Enhancement of Esterification Reaction Rates in Solvent-Free Aerosol Droplets.

Area of Science:

• Chemical Kinetics
• Physical Chemistry
• Aerosol Science

Background:

• Aerosols offer high surface area-to-volume ratios and supersaturated states, ideal for accelerating chemical reactions.
• Previous studies using electrospray ionization-mass spectrometry lacked control over droplet parameters and reversibility.
• Bulk esterification requires high temperatures and long reaction times in non-aqueous solvents.

Purpose of the Study:

• To investigate esterification reaction kinetics in controlled aqueous aerosol droplets.
• To compare reaction rates in aerosol droplets versus macroscopic solutions.
• To explore the influence of droplet volume and water activity on reaction reversibility.

Main Methods:

• Controlled generation of picoliter and sub-femtoliter aerosol droplets.
• Confined picoliter droplets using Aerosol Optical Tweezers.
• Raman spectroscopy, aerosol mass spectrometry, and NMR spectroscopy for chemical analysis.

Main Results:

• Esterification was facile in aerosol droplets (<400 s in picoliter, <2 s in sub-femtoliter) upon dehydration at room temperature.
• Both forward and reverse esterification reactions were vastly accelerated in aerosols compared to bulk solutions.
• Controlled water activity range from dilute to solvent-free conditions was investigated.

Conclusions:

• Aerosol environments dramatically enhance esterification reaction rates and reversibility.
• Controlled aerosol chemistry can be leveraged to drive reactions efficiently on micro- and nanoscales.
• This work highlights the potential of aerosols for novel chemical synthesis and reaction studies.