Regeneration basic principles

The basic principle of regeneration was introduced in Figure 26.2. Regeneration is a treatment process but applied with the objective of reusing or recycling the water, rather than discharge to the environment. Regeneration of wastewater is most likely to be economic if... 

It was clear at the outset that the basic principle of this catalytic scenario may apply to other transformations as well. An obvious extension concerns the pinacol coupling since any McMurry reaction probably passes through the 1,2-diolate stage (c/. Scheme 1) [4]. In fact, several titanium-catalyzed procedures have been reported which rely on chlorosilane additives for the liberation of the product and the simultaneous regeneration of the TiClj salt. They involve either [CpjTiClj] cat., Zn, chlorosilane [8], or... 

For this purpose an electron transfer across the bilayer boundary must be accomplished (14). The schematic of our system is presented in Figure 3. In this system an amphiphilic Ru-complex is incorporated Into the membrane wall. An electron donor, EDTA, is entrapped in the inner compartment of the vesicle, and heptylviolo-gen (Hv2+) as electron acceptor is Introduced into the outer phase. Upon illumination an electron transfer process across the vesicle walls is initiated and the reduced acceptor (HVf) is produced. The different steps involved in this overall reaction are presented in Figure 3. The excited sensitizer transfers an electron to HV2+ in the primary event. The oxidized sensitizer thus produced oxidizes a Ru located at the inner surface of the vesicle and thereby the separation of the intermediate photoproducts is assisted (14). The further oxidation of EDTA regenerates the sensitizer and consequently the separation of the reduced species, HVi, from the oxidized product is achieved. In this system the basic principle of a vectorial electron transfer across a membrane is demonstrated. However, the quantum yield for the reaction is rather low (0 4 X 10 ). 

A tandem RCM-cleavable linker for application to the solid-phase synthesis of oligosaccharides has recently been reported [136]. The system makes use of a tri-ene linker system, resulting in the fact that the RCM regenerates the active Ru catalyst without the need for an alkene co-factor. The application of this hnker was demonstrated in the hberation of a cyclopent-2-enyl mannoside from the solid support. Subsequent isomerization to the vinyl ether glycoside led to the depro-tected mannose after iodine treatment. The basic principle of the approach is out-hned in Scheme 52. 

Regeneration step Basic principle Typical application... 

This bead-based procedure is a derivative of the solid-phase chemistry that has proven its merits in automated peptide synthesis [74], combinatorial chemistry [75] and also small-molecule synthesis [76]. The basic principle behind solid-phase synthesis is the attachment of a substrate to a polymer bead by a covalent linker and subsequently performing a chemical reaction on the substrate. Because the substrate is tightly bound to the polymer, excess reagents and by-products can simply be washed away, after which further chemical elaboration of the product may be performed. Finally, the dean product is deaved from the polymeric support, which usually can be regenerated for re-use. 

Research began as an investigation of electrically induced ionic adsorption on porous "inert" electrodes. Electrode pairs based on carbon have been developed which will demineralize saline water at low voltage, and can be regenerated upon reversal of polarity. Various carbon electrodes have been conveniently classified into cation- and anion-responsive types. As received carbons are normally cation-responsive, but anion-responsive types have been made by chemical treatment. Laboratory demineralization cells based on this principle have been constructed and operated. Owing primarily to the low cost of basic construction materials, the process shows great promise for the economical conversion of saline waters. 

Figure 8.3 illustrates the basic process principles for the reaction type A B + C. Sections I and IV have the same purpose as in the TMB process - they regenerate the... 

This linker system is based on the principle that triazenes can be efficiently generated by reactions of diazonium salts with amines. Under basic conditions, these triazenes are stable, but they can be cleaved under mildly acidic conditions to regenerate a diazonium salt and an amine. Based on this system, originally pubhshed by Moore and Tour [151, 152], two different hnkers have been developed. In the so-called T1 variant (Scheme 63), a secondary amine is created on the sohd support and reacted with a diazonium salt to yield the triazene 136. After the synthetic manipulations leading to 137, the triazene is cleaved, resulting in the formation of the initial support and the desired product [153]. Besides the traceless cleavage from the support, the diazonium salt formed as intermediate during the... 

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