Azide radical, reactions

Interniolecular hydrogen abstraction, 239 Intramolecular free radical reactions, 238 Intramolecular hydrogen abstraction, 239 Iodine azide, 24... 

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. 

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. 

The adducts of azodicarboxylate with EtsSi or PhsSi radicals [79], have been identified as hydrazyl radicals (Reaction 5.41). The addition of RsSi radical to alkyl azides takes place at the terminal nitrogen (Reaction 5.42) affording the triazenyl o-type radical in which the SOMO is in the NNN plane (only one canonical structure is shown) [80,81]. 

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). 

These results indicate that vacuum curing occurs through a radical reaction mechanism and is terminated by reaction of the ring-opened epoxy group with the azide group (not nitrene) under exposure. There is a possibility that polymerization initiated by an exposure-induced radical cation may occur. Furthermore, it is thought that reaction products from both the azide and epoxide serve as dissolution inhibitors, because the sensitivity of EAP is almost the same as that of EP, as shown in Figures 1 and 2. 

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... 

The utilization of the azido group as radical acceptor in radical reactions shown in equation 56, has been tested by Kim and coworkers84,85 using (TMS SiH, which is relatively inert towards azides when compared to BusSnH. Therefore, alkyl bromides and thionocarbonates can be used as precursors of radicals, generated by (TMS SiH which... 

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... 

Azidoselenenylations are known as well in these reactions, the azide ion serves as a nitrogen nucleophile.118-120 The resulting azides can then be used for further transformations to modify the nitrogen functionality. Under certain reaction conditions, however, a radical reaction pathway is possible leading to non-stereospecific addition products.121... 

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. 

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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