Charge-enhanced acidity and catalyst activation

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Catalysis

Background:

• Acidities are typically measured in polar solvents, posing challenges for reactions in nonpolar media.
• Catalytic reactions often require nonpolar solvents, necessitating methods to determine acidity in these environments.

Purpose of the Study:

• To determine relative acidities of phenols in nonpolar solvents.
• To investigate methods for enhancing Brønsted acidity and catalyst performance in nonpolar media.

Main Methods:

• Infrared (IR) spectroscopy was used to measure the relative acidities of phenols.
• Phenols were analyzed in both pure CCl4 and a 1% CD3CN/CCl4 mixture.

Main Results:

• Relative acidities of phenols in nonpolar solvents were successfully determined using IR spectra.
• The introduction of nonprotonated charged substituents with a suitable counterion dramatically increased Brønsted acidity.
• Catalyst performance was enhanced by orders of magnitude due to these modified acidities.

Conclusions:

• Infrared spectroscopy in CCl4 and CD3CN/CCl4 mixtures provides a viable method for assessing relative acidities in nonpolar solvents.
• Nonprotonated charged substituents are effective in significantly enhancing Brønsted acidity.
• This enhancement of acidity leads to substantial improvements in catalyst performance for reactions in nonpolar media.