An efficient catalytic route for the preparation of silyl ethers using alumina-supported heteropolyoxometalates (original) (raw)
Related papers
Chemcatchem, 2013
The preparation of 1-(3-triisopropoxysilylpropyl)-3-(2-methoxyethyl)imidazolium bromide or chloride salts and their reaction with [Rh(COD)(µ-OMe)]2 (COD = 1,5-cyclooctadiene) to afford the corresponding [Rh(COD)(NHC)X] (X = Br, Cl) (NHC = 1-(3triisopropoxysilylpropyl)-3-(2-methoxyethyl)-2-ilydene-imidazol) species is described. These new compounds were used as catalysts precursors for acetophenone hydrosilylation. The higher activity of the rhodium-chlorido complex evidences a clear halide effect in the activation of the catalyst. Immobilization of the catalytic precursor [Rh(COD)(NHC)Cl] on MCM-41 allows the preparation of the corresponding heterogeneous catalyst. Reduction of acetophenone to PhMeCH-O-SiMe(OSiMe3)2 by hydrosilylation with 1,1,1,3,5,5,5heptamethyltrisiloxane is effectively catalysed by both the homogeneous and the heterogeneous catalysts, being the homogenous system more active. Interestingly, the heterogeneous catalyst is reusable. Both homo-and heterogeneous catalysts are also effective for the copolymerization of terephthalaldehyde and 1,1,3,3,5,5-hexamethyltrisiloxane affording the corresponding poly(silyl ether), yielding the heterogeneous system polymers with higher molecular weights (Mw = 94.000) and a narrow molecular weight distribution (PDI = 1.5-1.7).
Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 2012
The protection of alcohols with hexamethyldisilazane (HMDS) in the presence of P 2 O 5 /SiO 2 at very mild and ambient condition with short reaction times is accomplished in excellent yields. P 2 O 5 /SiO 2 catalyst is an efficient solid acid and heterogeneous catalyst for this transformation and easily recovered and reused for several times without significant decrease in its activity. Selectivity studies showed competitive reaction of primary alcohols over secondary alcohols and phenols.
Catalysis Science & Technology, 2014
The new rhodium(I) complexes [Rh(Cl)(COD)(R-NHC-(CH 2 ) 3 Si(O i Pr 3 ) 3 )] (R = 2,6-diisopropylphenyl (2a); n-butyl (2b)) have been synthesised and fully characterised. The study of their application as ketone hydrosilylation catalysts showed a clear N-substituent effect, 2a being the most active catalyst precursor. Complex 2a has been immobilised in the mesoporous materials MCM-41 and KIT-6. The new hybrid materials have been fully characterised and used as catalyst precursors for the preparation of poly(silyl ether)s by catalytic hydrosilylation. The heterogeneous catalytic systems based on the materials 2a-MCM-41 and 2a-KIT-6 afford polymers with high average molecular weight (M w ) M w = 2.61 × 10 6 g mol −1 (2a-MCM-41) and M w = 4.43 × 10 5 g mol −1 (2a-KIT-6).
Materials Research Bulletin, 2016
Mesoporous silica materials (SBA-15 and MCF) were used as catalytic supports for the deposition of aggregated alumina species using the method consisting of the following steps: (i) anchoring 3-(mercaptopropyl)trimethoxysilane (MPTMS) on the silica surface followed by (ii) oxidation of À ÀSH toÀ ÀSO 3 H groups and then (iii) deposition of aluminum Keggin oligocations by ion-exchange method and (iv) calcination. The obtained samples were tested as catalysts for synthesis of dimethyl ether from methanol. The modified silicas were characterized with respect to the ordering of their porous structure (XRD), textural properties (BET), chemical composition (EDS, CHNS), structure (27 Al NMR, FTIR) and location of alumina species (EDX-TEM), surface acidity (NH 3-TPD, Py-FTIR) and thermal stability (TGA). The obtained materials were found to be active and selective catalysts for methanol dehydration to dimethyl ether (DME) in the MTD process (methanol-to-dimethyl ether).
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008
The direct incorporation of Keggin-type heteropolyacid H 3 PW 12 O 40 (PW) in a mesoporous organized silica molecular sieve during the synthesis was studied. The synthesis of silica-organized materials containing heteropolyacid was carried out in acidic media either by associating a nonionic/cationic surfactants or just a non-ionic surfactant. The decomposition temperature of solids containing PW and prepared with TX100/CTMA, Tergitol 15-S-12 and Tween 60 starts at 130, 115 and 135 • C, respectively. The BET surface area of these solids is measured to be 892, 735 and 787 m 2 /g, respectively. Their pore diameters are equal to 31, 24 and 34Å, respectively.
RSC Advances, 2021
The oxide system TiO 2-SiO 2 as well as a TiO 2-SiO 2 /lignin system have been obtained by the sol-gel synthesis method and applied as supports in Supported Ionic Liquid Phase (SILP) materials. In total 24 SILP systems were obtained with ionic liquids containing imidazolium, pyridinium, phosphonium or sulfonic cations and bis(trifluoromethylsulfonyl)imide or methylsulfate anions, and homogeneous complexes of rhodium or platinum as the active phase. The supports and catalytic materials were subjected to thorough characterization by elemental analysis, XRD, SEM-EDX, IR, and TGA, and their particle size distribution and porous properties were assessed. The new SILP materials were used in hydrosilylation of 1-octene with 1,1,1,3,5,5,5-heptamethyltrisiloxane. The effectiveness of hydrosilylation reaction catalyzed by the obtained SILP materials for the polar and nonpolar reagents was assessed. All the catalytically active materials were proved to be easy to isolate and reuse, and the best SILP systems have been shown to be active in 10 or more subsequent catalytic cycles.
Silica-supported heteropolyacids as catalysts in alcohol dehydration reactions
Journal of Molecular Catalysis A: Chemical, 2000
Catalysts based on Keggin-type heteropolyacids supported on silica were prepared for their use in dehydration of alcohols in liquid phase. Species present in the catalysts were characterized by diverse physicochemical techniques, disclosing that both molybdophosphoric and tungstophosphoric acids are found with their primary Keggin structure intact. Their catalytic behavior was studied in the dehydration of alcohol of interest for the production of intermediary compounds for fine Ž . chemical industries. Specifically, the dehydration of 1,2-diphenylethanol, 1-3,4-dimethoxyphenyl -2-phenylethanol and cholesterol was studied. It was obtained a process for the direct dehydration of cholesterol. It was found that the catalysts are very active and selective, also allowing an easy separation from the reaction medium. The same catalysts were used several times without appreciable loss of catalytic activity and after the reaction they showed physicochemical properties similar to those of the original catalysts. q
Canadian Journal of Chemistry, 2008
A highly efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, benzylic, secondary, hindered secondary, tertiary, phenols, and oximes with hexamethyldisilazane (HMDS), using Al(H2PO4)3 as a recyclable heterogeneous catalyst at room temperature in a few minutes with excellent yields under solvent-free conditions is described.Key words: trimethylsilylation, hexamethyldisilazane, aluminum tris(dihydrogen phosphate) [Al(H2PO4)3], solvent-free, hydroxyl groups.