Direct synthesis techniques

Fig. 3. Production diagram of methylchlorosilanes by direct synthesis technique 1 - container 2 - evaporator 3 - separator 4 - reactor 5 - filters 6-8 - condensers 9 - collector 10 - centrifugal pump 11 - Field tube.

Assessing on the whole the method of the production of alkyl- and aryl-chlorosilanes based on the interaction of alkyl- and arylchlorides with free silicon (i.e. direct synthesis), we should say that this method in comparison with metalorganic synthesis is more efficient, especially for the production of methyl- and phenylchlorosilanes. As for unsaturated chlorosi-lanes (vinyl- and allylchlorosilanes) and organochlorosilanes with higher radicals (hexyl-, heptyl-, octyl- and nonylchlorosilanes), no direct synthesis technique has yet been developed. 

Ion exchange methods and direct synthesis techniques can be used to incorporate Co ions into ZSM5 zeolites at well defined positions. The solid state ion exchange led to the formation of two new (Lewis acid) sites. One was affiliated with the presence of Co cations equimolar exchanged with the protons of SiOHAl groups. The other site, which revealed a very strong Lewis acid character, was associated with the presence of (CoCl) and (CoOH) species. 

The synthetic technology of isomerous xanthate is similar to that of normal xanthate. For example, the synthesis conditions of isobutyl xanthate with direct synthesis technique are as follows ... 

In this section, the Direct Synthesis (DS) method presented in Section 12.2 is extended to the design of digital controllers. We begin with special cases that lead to a PID controller, and then show how other types of digital feedback controllers can be derived using the Direct Synthesis technique. Both Gc and G must be expressed as discrete-time in the closed-loop transfer function (17-59). In Direct Synthesis, the designer specifies the desired closed-loop transfer function YlYg d- The controller that yields the desired performance is obtained from (17-59)... 

Aerosol-Based Direct Fluorination. A technology that works on Hter and half-Hter quantities has been introduced (40—42). This new aerosol technique, which functions on principles similar to LaMar direct fluorination (Fig. 5), uses fine aerosol particle surfaces rather than copper filings to maintain a high surface area for direct fluorination. The aerosol direct fluorination technique has been shown to be effective for the synthesis of bicycHc perfluorocarbon such as perfluoroadamantane, perfluoroketones, perfluoroethers, and highly branched perfluorocarbons. 

Nonpowder Synthesis. Many ceramic composites (qv) under iavestigation utilize reinforcing ceramic whiskers or fibers to achieve toughening (19). Whiskers (17,19,20) are produced by vapor-synthesis techniques. SiC whiskers can be produced by the rice hull or vapor—soHd (VS) method whereby rice hulls are pyrolyzed to produce a mixture of carbon, C, and Si02, and whiskers are produced by directional growth by vapor... 

The direct synthesis of poly(3-sulfopropyl methacrylate)-fr-PMMA, PSP-MA-fr-PMMA (Scheme 27) without the use of protecting chemistry, by sequential monomer addition and ATRP techniques was achieved [77]. A water/DMF 40/60 mixture was used to ensure the homogeneous polymerization of both monomers. CuCl/bipy was the catalytic system used, leading to quantitative conversion and narrow molecular weight distribution. In another approach the PSPMA macroinitiator was isolated by stopping the polymerization at a conversion of 83%. Then using a 40/60 water/DMF mixture MMA was polymerized to give the desired block copolymer. In this case no residual SPMA monomer was present before the polymerization of MMA. The micellar properties of these amphiphilic copolymers were examined. 

The resulting product has a low apparent density. Other synthesis techniques have been reported (192), mainly the reaction of a stoichiometric mixture of P3N5 and P4O10, heated at 780°C for 48 h, which directly results in a crystalline powder (193). Crystallization of X-ray amorphous PON produced using the other preparation methods is obtained after heating the powder in an evacuated quartz ampoule at 700-800°C for several days. 

Direct copolymerization techniques have also been employed in the s)m-thesis of sulfonated poly(aryl ether ketones),i i polyimides, i 5 and poly(benzoimidazoles). The synthesis of random disulfonated biphenol poly(arylene ether sulfone) copolymers (BPSH x where x represents the percentage of disulfonated diphenylsulfone moieties in the polymer versus unsulfonated diphenylsulfone moities) (14) is shown in Scheme 3.5. 

In the past few years there still have been some research efforts focused on Mg NiH. The Akiyama s group in Japan [20-22] has developed a hydriding combustion synthesis technique for the direct fabrication of Mg NiH. The results showed that the product of Mg NiH from the hydriding combustion synthesis absorbed the maximum (3.4-3.6 wt%) near the theoretical value just after synthesis without any activation process. 

We then studied group 5 metals, especially tantalum-for which the laboratory already had great experience. Because of the studied reaction, alkyl or hydride-type compounds such as those developed in the laboratory could not be employed. Consequently, we became interested in alkoxo-type derivatives, either synthesized by reaction of the grafted complex with an alcohol or obtained by direct synthesis starting from an alkoxy-tantalum compound grafted on silica. In all cases, resulting complexes have been characterized by surface organometallic chemistry techniques, especially EXAFS and solid-state NMR (ID and 2D with C-labeled compounds). Indeed various compounds bonded by one, two or three surface bonds have been prepared and characterized. 

Substitution of silicon by other atoms like Ti or Al was reported to improve the thermal and hydrothermal stability to some extent [6]. It was also reported that improved hydrothermal stability could be achieved by adjusting the gel pH several times during crystallization process [7], Post-synthesis silylation technique has also been reported to enhance the hydrothermal stability of mesoporous materials by increasing the hydrophobicity of the samples [8,9]. However, it is most desirable to develop a method for preparing hydrother-mally stable mesoporous material by direct synthesis route. 

Niobium and titanium incorporation in a molecular sieve can be achieved either by hydrothermal synthesis (direct synthesis) or by post-synthesis modification (secondary synthesis). The grafting method has shown promise for developing active oxidation catalyst in a simple and convenient way. Recently, the grafting of metallocene complexes onto mesoporous silica has been reported as alternate route to the synthesis of an active epoxidation catalyst [21]. Further the control of active sites, the specific removal of organic material (template or surfactant) occluded within mesoporous molecular sieves during synthesis can also be important and useful to develop an active epoxidation catalyst. Thermal method is quite often used to eliminate organic species from porous materials. However, several techniques such as supercritical fluid extraction (SFE) and plasma [22], ozone treatment [23], ion exchange [24-26] are also reported. 

The direct homologation technique was then extended to the synthesis of various uncommon carbohydrate structures. Thus, higher sugars of the L-series were obtained Starting from 2,3-0-isopropylidene-4-O-benzyl-L-threose (43) [39c] (Scheme 13), and the amino tetrose 47 and pentose 48 were prepared from the a-amino aldehyde 46 derived from L-serine [46a] (Scheme 14). These amino sugars were used as chiral building blocks for the... 

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