How Interfaces Affect the Acidity of the Anilinium Ion
Jarukorn Sripradite1,2,3, Susannah A Miller2, Michael D Johnson4
1School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|February 17, 2016
Summary
The acidity (pKa) of anilinium ions decreases slightly at oil-surfactant-water interfaces within reverse micelles. This study quantifies the impact of these interfaces on molecular properties, crucial for understanding interfacial phenomena.
Area of Science:
- Physical Chemistry
- Supramolecular Chemistry
- Interfacial Science
Background:
- Acidity is key to molecular behavior in solution.
- Interfacial acidity measurements are rare, often assumed negligible.
- Reverse micelles offer a model for studying interfacial effects.
Purpose of the Study:
- To measure the effect of oil-surfactant-water interfaces on anilinium ion pKa.
- To investigate how reverse micelle size influences acidity.
- To understand molecular positioning at hydrophilic-hydrophobic interfaces.
Main Methods:
- Titrations by Nuclear Magnetic Resonance (NMR) spectroscopy.
- Varying bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane reverse micelle size (w(0)).
- Nuclear Overhauser Effect SpectroscopY (NOSEY) and dynamic light scattering (DLS).
Main Results:
- Anilinium ion pKa decreased from 4.85±0.02 to 4.62±0.02 as micelle size reduced.
- Aniline moiety localized at the surfactant interface, amine/ammonium in the waterpool.
- Aniline presence had a modest, variable effect on micelle size.
Conclusions:
- Interfacial environments, like reverse micelles, significantly affect molecular acidity.
- The positioning of molecules at interfaces influences their chemical properties.
- Results provide data for theoretical studies on interface phenomena.
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