Superoxide protonation by weak acids in imidazolium based ionic liquids

Area of Science:

• Electrochemistry
• Physical Chemistry
• Organic Chemistry

Background:

• Superoxide anion is a key reactive oxygen species.
• Understanding its reactivity with phenols is crucial in various chemical and biological processes.
• Ionic liquids offer unique solvent properties for studying such reactions.

Purpose of the Study:

• To investigate the reactivity of superoxide anion with substituted phenols.
• To compare this reactivity in an ionic liquid ([BMIm][TFSI]) versus a conventional solvent (DMF).
• To elucidate the reaction mechanism and influence of phenol structure and solvent on reactivity.

Main Methods:

• Cyclic voltammetry was employed to study the electrochemical behavior.
• Reactions were conducted in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm][TFSI]) and dimethylformamide (DMF).
• Identification of reaction intermediates (phenolates) via oxidation potentials.

Main Results:

• A consistent 2-electron reduction mechanism for O2 in the presence of phenols was observed in both media.
• Phenolate intermediates were identified, confirming the reaction pathway.
• Slight differences in phenol reactivity were noted between the ionic liquid and DMF.
• Superoxide protonation by phenols was confirmed as an uphill reaction, facilitated by electron transfer.

Conclusions:

• The reaction mechanism of superoxide with phenols is largely conserved across ionic liquids and DMF.
• Phenol substituents and solvent properties subtly modulate superoxide reactivity.
• The study provides insights into the fundamental reaction kinetics and thermodynamics involving superoxide and phenolic compounds.