One‐Pot Transformation of Lignin and Lignin Model Compounds into Benzimidazoles

Abstract

It is a challenging task to simultaneously achieve selective depolymerization and valorization of lignin due to their complex structure and relatively stable bonds. We herein report an efficient depolymerization strategy that employs 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) as oxidant/catalyst to selectively convert different oxidized lignin models to a wide variety of 2‐phenylbenzimidazole‐based compounds in up to 94 % yields, by reacting with o‐phenylenediamines with varied substituents. This method could take full advantage of both Cβ and/or Cγ atom in lignin structure to furnish the desirable products instead of forming byproducts, thus exhibiting high atom economy. Furthermore, this strategy can effectively transform both the oxidized hardwood (birch) and softwood (pine) lignin into the corresponding degradation products in up to 45 wt% and 30 wt%, respectively. Through a “one‐pot” process, we have successfully realized the oxidation/depolymerization/valorization of natural birch lignin at the same time and produced the benzimidazole derivatives in up to 67 wt% total yields.

Recent Scenario for the Synthesis of Benzimidazole Moiety(2020–2022)

“…Formic acid and o‐phenylenediamine eventually produce benzimidazole compounds as a result of their reaction (scheme 43). [46] …”

Recent Advancements in Strategies for the Synthesis of Imidazoles, Thiazoles, Oxazoles, and Benzimidazoles

“…Lignin, due to its complex structure and inert properties, is still underutilized compared to cellulose and hemicelluloses (Schemes 137 and 138). [163] In 2021, Mishra and his colleagues coincidentally discussed the concept of "click chemistry" and the utilization of coppercatalyzed organic transformations (Scheme 139). [164] They emphasized the benefits of copper-based catalysts, such as their affordability, high yield, lack of significant by-products, and environmentally friendly qualities.…”

Novel Mechanoenzymatic Strategy for Lignin Depolymerization

“…Despite being the second most abundant biopolymer on earth, the utilization of lignin remains highly inefficient. This inefficiency is largely attributed to the complex and irregular structure of lignin, which makes it resistant to degradation under typical chemical and biological denaturation conditions. − The current industrial applications of lignin are primarily limited, with most of it being used as solid fuels or concrete additives. − This inefficient utilization of lignin in the paper industry is a major issue due to the prevalent practice of incinerating lignin-rich black liquor for energy production, resulting in substantial resource loss. Moreover, lignin waste is not exclusive to the pulp and paper industry as lignocellulosic biomass refining processes also generate lignin-rich waste streams.…”