Selective ring CH bonds activation of toluene over Fe/activated carbon catalyst

•Iron interacted with carboxylic and lactonic groups forming COO(Fe) like species.•Activated carbon activated benzene ring resulting in ring CH bonds activation.•The ortho-selectivity might be due to the orientating role of activated carbon.•Fe/activated carbon catalysts were stable enough for the hydroxylation of toluene.

Direct hydroxylation of toluene and related aromatics over Fe/activated carbon catalyst using hydrogen peroxide as oxidant in acetonitrile was studied. The catalysts were characterized by ICP-AES, N2 adsorption, FTIR, XPS and ion exchange experiment. It was found that iron was anchored on the surface of activated carbon forming iron carboxylate like species acting as active phase for toluene hydroxylation. 13.4% yield (TOF, 34.4 × 10−2 h−1) and 74.3% selectivity to cresols were obtained under the optimal conditions, and o-cresol was dominant with 56% selectivity. The interaction between benzene ring and activated carbon might be responsible for the selective ring CH bonds activation. The ortho-selectivity might be due to the synergetic effect by activated carbon and high-valent iron-oxo species. The structure of the key intermediate for the titled reaction was proposed and confirmed by theoretical modeling using Gaussian 09 program package.

Graphical abstractInteraction between the benzene ring and activated carbon was responsible for the selective ring CH bonds activation. The carboxylic and lactonic groups on activated carbon played the role of ortho-positioning.Figure optionsDownload full-size imageDownload high-quality image (120 K)Download as PowerPoint slide