Chlorosilanes determination

Direct Process. Passing methyl chloride through a fluidized bed of copper and siUcon yields a mixture of chlorosilanes. The rate of methylchlorosilane (MCS) production and chemical selectivity, as determined by the ratio of dimethydichlorosilane to the other compounds formed, are significantly affected by trace elements in the catalyst bed very pure copper and siUcon gives poor yield and selectivity (22). 

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. ... 

These percentages were determined using 29Si and 13C NMR spectroscopies, the highest rates of Si-O bond formation being observed with X = OTf, whereas chlorosilanes rather led to pentacoordinated compounds. 

However, when the silica has been calcined at 800°C or above only chlorochromate is formed from chromyl chloride. This mimics the behavior of other reagents such as chlorosilanes, TiCl4, or BC13, which have been used to determine the extent of hydroxyl pairing on silicas (20-23). The chlorochromate species does not polymerize ethylene. 

Specihc functional groups are also analyzed by chemical methods. For example, the various chlorosilanes can be hydrolyzed and the resulting chloride ions determined by... 

Cementation consists in the formation of a surface alloy with a less reactive metal. For zinc, alloying can be effected with mercury (amalgamation), copper, silver, nickel.12 The reactivity of a cemented metal can be explained considering that the supporting metal plays only the role of an electron reservoir, the true chemistry is effected by the superficial additional metal. Zinc can also be activated by washing with aqueous ammonium chloride,13 or by reacting the powder with trimethyl-chlorosilane.14 In this latter case, Barbier reactions were effected even at 0°C in short times. The activation mechanism was not determined. 

Part of the difficulty in determining the nature of the attachment to the surface arises from the lack of direct spectral evidence. For high surface area metal oxides such as fumed silicas, infrared spectroscopy49,73,74,75 and NMR76,77 have been very successful in determining the nature of the attachment of chlorosilane molecules to the surface. 

Various "C-coordinated compounds" are obtained by the reaction of different chlorosilanes with 1 (Scheme 1) [4], Compoimd 7 is available as a colorless liquid 8 and 9 are colorless, crystalline solids, which are characterized by X-ray structure determinations (Fig. 3). 

Thus alumina membranes surface modified with silanes and sulfone [Shimizu et al. 1987] and with trimethyl chlorosilane TMS [Shimizu et al. 1989] and glass membranes adsorbed with surfactants [Busscher et al. 1987] have been studied this way. The results show that surface treatments alter the zeta potentials. Shimizu et al. [1989] have also demonstrated that under normal operating conditions the zeta potentials of alumina membranes do not change over time even for a period of two to three years. The isoelectric point for alumina particles thus determined is close to 4.00 as determined by direct measurement of membranes. 

Summary The reaction of two equivalents of lithium phosphinomethanides with di- or trifunctional chlorosilanes yields novel five- and six-membered heterocycles by multistep rearrangements or transmetallation reactions. Silaethene intermediates and hypervalent intermediates are likely to be involved. The reaction of one or two equivalents of lithium phosphinomethanide Li[C(PMe2)2(SiMe2Ph)] TMEDA with pTolSiCb and ci QHbcii iCb yields novel penta- and hexacoordinated silicon complexes. Both are the first examples of truly hypervalent organosilicon species with phosphorus donors characterized by X-ray structure determination. 

In certain cases, the trace element is kept in solution as a less volatile complex during the distillation of the sample matrix. In the determination of boron traces in chlorosilanes, silicon is removed as the volatile fluoride complex. To prevent the formation of volatile BF3, mannitol is added to form a non-volatile complex with boron [113]. 

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. 

The curcumin method (in either the rosocyanin or rubrocurcumin version) has been applied for determining traee amounts of boron in biologieal materials [10], soils and plants [17], waters [51], silicon [52], chlorosilanes [20], uranium [1,53], zirconium and its alloys [53,54], nickel [55,56], copper alloys [56], cast iron and steel [12,57-59], beryllium and magnesium [53], and phosphates [2]. This method was also used for determining boric acid admixtures (about 0.05%) in powdered boron [11]. Some synthetic compounds having the structure similar to that of curcumin, were used in determining boron in water [60]. 

Determining the Size Distribution of Products from a Fluidized-Bed Reactor for Chlorosilanes... 

Silicon reacts with copper chloride catalytically to form a solid product known as q-phase, which then catalyzes the reaction between silicon and methyl chloride to form methyl chlorosilanes. The formation of the q-phase is a unique example of an autocatalytic solid-solid reaction (we are not aware of any other example of such a reaction). Procedures for determining the kinetics of this reaction and the size distribution of the final products of the second reaction are described in this case study. The most important feature of the study is the unexpected discovery of autocatalysis in a solid-solid reaction, which leads us to the important lesson that one should vigorously pursue any such observation that falls outside the comfort zone of research, for that is where true discoveries lie. This advice is particularly relevant to engineers, since they generally do not accept the unexpected and would prefer to tread on safer ground. 

The structures of PhSiFs (by electron diffraction), bis(l,8-naphthylene)-dichloro-disilane and -disiloxane (by X-ray difffaction), and MesGeCl (from microwave rotational spectra) have been determined. PhSiFj and Me GeCl are tetrahedral molecules. The structures of the two chlorosilanes are shown in Figure... 

Chloride is determined by mercurimetric titration to the sodium nitroprusside end-point. Carbonates, acetates and borates do not interfere in the titration but large amounts of ammonium salts do interfere. The method has been applied to methyltrichlorosilane, dimethyldichlorosilane, diethyldichlorosilane, phenylmethyldichlorosilane and phenyltrichlorosilane. Methods have been described76,77 based on reaction with amines for the determination of chlorine directly linked to silicon in alkyl aryl chlorosilanes. One method76 is based on the formation of aniline hydrochloride according to the equation ... 

---