Aerobic Photooxidation of Toluene Derivatives into Carboxylic Acids with Bromine-Water under Catalyst-Free Conditions
Masayuki Kirihara* , Yugo Sakamoto, Sho Yamahara, Atsuhito Kitajima, Naoki Kugisaki, Yoshikazu Kimura*
*Shizuoka Institute of Science and Technology, Shizuoka 437-8555; Iharanikkei
Chemical Industry Co. Ltd., Shizuoka 421-3203, Japan,
Email: kirihara.masayukisist.ac.jp, kimura.yoshikazu
iharanikkei.co.jp
M. Kirihara, Y. Sakamoto, S. Yamahara, A. Kitajima, N. Kugisaki, Y. Kimura, Synlett, 2022, 33, 1670-1674.
DOI: 10.1055/a-1887-7885
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Abstract
Photoirradiation of toluene derivatives with two equivalents of bromine in benzotrifluoride-water provides benzoic acid derivatives in good yields using either a fluorescent lamp, blue LEDs (454 nm), or UV LEDs (385 nm). The reaction might proceed through dibromination of benzylic carbon, generation of the benzylic radical via oxidative C-H abstraction, formation of benzoyl bromide, and hydrolysis.
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Details
The document discusses a study on the aerobic photooxidation of toluene derivatives into carboxylic acids using bromine and water under catalyst-free conditions. The process involves the photoirradiation of toluene derivatives with bromine in benzotrifluoride-water, yielding benzoic acid derivatives. The reaction can be carried out using a fluorescent lamp, blue LED, or UV LED. The proposed mechanism includes the dibromination of benzylic carbon, formation of a benzylic radical, generation of benzoyl bromide, and hydrolysis to carboxylic acid. The method avoids toxic metal oxidants and operates under mild conditions, making it suitable for laboratory and industrial applications. The study found that both molecular oxygen and water are essential for the reaction, and the best results were obtained using benzotrifluoride-water as the solvent. The process was tested on various toluene derivatives, yielding high-purity carboxylic acids without the need for further purification. Control experiments confirmed the necessity of light and oxygen for the reaction. This method offers a convenient and efficient approach to synthesizing benzoic acid derivatives using readily available reagents.
Key Words
oxidation, toluene, benzoic acids, carboxylic acid, bromine, oxygen, photochemistry
ID: J72-Y2022