Phenyl silicate

Here the phenyl silicate represents a compound of an acidic alcohol with a nonacidic acid. Considerations such as these have led to the term ether as a more correct name from the standpoint of organic chemistry, and yet not all the carbon ethers hydrolyze as readily as do these silicon analogs. The names tetraethoxysilane and tetra-phenoxysilane would be more correct, although unwieldy. 

A range of m- and p-phenylenebis[trifluoro(phenyl)silicates] result from the... 

Zhao and Brittain [280-282] reported the LCSIP of styrene on planar silicon wafers using surface modifications of 2-(4-(ll-triethoxysilylundecyl)phenyl-2-methoxy-propane or 2-(4-trichlorosilylphenyl)-2-methoxy-d3-propane respectively. Growth of PS brushes from these SAMs has been successfully achieved factors that influence PS thickness included solvent polarity, additives and TiC concentration. Sequential polymerization by monomer addition to the same silicate substrate bearing the Hving polymer chains resulted in thicker PS films. FTIR-ATR studies using a deuterated initiator indicated that the initiator efficiency is low, and the... 

From the X-ray diffraction data and the calculated sizes of the dye molecules, the conformation of the dye molecules in the interlayer was briefly estimated. Fig. 1 shows the conformation of the dyes, in which the xanthene nucleus of pyronine or rhodamine was positioned parallel, and the phenyl group of rhodamine perpendicular, to the silicate layers of the clay. 

Lastly, Polystyrene (PS) brushes on silicate substrates were grafted via carbocationic polymerization from self-assembled monolayer (SAM) initiators as reported by Brittain et al The carbocationic initiators, 2-(4-(ll-triethoxysilylundecyl))phenyl-2-methoxypropane and 2-(4-trichlorosilyl-phenyl)-2-methoxy-d3-propane, and their corresponding SAMs were prepared on various substrates. The monolayers were characterized by FTIR-ATR, contact angles, and X-ray reflectometry. The growth of the PS brushes from... 

Mowery and DeShong used the commercially available hypervalent silicate complex TBAT as a phenylating agent for the cross-coupling reaction with allylic esters. They later reported on the use of the same organosilane for the coupling with aryl iodides and triflates and electron-deficient aryl bromides. The reactions were catalyzed by either Pd(dba)2 or [Pd(allyl)Cl]2 without the need of added phosphine ligands. 

Phenyl-functionalized silicate mesophases with hexagonal or cubic symmetries influence of synthesis parameters. 

Organically modified porous silicates have been prepared under acidic conditions, by direct reaction of a mixture of phenyltriethoxysilane (PTES) and tetraethoxysilane (TEOS), and an aqueous solution of cetyltrimethylammonium bromide (CTAB). For a 1 4 molar ratio between PTES and TEOS, the hexagonal (2d, p6m) phase, but also a cubic phase analogous to the already reported SBA-1 phase (Pm3n), can be prepared. The surfactant can then be efficiently removed by calcination at 350°C, leading to phenyl-functionalized microporous silicates with two types of architecture. The influence of several parameters (PTES/TEOS ratio ethanol content) that affect the organization of the samples, will be discussed. 

Most of the one-pot syntheses of organically functionalized mesoporous silicates have been done under basic conditions. Only hexagonal phases (2d, p6m) were reported so far, except one very recent example of a phenyl-functionalized cubic phase [17], analogous to the bicontinuous MCM-48 phase (la3d) [8]. The cubic phase prepared under acidic conditions from PTES and TEOS is indeed related to a different type of cubic mesophases, micellar mesophases, reported in the literature for various surfactant/solvent systems [23] as well as for lipid-containing systems [24]. 

Two procedures have been used to prepare phenyl-functionalized silicate mesophase under acidic conditions. The only difference between them, is the pre-hydrolysis step, which was added in preparation B to initiate the hydrolysis and condensation reactions of the two precursors, prior to reaction with the CTAB solution. This step may cause the formation of co-condensed species between PTES and TEOS, and thus prevent phase separation [25],... 

Figure 1. X-ray diffraction patterns of the as-synthesized phenyl-functionalized silicate mesophases obtained from preparations A (a) and B (b) (PTES/TEOS = 1 4). Data recorded with synchrotron radiation (X = 1.2836 A).

The results obtained in the present study are summarized in Table 1. The amount of phenyl groups introduced in the silicate framework and the nature and amount of alcohol present in the reaction mixture play a major role in the formation of the cubic versus hexagonal phase. 

These micellar cubic mesophases require large surface curvature and low charge density. Their formation is thus favored by the use of surfactant molecules with large polar head group, and acidic conditions under which the charge density at the silicate/surfactant is always limited. The fact that this phase can be prepared with CTAB when PTES is present, suggests the existence of specific interactions between the phenyl groups and the polar head of the surfactant molecules. It was indeed reported that benzene molecules are preferably located at the hydrophilic-hydrophobic interface [29]. 

Phenyl-functionalized Silicate Mesophases with Hexagonal or Cubic Symmetries 287... 

Silicate (Pentafluoro-phenyl)-letrafluoro- ElOb,. 427 (F.dnct)... 

In all the isomerization reactions carried out in heterogeneous conditions, the nature of the products and product ratio depended largely on the type of catalyst employed, and, moreover, in most of the cases no selectivity was found. Papers have recently appeared concerning the transformation of styrene oxide into phenyl acetaldehyde catalyzed by a series of natural silicates and amorphous silica-alumina (ref. 15) and by pentasil type zeolites (ref. 16). It is said that, in both cases, isomerization occurs on the acidic sites (si lands) of the external surface, which act as active centers even under mild experimental conditions. 

Our interest in silane coupling agents and in the preparation of silicates has led us to study the mechanisms involved in the various reactions. In a previous paper, we investigated the kinetics and mechanism of the alcoholysis of TMOS [13]. This present work studies the effects of changing the substituents on a para-substituted phenyl attached directly to the alkoxysilane. The alkoxysilane silanes used have only one alkoxy group present to eliminate complications from a competing second or third alcoholysis reaction. The resulting Hammett plot yields additional information on the mechanism of this reaction. 

The kinetics of the acid catalyzed hydrolysis of ethoxysilanes has been studied. Each of the silanes that were used had a phenyl or para-substituted phenyl group attached to the silicon atom. This permitted a study of the linear free energy relationships of this reaction. The reaction is of interest because of its role in silane coupling agent chemistry, in the preparation of zinc-rich silicate coatings, in the sol-gel process and in the preparation of silicones in general. 

The zwitterion X5-spirosilicate bis[2,3-naphthalendiolato][2-(dimethylammonio)phe-nyl]silicate (56 isolated as 57 = 56-1/2 MeCN) was synthesized by reaction of [2-(dimethylamino)phenyl]dimethoxyorganosilanes with 2,3-dihydroxynaphthalene in acetonitrile at room temperature. Reaction of 57 or of [2-(dimethylamino)phenyl]trimetho-xysilane with water in acetonitrile yielded the cage-like silasesquioxane 58 (R = 2 — Me2NCgH4). The crystal structures of 57 and 58 were studied by X-ray diffraction. In addition, 57 and 58 were characterized by solid-state 29Si CPMAS NMR142 (Figure 34). 

Lithiation of l-bromo-4-trisubstituted silylbuta-1,3-diene derivatives with r-BuLi has afforded substituted siloles (35) in high yields (e.g. Scheme 17).93 A pentaorgano-silicate has been proposed to be the intermediate for this reaction. Selective cleavage was observed when the silyl group possessed different substituents. Results have shown that vinyl and phenyl substituents on the silicon atom were substituted much... 

Chromatographic System (See Chromatography, Appendix IIA.) Use a gas chromatograph equipped with a flame-ionization detector, and containing a 2.4-m x 4-mm (id) boro-silicate glass column, or equivalent, packed with 2% liquid phase, 5% phenyl methyl silicone on 80- to 100-mesh support (Supelcoport, or equivalent). Maintain the column isother-mally at a temperature between 270° and 280°, and the injection port and detector block at about 310°. Use helium as the carrier gas at a flow rate of about 70 mL/min. 

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