Dimethyldichlorosilane preparation

As already discussed in Section 2.2, crystalline dimethylsilanediol 53 can be prepared by hydrolysis from hexamethylcyclotrisilazane 51, from dimethoxydimethyl-silane [40], and from octamethylcyclotetrasilazane (OMCTS) 52. The most simple preparation of 53 is, however, controlled hydrolysis of dimethyldichlorosilane 48 in the presence of (NH4)2C03 or triethylamine [41]. Likewise, hydrolysis of hexam-ethylcyclotrisiloxane 54 and of octamethylcyclotetrasiloxane 55 eventually gives rise to dimethylsilanediol 53. In all these reactions the intermediacy of the very reactive dimethylsilanone 110 has been assumed, which can be generated by pyrolytic [42, 43] and chemical methods [44—46] and which cyclizes or polymerizes much more rapidly, e.g. in contact with traces of alkali from ordinary laboratory or even Pyrex glassware [40, 47] to 54, 55, and 56 than trimethylsilanol 4 polymerizes to hexamethyldisiloxane 7. Compound 111 is readily converted into dimethylsilanone 110 and MesSil 17 [46] (Scheme 3.6). 

A typical synthetic route to the incorporation of pendent carboranyl units into a polymer chain is shown in scheme 3. Poly(o-carboranyl-organo-siloxane)s have been successfully prepared through hydrolysis of dimethyldichlorosilane in the presence of carboranedichloromethylsilane. The polymer has some of the elastomeric characteristics of the parent poly(siloxane) however, the thermal-oxidative cleavage of the o-carboranyl pendent group is reported to occurat lower temperatures than that for the thermooxidative cleavage of Si—O and Si—C bonds.10 Thermal studies have... 

West and co-workers [9,10] prepared polysilastyrene, a soluble and fusible polymer, by a Wurtz-coupling of dimethyldichlorosilane and methylphenyldichlorosilane (Eq. 4). Thermolysis of this polymer at 450°C results in a polycarbosilastyrene which can be cured by irradiation with UV-light in air at room temperature [11],... 

The preparation proceeds in the following way A telechelic alcohol-functional PIB is first reacted with butyllithium in order to form an alcoholate-functional PIB dianion and the latter is then reacted with hexamethylcyclotrisiloxane to generate a living poly(dimeth-ylsiloxane) chain at the end groups of the PIB. In a final step, the remaining anionic ends are capped with trimethylchlorosilane or dimethyldichlorosilane. In this way a block copolymer, is obtained. The pressure sensitive adhesive exhibits (83) ... 

These three problems will be dealt with in this presentation the MCM-48 support is prepared by a controlled extraction of the cationic gemini surfactant, in such a way that no thermal post-treatment step is required. Secondly, we present an approach of selective, partial hydrofobization of the silica walls, using dimethyldichlorosilane (DMDCS), rendering it essentially hydrophobic to withstand the water attack, but creating simultaneously sufficient active sites for a subsequent grafting of the surface. Finally, VOx surface species are grafted on the silylated MCM-48 surface, in such a way that leaching is almost completely suppressed. 

The mixture of chromium trioxide with one equivalent of trimethylsilyl chloride, with no solvent added, results in the formation of an explosive red liquid that is soluble in dichloromethane or tetrachloromethane.428 It is suggested, with no spectroscopic evidence, that it consists of trimethylsilyl chlorochromate [Me3Si-0-Cr(0)2-Cl]. This compound, which can safely be used in organic solvents, is able to oxidize alcohols to aldehydes or ketones, and interacts with r-butyldimethylsilyl ethers producing deprotection, followed by oxidation of the liberated alcohol.138 Compounds analogue to trimethylsilyl chlorochromate are also able to oxidize alcohols, although they possess lesser reactivity. They can be prepared by reaction of chromium trioxide with dimethyldichlorosilane and diphenyldichlorosilane.428b... 

The six-membered cyclotri- and the eight-membered cyclotetrasilazanes were the first well-defined silicon-nitrogen rings. They were prepared by Brewer and Haber by ammonolysis of dimethyldichlorosilane in 194813 (Scheme 1). 

A variation of the preparative method for octamethyltrisilane (XIII n=3) involves the reaction of dimethyldichlorosilane with lithium in the presence of a large excess of trimethylchlorosilane in tetrahydrofuran (60). The yields of the trisilane are good ( 65%), and small amounts of the next two higher homologs also are obtained. An advantage claimed for this procedure is that it is a one-step synthesis employing commercially available materials. 

Three permethylated cyclosilanes of the formula [(CH3)2Si]B with n=5-7 are prepared by allowing dimethyldichlorosilane to react with sodium-potassium alloy in tetrahydrofuran. From this reaction, an insoluble polymeric mass and a crystalline solid are produced (21, 177). The latter consists, for the most part, of dodecamethylcyclohexasilane but it also contains decamethylcyclopentasilane and tetradecamethylcycloheptasilane in small quantities. The amounts of both five- and seven-membered cyclosilanes are much increased if the reaction is worked up immediately after the addition of the dichlorosilane is completed with little or no refluxing. The three cyclosilanes can be separated by preparative gas chromatography 21). 

The mechanistic pathway for the preparation of dodecamethylcyclo-hexasilane by lithium coupling of dimethyldichlorosilane in the presence of triphenylsilyllithium (Section III, A, l,a) is illustrated analogously in the following equations (76) ... 

Konig et al. [95AG(E)661] have prepared a related series of Si-bridged macrocycles, including the first silacalix[4]arene, from the deprotonation of furan, thiophene, N-methylpyrrole or tert-butylanisole, followed by addition of dimethyldichlorosilane. 

Silicon carbides are generally synthesized by the pyrolysis of precursors, prepared by liquid phase methods. One possible way for precursor synthesis is the addition of carbon black or sucrose, to a gelling silica.8 In this method, the carbon is introduced from an external source. A more intimate contact between the carbon and silicon in the precursor is assured with the use of organometallic polymer precursors. The use of silane polymers for silicon carbide production was initiated by Yajima.9,10 Polymers having a -[Si-C]- backbone are crosslinked and pyrolysed to yield SiC." In the initial work, dimethyldichlorosilane was used as a starting monomer, which was subjected to a sodium catalyzed polymerization (reaction (C)). 

From container 18 dimethyldichlorosilane is sent into batch box 1 placed over apparatus 2, where a 2% solution of the initiator in dimethyldichlorosilane is prepared. Apparatus 2 is an enameled flask with an agitator and a filling hatch. While the agitator operates, one sends there dimethyldichlorosilane and adds the initiator solution in the amount necessary to form a 2% solution. After 30 minutes of agitation at 20 °C the mixture of dimethyldichlorosilane and initiator is poured into intermediate container 17, from where it is periodically pumped into pressure batch box 4. After that, the mixture self-flows through rotameter 6 into chlorinator 5. The chlorinator is a steel cylindrical apparatus with a heating jacket and a thermometer pocket the lower part of the apparatus contains a distribution device which feeds chlorine. The temperature in the chlorinator is maintained within 65-70 °C and regulated with vapour sent into the jacket of the apparatus and with the speed at which chlorine is fed. 

Fraction I, which mainly consists of dimethyldichlorosilane, is distilled at atmospheric pressure when the temperature at the top of the tower is below 72 °C. The vapours from the higher part of tower 9 condense in water-cooled refluxer 10. The condensate is sent into the separation box, from where part of it is returned to reflux the tower, and the rest is collected in receptacle 11. From the receptacle dimethyldichlorosilane with a density not exceeding 1.08 g/cm3 can be used to prepare the initiator solution. 

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. 

The production process (Fig.77) comprises two main stages the coammonolysis of methyltrichlorosilane and dimethyldichlorosilane the preparation of varnish of a required concentration. 

Dimethyldiacetoxysilane reacts in a similar manner to dimethyldichlorosilane. Pyridine, trimethylamine, etc., can serve as solvents [112,113]. In a similar way acetonid s [114] are prepared from diols prior to GC. 

The actual polymerization process involves a ring-opening reaction of dimethyl-substituted cyclic siloxanes. The preparation of the cyclic materials starts with the production of pure silicon via the reduction of quartz with coke in an electric arc furnace. The silicon metal then reacts with methyl chloride to give a mixture of silicones, from which dimethyldichlorosilane is removed by distillation.65 Subsequent hydrolysis gives the cyclic dimethylsiloxane. 

Dimethyl silicone may be prepared by hydrolyzing dimethyldichlorosilane or its esters, and then oxidized with air and a catalyst16 to attain the desired CHs/Si ratio. 

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). ... 

Prepare 50 ml 5% dimethyldichlorosilane by thoroughly mixing 2.5 ml of this compound with 47.5 ml toluene in a 125 ml Erlenmeyer flask. 5-5. Pour this mixture into the column until the level of solution reaches the very top of the column. 

Following the pioneering works of Verbeek and Yajima, numerous investigators began to explore the scope of polymer systems that would provide useful ceramic compositions. West and co-workers (8) prepared polysila-styrene (PSS) polymers by the sodium coupling of phenylmethyldichloro-silane and dimethyldichlorosilane (equation 4). 

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