The Azide Ion

The preparation of a tnflate salt may include the decomposition of tnflyl azide by azide ion Tnflyl azide can be prepared by the reaction of the azide ion with tnfluoromethanesulfonyl fluonde or tnfluoromethanesulfomc anhydnde [18] (equauonlS) Anotherone stepprocedureusesaquatemaryammoniumcountenon [J9] (equation 15) This tnflate can react with primary halides to form tn fluoromethyl sulfones [19 (equation 16) (Table 7)... 

If the intermediate is very unstable, large rate constants may be measured in this way. Thus, Amyes and Jencks studied the hydrolysis of a-azidoethers (Ns", the azide ion, being the common ion), finding (because k i had been independently measured) k2 values in the range 10 to 10 ° M s for the reaction with water. 

The thermal decomposition reactions of KN3, T1N3, and AgN3 have been studied in the corresponding halide matrices [301]. The formation of NCCT from trapped C02 was described and labelling with ISN established that only a single end-N atom of the azide ion was involved in NCO formation. The photodecomposition of PbN6 and the effects of dopants have been followed [302] by the changes produced in the near and the far infrared. 

Although a catalyst does not appear in the balanced equation for a reaction, the concentration of a homogeneous catalyst does appear in the rate law. For example, the reaction between the triiodide ion and the azide ion is very slow unless a catalyst such as carbon disulfide is present ... 

The azide ion is a highly reactive polyatomic anion of nitrogen, N3 . Its most common salt, sodium azide, NaN3, is prepared from dinitrogen oxide and molten sodium amide ... 

The azide ion is a weak base and accepts a proton to form its conjugate acid, hydrazoic acid, HN3. Hydrazoic acid is a weak acid similar in strength to acetic acid. 

Self-Test 15.IB (a) Write the Lewis structure for the azide ion and assign formal charges to the atoms. (b)You will find it possible to write a number of Lewis structures. Which is likely to make the biggest contribution to the resonance ... 

Treatment via chelation has been observed for 2-acetylpyridine thiosemi-carbazone derivatives, which have been found to possess inhibitory activity for the RNA-polymerases of the influenza virus [133]. The iron(III) complexes were shown to be 3 to 6 times more active as inhibitors of partially purified ribonucleotide reductase (no added iron) compared to uncomplexed thiosemi-carbazone [128]. Raina and Srivastava [134] prepared and characterized low spin iron(III) complexes of 2-acetylpyridine thiosemicarbazone, [Fe(8-H)2A] (A = NO3, OH, Cl, N3, NCS or NO2), which were proposed as being seven-coordinate. However, all but the azide complex are 1 1 electrolytes in DMF and their solid ESR spectra are rhombic with the g-values being about 2.20,2.15 and 2.00. Of the six complexes, the azide ion seems to interact ihost strongly with the iron(III) center. 

Diphenylphosphoryl azide reacts with alcohols in the presence of triphenylphosphine and DEAD.76 Hydrazoic acid, HN3, can also serve as the azide ion source under these conditions.77 These reactions are examples of the Mitsunobu reaction. 

By combining several click reactions, click chemistry allows for the rapid synthesis of useful new compounds of high complexity and combinatorial libraries. The 2-type reaction of the azide ion with a variety of epoxides to give azido alcohols has been exploited extensively in click chemistry. First of all, azido alcohols can be converted into amino alcohols upon reduction.70 On the other hand, aliphatic azides are quite stable toward a number of other standard organic synthesis conditions (orthogonality), but readily undergo 1,3-dipolar cycloaddition with alkynes. An example of the sequential reactions of... 

Only low yields of the azide ion adduct are obtained from the reaction of simple tertiary derivatives in the presence of azide ion 2145 46 and it is not possible to rigorously determine the kinetic order of the reaction of azide ion, owing to uncertainties in the magnitude of specific salt effects on the rate constants for the solvolysis and elimination reactions. Therefore, these experiments do not distinguish between stepwise and concerted mechanisms for substitution reactions at tertiary carbon. 

The difference in stability of ionic and covalent azides is sometimes explained in terms of resonance structures. The azide ion, N3 can be represented by the three resonance structures... 

There is an extensive chemistry associated with coordination compounds containing azide ions as a ligands. Like CN-, the azide ion is a pseudohalide ion, which means that it forms an insoluble silver salt, exists as the acid H-X, X-X is volatile, and it can combine with other pseudohalogens to give X-X. Although other pseudohalogens such as (CN)2 result from the oxidation of the CN- ion,... 

It is more difficult to interpret micellar effects upon reactions of azide ion. The behavior is normal , in the sense that k /kw 1, for deacylation, an Sn2 reaction, and addition to a carbocation (Table 4) (Cuenca, 1985). But the micellar reaction is much faster for nucleophilic aromatic substitution. Values of k /kw depend upon the substrate and are slightly larger when both N 3 and an inert counterion are present, but the trends are the same. We have no explanation for these results, although there seems to be a relation between the anomalous behavior of the azide ion in micellar reactions of aromatic substrates and its nucleophilicity in water and similar polar, hydroxylic solvents. Azide is a very powerful nucleophile towards carboca-tions, based on Ritchie s N+ scale, but in water it is much less reactive towards 2,4-dinitrohalobenzenes than predicted, whereas the reactivity of other nucleophiles fits the N+ scale (Ritchie and Sawada, 1977). Therefore the large values of k /kw may reflect the fact that azide ion is unusually unreactive in aromatic nucleophilic substitution in water, rather than that it is abnormally reactive in micelles. 

Recently the vibrational spectra of azide (Nj) on Ag has been investigated using PM FTIRRAS (50). In solution the azide ion has two vibrational modes, the Raman active symmetric mode at ca. 1340 cm-1 and the ir active asymmetric mode at... 

The nucleophilic displacement of the halogen from 2,4-dinitrohalobenzenes by azide ion is catalysed by macrotricyclic ammonium salts [69], Kinetic studies indicate that the azide ion is entrapped and transported within the macrocyclic cage. The highly explosive tetra-azido-p-benzoquinone is obtained when the tetrachloro-quinone is reacted with an excess of sodium azide under phase-transfer catalytic conditions [70]. When only a twofold excess of the azide is used, the 2,5-diazido-3,6-dichloro compound is obtained. 

Although aliphatic azides can be prepared under liquidrliquid phase-transfer catalytic conditions [3-5], they are best obtained directly by the reaction of a haloalkane with sodium azide in the absence of a solvent [e.g. 6, 7]. Iodides and bromides react more readily than chlorides cyclohexyl halides tend to produce cyclohexene as a by-product. Acetonitrile and dichloromethane are the most frequently used solvents, but it should be noted that prolonged contact (>2 weeks) of the azide ion with dichloromethane can produce highly explosive products [8, 9] dibromomethane produces the explosive bisazidomethane in 60% yield after 16 days [8]. 

A az, s ) and solvent (k, s ) to a carbocation intermediate of solvolysis are first determined from the ratio of the yields the azide ion and solvent adducts (equation (1)). The value for may then be calculated from this product rate constant ratio M ), and az = 5 X 10 s for the diffusion limited... 

The azide ion product selectivity (A az/A s)obsd = 0.7 observed for reactions of ring-substituted cumyl derivatives [XC6H4C(Me2)Y) when X is strongly electron-withdrawing is consistent with as 0.7M for formation of an association... 

Workentin et al. (1994) described another interesting solvent effect on the competition between electron transfer and the addition reaction between organic cation-radicals and azides. TEE and AN were compared as solvents. In TEE, the cation-radicals of 4-methoxystyrene (R =R =H), P-methyl-4-methoxystyrene (R =Me, R =H), or p,p-dimethyl-4-methoxystyrene (R =R =Me) react with the azide ion according to the following equation ... 

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