Synthesis heterogeneous medium

Fig. 13 (a) Acyloin cyclization, an example of macroeyelization in an heterogeneous medium (b) scheme for cyclization on a polymer support (c) and synthesis of a cyelopeptide on a polymer support. 

As the synthesis of the affinity support is carried out in a heterogeneous medium, the amount of immobilized ligand on the solid support may turn out to be rather low and difficult to appreciate. Moreover, due to steric hindrance and diffusion limitations, the accessibility of the target molecule to these binding sites may be somewhat limited. The binding capacity of the affinity matrix as well as the conditions for the release of the target molecule... 

Dridi et al. [498] described synthesis of a novel P(PV) derivative which is actually a copolymer, but is discussed here rather than in Chapter 10 because of its similarity in properties with and relevance to P(PV). Eg. 14.10 summarizes the synthesis and structure of this polymer. The synthesis was carried out in heterogeneous medium. 

Evidence exists that the relative solubility of amines and inhibitors in heterogeneous oil-water systems could be decisive in formation of nitrosamines and blocking these reactions, Nitrosopyrrolidine formation in bacon predominates in the adipose tissue despite the fact that its precursor, proline, predominates in the lean tissue (5,6,7). Mottram and Patterson (8) partly attribute this phenomenon to the fact that the adipose tissue furnishes a medium in which nitrosation is favored, Massey, et al, (9) found that the presence of decane in a model heterogeneous system caused a 20-fold increase in rate of nitrosamine formation from lipophilic dihexylamine, but had no effect on nitrosation of hydrophilic pyrrolidine. Ascorbic acid in the presence of decane enhanced the synthesis of nitrosamines from lipophilic amines, but had no effect on nitrosation of pyrrolidine. The oil-soluble inhibitor ascorbyl palmitate had little influence on the formation of nitrosamines in the presence or absence of decane. 

Texier-Boullet, F., Synthesis of a-hydroxyphosphonates in a heterogeneous solid-liquid medium and at the surface of inorganic solids. Study of factors of their formation in some two-phase systems, Bull. Soc. Sci. Bretagne, 56, 57, 1984. 

Supercritical carbon dioxide has been used as a dispersing medium for the manufacture and processing of polymeric materials. The process allows for the synthesis of high molar mass acrylic polymers in the form of micrometer-sized particles with a narrow size distribution. This procedure represents an environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations (Fox, 1994). 

The functional and morphological heterogeneity of a lamellar system of chloroplasts indicates that pH values in different compartments (in granal and intergranal thylakoids) differ. This type of structure makes it difficult to measure local pH values at different sites. Therefore, mathematical models taking into account the spatial structure of chloroplasts provide a tool for studying the effect of diffusion restrictions on pH distributions over the thy lakoid on the rates of electron transport, proton transport, and ATP synthesis. The rate of ATP synthesis depends on the osmotic properties of a chloroplast-incubation medium and, therefore, on topological factors. 

The Ziegler-Natta catalysts that are used most industrially are solids that are suspended in the reaction medium. The polymerization reaction that is favored depends on the catalyst components and on their state of aggregation and other details of their preparation. Heterogeneous catalytic systems appear to be necessary for the production of isotactic polyolefins, but soluble catalysts have been used for the synthesis of polyethylene and syndiotactic polypropylene. 

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