Number of Reaction Steps

If only multi-step reactions are to be retrieved, you can determine the number of reaction steps in the field Number of Steps (NS), generally ( =2) or with a certain number or an interval (Fig. 137)  

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The procedure employs the least expensive commercially available starting materials and requires the minimum number of reaction steps. 

The number of reaction steps, reaction stages and input materials are precisely determined. 

To further reduce the cost of production and the number of reaction steps, an entirely new reaction step was developed (scheme 3 in Figure ll).176... 

Rapid growth can be achieved by improved iterative methods, especially following a convergent-divergent pathway. In future this will be the method of choice as it facilitates the separation of unreacted material and minimizes the total number of reaction steps needed for the synthsesis of large molecules [50,61]. 

In the final section of this chapter, we would like to present some domino processes with a particular high number of reaction steps, and partly unusual transformations. 

Recently, an enantioselective total synthesis of ( )-18,19-dihydroantirhine has been reported by Kametani s group (140). They started from the chiral cyclopentanone derivative 211, obtained from the previously prepared (/ )-1,2-isopropylideneglyceraldehyde (141). Utilizing a number of reaction steps, 211 was transformed to 215 with the desired stereochemistry at the future C-15 and... 

Decreasing the number of reaction steps via a one-pot reaction associating two or more catalytic steps. This can be achieved by multistep reactions carried out by cascade catalysis without intermediate product recovery, thus decreasing the operating time and reducing considerably the amount of waste produced. 

As the number of reaction steps increases so, of course, does the complexity. A novel example is the six consecutive steps for hydrolysis of a cyanobridged polynuclear complex 9 ... 

The necessary condition for hydrogen storage is that the thermodynamic and kinetic conditions are fulfilled. In that case, a metal exposed to hydrogen gas absorbs hydrogen until equilibrium is established. There are a number of reaction steps that kinetically may hinder a hydrogen-storing system from reaching its... 

However, the complete reaction mechanism of the hydrogen oxidation reaction is much more complex, both in its number of reaction steps, number of intermediates (OOH and H2O2), and observed behavior. A mixture of H2 and O2 can sit in a diy bulb for many years with absolutely no H2O detected. However, if water is initially present, the reaction will begin, and if a spark is ignited or a grain of platinum is added to the mixture at room temperature, the reaction wiU occur instandy and explosively. 

The quantity Vmax also varies greatly from one enzyme to the next. If an enzyme reacts by the two-step Michaelis-Menten mechanism, Vmax = k2[Et], where k2 is rate-limiting. However, the number of reaction steps and the identity of the rate-limiting step(s) can vary from enzyme to enzyme. For example, consider the quite common situation where product release, EP — E + P, is rate-limiting. Early in the reaction (when [P] is low), the overall reaction can be described by the scheme... 

When we speak of the papers of the 1950s, we must not fail to mention articles published in 1954-1960 on muon catalysis (for a review with complete bibliography, see [43]). Various aspects of cold muon catalysis in nuclear reactions of hydrogen, deuterium, and tritium were considered. In recent years the ideas which lay at the foundation of these papers have been further developed and verified. In particular, it was Ya.B. [40] who noted the decisive role of muon adhesion to the helium nucleus which is formed in the reaction this process restricts the number of reaction steps, and the future for applying this process in energy engineering depends on it. 

These silyl imines are generated in situ from the corresponding aldehydes resulting in a reduction of the number of reaction steps and simplifies the work-up procedures (figure 8). Another option is to convert the aldehyde into a N-tosyl or a N,N-dimethylsulfamoyl irnine23. 

The formation of a dipeptide, for example, thus involves the condensation of the carboxyl group of one amino acid with the amino group of another. To achieve this apparently simple synthetic objective efficiently however, a number of reaction steps, requiring the use of appropriate functional group protection procedures (see p. 13), must be carried out. An illustrative synthesis is that of l-prolylglycine described in Expt 5.188, where the sequence is formulated in full. Note that proline is actually a secondary rather than a primary a-amino acid,... 

Limonene is used as a starting material for growth regulators of tobacco plants. Hydroaminomethylation is able to reduce the number of reactions steps for their production to one. The reaction takes place with yields up to 93% after 20 h with a rhodium dimer as a catalyst (Scheme 20). 

Apart from development of new catalysts with enhanced activity, few processes with innovative chemistry are currently developed for C-H transformation in aromatics. Though new processes using cheaper raw materials or reducing the number of reaction steps may seem attractive at first glance, efforts for process development including research, scale-up, pilot plant, and timeline must be considered. Especially for large scale-synthesis of bulk chemicals process economics... 

As already mentioned, also for the other oxygenated Cl compounds, i.e. formaldehyde [118, 138-147] and methanol [148-154], as well as for larger organic molecules, dynamic instabilities are reported. Many of them are compiled in Ref. [154], for formaldehyde oxidation on Rh and Pt [147] and methanol oxidation on Pt [155] the oscillations could be clearly identified as HN-NDR type oscillations. However, in view of the number of reaction steps involved in these oxidation reactions and of the possible complexity of the interaction of the supporting electrolyte with the dynamics even in the much simpler formic acid oxidation, it is not astonishing that any quantitative considerations should still be missing. There are some attempts to qualitatively explain the observed phenomena with reaction mechanisms that go beyond the simple dual-path model described above. However, at the time being, they are quite speculative. Therefore I shall not discuss them in more detail in this article. A summary of these works can be found in [156],... 

Two main problems were associated with the use of optically pure 3-p-tolyl-sulfinyl acrylates as dienophiles. The first was due to the high number of reaction steps and consequently low overall yields involved in their preparation, and the second to the fact that these dienophiles were insufficiently reactive with a... 

With the same idea in mind, i.e., limiting the number of reaction steps to reduce the costs of production, direct condensation of the ferrocenylmethyl (Fem) moiety on the endocyclic nitrogen of the CQ afforded the quaternary ammonium salt (Fig. 19). Nevertheless, such modification of CQ abolished the activity of the parent molecule on both Dd2 CQ-resistant and HB3 susceptible P. falciparum strains [115]. We can hypothesize that the charged species should not be able (1) to cross the membrane (2) to stack over the ferriprotoporphyrin ring due to unfavorable electrostatic interaction and/or steric hindrance. 

Methyl methacrylate (MMA) is one of the most important monomers [80-82]. It forms the basis of acrylic plastics and of polymer dispersion paints. The traditional production is by the formation of acetone cyanohydrin, elimination of water and hydrolysis of the nitrile group, followed by the ester formation. In the carbon-carbon bond forming reaction large amounts of excess HCN and ammonium bisulfate are left as waste. Although these problems have been addressed there is still much room for improvement. In particular the number of reaction steps should be reduced and, in order to achieve this, cyanide should be avoided. The building block to replace it is CO. 

If both forward and back reactions can take place, then 1/t depends on both k12 und k21. In the special case that the concentration of S is much greater than that of E, then the association rate constant is given by the equation l/r= k12cs + k21. Values of the two rate constants can be determined from the dependence of r on the substrate concentration cs a linear regression of 1/r vs. cs yields k12 as the slope of the plot and k21 as the Y intercept. For this analysis to be valid it is important to be sure that the observed reaction represents a single exponential process. If the reaction involves more than one exponential processes, then more complex models need to be considered, since the minimal number of reaction steps is given by the number of exponential processes. 

The fact that catalytic processes on grain surfaces cannot be neglected does not have its justification in that these processes are easier to understand in the case of complex molecules than for simple ones, but rather that ion-molecule reactions become harder to track, since the uncertainties compound for converting atoms into complex molecules the number of reaction steps have to increase, whereby reaction rates and branching ratios are less well known. For a large number of supposed reactions rates simply have not even been measured in the laboratory. However progress seems to come in mainly three areas, (i) Extensive studies have been made on reactions of the form... 

Consider two reactions of the type A B and B 5 C. If the third process A C is not feasible the number of elementary reactions is the same as the number of linearly independent reaction equations the reactions are said to be uncoupled. If A 4= C represents a feasible reaction the three processes are said to be coupled generally, coupling occurs whenever there is a redundancy in the number of reaction steps. 

Sinanoglu, O., Theory of chemical reaction networks. All possible mechanisms or synthetic pathways with given number of reaction steps or species. J. Am. Chem. Soc. 97, 2309-2320 (1975). 

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