Reaction self-catalyzed

Also autooxidation or auto-oxidation. A slow, easily initiated, self-catalyzed reaction, generally by a free-radical mechanism, between a substance and atmospheric oxygen. Initiators of autoxidation include heat, light, catalysts such as metals, and free-radical generators. Davies (1961) defines autoxidation as interaction of a substance with molecular oxygen below 120°C without flame. Possible consequences of autoxidation include pressure buildup by gas evolution, autoignition by heat generation with inadequate heat dissipation, and the formation of peroxides. 

In the case of the Cu-type enzyme from A. cycloclastes, it has been shown (Averill and Tiedje, 1990 Jackson et al., 1991) that nitrite can be reduced to N2O in the presence of NO in what resembles a self-catalyzed reaction. At the outset, NO was overwhelmingly the major product in the reduction of nitrite. 

Self-catalyzed reaction. If no acid catalyst is added, the reaction will still proceed because the add can act as its own catalyst. The rate of condensation at any time t can then be derived from the rate of disappearance of — COOH groups and... 

Nitro isobutyl glycerine trinitrate is less thermally stable than nitroglycerine. It would be slowly decomposed during storage. The decomposition will be accelerated by acids, bases, water, and other impurities, or under heat treatment because of the self-catalyzed reaction of nitrogen oxide released in the decomposition process. 

Glowing combustion and flame Combustion is the process of exothermic, self-catalyzed reaction involving either a condensed-phase or a gas-phased fuel, or both. The process is usually (but not necessarily) associated with oxidation of a fuel by atmospheric oxygen. Condensed-phase combustion is usually referred to as glowing combustion, while gas-phase combustion is referred to as aflame. 

The catalysis of isocyanate reactions has been extensively studied because of its critical importance in many of these processes. Noncatalyzed (or rather, self-catalyzed) reactions may sometimes be fast enough in practice isocyanate reactions with amines are so fast that only recent studies using stopped-flow methods could lead to useful data [255, 256], metallic or tertiary amine catalysts being ineffective in this case. 

Fig. 1.18 Solution of direct kinetic problem for self-catalyzed reaction...

Graph of time-dependence of self-catalyzed reaction rate, given in Fig. 1.18, shows the presence of maximum. Location of maximum point could be found from the condition equality of second derivative (fCB(f)/dt to zero ... 

The case of self-catalyzed reactions is rather frequent. For example, the condensation of monomers carrying carboxylic acids with antagonist monomers is self-catalyzed (by acids). In the absence of a strong acid, we obtain... 

As is the case during manufacture, contact with those metallic impurities that catalyze Friedel-Crafts condensation reactions must be avoided. The self-condensation reaction is exothermic and the reaction can accelerate producing a rapid buildup of hydrogen chloride pressure in closed systems. 

Thus the reactions of cyclic or acyclic enamines with acrylic esters or acrylonitrile can be directed to the exclusive formation of monoalkylated ketones (3,294-301). The corresponding enolate anion alkylations lead preferentially to di- or higher-alkylation products. However, by proper choice of reaction conditions, enamines can also be used for the preferential formation of higher alkylation products, if these are desired. Such reactions are valuable in the a substitution of aldehydes, which undergo self-condensation in base-catalyzed reactions (117,118). Monoalkylation products are favored in nonhydroxylic solvents such as benzene or dioxane, whereas dialkylation products can be obtained in hydroxylic solvents such as methanol. The difference in products can be ascribed to the differing fates of an initially formed zwitterionic intermediate. Collapse to a cyclobutane takes place in a nonprotonic solvent, whereas protonation on the newly introduced substitutent and deprotonation of the imonium salt, in alcohol, leads to a new enamine available for further substitution. 

Using excess ethylene glycol is the usual practice because it drives the equilihrium to near completion and terminates the acid end groups. This results in a polymer with terminal -OH. When the free acid is used (esterification), the reaction is self catalyzed. However, an acid catalyst is used to compensate for the decrease in terephthalic acid as the esterification nears completion. In addition to the catalyst and terminator, other additives are used such as color improvers and dulling agents. For example, PET is delustred hy the addition of titanium dioxide. 

In low density reactant compacts, the reaction is believed to involve gas phase oxygen diffusion whereas under conditions of improved contact, in high-density material, the mobile species is identified as Fe2+. The metal catalyzes decomposition of the oxidant (KMn04), an effect that is inhibited by small quantities of certain additives (e.g. NaF). There is a large and specialist literature devoted to self-heating reactions. 

Self-baking electrodes, 12 305, 755 Self-bonded reaction-sintered silicon nitride, 17 210, 211 Self-catalyzed polyols, 25 464 Self-cleaning materials, 22 108-127 problems and outlook for, 22 123-124 surface characteristics of, 22 108-109... 

Because TPA has a melting point of >300 °C and poor solubility in PDO, direct esterification is preferably carried out in the presence of a heel under a pressure of 70-150kPa and at 250-270 °C for 100-140min. A heel is an oligomeric PTT melt with a degree of polymerization (DP) of 3 to 7, purposely left in the reaction vessel from a previous batch to improve TPA solubility and to serve as a reaction medium. The esterification step is self-catalyzed by TPA. 

In the case of the esterification of the diacid, the reaction is self-catalyzed as the terephthalic acid acts as its own acid catalyst. The reverse reaction, the formation of TPA and EG from BHET is catalytic with regard to the usual metal oxides used to make PET, but is enhanced by either the presence of hydroxyl groups or protons. In the case of transesterification of dimethyl terephthalate with ethylene glycol, the reaction is catalytic, with a metal oxide needed to bring the reaction rate to commercial potential. The catalysts used to produce BHET are the same as those needed to depolymerize both the polymer to BHET and BHET to its simpler esters. Typically, titanium, manganese and zinc oxides are used for catalysts. 

The main issue wifh fhese maferials is oxidative stability at potentials above 1.0 V. The development of graphihzed blacks to address this is covered elsewhere in this chapter. The thermal stability of high area blacks is also an issue. Sfevens ef al. showed fhaf high area blacks such as BP2000 suffer excessive gas-phase oxidahon af 150°C in dry air when high loadings of Pt are deposifed onto fhem.i Oxidation rates increase in the presence of H2O/ air mixtures, indicating that Pt/C can self-catalyze the water-gas shift reaction at temperatures as low as 150°C. 

Strategies for functionalization have been developed that exploit the naturally occurring amino acids as well as the non-natural ones. Post-synthetic modifications have been reported that are based on reactive sites that self catalyze the incorporation of the new functionality at the side chains of Lys residues [24,25] and on the chemoselective ligation reaction [26-29]. These developments in combination with new methodology for the synthesis of large proteins [30] provide access to a highly versatile pool of new polypeptides and proteins. 

It is not yet understood how life began on Earth nearly four billion years ago, but it is certain that at some point very early in evolutionary history life became cellular. All cell membranes today are composed of complex amphiphilic molecules called phospholipids. It was discovered in 1965 that if phospholipids are isolated from cell membranes by extraction with an organic solvent, then exposed to water, they self-assemble into microscopic cell-sized vesicles called liposomes. It is now known that the membranes of the vesicles are composed of bimolecular layers of phospholipid, and the problem is that such complex molecules could not have been available at the time of life s beginning. Phospholipids are the result of a long evolutionary process, and their synthesis requires enzymatically catalyzed reactions that were not available for the first forms of cellular life. 

Fe(III) refers to the sum of all three-valent iron in solution, i.e., Fe(III) = Fe3++ FeOH2+ + Fe(OH)2+ + FeOHSO-, + FeSO + etc. Thus the rate of the iron-catalyzed reaction in the low-pH region decreases with increasing [H + ], This means that it shows the behavior depicted in Fig. 8.9a i.e., it is self-quenching. That is, as S(IV) is oxidized to the acid, the pH falls and the rate also decreases. 

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