Explosive Azides

The disorder produced by irradiation has been studied in only a limited number of the explosive azides. The selection of the azides for investigation has undoubtedly been determined by their usefulness for civilian and military applications. Hence silver azide, and, in particular, lead azide, have been studied. Other factors, such as ease of preparation, ease of handling, similarities in properties to azides of practical importance, and purely fundamental considerations have played a roll in the selection of materials. In addition to lead and silver azide only thallium and barium azides have Keen studied to any extent, and this section is devoted almost exclusively to these four materials. All results are for a-Pb(N3)2 unless otherwise stated. 

As noted in the introduction, the small band gap azides of lead, silver, and thallium exhibit many similar properties which differentiate them from the large band gap azides. Barium azide may be an intermediate case since with irradiation it shows properties similar to both groups of materials. The small band gap azides in question detonate while barium azide deflagrates but will not sustain detonation. When the small band gap azides, barium azide, and silver and lead halides are exposed to radiation, decomposition appears to take place in both the metal and anion sublattices. Apparently, colloidal metal is formed from the metal sublattice [7,8,81-84] and, in addition, nitrogen [85,86] or halogen gas [87,88] is liberated from the anion sublattice. The relationship 

Decomposition as discussed in this section has been studied by optical methods, X-ray diffraction, X-ray photoelectron spectroscopy, and infrared absorption. Although this section is concerned to a large extent with disorder resulting from decomposition of the metal sublattice, i.e., metal colloids, all types of disorder remaining after irradiation are considered, and some attention is given to the decomposition of the anion sub lattice. The decomposition of the anion sublattice of small band gap azides is considered in much greater detail in Section E dealing with gas evolution (primarily N2). 

It is essential to minimize the quantity of material and number of personnel at any location and to utilize all appropriate protective equipment (such as barriers, safety glasses, and flak jackets) to minimize personnel injury in the event of an unexpected detonation. Cleanliness, the avoidance of gritty or other explosive substances, the wearing of appropriate (antistatic) clothing, and the electrical grounding of personnel are standard precautions taken to avoid accidental initiations. 

Before beginning work with a compound for the first time, consult the references given at the end of this section (p. 80) that describe the properties and potentially hazardous situations. 

Hydrazoic acid is unique in that both the aqueous and gaseous phase are explosive hazards. Detonations of hydrazoic acid solutions are capable of causing serious injury. It is possible to work with gaseous HNs.if an inert diluent gas is used. 

Lead azide, which is normally stored in alcohol-water, reacts with the liberation of hydrazoic acid. It is possible to detect hydrazoic acid in the vapors over lead azide immersed in alcohol-water. With other azides, such as that of barium, water can generate hydrazoic acid readily. The normal laboratory preparation of hydrazoic acid is to acidify sodium azide and distill the hydrazoic acid with an inert gas carrier. The explosion limits of this substance have not been established with any degree of assurance however, it is known that hot spots and sparks will initiate gaseous mixtures of hydrazoic acid in air [1,2]. 

In addition to minimizing the amount, lead azide should not be stored Avith booster or main-charge explosives it should be kept in a separate magazine. Normally, any quantity of explosive azide greater than 10 g should be stored in 50% alcohol-50% water in order to minimize its sensitivity. It is sound practice to sample azides while they are wet and to dry only small portions as required. 

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The unstable explosive azide may be stabilised by adsorption for reprographic... 

Potential hazards arising from slow formation of explosive azides from prolonged contact of halogenated solvents with metallic or other azides are outlined. 

Aliphatic azides (CAUTION A highly explosive azide may be formed when dichloromethane is used as the solvent)... 

Azides, Thermochemistry of Explosive Azides was discussed by P. Gray T.E. Waddington in PrRoySoc 235, 106-10(1956)... 

Study of the Explosive Characteristics of Lead Azide Prepared Commercially 2)Wm.H.Rinkenbach, USP 1,914, 530(1933) "Method of Producing Noncrystalline Explosive Azide 3)W.E.Garner A.S.Gomm, JCS 1931, 2123 34 (Thermal de-compn and deton of LA crysts) 4)F.D. 

Never add sodium or powerful bases to chlorinated solvents - an explosion may occur. Reaction of azide salts with dichloromethane results in the formation of explosive azides. 

In 2006, two groups independently reported the novel asymmetric synthesis of tamiflu (106). Corey et al. reported a short enantioselective pathway for the synthesis of 106 from 1,3-butadi-ene and acrylic acid shown in O Scheme 22 [ 111 ]. The key steps of the synthesis are (1) Diels-Alder reaction of 1,3-butadiene (146) and trifluoroethyl acrylate (147) in the presence of chiral ligand 148 developed in the laboratory [112], (2) the introduction of two amino groups in tamiflu (106) without using potentially hazardous and explosive azide reagents, and (3) a novel S nBr4 - catalyzed bromoacetamidation. 

Gray and Waddiiigion [103, 104] determined cxpciimciUally and calculated enthalpies for the formation of azides. A great difference exists between nonexplosive and explosive azides, as can be seen in Table 73. 

Potential hazards arising from slow formation of explosive azides from... 

A useful method for the separation ofhydrazoic acid is by a column extraction technique using a mixed-bed ion-exchange resin, a strongly acidic resin in the [H form], and a weakly basic resin in the (OH" form). All cations and most anions are held on the column while hydrazoic acid runs through the column. Other cations and anions elute as water. Weak acids, e.g., boric, silicic, and carbonic will also run through the column. The technique has not been applied to the analysis of explosive azides however, it has been used for the analysis of alkali azides and for the preparation of standard solutions of hydrazoic acid [18]. 

For instrumental analysis explosive azides must be converted to the chlorides or nitrates using semiconductor-grade acids. The sample is dissolved in semiconductor-grade nitric acid and ashed. The lead nitrate is then analyzed using flame, emission, X-ray, or mass spectroscopy neutron activation analysis or X-ray... 

An approach applicable to any scale of operation is to recognize not only direct hazards due to the explosivity of explosive azides, but also the indirect hazards resulting mainly from hydrolysis. Hydrolysis gives hydrazoic acid, HN3, a toxic substance which is physiologically very active and is also the medium by which very sensitive heavy-metal azides, most notably copper azide, can be formed. 

Care must also be exercised in the storage of azides to see that no material can react to form hydrazoic acid. In long-term storage of explosive azides in the presence of atomospheric or absorbed moisture, explosive azides may form on brass or copper heating pipes, radiators, refrigerator coils, etc., and for this reason compatibility of metals with HN3 must be kept in mind. 

The normal and preferred means for destroying an explosive azide is to explode it. In a laboratory where small quantities are used, it is strongly recommended that samples, as they outlive their usefulness, be exploded in small quantities in an appropriate laboratory area. Nonexplosive azides, of course, may be decomposed thermally, if they do not present any flame or flash hazard. However, for such materials, the preferred method is chemical destruction. 

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