Fast decomposition

The initiation and growth of fast decomposition of azides have been extensively studied, and it will become clear from what follows that the literature is not short of mechanisms to explain their behavior for a variety of situations. However, in only a few cases can the reason for initiation or the process of growth be explained with certainty. The situation is not restricted to the azides but is common to most explosives. 

This chapter is arranged in three parts. The first deals with the different methods by which fast decomposition can be started, the second with the growth and propagation of reaction, and the final section gives general conclusions and discusses areas where further research would be useful. 

The material in this section is presented in terms of initiation by heat, friction, impact, shock, light, electric field, atomic particles, and so-called spontaneous processes. For many of these stimuli similar initiation mechanisms have been proposed. To avoid repetition in the various subsections, the more general mechanisms will be described first. In the case of initiation by the rapid collapse of gas pockets or voids, recent work on this topic will be described in some detail. 

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A classic shock-tube study concerned the high-temperature recombination rate and equilibrium for methyl radical recombination [M, Ml- Methyl radicals were first produced in a fast decomposition of diazomethane at high temperatures (T > 1000 K)... 

Many of the metal chlorites are not particularly stable and will explode or detonate when stmck or heated. These include the salts of Hg", Tl", Pb ", Cu", and Ag". Extremely fast decomposition with high heat evolution has been noted for barium chlorite [14674-74-9] Ba(Cl02)2, at 190°C, silver chlorite [7783-91-7] AgC102, at 120°C, and lead chlorite [13453-57-17, at 103°C (109). Sodium chlorite can be oxidized by ozone to form chlorine dioxide under acidic conditions (110) ... 

Most diaziridines are not sensitive towards alkali. As an exception, diaziridines derived from 2-hydroxyketones are quickly decomposed by heating with aqueous alkali. Acetaldehyde, acetic acid and ammonia are formed from (162). This reaction is not a simple N—N cleavage effected intramolecularly by a deprotonated hydroxy group, since highly purified hydroxydiaziridine (162) is quite stable towards alkali. Addition of small amounts of hydroxybutanone results in fast decomposition. An assumed reaction path — Grob fragmentation of a hydroxyketone-diaziridine adduct (163) — is in accord with these observations (B-67MI50800). 

M aqueous solutions of iodopentaminecobalt(lll) decompose with first-order kinetics at 45 °C with = 6.0x 10" sec 10" M solutions decompose faster after an initial induction period at the normal rate. Product analysis shows the fast decomposition to be a mixture of a redox process leading to iodine and substitution leading to aquopentaminecobalt(iri) and iodide. Addition of sodium iodide (to 10 M) accelerates the decomposition and... 

Furthermore, the reaction of [Fe(CO)(dppe)H2 Si(OEt)3 ] (B, Figure 57) with Me3PbCl led to the dppe-substituted sily 1-plum by 1-dihydrido complex Fe(CO)(dppe)H2 (PbMe3)[Si(OEt)3] (Figure 57). The dihydride complex is less stable than the dicarbonyl complex and tends to fast decomposition at — 25 °C, especially in polar solvents. 

A reaction is exothermic if heat (energy) is generated. Reactions in which large quantities of heat or gas are released are potentially hazardous, particularly during fast decomposition and/or complete oxidations. 

Explanation The ester polystyryl perchlorate is stabilised by M, but it decomposes slowly to Pn4. In the moderately pure system the [Pn+] are consumed by impurities, mainly water, and only when depletion of M leads to fast decomposition of E are enough Pn+ formed to give colour and conductivity. In the very pure system the scavenging of water, etc., by the ions is completed before all the M has been consumed, so that the Pn+ formed thereafter contribute to the rate. At the end of a typical polymerisation of this type the [Pn+] is ca. 10"7 mol l"1. If [H20] > [HClO4]0, the k1 is unaffected because the rate of reaction of E with H20 in CH2C12 is much smaller than the rate of polymerisation, but the Pn+ and/or the HC104 are hydrated so that no colour or conductivity appears. The visible and conducting ions are not polystyryl carbenium ions, but a cocktail of others in which the substituted indanyl ion is the most abundant [28]. 

Similarly, 2-iodoanilides of indolyl acetic acid 15 lead to the corresponding 7,12-dihydroindolo[3,2-d][l]benzazepin-6(5H)-ones 16 (Equation (3) (2005TL8177)). Contrary to N-phenylsulfonyl derivatives lla,b and EOM protected species 13a,c, Boc-derivatives 14b and 15a do not tolerate these reaction conditions, and their fast decomposition has been observed. 

The mechanism of fast SCR over a zeolite-based catalyst has also been addressed by Sachtler and co-workers using an IR technique [69, 70]. They concluded that nitrogen is produced through fast decomposition of ammonium nitrite (the hydrated form of nitrosamide), vhich is formed from equimolar NO/NO2 feeds via N2O3 and its reaction vith water and ammonia ... 

Accurate determination of H2O2 in the air is complicated by the presence of organic hydroperoxides for example, HMHP may undergo a relatively fast decomposition according to equation 22 if the working solution is neutral or alkaline . ... 

Since the ion exchange reactions are fast, decomposition of CPC does not occur at the pH range used [50]. In the stripping side, the presence of buffer anion (B ) of the buffer acid (BH) is likely to cause another ion exchange reaction according to... 

Carbon tetrachloride (5) and trichlorofluoromethane (6) react with xenon difluoride more slowly, but small amounts of hydrogen fluoride lead to fast decomposition of the reagent within one hour at room temperature. 

There are several examples of fast decomposition reactions of the a-adducts derived from 5-membered rings. These reactions can be viewed as resulting from effective kinetic competition of reaction paths other than return to the reactants. In all ascertained cases the products of decomposition result from ring opening, which presumably occurs subsequent to a-adduct formation. Thus 2-nitrothiophene reacts with aliphatic secondary amines to yield bis-(4-dialkylamino-l-nitrobuta-l,3-dienyl) disulfides 156. This compound is suggested to be the end product of a sequence originating from 153, whose formation is not as yet established, according to Scheme 10.187... 

They suggest that the rate determining step for the high temperature thermal decomposition is a proton-transfer on the surface of the solid followed by oxidation of the ammonia gas by radicals resulting from the decomposition of perchloric acid. It seems probable that perchloric acid should undergo fast decomposition at these temperatures, generating oxygen atoms which oxidize the ammonia ... 

The rate of pressure-rise increases with increasing initial pressure and decreasing initial temperature (Fig. 7.2-8). Below the operation-pressure of relief devices, rates of pressure-rise up to 1000 MPa/s can be measured during fast decompositions. 

From these experiments we conclude that for pure and highly crystalline celluloses, a fast decomposition to glucose with minimum by-products is possible. Carbohydrates, containing other sugar units than glucose, are hydrolyzed accompanied by destruction of monosaccharides. The conditions for complete breakdown of cellulose are too severe for other polysaccharides. The problem of achieving optimum hydrolysis conditions is, of course, not a new one and must be solved for each polysaccharide or polysaccharide-containing material. The problem was not pursued further. 

Basically the vanadium present in the large metal porphorin molecules is deposited on the outer surface of the catalyst, due to the fast decomposition of these molecules. 

The fast decomposition of the sacrificial electron acceptor prevents back electron transfer. The formation of molecular oxygen results from... 

The reaction in the bulk can be really neglected if the free radicals are unstable as a result of fast decomposition, discharging, or other reasons. But even in this case neither of the abovementioned models is an appropriate tool for the explanation of the phenomenon. The contact diffusional theory provides the alternative interpretation of the effect originating from either geminate recombination alone or together with the reaction in the bulk. 

The plasma ionic liquid interface is interesting from both the fundamental and the practical point of view. From the more fundamental point of view, this interface allows direct reactions between free electrons from the gas phase without side reactions - once inert gases are used for the plasma generation. From the practical point of view, ionic liquids are vacuum-stable electrolytes that can favorably be used as solvents for compounds to be reduced or oxidised by plasmas. Plasma cathodic reduction may be used as a novel method for the generation of metal or semiconductor particles, if degradation reactions of the ionic liquid can be suppressed sufficiently. Plasma anodic oxidation with ionic liquids has yet to be explored. In this case the ionic liquid is cathodically polarized causing an enhanced plasma ion bombardment, that leads to secondary electron emission and fast decomposition of the ionic liquid. 

A similar but, perhaps, more interesting case is that of the ion pairs between Co(sep)3+ and oxalate ions. Excitation of the ion pair in the IPCT band leads to the formation of the Co(II) complex and of an oxalate radical which undergoes a fast decomposition reaction. Thus, the back electron transfer reaction is prevented and Co(sep)2+, which is a good reductant, can accumulate in the system. When colloidal... 

It has been suggested562-564 that the fast decomposition of aralkyldimethylphenylammo-nium halides 385 to aralkyl halides and dimethylaniline in chloroform (equation 252) invloves the formation of the positively charged triple ion 386 (equation 253), consisting... 

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