Ammonium permanganate, decomposition

A mixture of 0.5% of potassium permanganate with an ammonium nitrate explosive caused an explosion 7 h later. This was owing to formation and exothermic decomposition of ammonium permanganate, leading to ignition. 

Ammonium permanganate, NH4Mn04, has distinct marked explosive properties, but it is unstable. Decomposition and alteration of the appearance of the compound can be discerned within 1-2 days, and within a few weeks its explosive properties are lost. This is probably due to the decomposition of ammonium permanganate, in accordance with the reaction ... 

The temperature of initiation is reported by different authors to be 110-130°C. Bircumshaw and F. M. Taylor [49] have examined the thermal decomposition of ammonium permanganate between 96 and 117°C. The activation energy of this decomposition was estimated as 27.9 kcal/mole. Within the temperature range from 70 to 80°C the energy of activation was 26.0 kcal/mole. An explosive decomposition brought about by an initiator procedes according to the reaction ... 

Reference has already been made to the dehydration of alums (Sect. 1.2 and Table 10), decomposition of ammonium metal phosphates (Sect. 4.1.5) and the use of KMn04—KCIO4 solid solutions in mechanistic studies of the decomposition of potassium permanganate (Sect. 3.6). 

In a review of the course and mechanism of the catalytic decomposition of ammonium perchlorate, the considerable effects of metal oxides in reducing the explosion temperature of the salt are described [1], Solymosi s previous work had shown reductions from 440° to about 270° by dichromium trioxide, to 260° by 10 mol% of cadmium oxide and to 200°C by 0.2% of zinc oxide. The effect of various concentrations of copper chromite , copper oxide, iron oxide and potassium permanganate on the catalysed combustion of the propellant salt was studied [2], Similar studies on the effects of compounds of 11 metals and potassium dichromate in particular, have been reported [3], Presence of calcium carbonate or calcium oxide has a stabilising effect on the salt, either alone or in admixture with polystyrene [4],... 

In addition, procedures have been described in which quaternary ammonium and phosphonium permanganates are preformed and isolated as semistable solids that can then be used as general oxidants in a wide variety of solvents (32,33). Precautions should be taken to avoid violent thermal decompositions when the latter procedure is used (34-36). 

This chapter considers together the thermal decompositions of metal salts of inorganic oxyacids. The decompositions of ammonium salts of these oxyacids (and other anions) are discussed in Chapter 15. The decomposition of potassium permanganate is considered first because it represents one of the earliest solid state reactions that was subjected to detailed mechanistic investigation. Substantial interest in the reaction has continued and has been extended to other metal permanganates. 

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