Doped graphene as a metal-free carbocatalyst for the selective aerobic oxidation of benzylic hydrocarbons, cyclooctane and styrene

Abstract

[EN] Nitrogen (N)-, boron (B)-, and boron,nitrogen (B,N)-doped graphene (G) act as carbocatalysts, promoting the aerobic oxidation of the benzylic positions of aromatic hydrocarbons and cyclooctane to the corresponding alcohol/ketone mixture with more than 90% selectivity. The most active material was the co-doped (B,N)G, which, in the absence of solvent and with a substrate/(B,N)G ratio of 200, achieved 50% tetralin conversion in 24h with a alcohol/ketone selectivity of 80%. An FT-Raman spectroscopic study of a sample of (B,N)G heated at 100 degrees C in the presence of oxygen revealed new bands that disappeared upon evacuation and that have been attributed to hydroperoxide-like species formed on the G sheet based on the isotopic shift of the peak from 819 to 779cm1 when 18O2 was used as the oxidizing reagent. Furthermore, (B)G and (N)G exhibited high catalytic activity in the aerobic oxidation of styrene to benzaldehyde (BA) in 4h. However, the product distribution changed over time and after 10h a significant percentage of styrene oxide (SO) was observed under the same conditions. The use of doped G as catalyst appears to offer broad scope for the aerobic oxidation of benzylic compounds and styrene, for which low catalyst loading, mild reaction temperatures, and no additional solvents are required.