Combination step series reactions

The citrate cycle is the final common pathway for the oxidation of acetyl-CoA derived from the metabolism of pyruvate, fatty acids, ketone bodies, and amino acids (Krebs, 1943 Greville, 1968). This is sometimes known as the Krebs or tricarboxylic acid cycle. Acetyl-CoA combines with oxaloacetate to form citrate which then undergoes a series of reactions involving the loss of two molecules of CO2 and four dehydrogenation steps. These reactions complete the cycle by regenerating oxaloacetate which can react with another molecule of acetyl-CoA (Figure 4). 

In this case, three time constants in series, X, %2 and X3, determine the form of the final outlet response C3. As the number of tanks is increased, the response curve increasingly approximates the original, step-change, input signal, as shown in Fig. 2.12. The response curves for three stirred tanks in series, combined with chemical reaction are shown in the simulation example CSTR. 

The calculation of AG from the caloric data is straightforward, independent of the path, that is, whether the reaction takes place in a single step or through a series of steps by using Hess s law and Nernst heat theorem [15-17]. Furthermore, we can calculate AG for the reaction of interest from the combination of other reactions involved for which the thermodynamic data are known. However, both the initial and final states in many cases are hypothetical. Even in the case of measurements executed very carefully and accurately, there might be problems in defining the states of the compounds, or even metals ( ) that take part in the reaction. 

Using a series of PASSflow reactors, with typical dimensions of 5 mm (i.d.) x 10 cm (long), Kirschning et al. (Kirschning and Gas 2003 Kirschning et al., 2001, 2006) demonstrated the ability to combine a series of immobilized reagents in order to perform a sequence of reaction steps. In one example, the group demonstrated an oxidation, followed by a silyl deprotection and reductive amination steps to afford a derivatized steroid 147, as illustrated in Scheme 38, in excellent yield and purity. 

Reaction Scheme. A series of one-step reactions that lead from a given reactant to a given product, by way of intermediate steps. A reaction search system should be able to find reac-tant/product combinations that span several intermediate reaetions. 

A series of experiments were performed in a diflFerent reactor to develop a kinetic model for the sulfur generation step see Reaction 2. The progress of the reaction was followed by analyzing the carbon for acid and sulfur content. Each run was made at a different combination of inlet hydrogen sulfide concentration and temperature. The ranges of variables tested were 250-325°F, 0-40% H,S, 0-30% H2O, and 0-24 lbs H2SO4/IOO lbs carbon. A rate equation was developed from these data by multiple-regression techniques ... 

In this chapter, transfer coefficients have been developed (hat describe a number of mechanistic possibilities (Section V). The stoichiometric number of a reaction emerges as an important parameter that may be determined by a number of methods. The only reason an electrochemical reaction pathway would show v values > 1 would be to satisfy the material balance for either a reductive (or chemical) dissociation step occurring before a rds as per Scheme 2 or a reductive (or chanical) combination step occurring after a rds as per Scheme 3 (recall that in these schanes reaction steps are written as a series of consecutive reductions, among which may be a chemical step). By considering the types of reaction steps that can give rise to v > 1 within a generalized scheme, an important restriction has... 

The next step in the methanol-to-hydrocarbons reaction, and in fact the crucial one for the generation of hydrocarbon products is C-C bond formation. Very many proposed mechanisms exist for potential routes at the acid sites of the zeolites, but recent evidence suggests that the reaction instead proceeds via a reactive hydrocarbon pool (See Chapter 8). In fact, an extensive series of high-level theoretical calculations suggests that no single combination of direct reaction steps can link methanol to ethene, and so provides strong indirect evidence that the hydrocarbon pool mechanism is the correct one. 

If the heats of formation for all reactants and products involved in a particular chemical reaction are known, the heat of reaction can be found by using Hess law to combine the formation reactions. Hess s law can be stated as follows When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps. 

One can combine a series of elementary reactions steps into a PED for a complete catalytic process. Let us take the ammonia synthesis reaction as an example. The overall reaction can be written as... 

The process is represented as a series of steps consisting of the sublimation of the metal, dissociation of the halogen, removal of the electron from the metal and placing it on the halogen, then combining the gaseous ions to form a crystal lattice. These steps lead from reactants to product, and we know the energies associated with them, but the reaction very likely does not literally follow these steps. Reaction schemes in which metal complexes function as catalysts are formulated in terms of known types of reactions, and in some cases the intermediates have been studied independently of the catalytic process. Also, the solvent may play a role in the structure and reactions of intermediates. In this chapter we will describe some of the most important catalytic processes in which coordination chemistry plays such a vital role. 

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