Nitrogen is a vital component of life, but today, the majority of the N atoms in synthetic N-containing compounds come from NH3, which is mass-produced using the Haber-Bosch method.
(a) Current production and application of NH3. Almost all synthetic nitrogenous organic compounds are synthesized from NH3. (b) Synthesis of N-containing organic compounds directly from N2 molecule and carbon sources. (c) Our general strategy to achieve the above goal: taking advantage of the heterogeneous process to generate active intermediate nitrogenous species, followed by taking advantage of the homogeneous synthetic methodology to make value-added organic compounds. (d) This work as proof of concept. Through a heterogeneous process, the N2 gas was first fixed with carbon and LiH to form reactive Li2CN2, which was then transformed into nitrogen-containing organic compounds through the homogeneous synthetic methodology. Image Credit: Science China Press
Despite being one of the greatest inventions in human history, the Haber-Bosch process has a significant negative impact on our environment and energy.
If we could synthesize complex organic compounds directly with dinitrogen and carbon bypassing ammonia, it will reduce operation procedures and thus may save a lot of energy and create huge economic value for the society.
Zhenfeng Xi, Study Corresponding Author and Professor, Department of Chemistry, Peking University
Researchers in this study suggested a homogeneous-heterogeneous synergy approach to address this issue. First, a heterogeneous process converts the N2 gas into an active-enough nitrogenous species (N*). Utilizing both research strategies, a second homogeneous reaction is carried out to create complicated nitrogen-containing organic compounds.
According to the specifications, the N2 gas and carbon were first fixed with LiH in a homemade reactor at 550 ºC (heterogeneous process), producing the reactive intermediate known as Li2CN2 with excellent selectivity and efficiency.
Li2CN2 was then transferred to a glass flask and processed as an organic synthon to create carbodiimide and pyrimidines, which are the building blocks of DNA and RNA (homogeneous process).
Furthermore, by using 15N2 as the feedstock, it was possible to easily manufacture the equivalent 15N-labeled carbodiimide and pyrimidines that could have a wide range of uses in biochemistry.
Hydrides (H-) here play a peculiar role in our dinitrogen fixation. It directs a different reaction pathway for N2 fixation and transformation compared to conventional transition metals, making the reaction gentle and controllable. Our products could be obtained facilely on a gram scale in the laboratory. Further amplifying the production by using a larger reactor equipped will be straightforward.
Ping Chen, Study Corresponding Author and Professor, Dalian Institute of Chemical Physics, Chinese Academy of Sciences
The homogeneous-heterogeneous synergy approach presented here is distinct from those earlier approaches. N2 gas typically needs to be reduced to interact with carbon electrophiles and create C-N bonds.
However, most of the time, reducing agents and carbon electrophiles are incompatible. In this study, the incompatibility issue has been resolved by employing carbon as the carbon source directly.
To create more beneficial organic compounds, the researchers intend to continue using this approach in the future.
The Basic Science Center of Transformation Chemistry of Key Components of Air, National Natural Science Foundation of China (No. 21988101), provided funding for the study. No conflicts of interest have been reported.
Shi, X., et al. (2022) Synthesis of Pyrimidines from Dinitrogen and Carbon. National Science Review. doi:10.1093/nsr/nwac168