Catalytic autocatalytic processes

Degenerate Explosion it was a free radical autocatalytic process and control was difficult, but manageable. The main disadvantage was that it produced as much or more acrolein as propylene oxide. Because no market existed for acrolein at that time, the project was abandoned. Within two years, the acrylic market developed and a new project was initiated to make acrolein and acrylic acid by vapor-phase catalytic oxidation of propylene. 

The oxidation of sulfides is a complex process involving a number of conversions [32,46], Disulfides are oxidized by hydroperoxide via the intermediate thiosulfinate RSSOR, which is very reactive to ROOH [32,52-54], The interaction of ROOH with phenolsulfoxides also gives rise to intermediate catalytic compounds, as a result of which the reaction proceeds as an autocatalytic process [46,55], The rate of the catalytic decomposition of R OOH is described by one of the following equations ... 

Shreion Lifson (1997) utilized a nice arithmetic to illustrate the power of the autocatalytic self-replication. He took the example of a normal hetero-catalytic process that makes one molecule of B from A at the rate of one per second. Then, it would require 6 x 10 s to make one mole of B. If instead there is an autocatalytic process by which B gives rises to 2B, and 2B give rise to 4B, and 4B to 8B, and so on, it requires only 79 s to make one mole of B. 

However, if one accepts the hypothesis that only microbially promoted processes are occurring, it becomes necessary to explain the approximately linear dependence of the oxidation rate on 02 partial pressure as a conveniently exact effect on metabolic reaction rates. Ross and Bartlett (76) suggested that oxidation of Mn2+ is initiated by bacteria but that subsequent reaction is dominated by abiotic autocatalytic processes, once catalytically active colloids and particles are formed in sufficient numbers. 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

Three types of add amplifiers have been so far developed in our laboratoiy. The first is a /erf-butyl acetoacetate (2a) widi a tosyloxymethyl residue at the a-position and confirmed to liberate TsOH as a result of the autocatalytic fragmentation to give isobutylene and CC. The second type is p-keto-sulfonate compound (3) which is readily deprotected under an addic condition to give a b-ketoalkyl sulfonate as an intermediate, leading to the p-elimination to yield a sulfonic add. The third one is cw-isomer of l-pheny-l-hydroxy-2-tosyloxycyclohexane and produce TsOT as a result of pinacol-type rearrangement The autocatalytic processes of these compounds were determined and confirmed both in solutions and in polymer films in the presence of a catalytic amount of TsOH. 

When one looks at real processes, one can see that they actually show several different types of kinetic behavior. As shown in Fig. 6.31, reaction rates (or conversion) vary as a function of concentration There are normal catalytic processes (curve a) and autocatalytic processes (curve b) that are dominant in microbial growth (cf. Equ. 2.7) (Levenspiel, 1972). Biotechnological processes are a combination of both (curve c). At the beginning they are autocatalytic later, after the exponential growth phase, they shift to ordinary kinetics. 

Figure 6.31. Dependence of the reaction rate, the rate of formation or of consumption, Tj, on the concentration of component i, Cj, in (a) a normal catalytic process, for example, an enzymatic process, (b) an autocatalytic process such as pure biological growth, and (c) a biotechnological process such as fermentation or waste water treatment with combined growth and product formation.

Figure 23 A-C illustrates the kinetie eurves of major products formation - CHP, DMPC and OZ. The rate of CHP formation for sample 5 with Mo V =1 1 ratio amounts to 1.6.10 M.s C The values of W jjp for samples Nos 7 and 8 are similar to that value. In case of sample Nol the initial rate of CHP formation is to 0.4.10 M.s and is the same as that for the noncatalysed reaction (curve K). The untreated SiO (sample 8) exerts also some catalytic properties. The integral areas below (under) the kinetic curves corresponding to the amount of the products formed vary in the presence and in the absence of the catalyst. For example, the area below the kinetic curve of CHP formation in the catalyzed reaction is greater as compared to that of the noncatalyzed one. The stationary concentration of CHP depends on the type of the catalyst and in relation to their catalytic activity the sample shows the following order 5>8>7>1>K. Curve K is characterized by a S-shape form whereby three periods are distinguished (1) the start of the product accumulation (2) stationary regime in relation to the product (3) autocatalytic process of product formation (Fig. 23, A).

Now the question is how to construct the simplest model of a chemical oscillator, in particular, a catalytic oscillator. It is quite easy to include an autocatalytic reaction in the adsorption mechanism, for example A+B—> 2 A. The presence of an autocatalytic reaction is a typical feature of the known Bmsselator and Oregonator models that have been studied since the 1970s. Autocatalytic processes can be compared with biological processes, in which species are able to give birth to similar species. Autocatalytic models resemble the famous Lotka-Volterra equations (Berryman, 1992 Valentinuzzi and Kohen, 2013), also known as the predator-prey or parasite-host equations. 

Later, Dixneuf, Jutand, and co-workers reported kinetic data on the reaction of [Ru(OAc)2(p-cymene)] with 2-phenyipyridine in acetonitrile that revealed a different C-H bond activation mechanism. " This involves an intermolecular deprotonation pathway via Se3 mechanism which is an autocatalytic process catalysed by the acetic acid produced during the C-H activation (Scheme 2). Kinetic analysis of the reaction between 6 and 2-phenylpyridine to give 9 showed that this process was considerably accelerated by the presence of acetic acid and water. A drastie retarding effect in the presence of 3 equivalents of K2CO3 was also observed which is consistent with the autocatalytic process, as K2CO3 neutralises the required AcOH. In order to explain the importance of the base, " it is essential to take into account the lasts steps to close the catalytic cycle. In most cases the C-H activation is followed by oxidative addition and reductive elimination to recover the active catalytic species. The C-H activation of 2-phenylpyridine was much faster (27 °C) than the following oxidative addition (120 °C) that becomes rate-determining. 

Figure 1 A general mechanism of the operational catalytic pathways within a network. When T and T are equal, the cycle describes an autocatalytic process othCTwise, the cycle describes cross-catalytic processes.

The same reaction, at a later stage, is catalyzed by the carboxyl groups. Indeed, the ring-opening step may be considered an autocatalytic process in which the catalytic function is exerted by the carboxyl groups. The overall rate constant, therefore, is given by the rate constant of the tmcatalyzed reaction plus that of the catalyzed reaction. The above polymerization may also be initiated by the addition of phosphoric acid or its alkylammonium salts, as will be mentioned later on. 

H. Nonlinear kinetics an autocatalytic process. Contrast the catalytic reaction... 

An autocatalytic reaction may be able to proceed in. the absence of the catalyst. In some cases the catalytic product may be removed as it forms, by distillation, extraction, precipitation, or some other means. The process, A => B + P, may have the rate equation... 

The point is also made [134] that the very high surface areas and the richly interconnected three-dimensional networks of these micron-sized spaces, coupled with periods of desiccation, could together have produced microenvironments rich in cat-alytically produced complex chemicals and possibly membrane-endosed vesides of bacterial size. These processes would provide the proximate concatenation of lipid vesicular precursors with the complex chemicals that would ultimately produce the autocatalytic and self-replicating chiral systems. A 2.5 km2 granite reef is estimated to contain possibly 1018 catalytic microreactors, open by diffusion to the dynamic reservoir of organic molecules. .. but protected from the dispersive effects of flow and convection [134] as well as protected from the high flux of ultraviolet radiation impinging on the early Earth. [123,137]... 

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