Trimethylethoxysilane liquid-phase hydrolysis equilibrium and dimerization kinetics: catalyst, non-ideal mixing, and the condensation route

S E Rankin, J Sefcik, A V McCormick

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

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 Si-29 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.

LanguageEnglish
Pages4233-4241
Number of pages9
JournalJournal of Physical Chemistry A
Volume103
Issue number21
DOIs
Publication statusPublished - 27 May 1999

Fingerprint

Dimerization
dimerization
hydrolysis
Condensation
Hydrolysis
liquid phases
condensation
routes
catalysts
Deprotonation
Catalysts
Kinetics
kinetics
Liquids
monomers
Monomers
Silicates
silicates
reaction kinetics
ethyl alcohol

Keywords

  • organoethoxysilane hydrolytic (poly)condensation
  • trimethylethoxysilane
  • acidic silanol
  • catalyst activity

Cite this

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abstract = "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 Si-29 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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Trimethylethoxysilane liquid-phase hydrolysis equilibrium and dimerization kinetics : catalyst, non-ideal mixing, and the condensation route. / Rankin, S E ; Sefcik, J ; McCormick, A V .

In: Journal of Physical Chemistry A, Vol. 103, No. 21, 27.05.1999, p. 4233-4241.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Trimethylethoxysilane liquid-phase hydrolysis equilibrium and dimerization kinetics

T2 - Journal of Physical Chemistry A

AU - Rankin, S E

AU - Sefcik, J

AU - McCormick, A V

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Y1 - 1999/5/27

N2 - 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 Si-29 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.

AB - 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 Si-29 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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