Reaction product hierarchy

Various centers of metabolic activity exhibit a high demand for photosynthates such that there is competition within the plant for available resources. Thus, during the development of the plant, at any moment in time, there exists a dominance hierarchy for photosynthates. In the Jerusalem artichoke, photosynthetically fixed carbon resources are allocated among maintenance reactions, production of additional structural components, and deposition within specialized storage sites within the plant. The allocation hierarchy shifts not only as the plant develops, but also in diurnal cycles. Therefore, photosynthate allocation depends upon both timing and assimilate availability. 

This set of rules is called the simple product hierarchy for CHNO explosives (and propellants). If the explosive had contained any metal additives, these would probably not oxidize until all the above oxidation steps were completed. By traces of NO, we mean less than 1%. An example of this is TNT, detonated in the open air, where measurements have shown from 0.2 to 0.5% total NO in the original undiluted products. Of this NO, approximately half was NO. Some examples of oxidizing reactions are shown in Figures 2.3, 2.4, and 2.5. 

The kinetics of the diffusion-controlled reaction A + B —> 0 under study is defined by the initial conditions imposed on the kinetic equations. Let us discuss this point using the production of geminate particles (defects) as an example. Neglecting for the sake of simplicity diffusion and recombination (note that even the kinetics of immobile particle accumulation under steady-state source is not a simple problem - see Chapter 7), let us consider several equations from the infinite hierarchy of equations (2.3.43) ... 

Data storage in REACCS is hierarchical related data are stored separately but also are grouped under a single descriptive category. For example, in the Theilheimer database, the treename is the complete hierarchical name of a piece of data and is composed of three components entity, parent datatypes or category of data, and field datatype. All REACCS databases include VARIATION. VARIATION is usually the highest parent datatype in the reaction hierarchy. VARIATION can be used to store more than one complete set of reaction data with a reaction. To keep track of the data associated with different variations or multiple reactants and products in the same reaction, line numbers are appended to some of the datatypes in a treename. 

In science, there is a hierarchy of questions (i) what , (ii) how , and (iii) why . The report of a given fact, e.g., the determination of a series of products and their yields, only answers the question what . Additional kinetic studies raise our level of understanding, as it answers the question how . The ultimate scientific question, why , has as yet rarely been answered, but this level of knowledge is a prerequisite for being able to predict a certain reaction without too many flanking experiments. Thus, it will be one of the main goals of future research to strive for an in-depth theoretical understanding. This, of course, has to be based on our present (and future) experimental data, and it is one of the intentions of this book to provide the necessary information in a compact form. 

In a recent survey [19] it was noted that a realistic model for catalytic oxidation reactions must include equations describing the evolution of at least two concentrations of surface substances and account for the slow variation in the properties of the catalyst surface (e.g. oxidation-reduction). For the synchronization of the dynamic behaviour for various surface domains, it is necessary to take into consideration changes in the concentrations of gas-phase substances and the temperature of the catalyst surface. It is evident that, in the hierarchy of modelling levels, such models must be constructed and tested immediately after kinetic models. On the one hand, the appearance of such models is associated with the experimental data on self-oscillations in reactors with noticeable concentration variations of the initial substances and products (e.g. ref. 74) on the other hand, there was a gap between the comprehensively examined non-isothermal models with simple kinetics and those for the complex heterogeneous catalytic reactions... 

The most detailed modelling approach summarized in Figure 1 is found at the mechanistic level. These models are explicit accounts of the chemistry of elementary steps. Thus the hierarchy of the levels, i.e., reaction models in Figure 1, now becomes quite clear. Mechanistic models, which provide the temporal and many times spatial variation of the composition of each component and reaction intermediate, are based at the lowest modelling level. Their output, however, is typically phrased in terms of ensembles of stable molecular constituents which is more characteristic of the intermediate level molecular models. The molecular models, in turn, require subsequent organization in order to connect to the global reaction models and relevant product fractions at the top or global level. 

When an explosive slowly decomposes, the products may not follow the previously described hierarchy or be at the maximum oxidation states. The nitro, nitrate, nitramines, acids, etc., in an explosive molecule can break down slowly. This is due to low-temperature kinetics as well as the influence of light, infrared, and ultraviolet radiation, and any other mechanism that feeds energy into the molecule. Upon decomposition, products such as NO, NO2, H2O, N2, acids, aldehydes, ketones, etc., are formed. Large radicals of the parent explosive molecule are left, and these react with their neighbors. As long as the explosive is at a temperature above absolute zero, decomposition occurs. At lower temperatures the rate of decomposition is infinitesimally small. As the temperature increases, the decomposition rate increases. Although we do not always, and in fact seldom do, know the exact chemical mechanism, we do know that most explosives, in the use range of temperatures, decompose with a zero-order reaction rate. This means that the rate of decomposition is usually independent of... 

This method assumes a different hierarchy of formation of product species from the detonation reaction of a CHNO explosive than the hierarchy used earlier, where CO is assumed to be formed preferentially prior to the formation of CO2. Here, with the Kamlet-Jacobs method, CO2 is assumed to be formed as the only oxidation product of carbon. As with the previous hierarchy assumptions, water is still formed first. The generalized reaction for an underoxidized explosive can be written as ... 

If methanol and acetic acid are available as raw materials and methyl acetate is the desired product, according to the property-difference hierarchy, an identity difference is first detected between the desired product and each of the raw materials. A known chemical reaction operator, namely the esterification reaction, can be applied to a mixture of the raw materials brought to the proper conditions to produce methyl acetate and eliminate the identity difference between the reaction effluent and the desired product. Thinking directly in terms of equipment, this operator may be immediately implemented, for example, as a stirred tank reactor. 

If the hierarchical means-ends analysis synthesis procedure is applied to the methyl acetate problem, the task identification, task integration, and equipment design stages are kept completely separate. Following the property-difference hierarchy, an identity-changing reaction task (Task A) is identified first, as before. When examining the differences between the result of this reaction task application and the product methyl acetate and by-product water destinations,... 

There have been correspondingly few papers describing this reaction on single crystal surfaces of metals. ° Four concern the reaction on various surfaces of platinum, but their value is unfortunately somewhat limited two of them used both Pt(lOO) and Pt(lll), but TOFs were given at quite different temperatures with another pair it is only possible to compare results on Pt(l 10). While activation energies (43 10 kJ mol ) and order of reaction where determined were broadly comparable (Table 8.4), values of TOF sometimes showed a marked variation between different surfaces, and it is not possible to define a unique hierarchy of activity. Most disappointingly there is little information on product selectivi-ties apart from Siot (Table 8.4) in one publication only partial information was... 

We can list the common carboxylic acid derivatives in a hierarchy of reactivity, with the most reactive at the top and the least reactive at the bottom. The nucleophile is the same in each case (water), as is the product, the carboxylic acid, but the electrophiles vary from very reactive to unreactive. The conditions needed for successful reaction show just how large is the variation on reactivity. Acid chlorides react violently with water. Amides need refluxing with 10% NaOH or concentrated HCl in a sealed tube at 100 °C overnight. We ve seen that this hierarchy is partly due to how good the leaving group is (the ones at the top are best). But it also depends on the reactivity of the acid derivatives. Why is there such a large difference ... 

---