrester and Thomson, 1964). 

The joint action of di-t-butyl nitroxide radicals and tetranitromethane on the hydrazine 371 in ether at room temperature yielded 75% of the Al-nitroso compound 372, togetha-with 10% of the dinitrohydrazone 373". ... 

Figure 4 shows our recent measurements of the FT-NMR of similar samples. Sample preparation was similar to that described earlier, except that we added the free radical, di-t-butyl nitroxide in an attempt to obtain narrower lines.29 The NMR measurements were made with a Bruker pulse spectrometer operating at a frequency of 13.004 MHz. 

The behaviour of CeFe in the presence of di-t-butyl nitroxide" and with respect to oxygen at various pressures - has been monitored by F-19 NMR. Similar studies have been made of its self-diiTusion and density as a function ofpressure and temperature both alone and as a binary liquid with n-parafiins. A dynamic F-19 NMR investigation has been made of the torsional barriers in pentaduorobenzaldehyde, its conjugate acid, and protonated pentafluoroacetophenone. ... 

Not many initiation events are needed, but the propagation cycle must be fast and efficient to afford a successful process. Radical probes have been used to demonstrate the formation of radicals along the propagation cycle and also as a synthetic tool. Thus, products from ring closure or ring opening or from rearrangement of the radicals were taken as evidence of the presence of these intermediates. Inhibition by radical traps with stable free radicals 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO), di-t-butyl nitroxide (DTBN), etc. has been extensively used to provide mechanistic... 

Pyrolysis at 400 °C of 1,2-benzocycloheptatriene was found to give naphthalene as well as 2-methylnaphthalene, 1-methylnaphthalenc, benzocycloheptene and 1,2-benzocyclohepta-1,3-diene. In the presence of excess benzene a small amount of toluene was produced. Addition of di-t-butyl nitroxide initiated the reaction at 300 °C and increased the yields of naphthalene and toluene. When cycloheptatriene was... 

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