Transformation kinetics

The 29Si CP-MAS solid state NMR spectra of the crystal modifications of 60 and its hydrate were found to depend on the crystal structure, as shown in Table 6. In fact, the chemical shift difference between the pure (anhydrous) crystalline modifications was used to demonstrate the kinetic transformation in the solid state of one crystal structure to the other (Figure 7)47. 

Mansell et al. (1977b) presented simulated results for a range of rate coefficients (reflecting a range of soil characteristics), that is, phosphorus sorption capacities, for the kinetic transformations during steady water flow initially devoid of phosphorus. 

A mathematical model is formulated to describe the first-order kinetics of ionic copper released into a marine environment where sorption on suspended solids and complexation with dissolved organic matter occur. Reactions are followed in time until equilibrium, between the three copper states is achieved within about 3 hr (based on laboratory determinations of rate and equilibrium constants). The model is demonstrated by simulation of a hypothetical slug discharge of ionic copper, comparable to an actual accidental release off the California coast that caused an abalone kill. A two-dimensional finite element model, containing the copper submodel, was used to simulate the combined effects of advection, diffusion, and kinetic transformation for 6 hr following discharge of 45 kg of ionic copper. Results are shown graphically. 

During the first hour, when the entire slug of copper is introduced, dispersion, dilution, and first-order kinetic reactions result in a two-dimensional pattern of labile copper of the shape illustrated in Figure 5. The pattern shows a distribution of concentration about the peak value as a result of initial mixing and subsequent dispersion. The peak is translated downcoast by the advective process and the distribution is skewed somewhat in this same direction as a result of the kinetic transformation of labile copper to bound and sorbed states. A peak value of 18.4 /xg/L is indicated which may be compared to a maximum possible value of about 40 /xg/L if the entire slug were simply mixed with the entire volume of the dispersion zone (the diamond-shaped area around the outfall). 

More recently, Trost el al. also examined the ability to use aliphatic alcohols as competent nucleophiles in the palladium-catalyzed DYKAT of MBH adducts. High yield and enantioselectivity were obtained for both the kinetic transformation and dynamic kinetic transformation to alford substituted pyran products. The utility of this method was further demonstrated in the context of a concise total synthesis of the gastrulation inhibitor ( + )-hippospongic acid A (Scheme 3.138). ° ... 

With their efficient procedure for deracemization of MBH adducts, Trost and coworkers have applied dynamic asymmetric kinetic transformation (DYKAT) to the total synthesis of furaquinodn E. As shown in Scheme 5.28, the asymmetric palladium-catalyzed alkylation of phenols combined with a reductive Heck reaction delivered an effident approach to the synthesis of the key synthon, which is the core structure of the furaquinocins. A general synthetic route to furaquinocin E was established in 14 steps from MBH adduct 159. Their work highlighted the ability to use racemic MBH adducts for asymmetric synthesis. They further extended the scope of their strategy by developing the synthesis of three more analogs of... 

The first half of this textbook introduced the basic tools needed to understand most kinetic processes. Specifically, we learned how to calculate the main thermodynamic driving forces behind kinetic transformations (Chapter 2), we learned how to calculate the rates of reaction processes (Chapter 3), and we learned how to calculate the rates of transport processes (Chapter 4). In the second half of this textbook, we will use these tools to model and understand a number of real-world kinetic processes involving gas-solid, solid-liquid, and solid-solid transformations. In this chapter, we begin with gas-solid kinetic processes. 

The kinetic rate laws of low-temperature oxidation are logarithmic, either direct or inverse. At high temperatures, parabolic kinetics are usually observed. For intermediate temperatures, logarithmic kinetics transform with time into the parabolic type. 

Androulakis, I.P. New approaches for representing, analyzing and visualizing complex kinetic transformations. Comput. Chem. Eng. 31,41-50 (2006)... 

On the other hand all the rare earths have been reported formed in the C-form oxide although from Nd203 to La203 they are probably metastable (Felsche, 1969) or stabilized in that form by impurities. Brauer and Mohr-Rosenbaum (1972) discuss the existence of C-type for the light rare earth oxides. Brauer (1966) had reviewed the status of this work earlier. Structural and kinetic transformation studies have been carried out on the C-type to either the B or A-type. Activation energies were also obtained (Stecura, 1%5). 

Kinetic transformation of nanofilamentary Au metal-metal composites, K. Wongpreedee and A. M. Russell, Gold Bulletin, 2004, 37(3-4), 174. 

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