Chlorosilanes analysis

Reduction of 1-benzyl-3,4-dibromophospholan oxide (125) with tri-chlorosilane, followed by debromination, gave 1-benzylphosphole. Determination of the molecular structure by X-ray analysis showed slight puckering of the ring with retention of pyramidal configuration at phosphorus. ... 

The reactions were carried out in a 150 ml glass reactor equipped with a turbine stirrer and a reflux condenser. Product samples were withdrawn periodically and analysed by gas chromatography. The stationary phase used for analysis was 5% mixed cyano-propyl silicane Ibilar-b cp + Silar-7 cp) on chromosorb W (AW) treated with dimethyl chlorosilane (column length 1.1 meter). 

A different approach but still in the frame of the chlorosilane method was adopted by Tsiang for the synthesis of (A-b-B)B3 miktoarm star copolymers, where A is PS and B is PB [29]. Living PB chains were reacted with SiCl4 in a molar ratio 3 1, followed by the addition of the living diblock PS-b-PBLi. The key step of the method is the succesfull synthesis of the (PB)3SiCl intermediate product. The reduced steric hindrance of the PBLi chain end poses questions about the purity of this polymer, since several byproducts, such as (PB)2SiCl2, (PB)4Si, PBSiCl3 can be formed in the first step of the synthesis. SEC analysis was performed to monitor the reaction sequence. 

Summary The rich variety of the coordination chemistry of silicon is discussed and some theoretical issues are raised. In an attempt to understand further the underlying chemistry, some thermodynamic and kinetic parameters for the formation and substitution of pentacoordinate silicon compounds have been measured by NMR methods. Values of -31 3 kJ mol for SHand -100 10 J K mor for A5-were measured for the intramolecular coordination of a pyridine ligand to a chlorosilane moiety. A detailed kinetic analysis of a nucleophilic substitution at pentacoordinate silicon in a chelated complex revealed that substitution both with inversion and retention of configuration at silicon are taking place on the NMR time-scale. The substitution with inversion of configuration is zero order in nucleophile but a retentive route is zero order in nucleophile at low temperature but shows an increasing dependence on nucleophile at higher temperatures. These results are analysed and mechanistic hypotheses are proposed. Some tentative conclusions are drawn about the nature of reactivity in pentacoordinate silicon compounds. 

An analysis of the thermodynamics of a CVD system, discussed further in Chapter 2, can provide valuable assistance in the choice of reactant concentrations, pressures and temperatures to use for a given chemical system. Such an analysis can also provide information on the composition of the deposited material as well as the maximum efficiency for use of reactants. However, a thermodynamical analysis only gives information on the theoretically-possible result, which may not actually be achievable. CVD systems are generally not operated at chemical equihbrium, although some systems, such as the deposition of silicon from chlorosilanes, come close. 

Several polysilylene copolymers have also been examined by Si NMR. West and co-workers (3) report that phenylmethyldichlorosilane, when copolymerized with either dimethyldichlorosilane or methylhexyldichlorosil-ane, yields a copolymer with a blocklike structure. In contrast, we have observed that the copolymers of dimethyldichlorosilane with di-n-hexyldi-chlorosilane and n-propylmethyldichlorosilane with isopropylmethyldichlo-rosilane have random structures. These several examples indicate clearly that Si NMR spectra can provide a complete analysis of chain microstructure for the soluble polysilylene homopolymers and copolymers. 

Summary The synthesis of trichlorosilane (TCS) from silicon and HCl produces considerable amounts of less desired chlorosilanes by side reactions, especially silicon tetrachloride (STC). The results of this paper support the view that the undesired STC is formed from TCS in a consecutive reaction, which is probably catalyzed by Si impurities and which is preferred at low space velocity and high temperatures. It seems that TCS selectivity losses are due to regions or spots in the industrial reactor with such conditions. XPS surface concentrations of Si impurities dramatically change with the proceeding synthesis reaction because of the mobility of the impurity species and do not correlate with results of Si bulk analysis. 

On the whole, the investigations show that the actual surface concentrations of impurities are more strongly controlled by the synthesis reaction and its conditions than by the original Si bulk concentrations of the impurities. Hence, simple relationships between results of chemical bulk analysis of Si and results of the chlorosilane synthesis are not to be expected and indeed have not been found. 

Hypercoordinate silicon complexes with tetradentate (O, N, N, 0)-chelating ligands of the salen type are expected to exhibit unusual chemical and physical properties because of the higher coordination number of the silicon atom [1,2]. Therefore, several attempts were made to synthesize such compounds [2, 3]. Starting from easily available silicon compounds such as SiCU or other chlorosilanes, conversion with salen type ligands mostly yielded complexes with a hexacoordinate [2, 3] and, in some cases, pentacoordinate silicon atom [4]. Unfortunately, there are only a few examples where the coordination geometry has been confirmed by X-ray structure analysis [2, 4]. 

In the analysis of a number of materials (e.g., silicon- and germanium compounds and volatile reagents) traces of boron are pre-concentrated and boron is then separated by volatilization of the matrix. Mannitol, which forms a non-volatile complex with boric acid, is added to retain all the boron present in the residue [20]. Boron is fairly volatile in acidic media. While boron traces are determined in chlorosilanes, it is advisable to add some chlorotriphenylmethane [21], which forms a non-volatile compound with boron thus preventing its volatilization, when the matrix is evaporated. Ref. 21 is not cited. 

Figure 31-4. Effect of electro-osmosis on resolution and analysis time. Top, Untreated. Bottom, Prereated with 10% trimethyl-chlorosilane in dichloromethane for 20 minutes. (A) asparagine, (B) isoleucine, (C) threonine, (D) methionine, (E) serine, (F) alanine, (G) glycine.

Various workers173- 176 have made an extensive study of non-aqueous titrimetric methods of analysis of alkyl and aryl alkyl chlorosilanes, and other types of organosilicon compounds containing nitrogen, carboxyl and thiocyanato functional groups177-179. 

An apparatus has been developed392 for the analysis of a mixture containing tri-chlorosilane, methyldichlorosilane, silicon tetrachloride, trimethylchlorosilane, di-methyldichlorosilane and methyltrichlorosilane by gas-liquid chromatography on a column of nitrobenzene supported on Celite 545. The column is eluted with nitrogen and the emergent gas is absorbed in flowing 0.01 N potassium ohloride. Hydrolysis of the silanes yields hydrochloric acid which alters the electrical resistance of the potassium chloride solution and this permits quantitative analysis of the silane mixture. 

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