Silane effect

The conclusion was reached that the mechanical properties of glass-reinforced unsaturated polyester are influenced by the chemical structure of the spacer groups in the methacrylate functional silane. Effective factors include hydro-phobicity, reactivity of the double bond, chain flexibility of the backbone, and adsorption behavior. 

Semihydrogenation of alkynes The surface of silica gel is covered with hydrosilane groups on reaction with trichlorosilane. The solid-supported silane effects hydrogenation of alkynes to (Z)-alkenes selectively. 

If we consider that the amount of sulfur is the most important factor governing the polar character of the surface layer, we should have observed both a higher viscosity and a stronger Payne effect with SiS2. However, if the adsorbed silane concentration is die dominant factor, then SiS2 leads to a higher surface population and enhanced silane effect and the results are consistent. 

Table 14.31 Azido Silane and Ucarsil Silane Effects on Heat Aging of Mica/Polypropylene Composites Long-Term Heat Aging Effects on Crazing of Mica -Polypropylene Composites Held at 150°C...

Silanes have little effect on carbon blacks. They are also not generally effective on surfaces such as sulfates and carbonates, although attempts have been made to improve silane effectiveness on such surfaces by pre-coating them with silica [45] or by phosphate layers [46]. It has been reported that some organo-silanes, notably, amino-silanes, can produce an effect on calcium carbonate by some form of encapsulation [47]. 

Abdelmouleh, M., Boufi, S., Belgacem, M.N., Dufresne, A., and Gandini, A. (2005) Modification of cellulose fibers with functionalized silanes effect of the fiber treatment on the mechanical performances of cellulose-thermoset composites. J. Appl. Polym. Sci., 98, 974-984. 

A traditional method for such reductions involves the use of a reducing metal such as zinc or tin in acidic solution. Examples are the procedures for preparing l,2,3,4-tetrahydrocarbazole[l] or ethyl 2,3-dihydroindole-2-carbox-ylate[2] (Entry 3, Table 15.1), Reduction can also be carried out with acid-stable hydride donors such as acetoxyborane[4] or NaBHjCN in TFA[5] or HOAc[6]. Borane is an effective reductant of the indole ring when it can complex with a dialkylamino substituent in such a way that it can be delivered intramolecularly[7]. Both NaBH -HOAc and NaBHjCN-HOAc can lead to N-ethylation as well as reduction[8]. This reaction can be prevented by the use of NaBHjCN with temperature control. At 20"C only reduction occurs, but if the temperature is raised to 50°C N-ethylation occurs[9]. Silanes cun also be used as hydride donors under acidic conditions[10]. Even indoles with EW substituents, such as ethyl indole-2-carboxylate, can be reduced[ll,l2]. 

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

Mechanistically the rate-determining step is nucleophilic attack involving the hydroxide ion and the more positive siUcon atom in the Si—H bond. This attack has been related to the Lewis acid strength of the corresponding silane, ie, to the abiUty to act as an acceptor for a given attacking base. Similar inductive and steric effects apply for acid hydrolysis of organosilanes (106). 

Alkylation and arylation of organosilanes occur readily with alkyl and aryl alkaU metal compounds. Yields from these reactions are good but are iafluenced by steric requirements on both silane and metal compounds. There is Httie iaductive effect by the organic groups attached to siUcon, as measured by the yield of products (126,127). These reactions proceed more readily ia tetrahydrofuran and ethyl ether than ia ligroin or petroleum ether, where R and are alkyl or aryl and M is Li, Na, or K. 

The effective absorption of radiation by a gas can be increased by the addition of a sensitizer. For example, when mercuty vapour is added to silane gas, the mercury vapour absorbs radiation to form an excited atom Hg which collides with a silane molecule to lead to partial dissociation... 

Trialkyltin substituents are also powerful ipso-directing groups. The overall electronic effects are similar to those in silanes, but the tin substituent is a better electron donor. The electron density at carbon is increased, as is the stabilization of /S-carbocation character. Acidic cleavage of arylstannanes is formulated as an electrophilic aromatic substitution proceeding through an ipso-oriented c-complex. ... 

Effect of silanes on bond strength of epoxide coatings... 

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