Oxidative Functionalization of Long-Chain Liquid Alkanes by Pulsed Plasma Discharges at Atmospheric Pressure

We introduce the oxidation of long aliphatic alkanes using non thermal, atmospheric plasma processing as an eco-friendly route for organic synthesis. A pulsed dielectric barrier discharge in He/O2 gas mixtures was employed to functionalize n-octadecane. C18 secondary alcohols and ketones were the main products, with an optimal molar yield of similar to 29.2%. Prolonged treatment resulted in the formation of dialcohols, diketones, and higher molecular weight oxygenates. Lighter hydrocarbon products and decarboxylation to CO2 were also observed at longer treatment times and higher power inputs. A maximum energy yield of 5.48 x 10-8 mol/J was achieved at short treatment times and high powers, associated with higher selectivity to primary oxygenates. Direct hydroxylation of alkyl radicals, as well as disproportionation reactions, are proposed as the main pathways to alcohols and ketones. The results hold promise for functionalizing long hydrocarbon molecules at ambient conditions using catalyst-free plasma discharges.

Automated summary

We introduce a method of oxidizing long aliphatic alkanes using non-thermal, atmospheric plasma processing as an eco-friendly route for organic synthesis. By employing pulsed dielectric barrier discharge in He/O2 gas mixtures, we could convert n-octadecane into C18 secondary alcohols and ketones, with a maximum molar yield of 29.2%. Longer treatment times and higher power inputs resulted in the formation of dialcohols, diketones, and higher molecular weight oxygenates. We also observed the production of lighter hydrocarbon products and decarboxylation to CO2 at longer treatment times and higher power inputs. The highest energy yield of 5.48 x 10-8 mol/J was achieved at short treatment times and high powers, accompanied by higher selectivity to primary oxygenates. We propose direct hydroxylation of alkyl radicals and disproportionation reactions as the main pathways to alcohols and ketones. This study shows the potential of catalyst-free plasma discharges for functionalizing long hydrocarbon molecules at ambient conditions.