Transfer from the Azides

In the second type of test the witness material is the secondary explosive in a configuration designed to reproduce or simulate that conceived for the azide and the explosive in an actual design. The approach assesses the efficiency of the azide as an initiator by determining the quantity necessary to assure reliable initiation of the secondary explosive for a given configuration and sample quantity. The secondary explosive may, for example, be RDX [18] or PETN [19]. 

The use of these empirical tests is necessary because of the inadequacy of data necessary for theory to provide a computational basis for determining the output parameters necessary to achieve initiation of a secondary explosive with lead azide. The foregoing sections indicate that even empirical data on the parameters that affect the azide output are fragmentary. Nevertheless, the theory can indicate potentially important conditions necessary for an optimum detonator, and a brief discussion of the status of the theory is given at the end of this section. 

Silver azide was also found to be more efficient than lead azide in detonators 

Fignre 17, Effect oflead azide loading pressure on density and detonator performance [33] 0.35 cm diam X 0.35 cm long 17 mg NOL-130, 51 mg lead azide, 18 mg RDX. 

As indicated in the foregoing subsection, the dent test, when utilized with secondary explosives in a detonator, is in part a measure of the efficiency with which the azide initiates the secondary explosive. 

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Rate constants (k X 10 9 M-1sec-1) were determined to be 7.0, 3.5, and 1.0 for the enumerated substrates, respectively. The change in kinetics for the three cation radicals with increasing steric hindrance at the (3-carbon is in accordance with the depicted addition reaction. In contrast with that, a reaction of the azide ion with these three cation radicals in acetonitrile proceeds with rate constants that are the same in all three cases ( 3 X 109 M-1sec-1). In acetonitrile, the reaction consists of one-electron transfer from the azide ion to a cation radical. As a result, a neutral styrene and the azidyl radical are formed. The azidyl radical reacts with the excess azide ion, and the addition reaction does not take place ... 

Macroscopic n-type materials in contact with metals normally develop a Schottky barrier (depletion layer) at the junction of the two materials, which reduces the kinetics of electron injection from semiconductor conduction band to the metal. However, when nanoparticles are significantly smaller than the depletion layer, there is no significant barrier layer within the semiconductor nanoparticle to obstruct electron transfer [62]. An accumulation layer may in fact be created, with a consequent increase in the electron transfer from the nanoparticle to the metal island [63], It is not clear if and what type of electronic barrier exists between semiconductor nanoparticles and metal islands, as well as the role played by the properties of the metal. A direct correlation between the work function of the metal and the photocatalytic activity for the generation of NH3 from azide ions has been made for metallized Ti02 systems [64]. 

Onium salts, such as tetraethylammonium bromide (TEAB) and tetra-n-butylammonium bromide (TBAB), were also tested as PTCs immobilized on clay. In particular, Montmorillonite KIO modified with TBAB efficiently catalyzed the substitution reaction of a-tosyloxyketones with azide to a-azidoketones, in a biphasic CHCI3/water system (Figure 6.13). ° The transformation is a PTC reaction, where the reagents get transferred from the hquid to the solid phase. The authors dubbed the PTC-modified catalyst system surfactant pillared clay that formed a thin membrane-hke film at the interface of the chloroform in water emulsion, that is, a third liquid phase with a high affinity for the clay. The advantages over traditional nucleophilic substitution conditions were that the product obtained was very pure under these conditions and could be easily recovered without the need for dangerous distillation steps. 

The visible spectrum of semimetHrNs includes an charge transfer band from the azide at 470 nm (51). The similarity of this band to the 446 nm band in metHrN3 indicates the azide is bound to the ferric ion of the mixed-valence form. 

This mechanism can be illustrated by the reaction of ferrous ions with hydrogen peroxide (42), the reduction of organic peroxides by cuprous ions (63), as well as by the reduction of perchlorate ions by Ti(III) (35), V(II) (58), Eu(II) (71), The oxidation of chromous ions by bromate and nitrate ions may also be classified in this category. In the latter cases, an oxygen transfer from the ligand to the metal ion has been demonstrated (8), As analogous cases one may cite the oxidation of Cr(H20)6+2 by azide ions (15) (where it has been demonstrated that the Cr—N bond is partially retained after oxidation), and the oxidation of Cr(H20)6+2 by 0-iodo-benzoic acid (6, 8), where an iodine transfer was shown to take place. 

A diazo group transfer from the benzthiazolium azide 97 to 2,6-diamino-pyridine gives the 5-aminotriazolopyridine 98.187... 

Azido and 3-azido-l-methylindole were prepared by azido group transfer from the corresponding lithioindoles using /Moluenesulfonyl azide. <95GCI151>... 

Recently Liu and coworkers used (porphyrin)iron(III) chloride complex 96 to promote 1,5-hydrogen transfer/SHi reactions of aryl azides 95, which provided indolines or tetrahydroquinolines 97 in 72-82% yield (Fig. 24) [148]. The reaction starts probably with the formation of iron nitrenoids 95A from 95. These diradicaloids undergo a 1,5- or 1,6-hydrogen transfer from the benzylic position of the ortho-side chain. The resulting benzylic radicals 95B react subsequently with the iron(IV) amide unit in an Sni reaction, which liberates the products 97 and regenerates the catalyst. /V,/V-Dialkyl-w// o-azidobenzamides reacted similarly in 63-83% yield. For hydroxy- or methoxy-substituted indolines 97 (R2=OH or OMe) elimination of water or methanol occurred from the initial products 97 under the reaction conditions giving indoles 98 in 74—78% yield. 

There is still the possibility that the low-energy z-polarized band in cytochrome-c and the azides of Hb and Mb is due to charge transfer from the axial ligand. This would have the same properties as the z-polarized porphyrin-to-metal charge transfer band, and would be expected to lie at a low energy in the azides. It may be noted that cyanides and hydroxides (24, 71, 78) sometimes appear to have low-spin bands around 15 kK. The enhanced intensity of this band in azides and in cytochrome-c could be due to mixing with the axial ligand-to-metal excited state. 

Figure 8. The azide anion, when enclosed in the dizinc(II) cryptate [Zn2(44)]causes the quenching of the facing anthracene fragment an electron is transferred from the electron rich anion to the photoexcited spacer. Inclusion of cyanate anion does not alter fluorescence emission, due to lack of the suitable redox potential allowing electron transfer.

In order to decide E(Ti) of azides, Saunders et al. measured quantum yields for nitrogen evolution in sensitized photolysis of azl-des(4) expecting such a relationship that the rate constants kq in the energy transfers from the triplet sensitizers to an azide might converge to a constant value provided E(T- ) of sensitized were larger than E(T- ) of the azide, as Hammond et al. had obtained in the sensitized cis-isomerization of trans-stilbene(7). In the cases of azides, however, kq increases monotonously according to the increase of E(T- )... 

The initial acceleratory process in the decomposition of CuNj studied between 443 and 468 K could be described [53] by the power law (n = 3 and E = IQ kJ mol" ) attributed to the three-dimensional growth of nuclei. The rate-limiting step is identified as the transfer of an electron from the azide band to the Fermi level of the metallic nuclei. 

Time-resolved IR studies of the photolysis of 2-(methoxycarbonyl)phenyl azide in solution at room temperature showed that the didehydroazepine (47) was the sole intermediate, at least on the ps time-scale. This contrasts with photolysis of the same compound in matrices at 10 K, where the nitrene, iminoketene (48) and azetinone (49) were observed as well as (47). Matrix photolysis of 2-hydroxy-phenyl azide gives at least three major products, all of which are photo-interconvertible. Two of these are identified as the EtZ mixture of iminodi-enones (50), while the third is the ring-opened compound (51), existing as a mixture of conformers. 2-Aminophenyl azide behaves in a similar manner. Rapid H-transfer from the ortho hydroxy or amino group to the nitrene centre in each case appears to suppress ring expansion completely. 

Diazo transfer from tosyl azide to diphenylphosphinoxide acetamide (33) is accomplished via 1,5 ring closure of 34 to afford 4-diphenylphosphinyl-5-hydroxy-l,2,3-triazole (35).14 However, triazole 35 is further thermally isomerized in DMF back to diazo acetamide (34). Tosyl azide in the presence of piperidine converts phosphinoxide acetophenone (36) to diazo acetophenone 37.15... 

Formylation followed by the deformylation diazo transfer reaction of 4-chromanone (65) produces 2-diazochromanone(66) in overall yield of 55-60%.24 Diazo transfer from methanesulfonyl azide to dimethylbenzosuberone (67) is achieved via deformylation.25... 

Treatment of 4-methylcyclohexane-l,3-dione (131) with tosyl azide in the presence of NEt3 led to the corresponding diazo cyclohexane-1,3-dione (132).53 Diazo transfer from tosyl azide successfully inserted the diazo group to cyclooctanedione (133) and provided 134 in 50% yield.54... 

The diazo transfer method 6 is also used for aromatic diazonium salts (see Zollinger, 1994, Sect. 2.6). Diazo transfer is, however, more relevant for the synthesis of aliphatic diazo compounds. In addition to the schematic presentation in Table 2-1, the transfer of N2 from the azide to the carbanion may be combined with the dissociation of certain groups attached to the anionic carbon (see Sects. 2.6 and 2.7). 

Singh observed that doping lead azide with small amounts of (BiNa) (0.24 wt %) results in increased rate and decreased activation energy for thermal decomposition [101]. On this basis it could be theorized that the rate-controlling step is the transfer of an electron from the azide ion to the conduction band and that if this energy barrier is reduced, for example by adding an impurity which introduces new energy levels in the band gap, decomposition rate is enhanced. 

Monoaddition of 1,3-butadiene followed by instantaneous halide transfer from the counter anion and selective formation of the trans-l,4-adduct (PIB-AUyl-X) was observed in hexanes/MeCl 60/40 (v/v) solvent mixtures at —80 °C at [1,3-butadiene] <0.05 mol 1 ([1,3-butadiene]/[chain end] <12). Simple nucleophilic substitution reactions on these chloro or bromoallyl functional PIBs allowed the syntheses of end functional PIBs including hydroxy, amino, carboxy, azide, propargyl, methoxy, and thymine end groups [131]. 

The direct diazo transfer from sulfonyl azides to methyl ketones is usually not a practicable process, with the exception of the a-diazotization of ketones with 2,4,6-triisopropylbenzenesulfonyl azide under phase-transfer conditions. However, diazomethyl ketones amenable to the Arndt-Eistert reaction can be easily prepared in two steps by a formylation-deformylation diazo-transfer sequence (Regitz procedure ). A related practical method advantageously applies the detrifluoroacetylation of a-trifluoroacetyl ketones tScheme 3 a). The preparation of 2-diazo-1,3-dicarbonyl compounds is commonly best performed with p-toluenesulfonyl azide (TsNg) as the diazo-transfer reagent tScheme 3.9h). > An issue... 

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