Photooxidation of Toluene Derivatives into Carboxylic Acids
Aerobic Photooxidation of Toluene Derivatives into Carboxylic Acids with Bromine–Water under Catalyst-Free Conditions: M. Kirihara, Y. Sakamoto, S. Yamahara, A. Kitajima, N. Kugisaki, Y. Kimura
Synlett 2022, DOI: 10.1055/a-1887-7885
Benzoic acids are key intermediates in organic chemistry, both for laboratory scale and industrial applications, as they are used for the formation of esters, amides, and acid chlorides. The standard preparation method for benzoic acid derivatives is the oxidation of the corresponding toluene derivatives. However, oxidation of the methyl group in aromatic compounds remains a challenging endeavor, unless toxic or aggressive metal oxidants – such as KMnO4 or Cr(VI) salts – are employed. Oxidation with molecular oxygen has been applied in the industrial field, but this approach requires high pressures and temperatures. Recently, a cross-sector collaboration between the groups of Professor Masayuki Kirihara (Shizuoka Institute of Science and Technology, Japan) and Dr. Yoshikazu Kimura (Iharanikkei Chemical Industry Co. Ltd, Japan) allowed the development of novel and more accessible conditions to perform the title transformation.
Professor Kirihara said: “Our newly developed method for the synthesis of benzoic acids from toluenes is free from catalysts or heavy metal oxidizing agents, uses only inexpensive bromine, water, and air as reagents. Furthermore, the reaction proceeds even with visible light irradiation; therefore, it is very practical and applicable to industrial synthesis.”