Silane selection

Silica gel modified with 3-mercaptopropyltrimethoxy silane Selective separation and preconcentration of selenite [Se(IV)] from aqueous solutions containing Se(IV) and Se(Vl) [63]... 

This book chapter is limited to Lewis acid-mediated reactions, and does not discuss the important field of Lewis base-mediated allylations, nor does it describe the reactions of allylsilanes with other electrophiles such as epoxides, imines, and allyl-X (X = -Cl, -OR, -OAc). The SaJcurai reaction has been covered under different forms in reviews focusing on The Stereochemistry of the Sakurai reaction , Intramolecular Addition Reactions of Allylic and Propargylic Silanes ," Selective Reactions Using Allylic Metals , Catalytic Enantioselective Addition of Allylic Organometallic Reagents to Aldehydes and Ketones , and Modem Carbonyl Chemistry . ... 

There are many versions of clays (hydrated aluminum silicate) available including soft clay, hard clay, air floated, water washed, calcined, and surface-treated versions. Surface treatments include stearates, mercapto-silane, vinyl silane, and amino silane. Select the silane treatment that is compatible with the cure system to be used. Clay may be used in large quantities, is inexpensive, easy to incorporate, calender or extrude and provides some reinforcement to NBR compounds. 

Anotlier important modification metliod is tire passivation of tire external crystallite surface, which may improve perfonnance in shape selective catalysis (see C2.12.7). Treatment of zeolites witli alkoxysilanes, SiCl or silane, and subsequent hydrolysis or poisoning witli bulky bases, organophosphoms compounds and arylsilanes have been used for tliis purjDose [39]. In some cases, tire improved perfonnance was, however, not related to tire masking of unselective active sites on tire outer surface but ratlier to a narrowing of tire pore diameters due to silica deposits. 

These examples show that silane reacts selectively with the y-position of aHyl compounds. However, ia its reaction with aHyl amine, a side reaction ia which silane biads to the -position takes place (40). 

ALLOYS, PURE silicon) and in epitaxial siUcon deposition (see Electronic materials Integrated circuits Semiconductors) as selective reducing agents as monomers and as elastomer intermediates (see Elastomers, SYNTHETIC). Not least is the use of these materials as intermediates for production of other silanes and sihcones. 

The physical and thermodynamic properties of silane in the context of semiconductor appHcations have been reviewed in detail (8). Tabulations of properties of various silanes in the context of inorganic chemistry have also been pubHshed (9). Table 1 contains selected physical properties of inorganic silanes. 

In choosing a SAM system for surface engineering, there are several options. Silane monolayers on hydroxylated surfaces are an option where transparent or nonconductive systems are needed. However, trichlorosilane compounds are moisture-sensitive and polymeri2e in solution. The resulting polymers contaminate the monolayer surface, which occasionally has to be cleaned mechanically. CarboxyUc acids adsorb on metal oxide, eg, AI2O2, AgO through acid—base interactions. These are not specific therefore, it would be impossible to adsorb a carboxyUc acid selectively in the presence of, for example, a terminal phosphonic acid group. In many studies SAMs of thiolates on Au(lll) are the system of choice. 

A teehnique that is a convenient source of radieals for study by EPR involves photolysis of a mixture of di-t-butyl peroxide, triethylsilane, and the alkyl bromide corresponding to the radieal to be studied. Photolysis of the peroxide gives t-butoxy radieals, whieh selectively abstract hydrogen from the silane. This reactive silicon radieal in turn abstracts bromine, generating the alkyl radieal at a steady-state eoncentration suitable for EPR study. 

Eigure 3.3 shows the calibration plots for Zorbax PSM columns. (The calibration plots for silanized and unsilanized columns are comparable.) These calibration plots allow the chromatographer to select the appropriate columns for samples. Eor example, the Zorbax PSM 60 column provides resolution of... 

Allyl(trimethyl)silanes react efficiently with Lewis acids to give the corresponding tertiary alcohols67. Although only modest diastereofacial selectivity was observed for reaction with menthyl esters67, improved selectivity was found for chiral a-oxo imides68 and a-oxo amides derived from proline69. 

When the chain bearing the allylsilane is one carbon longer, i.e., by the use of pentenylsilanes, cycloheptane rings can be formed. Both the (Z)- and (A )-isoiner of the (3-pentenyl)silanes can be synthesized selectively, but only the (Z)-(3-pentenyl)silane cyclized stereospecifically (complete 1,4-asymmetric induction). Both cthylaluminum dichloride and boron trifluoride diethyl ether complex promote the seven-membered ring formation35 43-48. 

The structurally simplest silicon reagent that has been used to reduce sulphoxides is the carbene analog, dimethylsilylene (Me2Si )29. This molecule was used as a mechanistic probe and did not appear to be useful synthetically. Other silanes that have been used to reduce sulphoxides include iodotrimethylsilane, which is selective but unstable, and chlorotrimethylsilane in the presence of sodium iodide, which is easy to use, but is unselective since it cleaves esters, lactones and ethers it also converts alcohols into iodides. To circumvent these complications, Olah30 has developed the use of methyltrichlorosilane, again in the presence of sodium iodide, in dry acetonitrile (equation 8). A standard range of sulphoxides was reduced under mild conditions, with yields between 80 and 95% and with a simple workup process. The mechanism for the reaction is probably very similar to that given in equation (6), if the tricoordinate boron atoms in this reaction scheme are replaced... 

Silanes And Base. In the presence of bases, certain silanes can selectively reduce carbonyls. Epoxy-ketones are reduced to epoxy-alcohols, for example with (MeO)3SiH and LiOMe. ° Controlling temperature and solvent leads to different ratios of syn- and anti- products.Silanes reduce ketones in the presence of BF3-OEt2 ° and transition metal compounds catalyze this reduction. ... 

Some reductions with silanes have already been described in previous chapters (in Section 4.8 reaction of 356 to give 359 in Section 5.4 reaction of 121 to give 717, 718 to 719 in Section 12.1 reaction of 1790 to give 1791). Because of the many applications of such reductions with silanes in the chemical literature only a selected number of examples can be given in this chapter. 

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