Methylsilicon chloride

Silicone polymers have a range of structures and applications (see Box 13.12), and, in their manufacture, control of the polymerization is essential. The methylsilicon chlorides are co-hydrolysed, or the initial products of hydrolysis are equilibrated by heating with H2SO4 which catalyses the... 

TMS derivatives of amino acids were also combined with other procedures and some difficulties were thus avoided. N-TMS-methyl and -ethyl esters of most protein amino acids were prepared by the action of TMSDEA on alkyl esters of amino acids and were chromatographed on methylsilicone stationary phases [246], Their retention times were found to be 15—20% lower than those of the corresponding TMS derivatives. Despite having an additional step in comparison with direct silylation, the procedure was applied by Hardy and Kerrin [259] to the GC analysis of twenty protein amino acids, including Hypro and CysH. Amino acids were esterified with a 3 N HC1 solution in n-butanol at 150°C for 15 min with subsequent silylation with BSTFA for 90 min at the same temperature. Acetonitrile and methylene chloride were used as solvents for the silylation. In the former solvent double derivatives of Gly and Lys (bis- and tris-) were produced, whereas in the latter the less silylated form only was produced. As Arg, in contrast to direct silylation, also leads to one peak in this instance, methylene chloride is recommended as the silylation solvent. The separation of all twenty amino acids was achieved on a simple column with 2% of OV-7 on GLC-110 textured glass beads (100—120 mesh). 

The Rochow Process. Rochow found that alkyl and aryl halides react directly with silicon when their vapors contacted silicon at elevated temperatures to produce complex mixtures of organosilicon halides. The reaction is promoted by a wide variety of metals from both the main group and the transition series, but the most efficient catalyst is copper. The most studied reaction of this type is the reaction between methyl chloride and silicon to give dimethyldichlorosilane and methyltrichlorosilane. Dimethyldichloro-silane is major feedstock silane for methylsilicon polymers. 

Silicon tetraisocyanate and methylsilicon isocyanates, of the type (CH3) Si(NCO)4 (n = 1, 2, or 3), were first prepared in 75 to 90% yields by treating silicon(IV) chloride or the appropriate methylchlorosilane with silver isocyanate in anhydrous benzene. Forbes and Anderson report that much smaller yields are obtained when lead cyanate is used instead of silver isocyanate. The following procedure, however, when performed with lead cyanate, produces 52 to 71% yields of the silicon isocyanates. Comments on the use of less expensive lead cyanate are therefore included along with the silver isocyanate method of preparation. 

The direct, copper catalyzed reaction of methyl chlorid with silicon, the Direct Process , is the most important reaction for the production of methylsilicon intermediates. A similar reaction with hydrogen chloride yields trichlorosilane, which in turn is the basis for trifiinctional intermediates and also for polycrystalline silicon, the raw material for the semiconductor industry. This Direct Process has been practiced for fifty years and much progress has been made by many towards understanding and optimizing the process, but much still remains to be learned about this complex series of heterogeneous reactions. 

To titrate alkylchlorosilanes such as trimethylsilicon chloride, dimethylsilicon dichloride, methylsilicon trichloride and silicon tetrachloride, titration in methyl cyanide with 0.05 n phenazone or nitron in methyl cyanide, or with a solution of amidopyrine in benzene by visual and potentiometric methods is suggested173. The indicators used are crystal violet, dimethylaminoazobenzene, bromocresol purple, methyl orange, bromo-phenol blue and gallo sea blue (C.I.-Mordant Blue 14) the addition of benzene, toluene, chlorobenzene or carbon tetrachloride does not effect the results. 

In the alkylation of silicon with methyl chloride, mono-, di-, and trimethyl chlorosilanes are formed. The reaction products must then be fractionated. Because the dimethyl derivative is bifunctional, it produces linear methylsilicone polymers on hydrolysis. 

Trichloracetyl and 4-carbethoxyhexafluorobutyryl chloride derivatives have been nsed to increase the molecular weight of the amphetamines. These particular derivatives consequently lengthen the elution times and help separate these compounds from potential interference (34,35). A-Monotrifluoroacetylated (TFA) derivatives of amphetamine analogues have been prepared by on-column derivatization with A -methylbis(trifluoroacetamide) (MBTFA) (36). A separation on a 12-m methylsilicone capillary column of four phenethylamines with closely related structures is shown in Figure 16.2 using this procedure. 

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