Halides silicon

The study of silicon halides began in the eady 1800s (1). Since then, essentially all of the monomeric silicon halides have been extensively studied and reported in the literature. These include mixed silicon halides and halohydrides. A large number of halogenated polysilanes have also been reported (1). Despite the extensive research in silicon halides, only two of these chemicals are produced on alaige industrial scale (excluding oiganohalosilanes). These are tetrachlorosilane [10026-04-7], SiCl and trichlorosilane [1025-78-2], HSiCl.  

The physical properties of silicon tetrahalides are listed in Table 1 those of the halohydrides are listed in Table 2. A more complex review of the physical properties of these chemicals is available (2). Detailed lists of properties of the colorless fuming liquids, silicon tetrachloride and trichlorosilane, are given in Table 3. A review of the physical and thermodynamic properties of silicon tetrachloride is given in Reference 3. 

Compound CAS Registry Number Mp, °C Bp, °C Density, e/cm Bond energy, kj /mof 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 17 

Sflicon halides are typically tetrahedral compounds. The silicone—halogen bond is very polar thus the silicon is susceptible to nudeophiUc attack, which in part accoimts for the broad range of reactivity with various chemicals. Furthermore, reactivity generally increases with the atomic weight of the halogen atom. 

Electron diffraction and spectroscopic studies show that in the gaseous state the halides 81X4 form tetrahedral molecules the simple molecular structure of SiF4 in the crystalline state has been confirmed by an X-ray study at -145°C.  

Many fluorides and chlorides of Si are known, but we confine our discussion to SiF4 and SiCli (Table 14.3) and some of their derivatives. Silicon and CI2 react to give SiCLi, and SiF4 can be obtained by fluorination of SiCli using SbF3, or by reaction 14.51 compare with equations 13.28 and 15.81. 

Both SiF4 and SiCli are molecular with tetrahedral structures. They react readily with water, but the former is only partially hydrolysed (compare equations 14.52 and 14.53). Controlled hydrolysis of SiCLi results in the formation of (Cl3Si)20, through the intermediate SiClsOH. 

Several of the mixed siUcon haUdes are formed simply by heating a mixture of the tetrahalosilanes at moderate temperature (4), eg.  

Mixed halosdanes can als o be prepared by heating a mixture of the appropriate haUdes of sdicon and aluminum (5,6). Some physical properties of these  

Both SiF4 and SiCl4 are molecular with tetrahedral structures. They react readily with water, but the former is only 

The reaction between equimolar amounts of neat SiCl4 and SiBr4 at 298 K leads to an equilibration mixture of SiCl4, SiBrCl3, SiBr2Cl2, SiBr3Cl and SiBr4 (see end-of-chapter problem 4.39) which can be separated by fractional 

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E. Hengge in V. Gutmaim, ed.. Inorganic Silicon Halides in Halogen Chemistry, Vol. 2, Academic Press, Inc., New York, 1967. 

Because carbon bonds so readily with itself, there are many hydrocarbons (see Chapter 18). Silicon forms a much smaller number of compounds with hydrogen, called the silanes. The simplest silane is silane itself, SiH4, the analog of methane. Silane is formed by the action of lithium aluminum hydride on silicon halides in ether ... 

Amorphous Si3N4 powder from silicon halides and ammonia at high temperature.P lP l The powder can also be produced by using the same reaction at 1000°C in an RF plasma with a mean particle size of 0.05-0.1... 

It has been noted (Section II,B,1) that reactions between transition metal carbonyl anions and silicon halides often fail to produce species containing silicon-transition metal bonds, and that such failure has been ascribed to nucleophilic attack by carbonyl oxygen. It is therefore interesting that compounds containing Si—O—C—transition metal linkages have recently been isolated from such reactions [Eqs. (105) (R = Me, Ph) 183) and (106)... 

Interesting cyclic ionic species are obtained from the reactions of di(phosphazenyl)silanes with silicon halides at room temperature ... 

However, the following monophosphazenes and silicon halides underwent straightforward exchange reactions... 

Another method of sand control is use of a silicon halide which reacts with water at the surface of sand grains forms SiO which can bond the grains together (55). Reducing the cost of sand consolidation could be very useful since the applicability of gravel packing methods is limited by the bottom hole circulating temperature and the limited temperature stability of polysaccharide polymers. 

Analogously to linear silicon halides, SigMenX does not react with Na[Co(CO>4]. However Na[Co(CO)3PPh3] and Na[Fe(CO)2cp] result in the respective transition metal-substituted silicon rings after reaction with SigMei X or 1,4-Si6Mei0X2. 

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

Collins, W. Silicon Compounds Silicon Halides. In Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed. Kroschwitz, J. I., Ed. Wiley New York, 1997 Vol. 22, pp 31-38. 

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