Fast decomposition reactions

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... 

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... 

Such a sacrificial mechanism, although fully successful, is less appealing than the intramolecular one because it leads to the formation of waste products. However, instead of using a sacrificial reductant, that is, an electron donor molecule that undergoes a fast decomposition reaction after electron transfer has taken place, a reversible reductant, giving rise to a stable oxidized form, may be successfully employed, provided that the back electron transfer process can be slowed down by a wise choice of the partners. 

Fast decomposition reactions. EO, in certain conditions, can decompose explosively, also in the absence of air or oxygen, into carbon monoxide and methane [37]. In the presence of rust, the decomposition produces methane, carbon dioxide, and water even if other decomposition products such as ethane, ethylene, and hydrogen have been observed [38,39]. This phenomenon can be prevented by dilution with a suitable inert gas. Not only nitrogen is usually chosen, but also methane and other diluents have been used. The dilution amount depends on temperature, pressure, and expected ignition source and duration [40]. The most thorough discussion of the EO decomposition process is presented in Ref. 39. The inert gas must be used also for blanketing of vessels and lines, and details about this procedure are given in Refs 38 and 40. 

Fast decomposition reactions have been investigated less extensively. However, with use of the recently available fast detection systems it is possible, in principle, to follow chemical reactions on a microsecond or shorter time scale. The first few steps in the decomposition reaction are of special interest. Due to the formation of, sometimes, reactive species (like NO2, OH, etc.), it is often difficult, if not impossible, to draw up these first steps from a long time scale product analysis of a slowly decomposing explosive. Furthermore, it has been stated that the reactions taking place in the various stages to detonation will probably be different [5]. As these stages will be passed through quickly, fast initiation and detection techniques are necessary. 

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). 

The principal difficulty with these equations arises from the nonlinear term cb. Because of the exponential dependence of cb on temperature, these equations can be solved only by numerical methods. Nachbar has circumvented this difficulty by assuming very fast gas-phase reactions, and has thus obtained preliminary solutions to the mathematical model. He has also examined the implications of the two-temperature approach. Upon careful examination of the equations, he has shown that the model predicts that the slabs having the slowest regression rate will protrude above the material having the faster decomposition rate. The resulting surface then becomes one of alternate hills and valleys. The depth of each valley is then determined by the rate of the fast pyrolysis reaction relative to the slower reaction. 

The BaO is produced in the form of very small particles of nearly atomic proportions which react immediately to form the silicate. Actually, the rate of reaction is proportional to the number of nuclei produced per unit vdlume. A nucleus is a point where atoms or ions have reacted and begun the formation of the product structure. In the case of the BaO reaction, the number of nuclei formed per unit of time is small and formation of the structure is diffusion limited. In the case of BaCOa decomposition, the atomic-proportioned BaO reacts nearly as fast as it is formed so that the number of nuclei per unit volume is enormously increased. It is thus apparent that if we wish to increase solid state reaction rates, one way to do so is to use a decomposition reaction to supply the reacting species, we will further address this type of reaction later on in our discussion. 

Moreover, triuret, ammeline, ammelide, melamine and other products may be formed from isocyanic acid, biuret and combinations of them. If urea is heated up very fast, these reactions are suppressed and the decomposition into ammonia and isocyanic acid is the preferred reaction. Due to the high reactivity of isocyanic acid, its primary formation may subsequently lead to the formation of the aforementioned compounds of higher molecular weight. In order to avoid the formation of by-products, the heating-up must be carried out fast. Only then ammonia and isocyanic acid are obtained as sole products. In any case, local undercooling of the gas duct should be avoided and rapid dilution of the thermolysis products in the exhaust gas has to be ensured in order to avoid locally high concentrations of reactive compounds. 

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]. 

A related explanation has to do with the stability of the peroxo dicopper(II) intermediate, since it will either attack the substrate or decompose the kinetics of formation of the intermediate relative to those of the ensuing decomposition reactions will thus be important. Nelson (53) and Sorrell (90) have both described systems that undergo a Cu 02 = 4 1 reaction stoichiometry for dicopper(I) complexes where they propose that degradation of the peroxo dicopperfll) intermediate proceeds by the fast bimolecular two-electron transfer fiom a second dicopper(I) molecule to the putative peroxo-dicopper(II) intermediate to give an aggregated oxo-copper(II) product. [The latter may form hydroxo-Cu(II) species in the presence of protic solvents]. 

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 ... 

This generic chain reaction can be sketched similarly to the acetaldehyde decomposition reaction as shown in Figure 10-2. The circular chain propagates itself indefinitely with a rate rp once initiated by rate ri, but it is terminated by rate ri, and in steady state Ti and rt control how fast the cycle runs. The overall reaction rate is controlled by the concentration or the chain-propagating radical Cr because this controls how many molecules are participating in the chain. This is why r and rt are so important in deterniining the overall rate. 

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... 

It is worth emphasizing that the reaction scheme above is able to explain not only the stoichiometry of the fast SCR reaction, and specifically the optimal equimolar NO to N02 feed ratio, but also the selectivity to all of the observed products, namely N2, NH4NO3 and N20, which derives from thermal decomposition of ammonium nitrate (Ciardelli et al., 2004b, 2007a Nova et al., 2006b) furthermore it is in agreement with the observed kinetics of the fast SCR reactions, which at low temperature is limited by the rate of the reaction between nitrate and NO. 

Co-oxidation of indene and thiophenol in benzene solution is a free-radical chain reaction involving a three-step propagation cycle. Autocatalysis is associated with decomposition of the primary hydroperoxide product, but the system exhibits extreme sensitivity to catalysis by impurities, particularly iron. The powerful catalytic activity of N,N -di-sec-butyl-p-phenylenediamine is attributed on ESR evidence to the production of radicals, probably >NO-, and replacement of the three-step propagation by a faster four-step cycle involving R-, RCV, >NO, and RS- radicals. Added iron complexes produce various effects depending on their composition. Some cause a fast initial reaction followed by a strong retardation, then re-acceleration and final decay as reactants are consumed. Kinetic schemes that demonstrate this behavior but are not entirely satisfactory in detail are discussed. 

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