Chlorosilanes, reaction

Trimethylsilyl hydroperoxide preparation bis(trimethylsilyl) peroxide hydrolysis, 801 tetraethylsilane ozonolysis, 810 trimethyl chlorosilane reaction, 776, 777... 

Calculations have been carried out on the. S n2 reactions between chloride ion and methyl chloride or chlorosilane at several DFT levels of theory up to the OLYP/TZ2P level.102 The OLYP/TZ2P method gave much better (excellent compared with the CCDD(T)/aug-cc-pVQZ level) values than the other density functionals for both the geometry and the energies of the reactant complex and transition state for the methyl chloride reaction and the stable transition complex that forms in the chlorosilane reaction. 

The interaction of the silica surface with trimethyliodosilane and trimethylbromosilane has been described by Tertykh and Belyakova.88 Both reactions proceed much faster than the previously described chlorosilane reaction. The reaction of silica with trimethylbromosilane is completed after 30 minutes at 323 K and the reaction with trimethyliodosilane even after 10 minutes at room temperature. 

Since in exploratory runs with the model carbamate N-Boc-cyclohexylamine slightly better yields of urea were produced with Hunig s base compared to tri-ethylamine, which is the commonly used base in chlorosilane reactions, the former base was generally used for the above transformations. 

The reaction of lithiated cumulenic ethers with ethylene oxide, trimethyl-chlorosilane and carbonyl compounds shows the same regiosnecificity as does the alkylation. 

The reductions of chlorosilanes by lithium aluminum hydride, lithium hydride, and other metal hydrides, MH, offers the advantages of higher yield and purity as well as dexibiUty in producing a range of siUcon hydrides comparable to the range of siUcon haUdes (59). The general reaction is as follows ... 

The analogous reaction between anhydrides and alkoxysilanes also produces acyloxysilanes. The direct reaction of acids with chlorosilanes does not cleanly lead to full substitution. Commercial production of methyltriacetoxysilane direcdy from methyltrichlorosilane and acetic acid has been made possible by the addition of small amounts of acetic anhydride or EDTA, or acceptance of dimethyltetraacetoxydisiloxane in the final room temperature vulcanising (RTV) appHcation (41—43). A reaction that leads to the formation of acyloxysilanes is the interaction of acid chlorides with silylamides. 

This method is also used with alcohols of the stmcture Cl(CH2) OH (114). HaloaLkyl chlorosulfates are likewise obtained from the reaction of halogenated alkanes with sulfur trioxide or from the chlorination of cycHc sulfites (115,116). Chlorosilanes form chlorosulfate esters when treated with sulfur trioxide or chlorosulfuric acid (117). Another approach to halosulfates is based on the addition of chlorosulfuric or fluorosulfuric acid to alkenes in nonpolar solvents (118). 

Similar reactions can also be written for the alkoxysilanes but in commercial practice the chlorosilanes are favoured. These materials may be prepared by many routes, of which four appear to be of commercial value, the Grignard process, the direct process, the olefin addition method and the sodium condensation method. 

The products are recovered from the reaction mixture by filtration to remove the magnesium chloride, followed by distillation. It is then necessary to distil fractionally the chlorosilanes produced. The fractional distillation is a difficult stage in the process because of the closeness of the boiling points of the chlorosilanes and some by-products (Table 29.1) and 80-100 theoretical plates are necessary to effect satisfactory separation. 

The hydrocarbon can be in either the liquid or vapour phase and the silicon is finely divided. The inclusion of certain solid catalysts in the reactive mass may in some instances greatly facilitate the reaction. A mixture of powdered silicon and copper in the ratio 90 10 is used in the manufacture of alkyl chlorosilanes. 

The direct process is less flexible than the Grignard process and is restricted primarily to the production of the, nevertheless all-important, methyl- and phenyl-chlorosilanes. The main reason for this is that higher alkyl halides than methyl chloride decompose at the reaction temperature and give poor yields of the desired products and also the fact that the copper catalyst is only really effective with methyl chloride. 

The direct process involves significantly fewer steps than the Grignard process and is more economical in the use of raw materials. This may be seen by considering the production of chlorosilanes by both processes starting from the basic raw materials. For the Grignard process the basic materials will normally be sand, coke, chlorine and methane and the following steps will be necessary before the actual Grignard reaction ... 

This reaction, based on the Wurtz reaction, tends to go to completion and the yield of technically useful chlorosilane is low. 

The chlorosilanes are dissolved in a suitable solvent system and then blended with the water which may contain additives to control the reaction. In the case of methylsilicone resin the overall reaction is highly exothermic and care must be taken to avoid overheating which can lead to gelation. When substantial quantities of chlorophenylsilanes are present, however, it is often necessary to raise the temperature to 70-75°C to effect a satisfactory degree of hydrolysis. 

Thienyllithium has been used for the preparation of triphenyl-2-thienylsilane, 2-thienylsulfinic acid, and di-2-thienylketone by means of reactions with triphenyl chlorosilane, sulfur dioxide, and... 

---