Dichlorosilanes

WurtZ-Type Coupling of Dihalosilanes. Several approaches have been developed for the synthesis of polysdanes. However, the most commonly utilized method is based on the Wurtz-type alkah metal coupling of dichlorosilanes. Both homo- and copolymers can be prepared this way (eq. 10). 

Polymer Modification. The introduction of functional groups on polysdanes using the alkah metal coupling of dichlorosilanes is extremely difficult to achieve. Some polymers and copolymers with 2-(3-cyclohexenyl)ethyl substituents on siUcon have been made, and these undergo hydrogen hahde addition to the carbon—carbon double bond (94,98). 

Silicon reacts at elevated temperatures with the halogens, forming SiCl, Sil, SiBr, and SiF. There is also a series of halogen-substituted silanes such as trichlorosilane, SiH Cl, and dichlorosilane, S1H2CI2. Both SiCl and SiH Cl are relatively easy to make, purify, and reduce to silicon. These are the silicon compounds most often used as feedstocks in the manufacture of high purity silicon. 

Dichlorosilane. Dichlorosilane [4109-96-0] is produced in relatively modest commercial quantities compared to the above chlorosilanes. This silane is generally recovered as a by-product of the production of other silanes. It is used exclusively in the semiconductor industry to produce a range of inorganic films. 

The thermal decomposition of silanes in the presence of hydrogen into siUcon for production of ultrapure, semiconductor-grade siUcon has become an important art, known as the Siemens process (13). A variety of process parameters, which usually include the introduction of hydrogen, have been studied. Silane can be used to deposit siUcon at temperatures below 1000°C (14). Dichlorosilane deposits siUcon at 1000—1150°C (15,16). Ttichlorosilane has been reported as a source for siUcon deposition at >1150° C (17). Tribromosilane is ordinarily a source for siUcon deposition at 600—800°C (18). Thin-film deposition of siUcon metal from silane and disilane takes place at temperatures as low as 640°C, but results in amorphous hydrogenated siUcon (19). 

Oxidation. AH inorganic siUcon hydrides are readily oxidized. Silane and disilane are pyrophoric in air and form siUcon dioxide and water as combustion products thus, the soot from these materials is white. The activation energies of the reaction of silane with molecular and atomic oxygen have been reported (20,21). The oxidation reaction of dichlorosilane under low pressure has been used for the vapor deposition of siUcon dioxide (22). 

The most common catalysts in order of decreasing reactivity are haUdes of aluminum, boron, zinc, and kon (76). Alkali metals and thek alcoholates, amines, nitriles, and tetraalkylureas have been used (77—80). The largest commercial processes use a resin—catalyst system (81). Trichlorosilane refluxes in a bed of anion-exchange resin containing tertiary amino or quaternary ammonium groups. Contact time can be used to control disproportionation to dichlorosilane, monochlorosilane, or silane. 

Other specialty silanes used in microelectronic apphcations include dichlorosilane and disilane. Trihromosilane [7789-57-3] iodosilanes, and trisilylamine [13862-16-3] are of interest for microelectronics in low temperature deposition technologies. 

Di-tcrt-butyl dichlorosilane (DTBCI2) [18395-90-9] M 213.2, m -15°, b 190°/729mm, 195-197°/atm, d 1.01. Purified by fractional distn. It is a colourless liquid with a pleasant odour and does not fume in moist air, but does not titrate quantitatively with excess of dil alkali. [7 Am Chem Soc 70 2877 1948.]... 

Methylphenyl dichlorosilane (dichloro methyl phenylsilane) [149-74-6] M 191.1, b 114-115 /50mm, 202-205 /atm, d 1.17. Purified by fractionation using an efficient column. It hydrolyses ca ten times more slowly than methyltrichlorosilane and ca sixty times more slowly than phenyltrichlorosilane [J Phys Chem 61 1591 1957]. 

Methyl vinyl dichlorosilane (dichloro methyl vinyl silane) [124-70-9] M 141.1, b 43-45.5 /ll-11.5mm, 91 /742mm, 92.5 /743.2mm, 92.5-93 /atm, d 1.0917, n 1.444. Likely impurities are dichloromethylsilane, butadienyl-dichloromethylsilane. Fractionate through a column packed... 

Fluidized bed reactors do not have to perform poorly, but special conditions must be maintained for good performance. A basic process for silicone manufacturing, which is not practiced much anymore, is the reaction of silicon metal with methyl chloride to form dimethyl dichlorosilane ... 

In practice vapours of the hydrocarbon halide, e.g. methyl chloride, are passed through a heated mixture of the silicon and copper in a reaction tube at a temperature favourable for obtaining the optimum yield of the dichlorosilane, usually 250-280°C. The catalyst not only improves the reactivity and yield but also makes the reaction more reproducible. Presintering of the copper and silicon or alternatively deposition of copper on to the silicon grains by reduction of copper (I) chloride is more effective than using a simple mixture of the two elements. The copper appears to function by forming unstable copper methyl, CUCH3, on reaction with the methyl chloride. The copper methyl then decomposes into free methyl radicals which react with the silicon. 

In the case of phenylchlorosilanes some modifications are made to the process. Chlorobenzene is passed through the reaction tube, which contains a mixture of powdered silicon and silver (10% Ag), the latter as catalyst. Reaction temperatures of 375-425°C are significantly higher than for the chloro-methylsilanes. An excess of chlorobenzene is used which sweeps out the high boiling chlorophenysilanes, of which the dichlorosilanes are predominant. The unused chlorobenzene is fractionated and recycled. 

The elastomers consist of very high moleculcU weight (-0.5 X 10 ) linecu gums cross-linked after fabrication. In order to achieve such polymers it is necessary that very pure difunctional monomers be employed since the presence of monofunctional material will limit the molecular weight while trifunctional material will lead to cross-linking. Where dimethylsilicone rubbers are being prepared, the cyclic tetramer, octamethylcyclotetrasiloxane, which may be obtained free from mono- and trifunctional impurities, is often used. This tetramer occurs to the extent of about 25% during the hydrolysis of dichlorosilanes into polymers. 

Dichlorosilane C E T Nickel and nickel steels and Stainless steel for moist gas... 

DIMETHYL CHLOROTHIOPHOSPHATE sea DIMETHYL THIOPHOSPHORYL-DIMETHYL DICHLOROSILANE DIMETHYL ETHER... 

Diphenyl dichlorosilane, 59 Diphenyl oxide, 59 Diphenylamine, 58 1,2-DiphenyUiydrazine, 59 DIPLAST , phthalates, 59 Dipropyl ketone, 59 Dipropylamine, 59 Dipropylene glycol methyl ether, 59 Diquat, 59... 

Carbonylate anions are the most suitable starting material for the synthesis of silylmetal compounds. A prerequisite for the preparation of compounds with a formal M = Si double bond is the use of metallate dianions like Na2Fe(CO)4 (Collman s reagent) together with the respective dichlorosilanes [96]. 

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