Decomposition, dependence

The mechanism and rate of hydrogen peroxide decomposition depend on many factors, including temperature, pH, presence or absence of a catalyst (7—10), such as metal ions, oxides, and hydroxides etc. Some common metal ions that actively support homogeneous catalysis of the decomposition include ferrous, ferric, cuprous, cupric, chromate, dichromate, molybdate, tungstate, and vanadate. For combinations, such as iron and... 

Thermal Decomposition of GIO2. Chloiine dioxide decomposition in the gas phase is chaiacteiized by a slow induction period followed by a rapid autocatalytic phase that may be explosive if the initial concentration is above a partial pressure of 10.1 kPa (76 mm Hg) (27). Mechanistic investigations indicate that the intermediates formed include the unstable chlorine oxide, CI2O2. The presence of water vapor tends to extend the duration of the induction period, presumably by reaction with this intermediate. When water vapor concentration and temperature are both high, the decomposition of chlorine dioxide can proceed smoothly rather than explosively. Apparently under these conditions, all decomposition takes place in the induction period, and water vapor inhibits the autocatalytic phase altogether. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, HCl, HCIO, and HCIO. The ratios of products formed during decomposition depend on the concentration of water vapor and temperature (27). 

The Bamford-Stevens decomposition of tosylhydrazones by base has been applied to steroids, although not extensively. It has been demonstrated that the reaction proceeds via a diazo compound which undergoes rapid decomposition. The course of this decomposition depends upon the conditions in proton-donating solvents the reaction has the characteristics of a process involving carbonium ions, and olefins are formed, often accompanied by Wagner-Meerwein-type rearrangement. In aprotic solvents the diazo compound appears to give carbene intermediates which form olefins and insertion products ... 

For all three halates (in the absence of disproportionation) the preferred mode of decomposition depends, again, on both thermodynamic and kinetic considerations. Oxide formation tends to be favoured by the presence of a strongly polarizing cation (e.g. magnesium, transition-metal and lanthanide halates), whereas halide formation is observed for alkali-metal, alkaline- earth and silver halates. 

The overall pathway for the conversion of the unsaturated azido ether 281 to 2,5-dihydrooxazoles 282 involves first formation of the dipolar cycloaddition product 287, which thermolyzes to oxazoline 282 or is converted by silica gel to oxazolinoaziridine 288. While thermolysis or acid-catalyzed decomposition of triazolines to a mixture of imine and aziridine is well-documented [71,73], this chemoselective decomposition, depending on whether thermolysis or exposure to silica gel is used, is unprecedented. It is postulated that acidic surface sites on silica catalyze the triazoline decomposition via an intermediate resembling 289, which prefers to close to an aziridine 288. On the other hand, thermolysis of 287 may proceed via 290 (or the corresponding diradical) in which hydrogen migration is favored over ring closure. 

Although the concerted mechanism described in the preceding paragraph is available only to those azo compounds with appropriate orbital arrangements, the nonconcerted mechanism occurs at low enough temperatures to be synthetically useful. The elimination can also be carried out photochemically. These reactions presumably occur by stepwise elimination of nitrogen, and the ease of decomposition depends on the stability of the radical R ... 

The rate constant of their decomposition depends on the peroxyl radical structure and temperature (see Table 7.5). 

Amenates acylated at the exocydic nitrogen are stable as solid compounds but decompose in aqueous solutions releasing NO. This decomposition depends on the pH and most importantly on their chemical structure [147, 152]. The proposed mechanism of NO-release is shown in Scheme 6.24. It is related to that postulated for sydnonimines. The main difference is that here 5-substituted amenates 128 are able to react with water to form acyclic nitroso semicarbazides 129 directly without needing enzymatic cleavage, and these intermediates release NO by an oxidative or thiol mediated mechanism that is not fully understood [153]. 

The relative importance of these two pathways for radical-cation decomposition depends on the nucleophilicity of the solvent and on the structure of the alkene... 

The effective rate of decomposition depends on the ratio of NO to N02. Thus the acetylperoxy radical formed in the decomposition must be removed by further reaction, e.g., with NO,... 

The temperature of decomposition depends also on steric factors The spiro compound 196 c with the five-membered dithiaphospha ring is much more stable than the spiro compound 196 d with the six-membered hetero ring. Only in the latter compound can a stable 1.2-dithia-cycloalkane be formed by radical cleavage Once again the preparative behaviour is in accord with the results of mass spectroscopy (p. 112). 

The products with the dibasic adds are only partially decomposed, the degree of decomposition depending upon the relative proportions of water, acid, and neutral salt. In accord with the solubility law, the solubility of chlorides in cone, hydrochloric acid is generally less than in water, but in some cases, the solubility is greater. For instance, this is the case with mercuric chloride, and M. le Blanc and A. A. Noyes found the f.p. of soln. of mercuric chloride in hydrochloric acid to be progressively depressed only up to the point where the soln. contains the.eq. of HgCl2.2HCl. 

The rate and activation energy of decomposition depend to a great extent on the type of solvent used. 

For every 10 °C increase in temperature, the rate of decomposition is approximately doubled, but may increase as much as 50 times if the explosive is in the molten state. The rates of decomposition depend on the condition of storage and the presence of impurities which may act as catalysts. For example, nitroglycerine and nitrocellulose decompose at an accelerated rate due to autocatalysis, whereas the decomposition rate of TNT, picric acid and tetryl can be reduced by removing the impurities which are usually less stable than the explosive itself. With many of the explosives the presence of moisture increases the rate of decomposition. 

On this decomposition depends the effectiveness of the suggested method for freeing crude tellurium tetrabromide from any oxybromide present in it. 

He cautions that the correlation may underestimate the true solubility, since due to ozone decomposition (depending on ionic strength 31 as well as the type of ions (see below) and... 

The frequency of decompositions depends on the process, whether the plant is equipped with a tubular reactor, a multi-chamber autoclave, or single autoclaves. Important factors are the pressure, temperature, and residence time in the reactor and in the high-pressure separator. The frequency of decompositions is also influenced by the raw materials and the resins which are manufactured. Last, but not least, the frequency of decompositions depends on the shape of the plant, on the training of the operators, and on the know-how of the company or the assistance of the licensor. 

Electrochemical studies on Ru(R2Dtc)3 derivatives have been reexamined (309). The reversible reduction (Eq. 33) previously reported (434) was verified. The oxidation of Ru(R2 Dtc)3 also was described as generally not reversible however, a substituent dependence on the degree of reversibility was noted. It was suggested that the Ru(R2Dtc)3 exhibits various degrees of instability toward decomposition depending on the substituents. 

Ti(OR)4 and Zr(OR)4 are the most thoroughly studied alkoxides from the point of view of their hydrolytic decomposition. Depending on the hydrolysis technique, different products such as films, fibers, glasses, and powders of Ti02 and Zr02 may be obtained, numerous preparation techniques are described in dozens of patents. On the other hand the physico-chemical aspect of hydrolysis received considerably less attention. 

A student investigated how the rate of decomposition depends on the catalyst. She tested two catalysts manganese(IV) oxide (experiment 1) and copper (experiment 2). The volume of oxygen produced by the reaction was measured at different times using the apparatus shown. 

The rate of decomposition has been measured as a function of C02 pressure by Centnerszwer and Brusz14 and Prodan and Pavlyuchenko.15 The decomposition yields CdO without the formation of intermediates. In vacuum the activation energy is 151 kJ. The rate of decomposition depends on the method of preparation. The kinetics follows the contracting sphere model. 

Nitrites decompose at lower temperatures than the corresponding nitrates. The course of decomposition depends on the nature of the salt and the gas phase composition. Nitrites of the more electropositive elements decompose to form the oxide directly by reactions of the type 2 MN02 = M20 + NO +N02, but if the gases are not immediately removed, the nitrite is easily oxidized to the nitrate by N02, if the latter salt is stable at the decomposition temperature. In some cases, particularly the rare-earth nitrites, the first decomposition product is an oxynitrite. According to Addison and Sutton,5 simple nitrites will be stable only if a higher valent-state of the metal is not readily available. Otherwise, decomposition to oxynitrites will occur to achieve the more stable valence of the metal. This view is supported somewhat by the nonexistence of many nitrites of metals in the first two long periods of the periodic table. 

Decomposition reactions appear to be similar to those of the other alkali metal nitrites, i.e., the course of the decomposition depends on the gas phase. If the gas is continually removed, the reaction proceeds directly to the oxide ... 

The salt is rather unstable, but its precise mode of decomposition depends on the rate at which it is heated.5,6 If it is heated slowly or at a constant temperature in the range 130 to 180°C, it disproportionates according to... 

Results are shown in Figs. 12 and 13. All blend specimens were set iso-thermally above LCST and kept there for a maximum of 5 min. As will be seen, this corresponds only in some cases to an early stage of spinodal decomposition depending on temperature. The diffusion coefficients governing the dynamics of phase dissolution below LCST are in the order of 10"14 cm2 s"1. Figure 12 reflects the influence of the mobility coefficient on the phase dissolution. As can be seen, the apparent diffusion coefficient increases with increasing temperature of phase dissolution which expresses primarily the temperature dependence of the mobility coefficient. Furthermore, it becomes evident that the mobility obeys an Arrhenius-type equation. Similar results have been reported for phase dis-... 

Clearly the addition of epichlorohydrin to these formulations played a substantial role in enhancing stability and accelerating decomposition, depending on which solvent system is chosen. 

Reports of the presence of methionine sulfoxide are less frequent with respect to protein hydrolyzates than to free amino acid extracts. This is at least partially due to the fact that reduction and other changes occur upon hydrolysis with hydrochloric acid (16). The extent of decomposition depends on the conditions of hydrolysis and may approach 100%. One occasionally finds a published report of an amino acid analysis of protein in which data for methionine sulfoxide but not methio-... 

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