Zum Kondensationsverhalten von Silanolen. VII. Zur Reaktion von Silanolen mit Alkoxysilanen

Spitzner, H.; Wandschneider, Silke; Lange, D.; Kelling, H.

doi:10.1002/prac.19963380172

Cited by 7 publications

(2 citation statements)

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“…We are encouraged in this conclusion because Assink and Kay 23 found the same thing to be true in low-water tetraethoxysilane condensation. Kelling and coworkers 17 have reported that the rate of acid-catalyzed methanol-producing condensation of trimethylsilanols competes with that of water-producing condensation. However, if the rate coefficient for ethanol-producing condensation is over an order of magnitude lower than methanolproducing condensation (as it is under basic conditions 17 ), waterproducing condensation could indeed be dominant, as we have observed.…”

Section: Resultsmentioning

confidence: 99%

“…Kelling and coworkers studied in detail the kinetic behavior of organodimethylsilanols in dioxane/water and toluene/water. − They report, for instance, that triorganosilanol dimerization is second order with respect to silanol concentration with acid and first-order with respect to silanol concentration with base, and that condensation is usually first-order with respect to catalyst concentration. However, they consider conditions unusual for sol-gel processing (specifically, dioxane or toluene as solvent), and the characterization technique (gas chromatography) is invasive.…”

Section: Introductionmentioning

confidence: 99%

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Trimethylethoxysilane Liquid-Phase Hydrolysis Equilibrium and Dimerization Kinetics: Catalyst, Nonideal Mixing, and the Condensation Route

1999

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Although the kinetics of organoethoxysilane hydrolytic (poly)condensation have been studied under kinetically simplified conditions, materials are actually synthesized from nonideal mixtures with high monomer and catalyst concentrations. Using 29 Si nuclear magnetic resonance, we study the hydrolysis of trimethylethoxysilane and the dimerization of the resulting silanol in aqueous ethanol at monomer and catalyst concentrations typical of organically modified silicate synthesis. Under acidic conditions, we find that when (and only when) the effects of solvent composition on catalyst activity are considered, it becomes clear that water-producing condensation is the dominant dimerization route. Under basic conditions, the extent of deprotonation of the weakly acidic silanol passes through a minimum during reaction, thereby producing an anomolous trend in reaction rate. This necessitates a kinetic model which is first order in both silanol and deprotonated silanol and which accounts for changing deprotonation.

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Section: Resultsmentioning

confidence: 99%