Radicals azide

An inner-sphere oxidation of HN3 by CoOH to N3- is proposed, the azide radicals yielding nitrogen in a bimolecular process. 

Table 11 summarizes results of spin trapping experiments where PBN-Nu and other ST-Nu" systems have been oxidized anodically at platinum. Originally, all the reactions were suggested to proceed via Nu radicals (Janzen et al., 1980 Walter et al., 1982), but the fact that PBN is oxidized at a lower potential than Cl-, CNO and CN- (Tables 1 and 5) clearly shows that the faster electrochemical process must be PBN— PBN + at the potentials employed. On the other hand, azide ion is oxidized in a faster reaction than any of the spin traps used and thus azide radical is implicated as being trapped. The Cr 4MePyPBN [17] system is a case where possibly Cl is involved in view of the high pa of this spin trap. 

Also azide radicals generated by anodic oxidation of sodium azide in the presence of olefins afford in acetic acid additive dimers, products of allylic substitution and... 

Anodic regioselective acetamidosulfeny-lation of alkenes is similarly achieved by oxidation of diphenyldisulfide in acetonitrile [81]. Cyclic enamines, which are intermediates in the oxidation of cyclic N-methoxycarbonyl amines, react in aqueous acetonitrile that contains chloride ions to a-hydroxy- 8-chloro compounds via intermediate chloronium ions [82]. Enolethers undergo a regioselective azidomethoxyla-tion to yield acetals of a-azido carbonyl compounds upon electrolysis in methanol containing sodium azide [83]. The reaction proceeds possibly via addition of an anodicaUy generated azide radical. 

Azide ions are oxidised at low positive potentials and generate azide radicals. Azide radicals will add to an alkene. Thus the anodic oxidation of enol ethers in... 

Shoute, L. C. T., Z. B. Alfassi, P. Neta, and R. E. Huie, Temperature Dependence of the Rate Constants for Reaction of Dihalide and Azide Radicals with Inorganic Reductants, J. Phys. Chem., 95, 3238-3242 (1991). 

According to detailed electrode kinetic investigations, this reaction starts with the anodic generation of azide radicals from azide anions (216). 

Coordinated azide ion will undergo a number of reactions which involve attack at the azide ligand. A number of examples are summarized in Scheme 9.1172-1175 The azide ligand is photochemically dissociated from bis azide complexes. Irradiation of Pt(CN)4(N3) gives Pt(CN)4 and the azide radical (equation 366),1176 whereas with Pt(N3)2(PPh3)2 the nitrogen-containing product is believed to be N6 (equation 367).1177... 

Lead azide is dissolved by an aqueous solution of ammonium acetate, but it is not destroyed by it. The solution contains azide ions and lead ions, the latter quantitatively precipitable as lead chromate, PbCr04, by the addition of potassium dichromate solution. Lead azide in aqueous suspension is oxidized by ceric sulfate with the quantitative production of nitrogen gas which may be collected in an azotometer and used for the determination of the azide radical. 

Magnus and coworkers have published full details55 on the direct a- or /J-azido functionalization of triisopropylsilyl (TIPS) enol ethers using an iodosylbenzene-TMS-azide combination (equation 13) the w-pathway, favoured at —78 °C, is an azide radical addition process, whereas the -pathway, favoured at —15 to — 20 °C, involves ionic dehydrogenation. Attempts to extend the /3-functionalization to other TMSX derivatives failed. 

Faraggi M, Klapper MH (1993) Reduction potentials determination of some biochemically important free radicals. Pulse radiolysis and electrochemical methods. J Chim Phys 90 711-744 Faraggi M, Klapper MH (1994) One electron oxidation of guanine and 2 -deoxyguanosine by the azide radical in alkaline solutions. J Chim Phys 91 1062-1069 Faraggi M, Broitman F, Trent JB, Klapper MH (1996) One-electron oxidation reactions of some purine and pyrimidine bases in aqueous solutions. Electrochemical and pulse radiolysis studies. J Phys Chem 100 14751-14761... 

The value of Eox for BH 4 is not known, but the borohydride radical, BH4 has been characterized by e.s.r and UV spectroscopy in oxidations of the anion by hydroxyl or azide radicals under pulse-radiolysis conditions (Symons et al., 1983 Horii and Taniguchi, 1986). Most borohydride reductions seem to be straightforward hydride transfers, but stepwise processes occur in the reductions of aryl bromides or iodides under photochemical or di-t-biftyl peroxide initiation. Radical intermediates are shown by the formation of 3-methyl-2,3-dihydrobenzofuran in the reduction of o-allyloxyiodobenzene (Abeywickrama and Beckwith, 1986). 

Lepidine (4-methylquinoline) was found to react with alcohols and DIB-NaN3 in trifluoroacetic acid, producing 2-hydroxyalkyl derivatives. Here, the azide radical abstracts an a-hydrogen from the alcohol, generating new radicals (CH2OH, CH3C HOH, etc.) which are the reactive species, e.g. [110] ... 

Hexazine has constituted an intriguing fictitious molecule. It was studied theoretically in order to understand why it cannot be observed experimentally. Glukhovtsev and Schleyer concluded that among Ne possible isomers, hexazine is less stable than a twist open-chain dimer of two azide radicals with C2 symmetry (which, however, is thermodynamically unstable relative to the exothermal decomposition into 3N2 releasing 188.3 kcal/mol). In marked contrast to benzene, hexazine is calculated to be non-planar due to lone-pair repulsion into the cr system. Homodesmotic reactions ... 

The azide radical Ns- (linear, ground state Hg, d(N N) 118.1pm) is produced in the reaction of HN3 with fluorine atoms (A//r = —ISOkJmoR ) ... 

The enthalpy of formation of the azide radical is 467 SkJmoR. The spin-allowed dissociation to N( D) and N2(X 1 +) is endoergic by 225kJmol, the dissociation enthalpy to N( S) - -N2(X i +) is 0.5 IkJmol. The azide radical is only stable because this spin-forbidden decomposition pathway has an appreciable energy barrier. In aqueous solution, it primarily exists as a monomer, in contrast to other halide or pseudohaUde radicals that exist as the less reactive dimers (e. g. Brs (SCN)2 ). Reaction ofthe azide radical with halogen atoms or other small molecules hke O2, NO, CO, and CO2 produces molecules in electronically excited states because of propensity rules, which can be used for chemically pumped lasers. The azide ion is also formed during high-pressure photolysis of sodium azide. 

The reaction of the azide radical Ns- with excess azide ions in solution forms the hexanitrogen radical anion = 18kJmol- ). ... 

Of great use is the azidonitration of glycals by a similar procedure85,86. It is probable, but not certain, that the reaction is initiated by attack of an azide radical at the double bond rather than by a ceric azide species, although the steric bulk of the latter can explain the stereochemical course of the reaction. 

The first experimental evidence that Met in j8-APl-42 is more easily oxidized than in other peptides and proteins comes from one-electron oxidation of /3AP1-40 using azide radicals (Nj) produced by pulse radiolysis.Thermodynamic considerations indicate that Nj should not oxidize Met residues unless the one-electron reduction potential of Met is lowered because of favorable environment. It was shown that Met is the target in /3-AP(l-40) oxidation. Conversely the oxidation of /3-AP(40-l) with a reversed sequence of amino acids has shown that Tyr is the target of Nj radicals. These observations are the first experimental evidences that (i) Met in AP(l-40) is more easily oxidized than in other peptides or proteins, and (ii) a change in a primary sequence drastically affects the one-electron reduction potential of Met, even in a small peptides. 

Butler J, Land EJ, Swallow AJ, Prutz W. (1984) The azide radicals and its reaction with tryptophan and tyrosine. Rad Phys Chem 23 265-270. 

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