In recent years, with the increasing shortage of fossil resources and the deterioration of human living environment, the efficient and sustainable use of renewable resources such as biomass has become the focus of research and attention of scientists around the world. Formic acid, one of the main by-products in biorefining, has the characteristics of cheap and easy to obtain, non-toxic, high energy density, renewable and degradable, etc. Applying it to new energy utilization and chemical transformation not only helps to further expand the application field of formic acid, but also helps to solve some common bottleneck problems in the future biorefining technology. This paper briefly reviewed the research history of formic acid utilization, summarized the latest research progress of formic acid as an efficient and multi-purpose reagent and raw material in chemical synthesis and catalytic conversion of biomass, and compared and analyzed the basic principle and catalytic system of using formic acid activation to achieve efficient chemical conversion. It is pointed out that the future research should focus on improving the utilization efficiency of formic acid and realizing high selectivity synthesis, and further expand its application field on this basis.
In chemical synthesis, formic acid, as an environmentally friendly and renewable multi-functional reagent, can be used in the selective conversion process of various functional groups. As a hydrogen transfer reagent or reducing agent with high hydrogen content, formic acid has the advantages of simple and controllable operation, mild conditions and good chemical selectivity compared with traditional hydrogen. It is widely used in the selective reduction of aldehydes, nitro, imines, nitriles, alkynes, alkenes and so on to produce corresponding alcohols, amines, alkenes and alkanes. And the hydrolysis and functional group deprotection of alcohols and epoxides. In view of the fact that formic acid can also be used as C1 raw material, as a key multi-purpose basic reagent, formic acid can also be applied to the reduction formylation of quinoline derivatives, formylation and methylation of amine compounds, carbonylation of olefin and reduction hydration of alkynes and other multistage tandem reactions, which is an important way to achieve efficient and simple green synthesis of fine and complex organic molecules. The challenge of such processes is to find multifunctional catalysts with high selectivity and activity for the controlled activation of formic acid and specific functional groups. In addition, recent studies have shown that using formic acid as C1 raw material can also directly synthesize bulk chemicals such as methanol with high selectivity through catalytic disproportionation reaction.
In the catalytic conversion of biomass, the multifunctional properties of formic acid provide potential for the realization of green, safe and cost-effective biorefining processes. Biomass resources are the largest and most promising sustainable alternative resources, but transforming them into usable resource forms remains a challenge. The acid properties and good solvent properties of formic acid can be applied to the pretreatment process of biomass raw materials to realize the separation of lignocellulose components and cellulose extraction. Compared with the traditional inorganic acid pretreatment system, it has the advantages of low boiling point, easy separation, no introduction of inorganic ions, and strong compatibility for downstream reactions. As an efficient hydrogen source, formic acid has also been widely studied and applied in the selection of catalytic conversion of biomass platform compounds to high value-added chemicals, lignin degradation to aromatic compounds, and bio-oil hydrodeoxidation refining processes. Compared with the traditional hydrogenation process dependent on H2, formic acid has high conversion efficiency and mild reaction conditions. It is simple and safe, and can effectively reduce the material and energy consumption of fossil resources in the related bio-refining process. Recent studies have shown that by depolymerizing oxidized lignin in formic acid aqueous solution under mild conditions, a low molecular weight aromatic solution with a weight ratio greater than 60% can be obtained. This innovative discovery brings new opportunities for the direct extraction of high-value aromatic chemicals from lignin.
In summary, bio-based formic acid shows great potential in green organic synthesis and biomass conversion, and its versatility and multipurpose are essential to achieve efficient utilization of raw materials and high selectivity of target products. At present, this field has made some achievements and has been rapidly developed, but there is still a considerable distance from the actual industrial application, and further exploration is needed. Future research should focus on the following aspects: (1) how to select suitable catalytic active metals and reaction systems for specific reactions; (2) how to efficiently and controllably activate formic acid in the presence of other raw materials and reagents; (3) How to understand the reaction mechanism of complex reactions from the molecular level; (4) How to stabilize the corresponding catalyst in the relevant process. Looking forward to the future, based on the needs of modern society for environment, economy and sustainable development, formic acid chemistry will receive more and more attention and research from industry and academia.
Post time: Jun-27-2024