Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

Abstract

13C NMR spectra and relaxation parameters (T 1 H, T 1 C, T 1 ρ H, T CH) were measured via CP-MAS and DP-MAS techniques as a function of acetone loading level in acetone/SiO2 samples at 25 °C. T 1 H and T 1 ρ H values were also measured via 29Si CP-MAS experiments. Peak positions and relaxation parameters are averaged by rapid exchange between different acetone interaction sites on the surface. The data were analyzed in terms of a surface equilibrium of adsorbed acetone units between hydrogen-bonding and non-hydrogen-bonding sites. Data analysis by this model yielded the surface concentration of hydrogen-bonding (silanol) sites (1.5 nm-2) and the equilibrium constant (K = 3.0 nm2). Variable-temperature experiments (124−297 K) at three loading levels yielded values of ΔH° (−5.8 ± 0.3 kJ mol-1) and ΔS° (−12.5 ± 0.7 J K-1 mol-1). A self-consistent, qualitative interpretation of measured relaxation parameters is made in terms of the relative mobilities of hydrogen-bonded (less mobile) and non-hydrogen-bonded (more mobile) acetone on the SiO2 surface.

Substrate inhibition in the heterogeneous catalyzed aldol condensation: A mechanistic study of supported organocatalysts

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Multitasking mesoporous nanomaterials for biorefinery applications

“…The role of silanols in the reaction can be explained by the fact that carbonyl compounds adsorb on the surface of silica via hydrogen bonding. [26,[51][52][53][54][55][56] We confirmed this interaction by measuring NMR spectrum of 13 C-labeled acetone set in contact with non-functionalized MSN ( Figure S6), which exhibited a downfield shift of the carbonyl carbon signal compared to that of neat acetone (~213 ppm versus 206 ppm). Our earlier solid-state NMR and theoretical studies demonstrated that surface silanols on silica also interact with the amine functionalities.…”

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