Initiator-free hydrocarbon oxidation using supported gold nanoparticles†
The oxidation of cyclic alkenes (cyclopentene, cyclohexene, cycloheptene and cyclooctene) has been carried out under green solvent-free conditions using ambient air as the oxidant gas with a carbon-supported gold catalyst. We show that radical initiators are only required for this reaction when the cyclic alkene contains a stabilizer molecule, such as 6-bis(t-butyl)-4-methylphenol (BHT) or 3-octadecyl-(3,5-di-t-butyl-4-hydroxyphenyl)-propanoate (irganox 1076). We show that either removing the stabilizer chemically or sourcing the cycloalkane without the stabilizer the oxidation, both with and without radical initiator, is identical. This indicates that the only function of the radical initiator is to counteract the stabilizer. We have extended this work to show that stabilizer-free internal linear alkenes can be effectively epoxidised with air using the carbon-supported gold catalyst. However, unfortunately linear α-alkenes still require the addition of an initiator to achieve reaction. This work demonstrates that removal of a sacrificial reagent from a reaction is possible which adheres to the principles of green chemistry.