Siloxanes formation

The presence of bulky substituents such as Bul on silicon greatly reduces the tendency towards siloxane formation, and with two or more such groups present the precautions suggested in points 1, 2, and 3 can often be relaxed. For example, the hydrolysis of highly sterically hindered halosilanes may require rather severe conditions. 

The decomposition of the S-methylxanthate ester of 1,1-dimethyl-1-silacyclopcnt-4-cn-3-ol takes place in refluxing ether, but this ester cannot give the silole 4 which dimerizes in situ (61% yield), together with siloxane formation (Me2SiC4H5)20 (31%) due to a ft C—Si elimination14. 

Siloxanes, formation of, by hydrolysis of hexamethylcyclo-trisilazane and octamethyl-cyclotetrasilazane, 5 63 Silver, 1 4... 

Concluding, the processes occurring under various curing conditions have been modelled. In the curing phase, the aminosilane layer is stabilized by covalent bonding to the surface. Siloxane bonds are formed between silane and silica surface atoms. The velocity of the siloxane formation is dependent on the initial number of ethoxy... 

Summarizing, the curing process can be characterized as follows. Upon thermal treatment of the loaded substrate, silane molecules are chemically bonded by siloxane formation. These bonds are formed between neighbouring silanes or between the... 

This reaction has been improved to a catalytic version by heating the mixture of zinc dust, a catalytic amount of TiCls, the oxoamides, and an excess amount of silane (such as RsSiCl in MeCN or DME). The scope of such version of Ftirstner indole synthesis depends on the competition by uncatalyzed zinc-induced reduction. It is found that bis(chlorosilane)—Such as (ClSi(Me)2CH2CH2Si(Me)2Cl—gives abetter turnover number due to the intramolecular siloxane formation. In addition, Sml2 has been successfully applied to the Ftirstner indole synthesis.Moreover, in terms of intramolecular cyclization, the Ftirstner indole synthesis has been extended to the preparation of benzofurans. ... 

Siloxanes Formation of Si02 and microcrystaUine quartz due to combustion deposition at spark plugs, valves and cylinder heads abrading the surface... 

This procedure does not liberate HCl, however methyl chloride and methyl formate are formed as by-products. Thus, no catalyst is produced to affect the isomerization of the product, and no water is formed preventing siloxane formation and condensation. 

Optimization of the methanolysis for the fumarate derivative is achieved by reducing the reaction temperature to 70 °C during the methanol addition while applying a partial vacuum, 50 mm Hg, to remove HCl and water. Incorporation of this modification resulted in negligible amounts of siloxane formation. 

Fig. 5 (a) Proposed mechanism for dehydrocarbonative condensation, (b) Stereoselective siloxane formation... 

Fig. 8 Steric control over siloxane formation, (a) facile reaction with steiically undemanding silicones. (b) reduced reactivity when both alkoxysilane and hydrosilicone are encumbered...

We noticed that the reactivity of the silane and silanol (alkoxysilane) components in the condensation was very much dependent on the steric environment of the silicon atom bearing the functional group. To construct new polymer structures consisting of only POSS cage, understanding the reactivity of silane and silanol in POSS structures during siloxane formation is essential. 

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