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Abstract The Katritzky reaction in bulk solution at room temperature is accelerated significantly by the surface of a glass container compared to a plastic container. Remarkably, the reaction rate is increased by more than two orders of magnitude upon the addition of glass particles with the rate increasing linearly with increasing amounts of glass. A similar phenomenon is observed when glass particles are added to levitated droplets, where large acceleration factors are seen. Evidence shows that glass acts as a “green” heterogeneous catalyst: it participates as a base in the deprotonation step and is recovered unchanged from the reaction mixture. Reaction acceleration at two separate interfaces is recognized in this study: i) air/solution phase acceleration, as is well known in microdroplets; ii) solid/solution phase, where such acceleration appears to be a new phenomenon.
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Reaction acceleration at air‐solution interfaces: Anisotropic rate constants for Katritzky transamination
Abstract To disentangle the factors controlling the rates of accelerated reactions in droplets, we used mass spectrometry to study the Katritzky transamination in levitated Leidenfrost droplets of different yet constant volumes over a range of concentrations while holding concentration constant by adding back the evaporated solvent. The set of concentration and droplet volume data indicates that the reaction rate in the surface region is much higher than that in the interior. These same effects of concentration and volume were also seen in bulk solutions. Three pyrylium reagents with different surface activity showed differences in transamination reactivity. The conclusion is drawn that reactions with surface‐active reactants are subject to greater acceleration, as seen particularly at lower concentrations in systems of higher surface‐to‐volume ratios. These results highlight the key role that air‐solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction‐increased rate constant is at least in part due to limited solvation of reagents at the interface.
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- Award ID(s):
- 1905087
- PAR ID:
- 10452881
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Mass Spectrometry
- Volume:
- 56
- Issue:
- 4
- ISSN:
- 1076-5174
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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