Alcohol oxidation to carbonyl compounds is one of the most commonly used reactions in synthetic chemistry. Herein, we report the use of base metal layered double hydroxide (LDH) catalysts for the oxidation of benzylic alcohols in polar solvents. These catalysts are ideal reagents for alcohol oxidations due to their ease of synthesis, tunability, and ease of separation from the reaction medium. LDHs synthesized in this study were fully characterized by means of X-ray diffraction, NH3-temperature programmed desorption (TPD), pulsed CO2 chemisorption, N2 physisorption, electron microscopy, and elemental analysis. LDHs were found to effectively oxidize benzylic alcohols to their corresponding carbonyl compounds in diphenyl ether, using O2 as the terminal oxidant. LDH catalysts were also applied to the oxidation of lignin β-O-4 model compounds. Typically, for all catalysts, only trace amounts of the ketone formed from benzylic alcohol oxidation were observed, the main products comprising benzoic acids and phenols arising from β-aryl ether cleavage. This observation is consistent with the higher reactivity of the ketones, resulting from weakening of the Cβ–O4 bond that was shown to be aerobically cleaved at 180 °C in the absence of a catalyst.

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Published in Inorganics, v. 6, issue 3, 75, p. 1-18.

© 2018 by the authors. Licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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This material is based on work supported by the National Science Foundation under Cooperative Agreement No. 1355438, NSF MRI Award No. 1531637 and NSF-EFRI-0937657 as well as the DOE Great Lakes Bioenergy Research Center (DOE Office of Science BER DE-FC02-07ER64494).

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The following are available online at https://www.mdpi.com/2304-6740/6/3/75/s1, details of catalyst preparation, catalyst leaching study, catalyst reusability, synthesis of lignin model compounds, gas chromatography analysis, catalyst acidity and basicity measurements, Figure S1: X-ray diffractogram of Ni-Al-LDH-1 pre-treated at 160 °C, Figure S2: Scanning electron micrograph of Ni-Al-LDH-1, Figure S3: Scanning electron micrograph of Ni-Cr-LDH, Figure S4: FT-IR analysis of LDH catalysts, Figure S5: NH3-TPD of Ni-Al-LDH-1, Figures S6–S9: NH3-TPD of Ni-Al-LDH-2, Mg-Al-LDH-1, Ni-Cr-LDH, and Ni-Cu-Cr-LDH, Figure S10: X-ray diffractogram of Ni-Cr-LDH after 3 cycles of use in the oxidation of 1, Figure S11: X-ray diffractogram of Ni-Al-LDH-1 after 2 cycles of use in the oxidation of 1, Figure S12: X-ray diffractogram of Ni-Al-LDH-2 after 1 cycle of use in the oxidation of 2. References [45,46,47,48,49,50,51,52] are cited in the supplementary materials.

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Supplementary Material