Alkylsilanes methylation

Figure C3.2.4. Plot of the log of photocurrent against number of methyl units in a alkylsilane based monolayer self-assembled on a n silicon electrode. The electrode is immersed in a solution witli an electron donor. Best fits of experimental data collected at different light intensities ( ) 0.3 mW cm ( ) 0.05 mW cm. From [10].

CYCLOPENTANONES FROM CARBOXYLIC ACIDS VIA INTRAMOLECULAR ACYLATION OF ALKYLSILANES Z-METHYL-2-VINYLCYCLOPENTANOHE (Cyclopentanone, 2-ethenyl-2-methyl-)... 

Acid catalysis—hydrolysis. Several series of alkylsilane esters were studied to determine the effect of silane structure on the hydronium ion catalyzed hydrolysis reaction. The hydronium ion catalyzed hydrolysis rate constants for a series of alkyl tris-(2-methoxyethoxy)silanes in aqueous solution were used to define the modified Taft equation log(A /Ah ) = 0.39a + 1.06ES, where Ho is the rate of hydrolysis for methyl tris-2-(methoxyethoxy)silane [42], The hydronium ion catalyzed hydrolysis rate constants and the reaction half-lives are reported in Table 2. In a similar manner, the hydronium ion catalyzed hydrolysis rate constants for a series of trialkylalkoxysilanes in 55% aqueous acetone were used to obtain the modified Taft equation log(/cH//cHo) = -0.37 a + 2.48 E where kHo is the rate of hydrolysis for trimethylalkoxy-silane. 

In Ref 7 are given the temp-compn limits of spontaneous expln for 9 alkylsilanes with air at atm press, and in Ref 8 are discussed the combustion and expln limits of several alkylsilanes at 1 atm press. The expln temp decreases in the order tetramethylsilane tfimethyl Silane dim ethyl silane methyl-silane > vinyisiiane... 

Kuwajima, I. Urabe, H. Cyclopentanones from carboxylic adds via intramolecular acylation of alkylsilanes 2-methyl-2-vinylcyclopen-tanone. Org. Synth. 1993, Coll. Vol. VIII, 486-490. 

Stationary phase technology has also seen significant improvements over the past years. The silica base material is nowadays often a hybrid material, synthesized from tetraalkoxysilanes and functionalized trialkoxysilanes, for example, methyl-trimethoxysilane (MTMS). The introduction of alkyl-trialkoxysilanes into the silica backbone makes the material more resistant to hydrolytic attack and also improves their separation behavior for basic analytes.30 C18 (= octadecylsilane) stationary phases are still the materials typically used in environmental analysis, and the enormous choice of materials with gradually different properties allows columns to be selected that are particularly well suited to a given separation task.31 Reversed phase separations with materials of shorter alkylsilane chain length (C8, C4, and Cl) are less frequently used. 

If two manufacturers use the same silica, the same silica preparation, and the same monochlorosilane reaction, there could still be a difference, if one manufacturer does a second bonding reaction and one does not. Since the primary reaction with the original alkylsilane (e.g., monochlorooctadecyidi-methyl silane) cannot cover 100% of the surface silanols owing to steric... 

The same reaction proceeds at RT when catalyzed by methyl radicals to afford B H in 67% yield. Similar conversions of B-halide bonds to B—H bonds are available from reactions of trichloroborane with disilane or alkylsilanes. ... 

The disproportionation (or alkyl exchange) and the alkylation reactions of alkylsilanes have been carried out in a closed recirculation reactor at 373 - 623 K and 373 - 473 K, respectively, by using 100 - 200 mg of catalysts. For the disproportionation reaction, 30 Torr of diethylsilane (E2), diethyidimethylsilane (E2M2), and triethylsilane (E3) were used. For the alkylation reaction, 30 Torr of E2 and 30 Torr of alkylating reagents (propene, 1- and c/s-2-butene, 2-methyl-1-butene, 1,3-butadiene, methylacetylene, ethylacetylene) were used. Cyclic olefins, nitriles, benzene and carbonyl compounds were also tested. 

Fig. 17 Generalized bonding reaction for derivatization of silica surface by alkylsilanes. X = leaving group. R and R are any desired functionalities R is typically methyl, and R is C8, C18, etc.

We have stndied the macroscopic frictional properties of high-density polymer brushes prepared by surface-initialed ATRP of methyl methacrylate (MM A) [31] and hydrophilic methacrylates [32, 33] from silicon substrates. Friction tests were carried out using a stainless steel or glass ball as the sliding probe under a normal load of 100 MPa from the viewpoint of practical engineering applications. This chapter reviews the macroscopic frictional properties of polymer brushes under a high normal load, the dependence of solvent qnaUty, the effect of humidity on hydrophilic brnsh, and wear resistance, and we compare these with alkylsilane monolayers. 

Hydrometalation. The hydrosilylation of alkenes, 1,3-dienes, and 1,4-diene may be realized by Pd(PhCN)2Cl2 with PPhs as the ligand (eqs 118-122). For terminal alkenes, only 2-alkylsilanes were afforded (eq 118). For 2-methyl or 2,3-dimethyl buta-1,3-dienes, a mixture of 1,2- or 1,4-addition products were formed (eq 119). For 2-substituted or 1,2-disubstituted buta-1,3-dienes, 1,4-additon products were generated highly selectively (eq 120). The reaction of cyclopentadiene with HSiCls afforded 2-cyclopentyl trichlorosilane (eq 121), while those of eye lohexa-1,3-diene or cyclohexa-1,4-diene afforded a mixture of trichloro(cyclohex-2-enyl)silane and trichloro(cyclohex-3-enyl)silane (eq 122). 

---