Halogenation Halosilanes

Dkect synthesis is the preparative method that ultimately accounts for most of the commercial siUcon hydride production. This is the synthesis of halosilanes by the dkect reaction of a halogen or haUde with siUcon metal, siUcon dioxide, siUcon carbide, or metal sihcide without an intervening chemical step or reagent. Trichlorosilane is produced by the reaction of hydrogen chloride and siUcon, ferrosiUcon, or calcium sihcide with or without a copper catalyst (82,83). Standard purity is produced in a static bed at 400—900°C. 

An alternative method for preparing phosphinous amides makes a profit on the high affinity between silicon and halogen atoms. This is the driving force of the reactions between halophosphanes and Ar-(trimethylsilyl)anilines, AT-(tri-methylsilyl)amides or AT-(trimethylsilyl)ureas and thioureas, as represented in the Scheme 6. In these processes the desired P-N bond and an halosilane are simultaneously formed [53,58-60]. 

An important reaction of silicon compounds containing electronegative substituents, such as the halogens or a Group 15 or 16 element, is hydrolysis, which often occurs very readily even with atmospheric moisture. The primary reaction in silicone production is the hydrolysis of halosilanes, usually the readily available chlorosilanes, to give silanols, which then undergo acid-catalyzed condensation with loss of water, as shown in Scheme 1. 

The rate of step 4 involving elimination of halosilane also depends on the nature of the halogen atom but in the inverse order F < < Br. For Hal=Br, intermediates (32) are impossible to detect. By contrast, for Hal=F, elimination of Si F is the rate-determining step, which requires a special procedure, for example, refluxing of intermediate (32) (Hal=F) in acetonitrile for 1 h. (Preliminary data show that the microwave technology makes it possible to sharply decrease the time required for completion of step 4 (90)). A decrease in the elimination rate in the series F < < Br is evidence that this reaction is not... 

HALOBORANES, A-HALOGEN COMPOUNDS HALOPHOSPHINES, HALOSILANES PERFLUOROSILANES... 

Xenon difluoride, 4326 Xenon difluoride oxide, 4313 Xenon hexafluoride, 4371 Xenon tetrafluoride, 4347 HALOBORANES N-HALOGEN COMPOUNDS HALOPHOSPHINES HALOSILANES PERFLUOROSILANES... 

Information has been obtained on the formation of these compounds. Condensation of iV-tri methylsily 1-8-lactam with an halomethyldimethylhalosilane at low temperatures led to the transsilylation reaction at nitrogen. The /V-halomethyldi-methylsilylated lactam then isomerizes at — 40 °C into the /V-silylmethylated derivative susceptible to halogen exchange with the starting halosilane, and finally, internally coordinated.43... 

Halosilanes are also potent halogen donors, particularly in exchange reactions with alkyl fluorides, due to the strong Si-F bond formation. Tertiary- and secondary-alkyl fluorides are reacted with iodotrimethylsilane to yield alkyl iodides in high yields (equation 19)214 ... 

Halosilane. A halogen derivative of a silane a compound of silicon containing at least one Si—X bond, where X represents a halogen. 

Summary A series of halosilanes R2SiH(Hal) (R = 2-(Me2NCH2)CgH4) has been synthesized. The influence of the leaving group ability of the halogen substituent, the polarity of the solvent, temperature, and concentration on the formation of intramolecularly coordinated silyl cations has been investigated. 

Similarly to allylic silanes, alkenylsilanes react with a variety of electrophiles. The anti addition of halogens to alkenylsilanes followed by the anti elimination of halosilanes yields alkenyl halides with inversion of configuration (eq (15)) [12]. 

The silicon-halogen bonds, on the other hand, occupy a position of great importance in organosilicon chemistry as most all organosilicon compounds must be synthesized ultimately through halosilane intermediates. The three general methods available for the preparation of halosilanes from silicon are listed in Scheme IV. 

The sagging pattern which is so characteristic of sequential halogen substitution in alkyl and aryl silanes is not observed in the simple mixed silicon halides (Y4 SiX ). The sagging pattern apparently arises as a result of a substantial electronegativity difference between X and Y which is not present in the mixed halides. The chemical shift trends for the mixed halosilanes are shown in Figure ll69,70. 

In contrast to the BSD anion-forming reductions of BSD with the more electropositive metals, the oxidation of BSD with the most electronegative nonmetals does not lead to the BSD cation. The products of reaction of BSD with halogens (even at very low temperatures) are nitrogen and trimethyl-halosilane (50) [Eq. (56)]. 

The two most general means of synthesis of organosilanes are nucleophilic displacement of halogen from a halosilane by an organometallic reagent and addition of silanes at double or triple bonds (hydrosilation). Organomagnesium and organolithium compounds... 

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