Evaluation of acidity of strong acid catalysts. 2. The strength of boron trifluoride-water systems

The method of determining a thermodynamic acidity function from the chemical shift changes of {sup 13}C signals of unsaturated ketones at infinite dilution in the investigated acid established by the authors was applied to the system boron trifluoride-water (III) ranging from the monohydrate (BF{sub...

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Bibliographic Details
Published in:Journal of catalysis 1992-03, Vol.134:1
Main Authors: Farcasiu, D., Ghenciu, A.
Format: Article
Language:English
Subjects:
ABSORPTION SPECTROSCOPY
BORON COMPOUNDS
BORON FLUORIDES
CARBON 13
CARBON ISOTOPES
CATALYSTS
CHALCOGENIDES
CHEMICAL SHIFT
DISPERSIONS
ELECTROMAGNETIC RADIATION
EVEN-ODD NUCLEI
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
ISOTOPES
KETONES
LEWIS ACIDS
LIGHT NUCLEI
MAGNETIC RESONANCE
MIXTURES
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
RADIATIONS
RESONANCE
SPECTROSCOPY
STABLE ISOTOPES
SULFUR COMPOUNDS
SULFUR OXIDES 400201 > Chemical & Physicochemical Properties
SULFUR TRIOXIDE
THERMODYNAMIC ACTIVITY
ULTRAVIOLET RADIATION
VISIBLE RADIATION
WATER
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Summary:The method of determining a thermodynamic acidity function from the chemical shift changes of {sup 13}C signals of unsaturated ketones at infinite dilution in the investigated acid established by the authors was applied to the system boron trifluoride-water (III) ranging from the monohydrate (BF{sub 3} {center dot} H{sub 2}O) to the trihydrate (BF{sub 3} {center dot} 3H{sub 2}O). The indicators used were mesityl oxide and 4-hexen-3-one. It was found that III is significantly stronger than indicated by earlier measurements conducted by the classical Hammett method based on UV-visible spectroscopy. The mixtures with about 1.25 mol of water per mol of BF{sub 3} or less are stronger than pure sulfuric acid and are therefore superacidic. The stronger acidity of III can be understood because boron trifluoride is a much stronger Lewis acid than sulfur trioxide: therefore the complex with a hydroxyl anion of the former (hydroxytrifluoroborate anion) should have a lower affinity for a hydron than the corresponding complex of sulfuric anhydride (bisulfate anion). Preliminary experiments indicate that the {sup 13}C NMR method can be applied successfully to working catalysts based on III, which are colored and contain dissolved organic materials.
ISSN:0021-9517
1090-2694