Lead azide, decomposition, additives

The Curtius rearrangement also occurs in the direct photolysis of acylazides, but additional products have been isolated and have been shown to arise from typical nitrene reactions . For example, Horner et have trapped benzoyl nitrene with a variety of scavengers. Similarly to the Wolff rearrangement (vide infra) it has been shown ° that the Curtius rearrangement occius via a singlet intermediate this intermediate can be a nitrene or an excited azide molecule in which a concerted decomposition leads to isocyanate derivatives. This reaction could occur in competition with nitrene formation or, alternatively, originate from a vibrationally-excited ground state azide molecule. 

Photochemical decomposition of 2-azido-l-methoxyphenazine forms singlet and triplet nitrenes, which are trapped with the azide leading in acetonitrile at —20°C to the dimeric product 3-[3-[[(l-methoxy-2-phenazinyl)imino]methoxymethyl]-2-quinoxalinyl]-2-propenenitrile <9lJOC6993>. Higher reaction temperatures result in the additional formation of aminophenazines and other 2,3-disubstituted quinoxalines <87J0C1245>. 

In the first study on the decomposition of phenyl azide in the presence of electrophilic reagents it has been shown that both thermal and photochemical reactions lead to the azepinone (2) and to disubstituted arenes such as (4). The azepinone is thought to be formed by the addition of acetic acid to the didehydroazepine intermediate (1) and subsequent acetolysis, and the disubstituted arenes are formed from the nitrenium ion (3). 

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... 

The addition of HN3 to nonactivated alkenes with formation of the saturated azides requires drastic conditions and a catalyst. Olefinic double bonds activated by conjugated, electron-withdrawing groups like -CN, -NO2, or -C(0)R react easily [8, 9]. The photolysis [10] and the pyrolysis [7] of HN3 with alkenes yields nitriles, N2, and decomposition products. The reaction of HN3 with alkines usually leads to 1,2,3-triazoles. Single or double addition with formation of vinyl azides or saturated diazides are rare [8, 9]. Arenes and HN3 form aniline derivatives directly and efficiently in the presence of trifluoroacetic acid and the strongly acidic trifluoromethanesulfonic acid [11]. The yield is frequently low in the presence ofH2S04[1]. 

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