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A University of Pittsburgh team reported a Birch reduction method that replaces liquid ammonia with tetrahydrofuran (THF), using lithium and ethylenediamine in the reducing system. Chemistry World reported that the method operates at temperatures up to 26 °C, avoiding the deep cooling conventionally used to keep ammonia from evaporating. It is an alternative way to carry out dearomatisation—not a new definition of the reaction—and it still involves reactive laboratory chemicals.
What the method changes
Birch reduction converts an aromatic ring, such as benzene, into a cyclohexadiene. In the conventional approach described by Chemistry World, an alkali metal is dissolved in liquid ammonia to produce solvated electrons that drive the reduction. Because ammonia evaporates readily, the report says traditional protocols require cooling below −33 °C.
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The Pittsburgh approach swaps THF for liquid ammonia and uses lithium with ethylenediamine. Chemistry World reported the method working at temperatures up to 26 °C. That figure is a reported upper operating temperature, not evidence that every substrate, reaction scale, or implementation works at that temperature.
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Liquid-ammonia handling and cryogenic cooling can make conventional Birch reductions demanding. Chemistry World characterized earlier ammonia-avoiding alternatives as difficult to control, cryogenic, or reliant on expensive reagents. That is the report’s broad comparison, not an exhaustive review of all current methods.
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“Without nasty reagents” is relative shorthand, not a claim that the alternative is harmless. It still uses reactive laboratory chemicals, and the available reporting does not provide a complete hazard comparison or detailed safety controls. The reported result is not a basis for attempting the reaction outside a properly equipped laboratory.
What the reported figures mean
- Up to 26 °C: Chemistry World’s 2021 report gives this as the method’s upper operating temperature.
- Below −33 °C: The same report describes this as the cooling traditional protocols need to prevent ammonia evaporation.
- $2.67 per mole: Chemistry World reported this as the historical cost of the ethylenediamine reagent in 2021; it is not a current market price.
- Over $1,000 (£742) per mole: The report used this figure for reagents in some earlier alternatives, not as a universal cost benchmark.
What is not established by the available report
The Chemistry World summary does not establish the method’s substrate range, yields, selectivity, reaction times, scale-up performance, waste handling, or a full comparison of hazards. Those details should not be inferred from the solvent substitution or temperature figure. The primary paper is J. Burrows, S. Kamo and K. Koide, Science (2021), DOI 10.1126/science.abk3099; its experimental data are needed to assess those questions.
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Sources
Jamie Durrani, “Dearomatisation, but without nasty reagents,” Chemistry World, 15 November 2021. The report identifies the team as being from the University of Pittsburgh and cites the primary paper by Burrows, Kamo and Koide.
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