Reaction acceleration at air-solution interfaces: Anisotropic rate constants for Katritzky transamination

Area of Science:

• Physical chemistry
• Chemical kinetics
• Droplet microreactors

Background:

• Droplet-confined reactions can exhibit unique kinetics.
• Understanding factors controlling reaction rates in microenvironments is crucial for chemical synthesis and atmospheric chemistry.

Purpose of the Study:

• To investigate the factors controlling accelerated reaction rates in droplets.
• To elucidate the role of interfaces and reactant properties in droplet reactions.

Main Methods:

• Studied the Katritzky transamination reaction in levitated Leidenfrost droplets.
• Utilized mass spectrometry to monitor reaction rates.
• Varied droplet volume and reactant concentration while controlling for solvent evaporation.

Main Results:

• Reaction rates were significantly higher in the droplet surface region compared to the interior.
• Observed similar concentration and volume effects in bulk solutions.
• Surface-active pyrylium reagents showed differing transamination reactivity.
• Higher surface-to-volume ratios and surface-active reactants led to greater reaction acceleration, particularly at lower concentrations.

Conclusions:

• Air-solution interfaces play a key role in accelerating the Katritzky reaction.
• Limited solvation of reagents at the interface contributes to the increased rate constant.
• Reaction acceleration in droplets is influenced by surface activity and system geometry.