Photocatalysis in flow functionalizes light hydrocarbons

It typically takes some dramatic chemistry to turn light hydrocarbons like methane and propane into molecules that can be used as something other than fuel. Making them into one useful class of molecules, alkyl halides, requires using chlorine or bromine gas and sometimes temperatures in excess of 500 °C. Alkyl halides made this way are often turned into organometallic nucleophiles that form C–C bonds. Seeking a more direct way to use light hydrocarbons to make C–C bonds, chemists led by Eindhoven University of Technology’s Timothy Noël have now turned to the photocatalyst decatungstate (Science 2020, DOI: 10.1126/science.abb4688). In the presence of near-ultraviolet light, decatungstate can pull a hydrogen atom from C–H bonds in methane, ethane, propane, or isobutane in a predictable manner. The resulting radical then reacts with a conjugated olefin to create a new C–C bond (example shown). Noël’s team performed the transformation in a microflow reactor under pressure, which can safely handle the combustible gases. The reactor forces the light hydrocarbons into the liquid phase, which makes them more likely to encounter decatungstate. Because the reaction conditions are mild and the photocatalyst is easy to prepare, the chemists say, the reaction is ideal for turning feedstock chemicals into more-interesting molecules.