Leidenfrost chemistry

28 July 2016 - Proofs of Concept

Leidenfrost Bain 2016.PNGA nice proof of concept here at The Angewandte exploiting the Leidenfrost effect in a chemical reaction. Ryan Bain et al. have asked themselves the question: can a reaction accelerate when confined to a tiny droplet levitating on a hot surface?
The experimental setup was a simple petri dish on top of a heater at 500°C. The reagents were isatin and phenylhydrazine with some HCl added forming the hydrazone. The solvent was methanol and the droplet size 0.5 mL. After 2 minutes the reaction was done and ready for electrospray ionization (ESI) analysis. The reaction turns out to be six times as fast as the bulk reaction!
The same reaction is known to be accelerated inside the same ESI machine when the time-of-flight between source and mass spectrometer of the droplets is increased. In both cases the effect is the result of solvent evaporation and increased concentrations. Temperature does not play a role as the expected temperature inside a droplet does not exceed 45°C. The reaction preferably takes places at the solvent air interface. The smaller the droplet the larger the acceleration, adding a surfactant killed the kinetic effect.