Silanes tetraalkoxysilanes

A plot of the ln[silane] vs. time (Fig. 1) exhibits the similar phenomenon found in our earlier work [13] with the tetraalkoxysilanes. The reverse reaction quickly becomes important and one must correct for it, though the earlier work had an additional complication of successive substitution reactions. As in the earlier paper, this could take the form ... 

Silane reacts with methanol to give the alkoxysUanes (MeO) SiH4 (n = 2, 3, 4) and with higher alcohols in the presence ofbase to give tetraalkoxysilanes (equation 8). This type of reaction is, however, rarely carried out as the alkoxysi-lanes produced are more conveniently prepared from alcohols and SiCU (which is more readily available than SiELi and much more easily handled). Similarly, silyl esters, Si(OCOR)4, are also usually prepared from polyhalogenosUanes rather than from silane and a carboxylic acid. 

Silane reacts with methanol at room temperature to produce methoxymonosilanes such as Si(OCH2)4 [78-10A]y HSi(OCH2)3, and H2Si(OCH3)2 [5314-52-3] but not H SiOCH [2171 -96-2] (23). The reaction is catalyzed by copper metal. In the presence of alkoxide ions, SiH reacts with various alcohols, except CH3OH, to produce tetraalkoxysilanes and hydrogen (24). 

Apart from the reaction with halogen derivatives, use was also made, for the synthesis of silicon-containing cellulose esters, of the reaction of alcoholysis, with cellulose, of tetraalkoxysilanes or alkyl(aryl)trialkoxy-silanes and the amides of siliconic acids (64) ... 

An alternative route to alkoxyorganylsilanes is the application of organometallic compounds. Tetraalkoxysilanes with Grignard reagents yield mono, di-regular print or trialkoxysilanes, depending on the silane Grignard ratio (equation 285)318-321. 

Garz6 et all42 reported retention indices for a considerable number of organosilicon compounds, but only two of the compounds were tetraalkoxysilanes, namely tetramethoxy- and tetraethoxy-silane. 

There is an approximately linear relationship between retention index and carbon number for any homologous series of terraalkoxy-silanes, e.g. (RO)3 SiOCnH2n > counted from n = 4. This follows from the fact that the differences between group retention indices become approximately constant from I(BuO)Si onwards and that the same applies to the correction term in equation (2), The linear relationship is demonstrated in Figure 59 for some homologous series of tetraalkoxysilanes. 

The retention indices of homologous series of mixed tetraalkoxy-silanes (RO) Si(RO)i+-x linear functions of the retention indices of the symmetrical counterparts (see equation (3)). The way in which this fact can be utilized for calculating retention indices of mixed tetraalkoxysilanes is discussed below. In addition, the temperature dependence of the retention indices of tetraalkoxysilanes is discussed and a comparison made between retention indices measured on packed and capillary columns. 

Table 82 gives the retention indices for AI values of tetraiso-propoxy-, tetraisobutoxy-, tetra n-propoxy and tetra-sec-butoxy silanes. For comparison, the data for corresponding normal tetraalkoxysilanes, taken from the work of Ellrdn et al 02 also given. The retention indices of the branched compounds are considerably lower than those of the normal compounds, which was to be expected because of their lower boiling points. The marked difference between the AI values of normal and branched compounds reflects the increased shielding of the polar Si-0 and C-0 bonds in the latter, which increases their activity on the polar XE-60 stationary phase. 

Several reports have shown that hollow silica particles can be prepared by hydrolysis and polycondensation of tetraalkoxysilane in the presence of aggregates of polymers such as polyamines [5], polylysine [6], poly(acrylic acid) (PAA) [7], and poly(JV-isoprop)dacrylamide) [8]. Although this method often results in broad particle size distributions (100 nm to several micrometers), relatively fine control of the size (in the range of 25-400 nm) and shell thickness was achieved with PAA [7]. The synthesis route involves (i) the formation of spherical aggregates of PAA in an ethanol solution, (ii) the formation of silica particles from tetraethoxy-silane (TEOS) by the modified Stober method [9], and (iii) subsequent removal of PAA by washing. 

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