Silanes alkyl

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

Cyclopentanones from carboxylic acids by intramolecular acylation of alkyl-silanes... 

Silanes (R3SiH) also add to alkenes to form a new alkyl silane (RaSi—R ) in the presence of a hyponitrite. Silanes add to dienes with a palladium catalyst, and asymmetric induction is achieved by using a binapthyl additive. ° ... 

Among the Friedel-Crafts alkylations of aromatic compounds with (chlorinated alkyl)silanes, the alkylation of benzene with (tt>-chloroalkyl)silanes in the presence of aluminum chloride catalyst was generally affected by two factors the spacer length between the Cl and silicon and the electronic nature of substituents on the silicon atom of (w-chloroalkyl)silanes. As the spacer length between the C—Cl and silicon increases from (chloromethyl)silane to (/i-chloroethyl)silane to (/-chloropropyl)silane, the reactivity of the silanes increases. As the number of chloro-groups on the silicon decreases from (chloromethyl)trichlorosilanes to (chloromethyl)methyldichlorosilanes to (chloromethyl)trimethylsilanes, the... 

B. Jambe, Ph.D. Thesis Thermal Behavior of Poly(methyl n-alkyl silane)s (Prom J. Devaux) Louvain-la-Neuve (1997). 

To the stirring ethanol/ammonia solution, add 3.3 ml of TEOS along with the completed reaction solution from step 1, which is now the conjugate of fluorescein and APTS linked through the amino group on the alkyl silane. 

Surface functionalization of silica particles or fluorescent silica particles typically is done using functional alkyl silanes. The process may be used to add a reactive group to the surface of the particles for spontaneous coupling to biomolecules or it may be used to add the appropriate nucleophilic group to the surface, such as an amine or a carboxylate. Silane modification chemistry is discussed in more detail in Chapter 13. 

One of the reasons for the low selectivity of the mesoporous Ti silicates is their surface hydrophilicity, which is caused by the presence of a large number of surface Si-OH and Ti-OH groups. Because these mesoporous materials are better suited than TS-1 to the oxidation of large, bulky molecules, the passivation of these OH groups (e.g., by silylation) may improve catalyst activity and selectivity. Attempts have been made to reduce the concentrations of such OH groups by silylating them with various alkyl silanes (Table LI) (273). 

The reactivity series ofRF depends on the nature ofX and is I > Br > Cl. In addition, the longer the RF group and the higher the steric hindrance, the lower the yield of l.23 Further, the more hindered RF, the more dimer produced. In order to prepare tetrafluoroalkyl silanes, such fluorinated magnesians must react with alkyl silane halides as follows ... 

Stereoselective oxidation of alkyl-silanes into the corresponding alkyl-alcohols using peracids. 

Stationary phases with a high density of bonded alkyl groups can differentiate between two molecules of identical size where one is planar and the other twisted out of plane. This shape selectivity has been described by Sander and Wise [53] for polymeric stationary phases, where in the preparation, water has been added on purpose and trichloro alkyl silanes have been used. The selectivity for the retention of tetrabenzonaphthalene (TEN) and benzo[a]pyrene (BaP) was taken as a measure to differentiate between polymeric and standard RP columns. With standard ( monomeric ) RP columns, the twisted TBN elutes after the planar BaP, which on the other hand is more strongly retarded as TBN on polymeric stationary phases. In these cases the relative retention of TBN/ BaP is smaller than 1, whereas with monomeric phases the value is >1.5. The separation of the standards on three different phases is shown in Figure 2.9. These stationary phases have superior selectivity for the separation of polyaromatic hydrocarbons in environmental analysis. Tanaka et al. [54] introduced the relative retention of triphenylene (planar) and o-terphenyl (twisted), which are more easily available, as tracers for shape selectivity. However, shape selectivity is not restricted to polymeric phases, monomeric ones can also exhibit shape selectivity when a high carbon content is achieved (e.g., with RP30) and silica with a pore diameter >15 nm is used [55]. Also, stationary phases with bonded cholestane moieties can exhibit shape selectivity. 

To resolve this dilema, we propose that the polymer is interacting with the additive in the excited state, (27) perhaps via electron transfer, and that this interaction leads to the irreversible degradation of the polymer. The direct interaction of photoexcited monomeric polysilanes with halogen derivatives resulting in the cleavage of Si-Si bonds had been reported (28). In a similar fashion, we must conclude either that this interaction does not occur with the alkyl silane polymers or that it does not result in rapid polymer degradation. 

In Ref 7 316 given the temp-compn limits of spontaneous exp In for 9 alkyl silanes with air at atm press, and in Ref 8 are discussed the combustion and expln limits of several alkyl silanes at 1 atm press. The expln temp decreases in the order tetram ethyl si lane trim ethyl silane dim ethyl silane methyl-silane > vinylsilane... 

Some alkyl silanes may be considered as suitable components of liquid rocket fuels Refs l)A.Ladenburg, Ann 164, 300-332... 

RX.Schalia al, "Combustion Studies of Alkyl silanes," paper reported in the 5th Symp on Combust, ft einhold NY( IQ 55),TO 5 10(7 refs)... 

It must be mentioned that sensitive compounds, like alkyl silanes,112 alkyl stannanes113 and vinyl stannanes,114 are not affected under the conditions of the Parikh-Doering oxidation. 

Figure 10.5 Silanization reaction scheme for an alkyl silane.

Reagents A Convenient Route to sec- and tert- 6-Alkylpurines. Tetrahedron Lett. 1996, 37, 1285-1288. (c) Dvorakova, H. Dvorak, D. Holy, A. Synthesis of Acyclic Nucleotide Analogues Derived from 6-(sec- or tert-Alkyl) purines via Coupling of 6-Chloropurine Derivatives with Organocuprates. Collect. Czech. Chem. Commun. 1998, 63, 2065-2074. (d) Hocek, M. Holy, A. Perfluoroalkylation of 6-Iodopurines by Trimethyl(perfluoro-alkyl)silanes. Synthesis of 6-(Perfluoroalkyl)purine Bases, Nucleosides and Acyclic Nucleotide Analogues. Collect. Czech. Chem. Commun. 1999, 64, 229-241. 

Scheme 4.22. Alkyl silane dendrimer construction by Pt-mediated silane alkenylation and vinylation.

Silicon-Carbon Bond Energy in Polydimethylsiloxanes and Alkyl-silanes. Technol. Rep. Osaka Univ. 10, 825—831 (1960) C. A. 55, 13959a (1961). 

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