Safe acetylene source

09 May 2015 - Bench work

Matake, Niwa, and Matsubara report a new way to generate acetylene for research laboratory use. (DOI) The method is based on a phase-vanishing reaction (PV method): in a test tube a layer of fluorous solvent separates two reactive media that exchange reactants by slow diffusion, the reaction product then migrates to the top fourth reaction layer.

In the latest incarnation a PV method was deployed to generate acetylene in-situ in a Sonogashira coupling. A test tube was first filled with some calcium carbide, then a perfluoropolyether layer was added, then (carefully!) a layer of water and then on top a layer of tetrahydrofuran. This reaction layer contained all the ingredients for the coupling to take place: iodobenzene, tetrakis(triphenylphosphine)palladium(0), copper iodide and triethylamine. Heating to 55 °C was required in order to get the carbide react with water but then conversion reached 94% after 20 hours of stirring with complete disappearance of the calcium carbide.

Safe to use? Handling acetylene cylinders potentially pose bigger risks but the experimental setup still looks a bit adventurous: you still require to stir a heated test tube and then hope the carbide ball stays well away from the water.