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In this communication we present the results of initial kinetic studies in which we have established that alkoxysilanes and chlorosilanes react with Grignard reagents in entirely different ways. The Grignard reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium centre by silane, followed by a subsequent rearrangement of the complex to the products. Chlorosilanes react without solvent molecule replacement. 相似文献
3.
The Tamao oxidation of alkoxysilanes was investigated computationally to determine the role of fluoride, a key additive, in this reaction. A sequence of fluoride equilibria as well as possible transition states, mediated by basic and neutral peroxide, respectively, were examined, and a potential energy surface was calculated which was consistent with the typical synthetic methods required for the conversion of alkoxysilanes to alcohols. 相似文献
4.
Hynek Bene? Jocelyne Galy Jean-Fran?ois Gérard Josef Ple?til Ludovic Valette 《Journal of Sol-Gel Science and Technology》2011,59(3):598-612
Prehydrolyzed-condensed precursors containing amino or glycido groups were prepared via sol gel process using various alkoxysilanes
in the bulk, without addition of solvent in any step of their preparation. The influence of the experimental set-up, the functionality
and ratio of alkoxysilanes, and type of catalyst, on the structure buildup was studied. In the case of amino precursors, the
sol–gel process was carried out at weak basic conditions while in the case of glycido precursors the sol–gel process was catalyzed
by acid or neutral pH. The sol–gel process was monitored by 29Si NMR in solution and the structure of the prehydrolysed-condensed precursors was characterized by small-angle X-Ray scattering.
The systems with high content of tetraethoxysilane led to the fast gel formation. In weak acid medium tetraethoxysilane formed
larger, more condensed species as well as small structures (based on Q
1, Q
2 and Q
3 species) with silanol groups. Strong acidic conditions led to the fast formation of insoluble silica particles in liquid
(sol) phase containing monomeric alkoxysilanes. The most suitable precursor formulations based on the alkoxysilanes with amino
groups, as well as the most efficient set-up, were selected and used to prepare hybrid organic/inorganic networks based on
an epoxy matrix. These networks were characterized using dynamic mechanical analysis. 相似文献
5.
Carbonyl compounds are readily acetalized by alkoxysilanes in the presence of trimethylsilyl trifluoromethanesulfonate catalyst. 相似文献
6.
Pace Samantha J. Nguyen Eric Baria Maximillian P. Mojica Elmer-Rico E. 《Mikrochimica acta》2015,182(1-2):69-76
Microchimica Acta - Linear alkyl alkoxysilanes (methoxy and ethoxy-based) of varying length were used in preparing tetracycline surface imprinted silica xerogels by the sol–gel process. The... 相似文献
7.
Few routes to well-defined 3D silicone structures exist because of their susceptibility to depolymerization/metathesis in the presence of acids or bases. The Lewis acid B(C6F5)3 can be employed to condense hydrosilanes with alkoxysilanes, producing siloxanes and alkanes (R3SiH+R'OSiR' '3 --> R3SiOSiR' '3 + R'H). We demonstrate that balancing the steric demands at both the hydrosilane and alkoxysilanes, and the careful control of reaction conditions, permits clean condensation reactions to occur in the absence of competing metathesis processes. The resulting linear or highly branched siloxane compounds can be rapidly and easily assembled into explicit, complex 3D silicone structures in high yield. 相似文献
8.
Addition of triethylsilane to pivalophenone and benzoyltrimethylsilane catalysed by indium trichloride leads to the corresponding alkoxysilanes. Pivalophenone reacts about three times faster than benzoytrimethylsilane. 相似文献
9.
Melting gels are a class of organically modified silica gels that are rigid at room temperature, flow at temperature T1 and
consolidate at temperature T2 (T2 > T1), when crosslinking is complete. The process of (a) softening, (b) becoming rigid and
(c) re-softening can be repeated many times. Mixtures of mono-substituted alkoxysilanes and di-substituted alkoxysilanes have
been studied in a systematic way to identify suitable melting gel compositions. The mixtures and the resulting melting gels
have been characterized for their softening temperatures and consolidation temperatures. With an interest in using these materials
for sealing microelectronics, their physical properties have been measured. 相似文献
10.
Synthesis of optically active alkoxysilanes by asymmetric hydrosilylation of ketones, in the presence of a chiral phosphine—rhodium complex, is described; optical yields up to 46% are observed. 相似文献
11.
Melting gels are a class of organically modified silica gels that are rigid at room temperature, flow at temperature T1 and
consolidate at temperature T2 (T2 > T1), when crosslinking is complete. The process of (a) softening, (b) becoming rigid and
(c) re-softening can be repeated many times. Mixtures of mono-substituted alkoxysilanes and di-substituted alkoxysilanes have
been studied in a systematic way to identify suitable melting gel compositions. The mixtures and the resulting melting gels
have been characterized for their softening temperatures and consolidation temperatures. With an interest in using these materials
for sealing microelectronics, their physical properties have been measured. 相似文献
12.
Tuulmets A Nguyen BT Panov D Sassian M Järv J 《The Journal of organic chemistry》2003,68(26):9933-9937
Kinetics of the reactions of butylmagnesium chloride and phenylmagnesium bromide with tetraethoxysilane and methyltrichlorosilane was investigated in diethyl ether and diethyl ether-toluene mixtures. Replacement of ether by toluene significantly accelerates the reaction with alkoxysilanes, while no effect was found for the reaction with chlorosilanes. We established that the reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium center by the silane followed by subsequent rearrangement of the complex to products through a four-center transition state. Chlorosilanes react differently without solvent molecule replacement but also via a four-center transition state. Large negative activation entropies are consistent with formation of cyclic transition states. Small activation enthalpy values together with remarkable exothermicity point to early transition states of the reactions. 相似文献
13.
A new class of porous nanocomposite materials have been prepared by reaction of alkoxysilanes with alkylammonium-exchanged phyllosilicates (clay minerals), using a sol-gel procedure which produces the complete delamination of these layered solids. 相似文献
14.
B(C(6)F(5))(3) promotes regio- and stereoselective cyclizations of unsaturated alkoxysilanes to generate oxasilinanes and oxasilepanes. The same products are available directly from alkenols via tandem silylation and hydrosilylation. 相似文献
15.
Selective Formation of Alkoxychlorosilanes and Organotrialkoxysilane with Four Different Substituents by Intermolecular Exchange Reaction
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Yasuhiro Tamura Prof. Hiroaki Wada Prof. Atsushi Shimojima Prof. Kazuyuki Kuroda 《化学:亚洲杂志》2016,11(22):3225-3233
Alkoxychlorosilanes are scientifically and industrially important toward preparing silicone and silica as well as preparation of siloxane‐based nanomaterials by stepwise reactions of Si?OR (R=alkyl) and Si?Cl groups. Intermolecular exchange of alkoxy and chloro groups between alkoxysilanes and chlorosilanes (functional group exchange reaction) provides an efficient and environmentally benign route to alkoxychlorosilanes. BiCl3 as a Lewis acid catalyst can promote the functional group exchange reactions more efficiently than conventional acid catalysts. Higher reactivity has been observed for chlorosilanes with smaller numbers of Si?CH3 groups and for alkoxysilanes with larger numbers of Si?CH3 groups. The reaction mechanism is proposed and selective syntheses of alkoxychlorosilanes are demonstrated. These findings also enable us to synthesize an organotrialkoxysilane with four different substituents. 相似文献
16.
An equilibrium reaction of the exchange of silyl radicals taking place between organylchlorosilanes and acyloxy- and alkoxysilanes has been found. In the rase of alkenyloxytrimethylsilane and chloro-H-silanes. in addition to the transsilylation reaction, intramolecular hydrosilyation takes place, leading to the formation of oxasilacycloalkanes. 相似文献
17.
Richard M. Laine Joseph C. Furgal Phi Doan David Pan Vera Popova Xingwen Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(3):1077-1081
The direct depolymerization of SiO2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Simet, followed by treatment with ROH. We report herein the base‐catalyzed depolymerization of SiO2 with diols to form distillable spirocyclic alkoxysilanes and Si(OEt)4. Thus, 2‐methyl‐2,4‐pentanediol, 2,2,4‐trimethyl‐1,3‐pentanediol, or ethylene glycol (EGH2) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H2O and distillable spirocyclic alkoxysilanes [bis(2‐methyl‐2,4‐pentanediolato) silicate, bis(2,2,4‐trimethyl‐1,3‐pentanediolato) silicate or Si(eg)2 polymer with 5–98 % conversion, as governed by surface area/crystallinity. Si(eg)2 or bis(2‐methyl‐2,4‐pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt)4 in 60 % yield, thus providing inexpensive routes to high‐purity precipitated or fumed silica and compounds with single Si−C bonds. 相似文献
18.
Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic,Green, and Sustainable Sources
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Richard M. Laine Joseph C. Furgal Phi Doan David Pan Vera Popova Xingwen Zhang 《Angewandte Chemie (International ed. in English)》2016,55(3):1065-1069
The direct depolymerization of SiO2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Simet, followed by treatment with ROH. We report herein the base‐catalyzed depolymerization of SiO2 with diols to form distillable spirocyclic alkoxysilanes and Si(OEt)4. Thus, 2‐methyl‐2,4‐pentanediol, 2,2,4‐trimethyl‐1,3‐pentanediol, or ethylene glycol (EGH2) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H2O and distillable spirocyclic alkoxysilanes [bis(2‐methyl‐2,4‐pentanediolato) silicate, bis(2,2,4‐trimethyl‐1,3‐pentanediolato) silicate or Si(eg)2 polymer with 5–98 % conversion, as governed by surface area/crystallinity. Si(eg)2 or bis(2‐methyl‐2,4‐pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt)4 in 60 % yield, thus providing inexpensive routes to high‐purity precipitated or fumed silica and compounds with single Si?C bonds. 相似文献
19.
Atsushi Itagaki Kazuki Nakanishi Kazuyuki Hirao 《Journal of Sol-Gel Science and Technology》2003,26(1-3):153-156
The phase separation behavior of gelling systems containing the mixture of 3-functional and 4-functional alkoxysilanes has been investigated. The relation between the starting composition and resultant macroporous morphology was examined using tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as starting alkoxysilanes, formamide (FA) as an additive, under an acidic condition. Up to TMOS:VTMS molar ratio of 0.5:0.5, the phase relation remained almost unchanged from that of pure TMOS system which exhibits morphology with well-defined co-continuous macropores in a very limited concentration region. On the VTMS-rich side typically TMOS:VTMS = 0.2:0.8, however, the co-continuous macroporous morphology was obtained in a broader composition range than those of either pure TMOS or VTMS system. A dome-like pseudo binary region was obtained with the two-phase region extending toward FA-rich direction. The domain size and pore volume of the gels with macroporous morphology could be controlled by alkoxide:water ratio and total solvent fraction, respectively. 相似文献
20.
Distillable nonionic chloride impurities at 50 to 2000 ppm Cl are conveniently removed from alkoxysilanes by treatment with sodium metal. When free of these contaminants, thought to be 2° and 3° alkyl chlorides, MeSi(OMe)3 hydrolyzes substantially more slowly than before treatment. 相似文献