Catalytic Oxidative Cleavage of C(OH)-C Bonds in Lignin Model Compounds to Carboxylic Acids by Fe(NO3)3.9H2O/NaI/DMSO

Xuerong Wang; Huilin Sun; Caicui Li; Shuijiao Niu; Yu Gao; Ying Chen; Tianwei Xu; Jinhui Wang; Huanjun Xu

doi:10.3389/fchem.2022.933763

Catalytic Oxidative Cleavage of C(OH)-C Bonds in Lignin Model Compounds to Carboxylic Acids by Fe(NO₃)₃.9H₂O/NaI/DMSO

Front Chem. 2022 Jul 1:10:933763. doi: 10.3389/fchem.2022.933763. eCollection 2022.

Authors

Xuerong Wang^{1

2}, Huilin Sun², Caicui Li², Shuijiao Niu³, Yu Gao⁴, Ying Chen², Tianwei Xu^{1

2}, Jinhui Wang^{1

4}, Huanjun Xu^{1

2}

Affiliations

¹ Key Laboratory of Child Cognition & Behavior Development of Hainan Province, Qiongtai Normal University, Haikou, China.
² School of Science, Qiongtai Normal University, Haikou, China.
³ Shandong Institute for Food and Drug Control, Ji'nan, China.
⁴ Department of Medicinal Chemistry and Natural Medicine Chemistry, College of Pharmacy, Harbin Medical University, Harbin, China.

Abstract

The secondary C(OH)-C bonds are abundant in biomass such as lignin and cellulose. Thus, selective cleavage of the C(OH)-C bonds into value chemicals attracted much attention. Molecular iodine has received considerable attention as an inexpensive and readily available catalyst to yield the corresponding products in excellent yields with high selectivity, but it is highly corrosive and toxic, making its use somewhat unattractive. In this study, I₂ was generated in situ from Fe(NO₃)₃.9H₂O/NaI, which was further combined with Fe(NO₃)₃.9H₂O to catalyze the oxidation process. In the reaction, the H₂O molecule from the reaction and Fe(NO₃)₃.9H₂O attacked the phenylglyoxal to form benzaldehyde, which was further oxidized to benzoic acid. Aryl primary and secondary benzylic alcohols from lignin were successfully transformed into aryl carboxylic acids by Fe(NO₃)₃.9H₂O/NaI/DMSO. The catalytic system was green and efficient, avoiding the usage of toxic and corrosive molecular I₂. From the experiments, it was clear that the yield of the product from the substrates with an electron-donating group was higher than that of electron-withdrawing substituted substrates, which was similar to the aryl secondary alcohols. Aryl alkyl ketones were also successfully conducted by the Fe(NO₃)₃.9H₂O/NaI/DMSO catalytic system.

Keywords: C(OH)-C bonds; Fe(NO3)3.9H2O/NaI/DMSO; carboxylic acids; catalytic oxidative cleavage; lignin model compounds.