Reaction network schemes

The anion radical of this substituted product initiates a chain reaction network, Scheme 1-11 ... 

The four materials are (1) polymer 1 linear and polymer 2 crosslinked (2) polymer 1 crosslinked and polymer 2 linear (3) and (4) are obtained by interchanging polymers 1 and 2. In each case the second polymerized material is grafted to the first polymerized material. Equations 9-14 and the related discussion result in 72 possibilities. The difference lies in the counting or omission of the time sequence of events. The reaction network scheme does not consider the importance of the time-order of events. Thus Equation 31 yields the minimum number of distinguishable materials. 

When propylene is used as the feed, acrolein is observed as the major primary oxidation product. These are significant mechanistic observations, since it follows therefrom that all higher oxidized products, when starting with propane as feed must derive from the first formed propylene or a subsequently formed intermediate. A reaction network (Scheme 1) consistent with these observations portends that propane is first oxidized to propylene, which... 

Under the experimental conditions used, the reaction was found to proceed, on all the catalysts tested, through a complex consecutive/parallel reaction network (Scheme 1), The reaction pathway involves the formation of 4-(hydroxyamino)-2-nitrotoluene (4HA2NT), 2-(hydroxyamino)-4-nitrotoluene (2HA4NT), 4-amino-2-nitrotoluene (4A2NT) and 2-amino-4-nitrotoluene (2A4NT) as relevant reaction intermediates. No significative formation of the hydroxyamino-aniinotoluene isomers was instead observed. Most likely, this is due to the high reactivity of these intermediates. 

Ammonia also reacts with the acrolein intermediate, via the formation of an imine or possibly oxime intermediate which transforms faster to the acrylonitrile than to the acrylamide intermediate. This pathway of reaction occurs at lower temperatures in comparison to that involving an acrylate intermediate, but its relative importance depends on the competitive reaction of the acrolein intermediate with the ammonia species and with catalyst lattice oxygens. NH3 coordinated on Lewis sites also inhibits the activation of propane differently from that absorbed on Brsurface reaction network in propane ammoxidation. 

Example A.l. Identification of the stoichiometry in a three-reaction network (after Filippi et al. (1989)) A process proceeds according to the following reaction scheme... 

There are four species containing Rh in the reaction scheme in Figure 3.2B Xo, Xi, Xi and X2. Since quasi-equilibrium between Xj and Xj is assumed, these two can be lumped into one pseudo-component X, thereby reducing the total number of intermediates containing Rh from 4 to 3. This results in a simplified reaction network as shown in Figure 3.2C. However, the mathematical expressions for [XJ, Kqs, and s2need to be established the detailed derivation is described below. 

Typical products distribution, and selectivity profiles were similar to what was reported in the earlier publication (1). The reaction network is shown in Scheme 1. The catalyst properties and test data are given in Table 1. 

Scheme 1 Reaction network for the gas-phase methylation of m-cresol.

Scheme 1. Reaction network in the ethylene oligomerization process...

From Table 2 it can also be observed that the selectivity towards different hydrocarbon groups strongly depended on the acid properties of solids. Large amounts of C4 and C6 olefins were obtained for the mesoporous NiMCM-41 and NiMCM-48 catalysts with the lowest acid site concentration. In this case, a near Schulz-Flory-type product distribution (C4>C6>C8>Cio) was observed. The increase in acid site density (for the catalysts NiY, NiMCM-36, NiMCM-22) results in decrease of C 6/C8 ratio. These results are in agreement with the reaction network proposed in Scheme 1. 

A kinetic description of large reaction networks entirely in terms of elementary reactionsteps is often not suitable in practice. Rather, enzyme-catalyzed reactions are described by simplified overall reactions, invoking several reasonable approximations. Consider an enzyme-catalyzed reaction with a single substrate The substrate S binds reversibly to the enzyme E, thereby forming an enzyme substrate complex [/iS ]. Subsequently, the product P is irreversibly dissociated from the enzyme. The resulting scheme, named after L. Michaelis and M. L. Menten [152], can be depicted as... 

This transformation avoids problems with the change of polarity during the reaction, which occurred in the telomerization, because two aromatic compounds react with each other to form a new aromatic product. The synthesis of 4-nitrodiphenylamine via a Pd-catalyzed Buchwald-Hartwig-type amina-tion from 4-chloronitrobenzene and aniline was chosen as the next test reaction in a cooperation with Lanxess as industrial partner of the network (Scheme 5). 

If the number of components is very large, a mixture can be regarded as continuous and sharp distinctions between individual components are not made. Methods for dealing with stoichiometry, thermodynamics and kinetics for continuous mixtures are discussed by Aris and Gavalas [33]. An indication is given that rules for grouping in such mixtures depend on the nature of the reaction scheme. Wei and Kuo [34] considered ways in which species in a multicomponent reaction mixture could be lumped when the reaction network was composed of first-... 

A number of mechanistic modeling studies to explain the fluid catalytic cracking process and to predict the yields of valuable products of the FCC unit have been performed in the past. Weekman and Nace (1970) presented a reaction network model based on the assumption that the catalytic cracking kinetics are second order with respect to the feed concentration and on a three-lump scheme. The first lump corresponds to the entire charge stock above the gasoline boiling range, the second... 

In general, the lumping scheme and reaction network of our model are considerably less complicated than that of Kmak (9). 

Another approach is to conduct competitive experiments with binary mixtures in which the complete reaction pathway is developed according to a reaction scheme like that of Scheme 1 described in the beginning of this review or like those shown in Figs. 12-15. Much of the confusion found in past reports of the kinetics of dibenzothiophene and its alkylated derivatives has come from incomplete deconvolution of the reaction network. Selectivity is often reported as the ratio of the yields of biphenyls (direct sulfur extraction) to the yields of cyclohexylbenzenes (hydrogenative route). As discussed in Section IV, cyclohexylbenzenes are produced via two different routes and, unfortunately, even low-conversion studies do not circumvent this confusion. To illustrate how conclusions can often be confused if the wrong model is used, some examples of reported competitive inhibition experiments will be discussed. 

Studies conducted since the mid-1990s have lent additional support to the reaction network shown in Scheme 3.1 and emphasized the interesting class of heterogeneous-homogeneous radical nature of the system.539 Isotope labeling experiments have demonstrated that at small conversions levels most of the C02 is derived from methane, whereas at high conversion levels required for practical applications, ethylene is the dominant source of C02.543... 

A typical reaction network for the oxidation of naphthalene includes naphthoquinones as intermediates1006 1033 (Scheme 9.27). 

A formal reaction scheme, given by Germain and Laugier to describe the formation of all observed partial oxidation products, is shown below. This scheme comprises three reaction paths corresponding to side chain oxidation, oxidative coupling and direct oxidation of the nucleus as initiating reactions. In reality, an even more complex reaction network is to be expected. 

Scheme 1. Reaction network for the hydroprocessing of chloronitrobenzenes over HR 306 and HR 340 catalysts.

Experimental concentration vs time plots for the hydroprocessing of 4-chloronitrobenzene over the sulfided HR 306 and HR 348 catalysts at 200°C and 20 bar Hg are presented in Fig.l and Fig.2, respectively.The curves drawn in Fig.l and Fig.2 are computer-simulated based on the consecutive reaction network shown in Scheme 1. 

It also shows that 2-methylpentane (16, 2MeP), 3-methylpentane (17, 3MeP), and 2,3-dimethylbutane (18, 2,3DiMeBu) appear simultaneously and their concentration reaches a maximum at the same time. Their relative ratio stays the same at all times and is identical to the thermodynamically calculated one. 2,2-Dimethylbutane (19, 2,2DiMeBu), however, appear much more slowly. The reaction network is depicted in Scheme 5.11. 

Scheme 1. Known reaction network for hydrodenitrogenation of quinoline...

Scheme 2. Proposed reaction network for hydrodenitrogenation of isoquinoline...

Most of the above reviewed approaches, including those based on the mathematical model of the system, are developed and tested for simplified reaction networks and/or for particular reactive systems. Nonetheless, it is worthwhile to focus on more general reaction schemes and on the rigorous analysis of the main structural properties (i.e., stability and robustness) of the closed-loop system. 

The reaction of copper(II) acetate with ethyl aminomethylene cyanoacetate of type H2(L22) (55) provides highly stable polymer 1Cu(L22) (56). The supra-molecular 2D geometry of 56 depends basically on the lateral groups of the chelate ligand. The two cyano donors of monomer [Cu(L22)] (57) coordinate differently, with the result that 56 is rather composed of zig-zag-lD-strands, linked among each other to give a 2D-network (Scheme 21) [167]. 

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