Tetraethyl orthosilicate reactions

Tetraethyl orthosilicate (104.2 g) and deuterium oxide (40 g) are stirred in a stoppered distillation flask at room temperature until a viscous, miscible solution is obtained (approximately 24 hr). (A small amount of acid catalyst, such as deuteriochloric acid, speeds up the reaction considerably. ) A distillation head and a receiver cooled in a dry ice-acetone bath are attached and the solution is distilled at 2 mm pressure until no further product is obtained. A 90% yield of ethanol-OD is obtained having an isotopic purity equal to that of the deuterium oxide used. ... 

MOCVD of Silica. Considerable work is being done with the MOCVD of silica, which is rapidly expanding in semiconductor processing. The most common MOCVD reaction is the decomposition of tetraethyl orthosilicate (TEOS), shown in simplified form as follows ]... 

A widely used glass is phosphosilicate (PSG), which is used extensively in semiconductor devices as a passivation and planarization coating for silicon wafers. It is deposited by CVD by the reaction of tetraethyl orthosilicate (TEOS) (C2H50)4Si, and trimethylphosphate PO(OCH3)3, in a molecular ratio corresponding to a concentration of 5 to 7% P. Deposition temperature is usually 700°C and pressure is 1 atm. 

Later, Thangaraj et al. (275,281) developed a novel, improved route (prehydrolysis method) for the preparation of good quality TS-1 samples. In this method the silica source (tetraethyl orthosilicate TEOS) in Ao-propanol was first hydrolyzed with 20% aqueous TPAOH solution prior to the (dropwise) addition of titanium butoxide in dry iso-propanol under vigorous stirring. Crystallization was done statically at 443 K for 1-5 days and the solid was calcined at 823 K for 10 h. The TS-1 samples thus obtained exhibited high catalytic activity in hydroxylation reactions. 

The 4,4 -dibromobiphenyl was used as the starting material The strategy taken for the synthesis of the organosilica was to carry out Grignard-type reaction to incorporate tetraethyl orthosilicate (TEOS) to 4,4 -dibromobiphei5rl to create 4,4 -Bis(triethoxysilyl)biphenyl. Materials from this procedure had been subjected to polymerization surfactant-mediated polymerization. The product obtained was a white powder aggregate. Shown in Table 47.1 are the formulations used for the samples and the heat treatment. 

Reactions with alcohols yield esters of orthosilicic acid. For example, with ethanol the product is tetraethyl orthosilicate or tetraethoxysilane, Si(OC2H5)4 ... 

Lactone 86 undergoes an intramolecular conjugate addition reaction in the presence of cesium fluoride and tetraethyl orthosilicate to give furo[3,2- ]pyridine dione 87 (Equation 25). After 12 h, a 1 1 mixture of 3-ethyl epimers is found however, extending the reaction time to 72 h results in exclusively /3-ethyl isomer 87 in good yield <2005JOC384>. 

In 1995, Tanev and Pinnavaia [1] have reported the synthesis of a new type of mesoporous molecular sieve designated as the hexagonal mesoporous silica (HMS). Instead of using the ionic inorganic precursor and surfactant as in the case of MCM-41 [2], HMS is manufactured by hydrolysis reaction between a neutral inorganic precursor, tetraethyl-orthosilicate (TEOS) and a neutral primary amine surfactant (8-18 carbons). HMS possesses numerous favourable characteristics, but, like MCM-41, its synthesis process can only be concluded by the removal of the surfactant. This was reportedly done either by calcination at 630°C or by warm ethanol extraction [1]. 

Starting in the 1950s a process was developed that leads from small-molecule silicon alkoxides such as tetraethoxysilane (tetraethyl orthosilicate), to organosiloxane oligomers and low polymers, and eventually to silica via a low temperature synthesis route.14 24 A simplified outline of the basic chemistry is shown in reactions (l)-(4), where R is an ethyl or higher alkyl unit. Any or all of the Si-OR bonds can be... 

In our studies we synthesized surfactant salts of phosphomolybdic acid (PMA) and reacted them with tetraethyl orthosilicate (tetrabutyl titanate) in a salt-gel reaction in order to obtain a three-dimensional tunnel structure. It is based on the hydrothermal reaction using cetyltrimethylammonium bromide as a structuredirecting agent. Phosphomolybdic acid is unstable when the temperature is over 723 K. Calcination to decompose the template will make the inorganic portion of the structure to collapse invariably and to form dense M0O3.X phases. Therefore, we... 

Cu-MCM-41 and Cu-Al-MCM-41 samples have been obtained by ion exchange of the MCM-41 and Al-MCM-41 matrices prepared by hexadecyltrimethylammonium cloride, tetraethyl orthosilicate, aluminum isopropoxide and an ammonia solution. The aluminum concentration affects the MCM-41 textural properties and large amount of extra-framework aluminum species are supposed to be present in Al-MCM-41 with Si/Al = 30. Cu-MCM-41 and Cu-Al-MCM-41 catalysts have been tested for NO selective catalytic reduction by propane in the presence of oxygen, in comparison with microporous Cu-S-1 and Cu-ZSM-5 catalysts with similar copper loading and Si/Al atomic ratio. Cu-Al-MCM-41 catalysts are less active and selective with respect to the Cu-ZSM-5 catalysts indicating that they are not suitable for NO abatement reactions. 

Silicic acid esters, Si(OR)4, are produced by the reaction of SiCl4 with the appropriate alcohols. The most important representative of this group is tetraethoxysilane (tetraethyl orthosilicate) Si(OC2H5)4, which is used directly, or after hydrolysis to ethylpolysilicates, as a binder for ceramic pastes, for inorganic zinc dust paints (corrosion protection), for the surface treatment of glass and for the modification of silicates. Silicic acid esters are further used for rendering polymer surfaces scratch-resistant. 

The sol-gel process is a novel technique for the preparation of various inorganic oxide glasses at low temperatures without melting.51 They are produced by condensation-polymerization of a suitable metal alkoxide. For instance, the sol-gel process of tetraethyl orthosilicate (TEOS) consists of the hydrolysis reaction... 

The chemistry involved in the formation of mesoporous silica thin films is qualitatively well understood. However, specific reaction mechanisms of the individual steps are still debated. In addition, owing to the complexity of the sol-gel reaction pathways and cooperative self-assembly, full kinetic models have not been developed. From the time of mixing, hydrolysis reactions, condensation reactions, protonation and deprotonation, dynamic exchange with solution nucleophiles, complexation with solution ions and surfactants, and self-assembly, all occur in parallel and are discussed here. Although the sol-gel reactions involved may be acid or base catalyzed, mesoporous silica film formation is carried out under acidic conditions, as silica species are metastable and the relative rates of hydrolysis and condensation reactions lead to interconnected structures as opposed to the stable sols produced at higher pH. Silicon alkoxides are the primary silica source (tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, etc.) and are abbreviated TMOS, TEOS, and TPOS, respectively. Starting from the alkoxide, Si(OR)4, in ROH and H2O solution, some of the general reactions are ... 

The surface silylated zeolites were prepared by suspending the H-ZSM-5 or FeH-ZSM-5 zeolite in n-hexane into which a calculated amount of tetraethyl orthosilicate was added to obtain addition of 1.5 wt. % of Si in the final product (abbrev. SiH-ZSM-5 or SiFeH-ZSM-5). n-Hexane was evaporated and the zeolites were dried and calcined in an oxygen stream at 770 K for 5 hours. To add some Fe cations to the surface of silylated zeolites, the SiH-ZSM-5 was introduced into a FeCl solution, filtered and dried (abbrev. FeSiH-ZSM-5). The characteristics of the parent and modified zeolites are given in the Table. The alkylation of toluene with ethylene was carried out in a vapour phase continuous flow microreactor at atmospheric pressure. Nitrogen as a carrier gas was saturated with toluene to 18.5 vol. %, the toluene to ethylene molar ratio was 3.8. The reaction products were analyzed by an "on-line" gas chromatograph (Hewlett-Packard 5890) with MS and FID detection. 

TETRAETHYL ORTHOSILICATE (78-10-4) Forms explosive mixture with air (flash point 99°F/37°C). Reacts slowly with water, forming ethyl alcohol. Violent reaction with strong oxidizers. Incompatible with strong acids, nitrates. Attacks some plastics and rubber. 

In contrast to silica-supported H3[PWi204o], the sol-gel H3[PWi204o] catalysts prepared by the hydrolysis of tetraethyl orthosilicate showed only a negligible activity in the Fries reaction of phenyl acetate, yielding mainly phenol with 92 - 100% selectivity. This may be explained by a weaker acid strength of the sol-gel catalysts due to strong interaction of the HPA protons with the silica matrix and the presence of relatively high amount of water in sol-gel catalysts. ... 

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