Series Consecutive Reactions

Series reaction networks are very important commercially. In many cases, the intermediate product, R, is desired and the terminal product, S, is undesired. 

Series reaction networks are not limited to two reactions. Butadiene (C4H6) is an important monomer that goes into a large number of elastomeric products, including automobile tires. Butadiene can be produced by the catalytic dehydrogenation of butane (C4H10) as shown below. 

Another example of a series reaction occurs in methanol synthesis, which we discussed in Section 7.3.1. Once CH3OH is formed, it can react further to dimethyl ether (CH3OCH3), 

The second reaction, the combination of two methanol molecules to form dimethyl ether plus water, actually is used for the commercial production of dimethyl ether. However, this reaction is undesirable when it occurs in a conventional methanol plant, as the presence of dimethyl ether and water complicates the design of the separation system. 

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A Fortran IV computer program developed by Redifer and Wilson (10) was used to predict thermodynamic equilibrium compositions for 400-700°K and 1 atm total pressure. The calculations are based on a procedure presented by Meissner, Kusik, and Dalzell (11) in which the set of simultaneous reactions is simplified to a set of series-consecutive reactions. Each reaction is carried out in turn on the reactant mixture as though a set of ideal batch equilibrium reactors were aligned in series in which the products from one equilibrium stage become reactants for the next reactor. After all the reactions have been completed, products from the last reactor are recycled to the first reactor, and the reaction sequence is repeated. Equilibrium of all components is complete when the product compositions at the end of two consecutive cycles are identical. The method compares favorably with the free energy minimization technique and is useful for changing conditions or input parameters. 

Series (Consecutive) Reactions. The simplest example of series reactions which will be used for illustration is the reaction type... 

In reactions occurring in series (consecutive reactions), reactant forms an intermediate product, which subsequently reacts to form another product ... 

Consecutive reactions are those in which the product of one reaction is the reactant in the next reaction. These are also called series reactions. Reversible (opposing) reactions, autocatalytic reactions, and chain reactions can be viewed as special types of consecutive reactions. 

Maddock and Sutin (56) observed the formation of numerous oxygenated products in neutron-irradiated AsPhj which, they argued, must have come from reaction of AsPh radicals with oxygen or water during the separation. The annealing effect of heating at 45° led to increased yields of AsPhj, while AsPhj products first increased and then decreased. This was interpreted as showing the involvement of phenyl radicals in a series of consecutive reactions ... 

The selectivity in a system of parallel reactions does not depend much on the catalyst size if effective diffusivities of reactants, intermediates, and products are similar. The same applies to consecutive reactions with the product desired being the final product in the series. In contrast with this, for consecutive reactions in which the intermediate is the desired product, the selectivity much depends on the catalyst size. This was proven by Edvinsson and Cybulski (1994, 1995) for. selective hydrogenations and also by Colen et al. (1988) for the hydrogenation of unsaturated fats. Diffusion limitations can also affect catalyst deactivation. Poisoning by deposition of impurities in the feed is usually slower for larger particles. However, if carbonaceous depositions are formed on the catalyst internal surface, ageing might not depend very much on the catalyst size. 

Competitive consecutive reactions are combinations of parallel and series reactions that include processes such as multiple halogenation and nitration reactions. For example, when a nitrating mixture of HN03 and H2S04 acts on an aromatic compound like benzene, N02 groups substitute for hydrogen atoms in the ring to form mono-, di-, and tri-substituted nitro compounds. 

Consecutive Reactions Where an Inter-mediate Is the Desired Product. Consecutive reactions in which an intermediate species (V) is the desired product are often represented as a series of pseudo first-order reactions... 

The cyclic process of fatty acid synthesis may be represented by a series of consecutive reactions (hereafter palmitate synthetase is... 

The authors chose pyruvic acid as their model compound this C3 molecule plays a central role in the metabolism of living cells. It was recently synthesized for the first time under hydrothermal conditions (Cody et al., 2000). Hazen and Deamer carried out their experiments at pressures and temperatures similar to those in hydrothermal systems (but not chosen to simulate such systems). The non-enzymatic reactions, which took place in relatively concentrated aqueous solutions, were intended to identify the subsequent self-selection and self-organisation potential of prebiotic molecular species. A considerable series of complex organic molecules was tentatively identified, such as methoxy- or methyl-substituted methyl benzoates or 2, 3, 4-trimethyl-2-cyclopenten-l-one, to name only a few. In particular, polymerisation products of pyruvic acid, and products of consecutive reactions such as decarboxylation and cycloaddition, were observed the expected tar fraction was not found, but water-soluble components were found as well as a chloroform-soluble fraction. The latter showed similarities to chloroform-soluble compounds from the Murchison carbonaceous chondrite (Hazen and Deamer, 2007). 

Progeny Ions Charged products of a series of consecutive reactions that includes product ions, first generation product ions, second generation product ions, etc. 

Complex pyrolysis chemistry takes place in the conversion system of any conventional solid-fuel combustion system. The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicellulose, and lignin. Pyrolysis of these biopolymers proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products which can be divided into char, volatile (non-condensible) organic compounds (VOC), condensible organic compounds (tar), and permanent gases (water vapour, nitrogen oxides, carbon dioxide). The pyrolysis products should finally be completely oxidised in the combustion system (Figure 14). Emission problems arise as a consequence of bad control over the combustion system. 

One important type of complex mechanism in electrode reactions is a series of consecutive reactions. One example of this type is electrochemical deposition from complexed ions. In this case the electrochemical reaction is preceded by a chemical reaction. Another example is that of inclusion of cathodic hydrogen evolution. We discuss these two cases next. 

Fig. 2. Schematic representation of paclitaxel biosynthesis. Dimethylallyl-diphosphate and isopentenyl-diphosphate are condensed through geranylgeranyl diphosphate synthase activity to render geranylgeranyl-diphosphate (GGPP). GGPP is converted into taxa-4(5), 11 (12)-diene in a reaction catalyzed by the taxane synthase (TS). A series of reactions catalyzed by cytochrome P450 monoxygenases lead to the production of a taxane intermediate that is further converted to baccatin III through enzymes-driven oxidation and oxetane ring formation. The side chain moiety of paclitaxel is derived from L-phenylalanine. Three consecutive arrows mean multiple steps. Ac, acetyl Bz, benzoyl.

In some reactions with thiocarbonyl ylides, 1,3-thiazine derivatives are formed by a series of consecutive reactions. For example, the interception of 3-thioxocy-clobutanone (5)-methylide (69) with thiobenzamide results in the formation of the bicyclic 1,3-thiazine (176) (100a) (Scheme 5.50). A conceivable intermediate is the 1,3-adduct 175 as shown in Scheme 5.50. 

In order to obtain both series of dendrimers a divergent stepwise synthetic approach was designed. Each generation growth step of this synthetic approach implies four consecutive reactions (a-b) two successive alkylation reactions that... 

Every reaction has an energy barrier associated with it. When, therefore, there are a series of consecutive reactions, one has a series of consecutive barriers (Fig. 7.71). The overall reaction corresponds to the passage in one direction of the point representing the system across all the barriers. 

As an example for reactions in series or consecutive reactions, the simple reaction scheme... 

The kinetic profile of Cr/AlP04 fits that expected from a transient species in a series of consecutive reactions. 

When the rale of a chemical process is dependent upon (I) two or more consecutive reactions, the observed rale is limited by the rale of the slowest reaction in the series, or (2) two or more concurrent reactions, the products are in the same raliu at any instant only when the reactions themselves are of the same rale. 

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