Potassium azide, decomposition

The decomposition of molten potassium azide has been shown to involve heterogeneous catalysis and induction periods which can be attributed to the presence of residual water in the melts. Homogeneous catalysis is of slight importance. 

The decomposition of potassium azide (530 to 623 K) is complicated by the volatility of the metallic product [43]. Potassium vapour catalyzes decomposition of the salt by the provision of electron traps, other than anion vacancies, with a decrease in E. The roles of charge carriers and ionic diffusion in the decomposition mechanism have been discussed [44]. 

Write formula unit equations for the following (a) thermal decomposition of potassium azide, KN3 (b) reaction of gaseous ammonia with gaseous HCl (c) reaction of aqueous ammonia with aqueous HCl (d) thermal decomposition of ammonium nitrate at temperature above 260°C (e) reaction of ammonia with oxygen in the presence of red hot platinum catalyst (f) thermal decomposition of nitrous oxide (dinitrogen oxide), N2O (g) reaction of NO2 with water. 

For Na, K, and Ba azides no such simple correlation can be made. The activation energy of the alkali-metal azides is not high enough for promotion of an electron even to the first exciton level. On the other hand, the mechanism proposed by Mott specifically to explain the thermal decomposition of barium azide is energetically more favorable. In this mechanism, an electron is first promoted to the conduction band of the metal to form metal, which catalyzes the reaction. Young [16], in fact, observed that the decomposition of potassium azide is promoted in the presence of potassium vapor, which prevents the evaporation of potassium nuclei as they are formed by decomposition. 

Early studies made in conjunction with thermal decomposition experiments [185] showed that for barium and strontium azide, preirradiation with UV light shortened the time elapsed before a previously selected pressure was achieved during thermal decomposition. It was observed that the UV light increased the number of centers at which small aggregates of barium metal or barium nitride could form during the subsequent thermal decomposition. Prolonged illumination was also observed to produce nuclei directly. In contrast, preirradiation of potassium azide with UV light had no effect on its subsequent thermal decomposition [210]. 

The further scheme for calculating the composition of the primary products for sodium and potassium azides, decomposing to gaseous products only, and for the silver azide melt was the same as for the nitrides (see above). The composition was determined by choosing the decomposition scheme for which the molar enthalpy would fit the experimental value. For the other azides, decomposing to the solid metal and a mixture of atomic and molecular nitrogen, the molar enthalpy for one or another product composition needs to be compared to the experimental value, taking into account a partial contribution of the heat of condensation, AcH. For this purpose, the tAcH /v quantity was subtracted from the experimental value of E. Their difference E — tAcH /v) corresponds to the molar enthalpy, of... 

Tompkins et al. [22, 85] studied the photochemical decomposition of potassium and barium azide. Originally they found that the rate of photolysis was proportional to the square of the intensity of the radiation. 

Potassium, rubidium, and cesium azides are of particular interest, since they undergo thermal decomposition at higher temperatures with the formation of the free alkali metals and the evolution of nitrogen in accordance with the equation... 

To explore further the structural requirements for this unexpected nitrile formation (51 — 52) the reaction of the 1-methyl derivative 56 with sodium azide was examined. In this case the diazido derivative 57 was obtained instead of the nitrile 58. In a control experiment the nitrile 58 was also prepared by methylation of 52 with trimethyl phosphate in the presence of potassium carbonate. 58 reacted in analogy to 52 with sodium azide to furnish the tetrazole 59. Attempted decomposition of the geminal diazide 57 in refluxing DMF failed to give the tetrazole 59 (which is very surprising in view of the easy conversion of 38 to 39) [90LA505],... 

FIGURE 25. The heterogeneous gas-phase dehydrochlorination of /1-chloroethyazide on solid potassium rm-butoxide yielding vinyl azide, and the subsequent thermal decomposition of the latter to 27/-azirine. The double-oven apparatus is equipped with cold traps for the by-product tert-butyl alcohol and the end product 2/7-azirine. The PES ionization patterns of the pure compounds were used for optimization of the reaction conditions. Reproduced by permission of Verlag der Zeitschrift der Naturforschung from Reference 215... 

The S3N5 ion, with its planar, partially jr-bonded structure (12-XVII) is also derived from S4N4 by the action of azide ion or metallic potassium. The S4N ion has been obtained by thermal decomposition of S4Ns. 

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