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Synthesis of carboxylic acids by oxidation of benzylic substrates

Recent Literature

The use of potassium persulfate enables an aerobic oxidation of benzyl substrates to provide aryl carbonyl compounds including acetophenones, benzophenones, imides, and benzoic acids under mild conditions in the presence of pyridine. Neither transition metals nor halogens are required as additives.
Y. Hu, L. Zhou, W. Lu, Synthesis, 2017, 49, 4007-4016.

The oxidation of substituted toluenes by molecular oxygen to the corresponding substituted benzoic acids using Co(C18H35O2)2/NH4Br or Co(OAc)2/NaBr/AcOH as catalysts in the presence of a radical initiator in non-acidic solvents was investigated.
F. Yang, J. Sun, R. Zheng, W. Qiu, J. Tang, M. He, Tetrahedron, 2004, 60, 1225-1228.

The use of CBr4 as initiator enables a mild and metal-free aerobic oxidation of substituted toluenes to carboxylic acids under irradiation from a 400 nm blue light-emitting diode.
K. Zheng, X. Yan, G. Zhang, X. Yan, X. Li, X. Xu, Synlett, 2020, 31, 272-274.

A methyl group at an aromatic nucleus is oxidized directly to the corresponding carboxylic acid in the presence of molecular oxygen and catalytic hydrobromic acid under photoirradiation.
S.-I. Hirashima, A. Itoh, Synthesis, 2006, 1757-1759.

An I2-promoted direct conversion of arylacetic acids into aryl carboxylic acids under metal-free conditions involves decarboxylation followed by an oxidation reaction enabled just by using DMSO as the solvent as well as an oxidant. Notably, aryl carboxylic acids are isolated by simple filtration technique and obtained in good to excellent yields, which makes this protocol applicable for large-scale synthesis.
H. P. Kalmode, K. S. Vadagaonkar, S. L. Shinde, A. C. Chaskar, J. Org. Chem., 2017, 82, 3781-3786.