Closed vessels decomposition

With development of the Carius tube, the field of closed-vessel decomposition was bom. Decomposition in autoclaves with metal inner reaction vessels was... 

During the past 25 years, hundreds of reports have appeared in the literature regarding the use of closed-vessel decompositions carried out in microwave ovens with the reagents described in Section 36B. These applications fall into two categories ... 

At temperatures above 50°C, irreversible hydrolysis to formate and ammonia becomes important. If the heat of reaction is not removed, the increased temperature accelerates the decomposition and can create high pressure in a closed vessel. 

The heat of decomposition (238.4 kJ/mol, 3.92 kJ/g) has been calculated to give an adiabatic product temperature of 2150°C accompanied by a 24-fold pressure increase in a closed vessel [9], Dining research into the Friedel-Crafts acylation reaction of aromatic compounds (components unspecified) in nitrobenzene as solvent, it was decided to use nitromethane in place of nitrobenzene because of the lower toxicity of the former. However, because of the lower boiling point of nitromethane (101°C, against 210°C for nitrobenzene), the reactions were run in an autoclave so that the same maximum reaction temperature of 155°C could be used, but at a maximum pressure of 10 bar. The reaction mixture was heated to 150°C and maintained there for 10 minutes, when a rapidly accelerating increase in temperature was noticed, and at 160°C the lid of the autoclave was blown off as decomposition accelerated to explosion [10], Impurities present in the commercial solvent are listed, and a recommended purification procedure is described [11]. The thermal decomposition of nitromethane under supercritical conditions has been studied [12], The effects of very high pressure and of temperature on the physical properties, chemical reactivity and thermal decomposition of nitromethane have been studied, and a mechanism for the bimolecular decomposition (to ammonium formate and water) identified [13], Solid nitromethane apparently has different susceptibility to detonation according to the orientation of the crystal, a theoretical model is advanced [14], Nitromethane actually finds employment as an explosive [15],... 

Dartnell, R. C. et al., Loss Prev., 1971, 5, 53-56 MCA Case History No. 1649 A batch of 8 t of material accumulated in storage at 154°C during 72 h decomposed explosively. Stability tests showed that thermal instability developed when 3-methyl-4-nitrophenol is stored molten at temperatures above 140°C. Decomposition set in after 14 h at 185° or 45 h at 165°, with peak temperatures of 593 and 521°C, respectively. In a closed vessel, a peak pressure of 750 bar was attained, with a maximum rate of increase of 40 kbar/s. Thermal degradation involves an initially slow exothermic free radical polymerisation process, followed by a rapid and violently exothermic decomposition at take-off. 

Interaction of alkenes with ozonised oxygen tends to give several types of products or their polymers, some of which show more pronounced explosive tendencies than others [1]. The cyclic ge/n-diperoxides are more explosive than the true ozonides [2], It has been calculated that ozonisation of the endothermic /rara-stilbene (AH°f +135.4 kJ/mol, 0.78 kJ/g) would give, in the event of decomposition of the unstable ozonide, an exothermic release of 1.41 kJ/g which would attain an adiabatic decomposition temperature approaching 750°C with a 27-fold pressure increase in a closed vessel [3],... 

Confinement—Deflagration rates of substances such as azo compounds, peroxides, and certain lead oxides may accelerate by pressure increase, especially when the governing decomposition reaction is gas-phase controlled [28]. Initiation of a deflagration at the bottom or at the center of a closed or partially closed vessel may lead to an increase of eh deflagration rate by a factor of more than 100 in comparison with top initiation. Autocatalytic decomposition by a volatile catalyst is enhanced by confinement. 

Maximum pressure after decomposition the maximum pressure obtainable in a closed vessel this pressure is a function of the adiabatic temperature rise and the specific gas production. 

The formula weight of this compound is 1419.6. The yellow-orange crystals are stable for an indefinite period in closed vessels at room temperature. They dehydrate to a yellow powder at low humidities or upon gentle heating. The density determined by flotation is 2.35 g/mL and the pH of a 5% aqueous solution is 6.7. Concentrated aqueous solutions show noticeable decomposition in 1 day at 25°, while dilute solutions = 0.01 M show little change in weeks. At 25° the compound has a solubility of 0.284 g/ml H20. 

With mineral acids, including nitric acid produced by the decomposition of powder, the N-nitroso compound undergoes rearrangement to form p-nitrosodiphenylamine (IV). This substance is readily oxidized to p-nitrodiphenylamine (V). Furthermore, the higher nitrated products, i.e. dinitro derivatives (VI) and (VII) and trinitro derivatives (VIII) may be formed in powder. Davis and Ashdown isolated 2,4,4 -tri-nitrodiphenylamine from American pyrocollodion powder by heating a sample in a closed vessel for 240 days at a temperature of 65°C. At the end of the heating period brown nitric oxides were given off by the powder. 

Thermal decomposition of oxides and peroxides. High pressure oxygen can be produced by the thermal decomposition of oxides (for example, CrOs, MnjO ) and peroxides (for example, BaO2, CaO2) in a closed vessel, the pressure of which can reach up to 50 000 atm. 

The similarity of these numbers shows that very littlo difference exists betwocn the results obtained from the distillation of the substance in close vessels, and from its decomposition in the fire by a blast of air. In the first case, howover, there remains an average of twenty-nine parts of charcoal, which might determine a preference for that method, were it not that the greater part of this is consumed in carbonizing the matter in the retort. 

---