Recrystallization realization

Plastic deformation, unlike elastic deformation, is not accurately predicted from atomic or molecular properties. Rather, plastic deformation is determined by the presence of crystal defects such as dislocations and grain boundaries. While it is not the purpose of this chapter to discuss this in detail, it is important to realize that dislocations and grain boundaries are influenced by things such as the rate of crystallization, particle size, the presence of impurities, and the type of recrystallization solvent used. Processes that influence these can be expected to influence the plastic deformation properties of materials, and hence the processing properties. 

Significant improvement in the catalytic activity of ALB was realized without any loss of enantioselectivity by using the second-generation ALB [27] generated by the self-assembled complex formation of ALB with alkali metal-malonate or alkoxide. This protocol allowed the catalyst loading to be reduced to 0.3 mol %, for example, the Michael addition of methyl malonate to cyclohexenone catalyzed by the self-assembled complex of (ff)-ALB (0.3 mol %) and KO Bu (0.27 mol %) in the presence of MS 4A gave the adduct in 94% yield and 99% ee [28]. This reaction has been successfully carried out on a 100-g scale wherein the product was purified by recrystallization. The kinetic studies of the reactions catalyzed by ALB and ALB/Na-malonate have revealed that the reactions are second-order to these catalysts (the rate constant ALB = 0.273 M 1h 1 ALB/Na-maionate = 1-66 M 1h 1) [27]. This reaction was used as the first key step for the catalytic asymmetric total synthesis of tubifolidine (Scheme 8D. 11) [28]. 

Realizing that protonation steps are important, reductions of 69 were performed in diglyme-0.5% H20. Like in DMF, in the absence of catalyst the potential was —3.10 V and the simple alcohol 71 was the only product (86%). The DMP+ mediated reduction, however, was different in this solvent. It took place at the same potential —2.70 V (SCE), but the reactant was consumed after only 1 F mol-1 and the correspoonding pinacol 72 was the only product (60% after repeated recrystallizations). 

First, see the section on Pipet Filtering—Solids in Chapter 7 where you remove solvent with a pipet. I also mention using a Hirsch funnel. Just reread the section on the Buchner funnel filtration (Chapter 13, Recrystallization ), and where you see Buchner substitute Hirsch and paste copies of the Hirsch funnel drawing over the Buchner funnel. Just realize that the tiny disk of paper can fly up more easily. Think small. 

The catalytic reduction of trifluoromethyl ketones was successfully realized by using catecholborane as reductant. In the case of the reduction of anthryl trifluoromethyl ketone, one recrystallization of the crude (i )-alcohol (94% ee) afforded the enantiopure carbinol [35]. Trichloromethyl ketones were also reduced... 

In order for the composites to become conductive, the TCNQ salt, initially dissolved in DMF solution before casting, should subsequently recrystall ze as pure microcrystals. To realize this condition with NMP TCNQ7, two approaches are possible one is to reduce the association through choosing weak donor polymers as matrices, and another is to dope the system with TCNQ so that TCNQ salt association with the polymer should be reduced through a competitive reaction with TCNQ, thereby facilitating salt crystallization. 

Fat crystallization tends to be very slow, unless the supersaturation is high the latter can generally be realized. Nucleation is for the most part heterogeneous, where existing fat crystals are very effective catalytic impurities for other crystals. In a multicomponent fat, considerable secondary nucleation occurs, which results in quite small crystals. Slow recrystallization can lead to the formation of large crystals, and possibly to oil separation from the mass of crystals. 

Early interest in the development of activated carbon was stimulated by a belief that a large potential market existed in the cane sugar industry. Some early studies seemed to indicate that powdered activated carbon could be applied directly to the raw cane juice and thereby eliminate the need for an intermediate stage in which raw sugar is first produced, which then must be redissolved and recrystallized. However, this hope was not realized factory operation disclosed that the intermediate stage of raw sugar was still necessary. 

Self-assembly is the most useful synthetic method. This is because (i) it permits the realization of a wide variety of structures from simple building blocks of metal ions and organic ligands, (ii) it allows an easy and rational modification of organic ligands, (hi) several types of interactions such as coordination bonds, hydrogen bonds, tt-tt interactions, CH-tt interactions, M—bonds, and van der Waals interactions can be incorporated and exploited, and (iv) there is the possibility of reaction control by temperature, pH, solvent, etc. For coordination polymers, recrystallization is unavailable due to their insolubility in most of solvents. Therefore, a new synthetic approach has been developed vide infra). 

Some examples of commercial active component production and production of substances with defined and uniform particle sizes (organic and inorganic materials) realized on pilot plant by using the RESS are given in Table 24.8. Other processes were also tested for synthesis of the particles with uniform size distribution as well as production of particles with specific structure (gas antisolvent recrystallization, GASR precipitation with a compressed antisolvent, PCA solution enhanced dispersion of solids, SEDS particles from gas-saturated solutions, PGSS) as shown in Table 24.9. All these processes are of special interest in pharmaceutical industry and in the production of different polymers. 

Another factor that has influenced realizable electro-optic coefficients is conductivity (which attenuates the poling field strength, Ep), Figure 14 illustrates this problem. As the glass transition temperature of the polymer lattice is approached, ionic contaminants become free to move the resulting conductivity attenuates the poling field and the optical nonlinearity decreases. A practical solution is frequently simply to purify chromophores by techniques such as repeated recrystallization. Moreover, the effect can be anticipated by performing conductivity measurements on spin-cast films. 

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