Categories: C=O Bond Formation > Synthesis of carboxylic acids >
Synthesis of carboxylic acids by oxidation of benzylic substrates
Recent Literature
Cost-effective and widely applicable protocols for controlled and predictably
selective oxidation of methyl-/alkylarenes to corresponding value-added
carbonyls have been developed, using a surfactant-based oxodiperoxo molybdenum
catalyst in water and hydrogen peroxide (H2O2) as an
environmentally benign green oxidant without any external base, additive, or
cocatalyst.
P. Thiruvengetam, D. K. Chand, J. Org. Chem., 2022, 87,
4061-4077.
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.
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.
M. Kirihara, Y. Sakamoto, S. Yamahara, A. Kitajima, N. Kugisaki, Y. Kimura, Synlett, 2022,
33,
1670-1674.
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.
Related
Benzyl chlorides and bromides can be directly oxidized to the corresponding
benzoic acids in an eco-safer way using 30% hydrogen peroxide with Na2WO4
* 2H2O as a catalyst and [CH3(n-C8H17)3N]+HSO4
as a phase-transfer agent (PTC) without any organic solvents.
M. Shi, Y.-S. Feng, J. Org. Chem., 2001,
66, 3235-3237.
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.