Chemists at Wageningen University & Research (WUR) and Utrecht University have developed a new method to produce a promising chemical building block from biomass. This compound can serve as a precursor for useful products such as plastics, pharmaceuticals, and flavour and fragrance ingredients. Conventionally, its production requires hazardous chemicals. The Dutch research team now demonstrates that the process can instead be driven by electricity, using a simple setup and without the addition of dangerous chemicals. They published the results in the scientific journal ChemSusChem.
The research centres on the compound 2(5H)-furanone, which has considerable industrial potential as a feedstock for a wide range of functional materials. Dmitri Pirgach, PhD candidate at Wageningen, succeeded in producing this compound from furfural, a liquid derived from sugars in plant-based residues such as agricultural waste. Scientists had previously also succeeded in converting this bio-based furfural into the versatile furanone, but these methods typically require liquid bromine, a toxic substance that entails strict safety measures.
No need to store toxic bromine
In the new method, Pirgach avoids the need to add bromine directly. Instead, the reaction takes place in an electrochemical reactor, a setup in which an electric current drives the chemical transformation. Instead of using liquid bromine, the researchers use bromide salts such as sodium bromide. These are relatively harmless salts in which bromine occurs in a bound form. When current passes through the reactor, the bromide is oxidised at the electrode to form bromine at the electrode. This reacts with water, triggering the oxidation of furfural and initiating a sequence of reaction steps that ultimately yield 2(5H)-furanone.
Indirectly, bromine therefore still plays a role, but it is formed only at the moment the reaction takes place and is immediately consumed. "The bromine forms only when required," explains Harry Bitter, Professor of Biobased Chemistry and Technology and senior author of the study. As a result, chemical plants would not need to store or transport stocks of the toxic red-brown liquid. That significantly improves the safety of the process.
A simpler reactor design
The idea of producing furanone electrochemically is not entirely new. Chemists have attempted this before, using so-called divided cells: electrochemical reactors with two compartments separated by a membrane. This separation prevents different reaction steps from interfering with one another, Pirgach explains. However, this approach also introduces drawbacks: membranes are costly, prone to degradation, and increase energy consumption. Bitter clarifies: "You can think of a membrane as a fine sieve through which ions must be forced, which requires additional electrical energy."
To address this, Pirgach opted for a simpler set-up: an undivided cell, an electrochemical reactor without a separating membrane. This makes the reactor both cheaper and more energy-efficient, but it also introduces a new challenge. With all reactants present in the same compartment, they can interact with each other and with both electrodes, leading to the formation of unwanted by-products.
Controlling the reaction pathway
To mitigate this issue, Pirgach added a small amount of sulphuric acid to the reaction mixture. Acid modifies the reaction environment, steering the reaction pathway and suppressing the formation of undesired products. As a result, the production of furanone becomes more selective and reliable. With this adjustment, the electrochemical route proved successful even in the simplified, membrane-free reactor. Energy consumption also remained limited: "In the lab, the reaction required less than 0.5% of the electricity used by an electric kettle for a single boil," Pirgach notes.
It should be emphasised that these experiments were conducted on a small scale. The researchers produced only 0.3 millilitres of furanone. That is sufficient, however, to analyse and optimise the reaction. "This is typical fundamental research," says Bitter. "You start small and first aim to understand the underlying chemistry. Only then do you consider scaling up and practical applications."
Towards industrial application
That next phase now slowly comes into view, making the research increasingly relevant for the chemical industry. Furanone is considered a versatile molecule that can serve as a precursor for polymers, flavourings, and pharmaceutical compounds. Because the starting material, furfural, is derived from plant-based residual streams, the process aligns well with the growing interest in bio-based chemistry. The electricity required for the reaction could, in principle, come from renewable sources.
Before industrial implementation becomes feasible, chemists will need to further optimise and scale up the process. Reactions that perform well on the gram scale often behave differently in larger reactors. Nevertheless, the researchers are optimistic that electrochemical routes such as this could contribute to more sustainable chemical manufacturing. "This is a great combination of using renewable electricity with renewable raw materials to create building blocks for circular products," says Daan van Es, co-author and expert in applied, sustainable, and circular chemistry. "There is still a long way to go before we can apply this industrially, but it has a lot of potential. The mild reaction conditions and the possibility of local production in the Netherlands are particularly relevant for the future of the European chemical industry."
Publication: Indirect Baeyer-Villiger Oxidation of Furfural by In Situ Formed HOBr in an Undivided Electrochemical Cell
