Kinetic separation

X and Y may be H2O or halide groups. A number of reactions of Pd(II) appear to fit this scheme.Ring opening and the subsequent slower displacement of single bonded amine are kinetically separable with M = Au(III), and each step proeeeds via a normal nucleophilic attack. 

Terabe, S., Otsuka, K., Ichikawa, K., Tsuchiya, A., Ando T. (1984). Electro-kinetic separation with micellar solution and open-tubular capillaries. Anal. Chem. 56 111-113. 

To obtain information on the coupling of the various intermediates one has to analyze the relationship between the corresponding titration curves. Scheme 3.4-3 shows typical steady-state curves for the (1) stepwise twofold association of ligand L with metal complex M, (2) association of L with two metal complexes M and N at equilibrium and (3) association of L to two metal complexes M and N being not at equilibrium (kinetically separated). From these three types of coupling most of the partial maps can be easily interpreted. 

Scheme 3.4-3. Typical selectivity curves of the titration of a catalytical process for the stepwise twofold assodation of ligand L to the intermediate M (Fig. 1), the association of L to two intermediates M and N at equilibrium (Fig. 2) and the assodation of L to two intermediates M and N being not at equilibrium (Fig. 3) (kinetic separation)...

Reetz and coworkers developed a highly efficient method for screening of enantioselectivity of asymmetrically catalyzed reactions of chiral or prochiral substrates using ESI-MS [60]. This method is based on the use of isotopically labeled substrates in the form of pseudo-enantiomers or pseudo-prochiral compounds. Pseudo-enantiomers are chiral compounds which are characterized by different absolute configurations and one of them is isotopically labeled. With these labeled compounds two different stereochemical processes are possible. The first is a kinetic separation of a racemic mixture, the second the asymmetric conversion of prochiral substrates with enantiotopic groups. The conversion can be monitored by measuring the relative amounts of substrates or products by electrospray mass spectrometry. Since only small amounts of sample are required for this method, reactions are easily carried out in microtiter plates. The combination of MS and the use of pseudo-enantiomers can be used for the investigation of different kinds of asymmetric conversion as shown in Fig. 3 [60]. 

The primary requirement for an economic adsorption separation process is an adsorbent with sufficient selectivity, capacity, and life. Adsorption selectivity may depend either on a difference in adsorption equilibrium or, less commonly, on a difference in kinetics. Kinetic selectivity is generally possible only with microporous adsorbents such as zeolites or carbon molecular sieves. One can consider processes such as the separation of linear from branched hydrocarbons on a 5A zeolite sieve to be an extreme example of a kinetic separation. The critical molecular diameter of a branched or cyclic hydrocarbon is too large to allow penetration of the 5A zeolite crystal, whereas the linear species are just small enough to enter. The ratio of intracrystalline diffusivities is therefore effectively infinite, and a very clean separation is possible. 

In molecular sieve adsorbents, such as zeolites and carbon molecular sieves, the micropore size distribution is extremely narrow, thus allowing the possibility of kinetic separations based on differences in molecular size. However, this feature is utilized in only a few commercial adsorption separation processes, and in the majority of such processes the separation depends on differences in the adsorption equilibrium rather than on the kinetics, even though a molecular sieve adsorbent may be used. 

The adsorptive separation is achieved by one of the three mechanisms steric, kinetic, or equilibrium effect. The steric effect derives from the molecular sieving property of zeolites. In this case only small and properly shaped molecules can diffuse into the adsorbent, whereas other molecules are totally excluded. Kinetic separation is achieved by virtue of the differences in diffusion rates of different molecules. A large majority of processes operate through the equilibrium adsorption of mixture and hence are called equilibrium separation processes. 

The gas phase kinetic separation factor fCgas is defined as ... 

Sulphur isotopes (32,33,34,36S) fractionate strongly in the earth s crust because (1) the element occurs in different oxidation states with differential preference for heavy isotopes, (2) the existence of volatile and easily soluble compounds favors kinetic separations, and (3) it is involved in biogenic cycles where the oxidation state is easily changed and kinetic processes are important. From theoretical calculations of Bigeleisen (1961) and data on the isotopic properties of sulphur compounds by Sakai (1957, 1968), the amount of S isotope fractionation and its temperature dependence is known. The information on experimental inorganic isotope fractionation in coexisting sulphide minerals which occur naturally was summarized by Thode (1970), who also discussed the application of S isotopes from sulphides for geo thermometry (cf. also Sakai, 1971). Analytical work on all types of sulphur compounds which occur in nature has been reviewed by Nielsen (1973). 

Plant Demonstration. This is the operation of the plant using actual chemicals. During this period all process conditions, rates, and step synchronization are confirmed. All critical process and mechanical conditions should be documented, e.g., yields, reaction kinetics, separation efficiencies, and motor amperages under various operating conditions. Documentation is important to determine baselines. If troubles occur later, the baseline data can be consulted for troubleshooting clues. 

Rege, S. U. Padin, J R. Yang, R. T. Olefin-Paraffin Separations by Adsorption Equilibrium Separation by n-Complexation vs. Kinetic Separation AIChE J., 1998,44, 799. 

Salil U. Rege Ralph T. Yang. Kinetic separation of oxygen and argon using molecular sieve carbon. Adsorption. 2000,6,15... 

Karz, E., and Willner, I. Kinetic separation of amperometric responses of composite redox-active monolayers assembled onto Au-electrodes Implication to the monolayer structure and composition. Langmuir 1997,13, 3364-3373. 

In 2002, Burton and co-workers demonstrated that the Z- and E-isomers of bromofluoro-methylene compound 63, easily obtained by the Wittig reaction of carbonyl compound with Ph3P-CFBr3-Zn, were obtained through efficient kinetic separation using the palladium-catalyzed carboalkoxylation reaction (see Scheme 10.22) [31]. Since the E-isomer... 

Xu, J. and Burton, D. J. (2002) Kinetic separation methodology for the stereoselective synthesis of (E)- and (Z)-a-fluoro-a,P-unsaturated esters via the palladium-catalyzed carboalkoxylation of 1-bromo-l-fluoroalkenes. Org. Lett., 4, 831-833. 

The analysis of a multicomponent mixture by kinetic methods is sometimes referred to as a kinetic separation. Explain the significance of this term. 

Goals Kinetic separation of isomers by crystal growth of the desired isomer on a seed bed of that isomer (desired all-growth process)... 

Kinetic separation of enantiomers in heavily seeded, all-growth, limited residence time crystallizers. 

Kapoor, A. and Yang, R.T. (1989). Kinetic separation of methanecarbon dioxide mixture by adsorption on molecular sieve carbon. Chem. Eng. Sci., 44, 1723—33. 

Figure 8.10 Electro-kinetic separation of three species a, and c. Left, The electro-osmotic flow carrying all of the charged or neutral species along with it, is directed towards the cathode. The negative species though attracted hy the positive pole cannot overcome the electro-osmotic flow and are therefore displaced towards the cathode. Right, separation of caffeine c and of the anions of aspartame a and of henzoate h from a sample of DIET COLA. Presentation in the form of a 3D electropherogram (reproduced courtesy of TSP).

Formation of an alkoxide ion as an intermediate has often been questioned, because the pKa of the alcohol would have to be reduced by about 10 units upon coordination. The possibility that hydride transfer from alcohol to NAD and hydroxyl proton release could occur simultaneously is attractive, but careful experiments have shown that the two steps must be kinetically separate.We summarize here the key information that leads to a full, although circumstantial, rationalization of the chemical behavior of the enzyme. 

Isolate genes for thermophilic enzymes by polymerase chain reaction (PCR) and subclone into expression vectors for production in mesophilic host Employ and analyze immobilization methods for optimal performance Determine enzyme kinetics separately and in combination to optimize hydrogen production... 

A in their smallest dimension, in that range, could be completely separated by selective adsorption. This high resolution is not achieved by homogeneous enlargement of the pore dimensions since the activating process involves chemical adsorption of oxygen molecules and desorption of a 3k entity like CO or CO2 molecules. In essence it is a kinetic separation (1) with a... 

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