Chemistry
Multistep Reaction
A multistep reaction is a chemical reaction that occurs in multiple stages, with intermediate products formed in each step before reaching the final product. Each step involves its own set of reaction conditions and may require different catalysts or reagents. Multistep reactions are common in organic synthesis and are used to create complex molecules with specific structures and properties.
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5 Key excerpts on "Multistep Reaction"
- John Happel(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Insofar as modeling is concerned, it is possible to treat intermediates at steady-state conditions as separate collections of species whether they are involved superficially or intraficially in a catalytic mechanism. In the latter case, a greater concentration of intermediates may be present than when adsorption and reaction are limited to monolayer coverage. The nature of the elementary processes that determine the mechanism of a catalytic reaction system is a subject that is at the forefront of present catalysis research. Information being developed in this area can provide an important basis to sharpen the selection of proposed reaction steps. This subject forms the final section of this chapter. 2.5 Elementary Reaction Steps Once intermediates have been listed, the next step is to develop a set of possible elementary steps involving them. Except for some homogeneous reactions, most chemical reactions are complex, consisting of sets of ele-mentary reactions or steps. A reaction is said to be unimolecular if there is only one molecule in the first member of the chemical equation representing it and bimolecular if there are two. Generally it is assumed unlikely that elementary reactions of molecularity greater than two will occur. Even with this assumption the number of possible elementary steps in most systems becomes very large (see Sinanoglu, 1975; Lee and Sinanoglu, 1981). One way of reducing the number of possibilities, proposed by Dowden (1973), is to split the overall reactions expected to occur among terminal species into sets of homogeneous reactions, each with a molecularity no greater than two. Intermediates are thus introduced that are also molecular species in the gas phase. These reaction steps are called virtual because the actual steps that occur on a catalyst involve chemisorbed species instead of such discrete molecules. A set of steps of this type is termed a virtual mechanism.
- T.F. Jamison, G. Koch(Authors)
- 2018(Publication Date)
- Thieme(Publisher)
[14] One should not, however, underestimate the escalating complexity associated with the telescoping of reaction sequences together. [15–17] It is important also to have the whole armory of modern day synthesis available to solve problems encountered in multistep processes, whether best conducted in batch or flow or in a combination of both proto-cols. [18,19] The complexity and labor-intensive components of synthesis imposes serious constraints on any potential enabling technologies, in that they must accommodate a vast array of reagents, including enzymes, and operate over a wide range of temperatures and pressures using different solvents and additives, often generating solids and slurries in the process. [20] Increasingly, sustainability issues, human resources, and energy requirements are having an impact on synthesis programs. [21] Moreover, the individual unit operations nec-essary to manage downstream intermediates and assist in product workup and purifica-tion are especially demanding in any machine-assisted multistep synthesis. [22] This is par-ticularly true when developing and integrating reaction optimizing algorithms or imple-menting new reaction discovery tools. [23–25] For these many reasons, immobilization tech-niques using a wide range of supporting materials and devices are attractive for flow-based processes, [26] in that they can afford inline delivery of pure materials from sequen-tial reaction steps and can be more readily recycled and reused, especially with cartridge-based formats. Reaction quenching, impurity scavenging, and phase switching, together with catch and release sequences, continue to form powerful enabling concepts for multi-step synthesis programs that can avoid, or at least minimize, traditional and time-con-suming methods such as chromatography, distillation, crystallization, pH adjustments, and water washes.
eBook - ePubBiotechnology of Microbial Enzymes
Production, Biocatalysis and Industrial Applications
- Goutam Brahmachari, Goutam Brahmachari, Arnold L Demain, Jose L Adrio(Authors)
- 2016(Publication Date)
- Academic Press(Publisher)
Both facilitate a number of chemical reactions in a coordinated fashion to produce a wide variety of compounds. However, aside from the differences in their spatial scales, they vary in terms of their number of reaction compartments. In chemical manufacturing processes, each reaction is normally separately operated in a distinct reactor and step-by-step separation and purification of intermediates are needed. In contrast, thousands of reactions composing the natural metabolic network are carried out in a single cell, which is compartmentalized into a limited number of organelles or is even uncompartmentalized in prokaryotic cells. Such a remarkable orchestration of enzymatic reactions is attributed to the excellent substrate specificity of enzymes, by which they can recognize their physiological substrates among the large number of intracellular compounds. Thus, in addition to classically well-interpreted features, such as their high regioselectivity, enantioselectivity, and catalytic ability under benign conditions, the industrial application of enzymes offers a significant operational advantage that enables us to implement multistep cascade reactions in a single reactor. In this chapter, the current status of commercially exploited multistep enzymatic reactions and ongoing challenges for expanding the industrial applicability of multienzyme systems are reviewed. 16.2 Multistep Reactions with a Small Number of Enzymes The world demand for industrial enzymes will rise 6.3% per year, approaching nearly $7.0 billion in 2017 (Freedonia Group, 2014). Biocatalytic conversion with single or a small number of enzymes has matured as a well-developed technology and is practically employed in a wide range of industrial fields, including food processing, diagnosis, and chemical manufacturing
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 16 Chemical Reaction A thermite reaction using ferric oxide A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical eq-uation, is applicable to transformations of elementary particles, as well as nuclear reactions. ________________________ WORLD TECHNOLOGIES ________________________ The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions. Different chemical reactions are used in combination in chemical synthesis in order to obtain a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions impossible under ordinary conditions are performed within a cell.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Chapter 8 Chemical Reaction A thermite reaction using ferric oxide A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reactions. ___________________WORLD TECHNOLOGIES____________________ The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions. Different chemical reactions are used in combination in chemical synthesis in order to obtain a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions impossible under ordinary conditions are performed within a cell. History Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen Chemical reactions such as combustion in the fire, fermentation and the reduction of ores to metals were known since antiquity.
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