Chlorosilanes dimethyldichlorosilane

Head fraction I, which is a mixture of methyldichlorosilane, methyltri-chlorosilane, dimethyldichlorosilane and a small amount of benzene, is separated in the 36-78 °C range and collected in receptacle 16. Then this fraction can enter batch box 4. Fraction II (benzene) is distilled in the 78-82 °C range and collected in receptacle 11, and then poured into receptacle 18. It can be re-used in the synthesis (in this case benzene from collector 18 is sent into batch box 3). Tank residue, which after the distillation of the first two fractions is a concentrate with 50% of methylphenyldichlorosilane, is sent from tank 12 into collector 19 and from there into tank 20, heated with vapour (1.4 MPa). 

The starting materials for the manufacture of diorganopolysiloxanes are the diorganodi-chlorosilanes. Dimethyldichlorosilane, which is the most important one, is made industrially by the Rochow process from methyl chloride and silicon metal in the presence of a copper catalyst at 250-300 °C. 

The reaction of dimethyldiethoxysilane ((CHj SftOQHj) with the isolated silanols proceeds under milder conditions than the chlorosilane analogue dimethyldichlorosilane ((CH3)2SiCl2). 

Apart from antimony, there are other good promoters of the direct synthesis of methylchlorosilanes, which increase the yield of dimethyldichlorosilane, such as arsenic and zinc chloride. If it is necessary to increase the yield of alkylhydridechlorosilanes, one should use univalent copper chloride, cobalt, and titanium. The addition of tin or lead into contact mass increases the yield of dimethyldichlorosilane up to 70% the yield of ethyldi-chlorosilane is increased to 50-80% when contact mass receives 0.5-2% of calcium silicide (Ca2Si). In the synthesis of phenylchlorosilanes effective promoters are zinc, cadmium, mercury or their compounds. In particular, the introduction of zinc oxide (up to 4%) into contact mass may increase the diphenyldichlorosilane content up to 50%, and the introduction of a mixture of zinc oxide and cadmium chloride, even up to 80%. 

The first rectification stage. From collector 10 the mixture of methyl-chlorosilanes is periodically fed into pressure container 11, from where at 50-65 °C it is sent through heater 12 (by self-flow) onto the feeding plate of rectification tower 13. From the tower the tank liquid (methyltrichloro-silane, dimethyldichlorosilane and tank residue) flows into tank 14, where the temperature of 80-90 °C is maintained, and from there is continously poured into collector 22. After the tower, vapours of the head fraction at a temperature below 58 °C, consisting of the rest of methylchloride, di- and trichlorosilane, dimethylchlorosilane, methyldichlorosilane and the azeotropic mixture of silicon tetrachloride and trimethylchlorosilane are sent into refluxer 15, cooled with water, and into refluxer 16, cooled with salt solution (-15 °C). After that, through cooler 17 the condensate is gathered in receptacle 19. Volatile products, which did not condense in reflux-ers 15 and 16, are sent into condenser 18 cooled with Freon (-50 °C). There they condense and also flow into receptacle 19. As soon as it is accumulated, the condensate is sent from receptacle 19 into collector 20. 

The presence of the chlorine atom in the methyl group of dimethyldi-chlorosilane increases the speed of hydrogen replacement in it that is why the chlorination of dimethyldichlorosilane with the preference of obtaining methyl(chloromethyl)dichlorosilane should be conducted superficially (to the conversion degree of 8-14%). The yield of methyl(chloromethyl)dichlorosilane will be 70-80% for the reacted dimethyldichlorosilane, and the unreacted dimethyldichlorosilane is returned into the cycle. 

Polyvinylmethyldimethylsiloxane elastomers (SKTV) are prepared by the hydrolytic cocondensation of dimethyldichlorosilane and vinylmethyldi-chlorosilane with subsequent copolymerisation of the mixture of the hydrolysate and the depolymerisate obtained in the production of SKT elastomer. The process comprises two main stages the hydrolytic cocondensation of dimethyldichlorosilane and vinylmethyldichlorosilane the copolymerisation of vinylmethyldimethylcyclosiloxanes and dimethylcyclosiloxanes. 

This unusual feature of the photolysis in dimethyldichlorosilane indicates that a direct reaction of photochemically excited polysilanes with the chlorosilane to give monochloropolysilanes occurs in competition with the generation of dimethylsilylene (31). 

As in other preparative methods for organosilicon compounds, the direct synthesis produces a mixture of methylchlorosilanes rather than the single compound shown in equation 3. Besides dimethyl-dichlorosilane, the mixture usually contains silicon tetrachloride, tri-chlorosilane, methyltrichlorosilane, methyldichlorosilane, trimethyl-chlorosilane, and even silicon tetramethyl. Under proper conditions, dimethyldichlorosilane is the principal product. Of the other compounds, methyltrichlorosilane usually is next in abundance this substance finds use in the cross-linked methyl silicone resins, or it can be methylated further by the Grignard method to increase the yield of dimethyldichlorosilane. There is no way of recycling it in the direct process, and so supplemental operations are required for the conversion. The interconversion of this and the other minor products of the direct synthesis, involving the exchange of methyl and chlorine groups as desired, has been a special study in itself.10... 

HSiCls and t-PrMgCl results in the formation of /-Pr2SiHCl, but the reaction with t-PrLi gives rise to t-Prs SiH. Preparation of t-butyldimethylchlorosilane from dimethyldichlorosilane requires the use of t-BuLi but an interesting accelerating effect of CN has been observed for the reaction of chlorosilanes with bulky r-BuMgCl. The reaction may proceed through a pentacoordinate intermediate (equation 6). ... 

The ratio of cycHc to linear oligomers, as well as the chain length of the linear siloxanes, is controlled by the conditions of hydrolysis, such as the ratio of chlorosilane to water, temperature, contact time, and solvents (60,61). Commercially, hydrolysis of dimethjidichlorosilane is performed by either batch or a continuous process (62). In the typical industrial operation, the dimethyldichlorosilane is mixed with 22% azeotropic aqueous hydrochloric acid in a continuous reactor. The mixture of hydrolysate and 32% concentrated acid is separated in a decanter. After separation, the anhydrous hydrogen chloride is converted to methyl chloride, which is then reused in the direct process. The hydrolysate is washed for removal of residual acid, neutralized, dried, and filtered (63). The typical yield of cycHc oligomers is between 35 and 50%. The mixture of cycHc oHgomers consists mainly of tetramer and pentamer. Only a small amount of cycHc trimer is formed. 

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. 

Silica is reduced via a carbothermic process to silicon, which is converted to a variety of chlorosilanes. The major monomer, dimethyldichlorosilane, is produced in well over a billion pounds per year by several basic producers... 

Since an active OH group is left at each end of chain, polymerisation reaction continues and the length of the chain continue to increase. The starting materials for the manufacture of silicones are alkyl or aryl substituted chlorosilanes. Methyl compounds are mainly used, though some phenyl derivatives are used as well. Hydrolysis of dimethyldichlorosilane (CH3)2SiCl2 gives rise to straight chain polymers and, as an... 

Methylchlorosilanes are used in the manufacture of a variety of resins, elastomers, and silicone oils. They are produced as a mixture of chlorosilanes, mainly dimethyldichlorosilane, by the reaction between silicon and methyl chloride by a direct route discovered independently by Rochow (1945) and Muller (1950). In this route, metallic copper, with or without promoters, is used to accelerate the reactions. The form of copper is important and depends on its preparation and association with the silicon phase. The whole system of solids comprising silicon metal, copper... 

To change the polarity of the surface of the solid phase so nonpolar compounds can be separated. Dimethyldichlorosilane is added to the solid phase to form a reactive chlorosilane on former -OH groups. Then water is added followed by a long chain dichlorosilane, and finally endcapped. 

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 ... 

The general procedure for the synthesis of 9-15 is shown in Scheme 1. Bromobenzene 1 was prepared accotding to Bickelhaupt et al. [3], and the novel bromobenzene 2 was synthesized by the reaction of two equivalents of sodium methane thiolate with one equivalent of 2,6-bis(bromomethyl)bromobenzene. Compounds 1 and 2 were then converted with butyllithium to the corresponding litfaialed species which reacted with one equivalent of either methyidichlorosilane, phenyldichlorosilane or dimethyldichlorosilane to afford the chlorosilanes 3-8. The chlorosilanes were then treated with one equivalent of trimethylsilyl triflate to yield the silyl triflates 9-14. Silyl triflate 10 could also be prepared by the reaction of chlorosilane 4 with one equivalent of triflic add. The silyl tetralds(pentafluorphenyl)borate 15 was synthesized by the reaction of chlorosilane 4 with one equivalent of lithium tetrakis(pentafluorphenyl)borate. Compounds 9-15 are dissodated in dichloromethane solution. 

Silicones are made from silicon and methyl chloride in a process known as the direct reaction or direct process. This reaction yields methyl chlorosilanes. They are distilled for purification and the dimethyldichlorosilane is hydrolyzed to give PDMS. This product can be formulated into thousands of different products, which are sold to every major industrial segment. 

The resulting reaction products are a mixture of chlorosilanes with varying degrees of substitution, as shown in Figure 4. The physical properties of these and other reaction products formed during the production of the basic materials are listed in Table 9 (21,22). The production process is optimized to yield dimethyldichlorosilane, the most important product for the synthesis of silicone polymers. The trifunctional unit is next in commercial importance followed by the mono and quadrafunctional units, respectively (3). The chlo-... 

Silicones are polymers with backbones consisting of—[Si(R>2—O]— repeating units. They are prepared by reacting chlorosilanes with water to form silanols that condense to form siloxanes. Silicone oils made from dimethyldichlorosilane and methyltrichlorosilane are used as additives to reduce surface tension. Chemically modified silicone fluids, such as polysiloxane/polyether block copolymers, with broader ranges of compatibility have been described (175). 

The representative organosilicon compounds having an Si—N bond are silazanes. The silazanes are usually prepared by the reaction of chlorosilanes with ammonia. For example, trimethylchlorosilane reacts with ammonia to give hexamethyldisi-lazane. Dimethyldichlorosilane reacts with ammonia to give a mixture of cyclic hexamethylcyclotrisilazane and octamethylcyclotetrasilazane [31]. 

Under appropriate conditions various substituents on the silicon atom can be exchanged for one another. This provides a convenient method of converting by-product chlorosilanes into more useful materials. A typical example, which is of practical interest, is the redistribution of a mixture of trimethylchlorosilane and methyltrichlorosilane to form dimethyldichlorosilane ... 

Patnode [11] in 1946 exploited the preparation of dimethylsilicones from dimethyldichlorosilane with or without the cohydrolysis with trimethyl-chlorosilane to give complex polymers and elastomers. If insufficient water is used then o ,cu-dichlorosilanes are obtained [Eqs. (14) and (15)] [12]. 

As revealed by the chromatograms, the sensitivity of the instrument to the individual chlorosilanes varies within a wide range, and is low even in the case of the most readily detectable trimethylchlorosilane. Besides the comparison of the chromatograms in Figure 55 this becomes also evident from the occurrence of a hexa-methyldisiloxane peak of the same height as the peak for trimethylchlorosilane in mixtures of trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and carbon tetrachloride. This peak is to be attributed to contamination products formed by hydrolysis of the trimethylchlorosilane component of the mixture. Its presence in the pure monomer is not detectable by a detector working on the principle of thermal conductivity. The total insensitivity of the detector to silicon tetrachloride is especially evident from Figure 55. 

Burson and Kennerfound that the dimethyl-, diethyl- and dibutyl-phthalates were the most effective of the phthalate ester stationary phases in making complete separations of chlorosilanes and methylchlorosilanes. The maximum temperature for these three phases is less than lOO C and, consequently, considerable column bleed is evident when the program nears this temperature. Dinonyl-phthalate has a higher temperature limit, but is not so effective in resolving the methyltrichlorosilane and dimethyldichlorosilanes. Dipropyltetrachlorphthalate is even less effective. 

Burson and Kenner determined the purity of trichlorosilane and silicon tetrachloride with the SF-96 column. DC-LSX-3-0295 tri-fluoropropyl silicone gum was found to be the best for analysing samples of the methylchlorosilanes. Figure 57 shows a chromatogram of a sample of methyltrichlorosilane containing as impurities 0.02% silicon tetrachloride, 0.03% methyldichlorosilane, 0.04% trimethyl-chlorosilane, 0.12% dimethyldichlorosilane, and 0.07% 1,1,3,3,-tetra-chloro-1,3-dimethyldisiloxane. The concentrations of these impurities were determined by comparison of peak areas with standards prepared by adding known amounts of these impurities to methyltrichlorosilane of 99.99% purity. 

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