Silicon containing compounds mechanisms

Several areas dealing with the photochemical processes in silicon containing compounds have also received renewed attention. Thus the photochemical reactivity of oligosilanes, polysilanes and silylenes has been the subject of a detailed review. Aspects of the mechanisms for the processes were highlighted. Other publications have been concerned with the photoreactions of silanes (cyclic and acyclic) disilanes, silenes, etc and the photoinduced electron-transfer reactions involving organosilicon compounds. ... 

In order to get a rapid and complete hydrolysis, an acid or a base catalyst may be used. In both cases the reaction occurs by a nucleophilic attack of the oxygen contained in water, to the silicon atom. Hydrolysis mechanisms were studied by Osterholz and Pohl,15 using alkyltrialkoxysilanes instead of tetra-alkoxysilanes. Both types of compounds are following the mechanism below. 

Whenever silicon nitride is synthesized in the presence of aluminum-containing compounds (frequently used as a flux material in process of growing whiskers), there is a high probability of the formation of /3 -SiA10Ns. Up to two-thirds of the silicon in /3-Si3N4 can be substituted by Al without a change of structure. The /3 -SiAl()N has mechanical and physical properties similar to y3-Si3N4. It is, however, thermodynamically more stable than silicon nitride. 

The acyclic compound l-NaphPh(H)SiOCOPh is not significantly converted to benzaldehyde on thermolysis, even at temperatures considerably higher than those (100-160 °C) which are effective with the chelate system. This reaction may proceed via the transient formation of a chelated silanone 82, since the trisiloxane 80 is isolated as the silicon-containing product. Confirmation of this mechanism was obtained in the reaction of 78 with carbon dioxide, from which the silyl ester of formic acid 81 can be isolated and... 

The mechanism of silicon resorption in the digestive tract is not known. It is assumed that the available forms of silicon (contained in the diet) are ort/io-silicic acid and soluble silicates. When given in the form of silicon aluminosilicates, only about 1% of siHcon is resorbed. In contrast, some organosiKcon compounds used in medicine (such as methylsilantriol salicylate) are resorbed of up to 70%. Resorption efficiency of silicon contained in the diet varies over a wide interval of 5-100%. Beer has a high bioavaQability (about 50%) of silicon. The efficiencies of silicon resorption from meat, dairy and soy products usually exceed 50%. From cereals and other foods containing high amounts of silicon, this element is resorbed poorly. Silicon is excreted mainly in the urine. 

While the decomposition of silacyclobutanes as a source of silenes has continued to be studied in the last two decades, the interest has largely focused on mechanisms and kinetic parameters. However, a few reports are listed in Table I of the presumed formation of silenes having previously unpublished substitution patterns, prepared either thermally or photo-chemically from four-membered ring compounds containing silicon. Two cases of particular interest involve the apparent formation of bis-silenes. Very low-pressure pyrolysis of l,4-bis(l-methyl-l-silacyclobutyl)ben-zene94 apparently formed the bis-silene 1, as shown in Eq. (2), which formed a high-molecular-weight polymer under conditions of chemical vapor deposition. 

---