Silane alkylsilanes

Silanes react with alkyllithium compounds, forming various alkylsilanes. Complete substitution is generally favored however, less substituted products can be isolated by proper choice of solvent. AH four methylsHanes, vinylsHane [7291-09-1and divinylsilane [18142-56-8] have been isolated from the reaction of SiH and the appropriate alkyllithium compound with propyl ether as the solvent (35). MethylsHane and ethyldisHane [7528-37-2] have been obtained in a similar reaction (36). 

The alkylation of halogen-substituted benzenes such as fluorobenzene and dichlorobenzenes with other (dichloroalkyl)silanes in the presence of aluminum chloride catalyst afforded isomeric mixtures of the corresponding (dihalogen-substituted phenyl)alkylsilanes in moderate yields (Eq. (13)). These results are summarized in Table Xll. 

See entry silanes olefins, platinum See related alkylsilanes... 

Formyl(triisopropyl)silane [] (Me2CH)3SiCO.H Soderquist, J. A. et al., J. Amer. Chem. Soc., 1992, 114(25), 10078 Pyrophoric. See other ALKYLSILANES CioH22OSi... 

ALKYLHALOSILANES, ALKYLSILANES HALOSILANES, ORGANOSILYL PERCHLORATES SILANES, SILICONE GREASE, SILICONE LIQUID, SILICONE OIL SILYLHYDRAZINES, TRIALKYLSILYLOXY ORGANOLEAD DERIVATIVES... 

Trifluoroacetic acid-Alkylsilanes, 123 Trifluoroacetic acid-Dimethylphenyl-silane, 123... 

Acid catalysis—hydrolysis. Several series of alkylsilane esters were studied to determine the effect of silane structure on the hydronium ion catalyzed hydrolysis reaction. The hydronium ion catalyzed hydrolysis rate constants for a series of alkyl tris-(2-methoxyethoxy)silanes in aqueous solution were used to define the modified Taft equation log(A /Ah ) = 0.39a + 1.06ES, where Ho is the rate of hydrolysis for methyl tris-2-(methoxyethoxy)silane [42], The hydronium ion catalyzed hydrolysis rate constants and the reaction half-lives are reported in Table 2. In a similar manner, the hydronium ion catalyzed hydrolysis rate constants for a series of trialkylalkoxysilanes in 55% aqueous acetone were used to obtain the modified Taft equation log(/cH//cHo) = -0.37 a + 2.48 E where kHo is the rate of hydrolysis for trimethylalkoxy-silane. 

It should be pointed out that the Si—C bond length is influenced by the hybridization state of the carbon atom. The Si—C distance in vinyl-, ethinyl- and phenyl-silanes is shortened as compared with that of corresponding alkylsilanes [examples13 H3SiCH3 (186.7 pm), H3SiCH=CH2(185.3 pm), H3SiC=CH(182.6 pm)]. 

In Ref 7 are given the temp-compn limits of spontaneous expln for 9 alkylsilanes with air at atm press, and in Ref 8 are discussed the combustion and expln limits of several alkylsilanes at 1 atm press. The expln temp decreases in the order tetramethylsilane tfimethyl Silane dim ethyl silane methyl-silane > vinyisiiane... 

Direct addition of H- and other nucleophilic anions to primary, secondary and tertiary alkylsilanes formed pentacoordinate silicate anions (equation 26). Interestingly, the parent silicate, Sills. could not be prepared in this way from silane and hydride65,68. Sills was prepared from alkylhydridosilicates by a hydride transfer reaction (equation 27). The reducing activity of alkylhydridosilicates toward various substrates via hydride transfer in the gas phase was discussed in detail in a previous review67. 

See entry SILANES Olefins, Platinum See related ALKYLSILANES... 

Apolar stationary phases suffer from hydrolytic instability at pH extremes. The use of mixed phases of long (Cg, Clg) and short (C, C3) chain alkyls produces stationary phases with increased hydrolytic stability.7,8 Crowding of the long alkyl chains does not allow the alkylsilane molecules to deposit in close packing on a smooth or flat surface. Silane molecules polymerize in vertical direction, loosing contact with the silica surface. The insertion of short chain alkyls allows horizontal polymerization of the silane molecules. Thus, alkyl chains are aligned in a parallel way. The stability of the silane layer is increased consequently (figure 8.1). 

Alkyl chains are generally deposited on the silica surface using the corresponding alkylsilane. The hydride intermediate route, developed by Sandoval and Pesek78,79 gives an alternative for this method. The one-step alkylsilane route, is replaced by a two-step silanization-alkylation procedure. The loss of process simplicity is compensated by the advantages of an increased alkyl density and enhanced coating stability. 

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