Researchers Crack One of Aromatic Chemistry’s Toughest Challenges

The method has applications in organic chemistry, particularly within the pharmaceutical industry.

A team of scientists has developed an electrochemical technique that enables precise, para-position single-carbon insertion into polysubstituted pyrroles. This advancement holds significant promise for synthetic organic chemistry, particularly in the development of pharmaceutical compounds.

“We set out to address the longstanding challenge of achieving single-carbon insertion into aromatic rings with precise positional control,” said Mahito Atobe, Professor, Faculty of Engineering, Yokohama National University.

Chemical transformations that alter aromatic rings are fundamental to creating pharmaceuticals and advanced materials. However, introducing a single carbon atom at a specific site, especially at the para position, has been extremely difficult to achieve. The para position refers to the specific arrangement of atoms in a molecule, where substituents (atoms that replace a hydrogen atom) are located opposite each other on an aromatic ring.

In this method, a single carbon atom is added directly into the molecular framework. This can extend a carbon chain or increase the size of a ring structure by one carbon atom, offering a powerful new tool for molecular design.

Introducing a Novel Electrochemical Strategy

“Our goal was to develop a new, electrochemically driven method that enables this transformation selectively and efficiently, while gaining mechanistic insights into how the electronic structure of the substrate controls the insertion position,” said Atobe. This study presents a novel concept for single-carbon insertion chemistry and expands a researcher’s chemical toolbox for synthesizing polysubstituted (hetero)aromatic compounds. Polysubstituted pyrroles are organic compounds that have a pyrrole ring and multiple substituents are joined to it. These compounds play a crucial role in diverse fields, such as natural products, pharmaceuticals, and functional materials. They hold particular interest for pharmaceuticals, where they are fundamental to many approved drugs.

“We discovered an electrochemical method that enables highly selective para-position single-carbon insertion into polysubstituted pyrroles an unprecedented transformation,” said Naoki Shida, Associate Professor, Faculty of Engineering, Yokohama National University. This reaction is enabled with distonic radical cation intermediates and is governed by the electronic properties of nitrogen-protecting groups. “Our findings establish a new strategy for site-selective molecular editing of aromatic rings, expanding the toolkit for synthetic organic chemistry,” said Shida.

Mechanism and Proof of Concept

The team demonstrated the electrochemical ring expansion reaction using α-H diazo esters as a carbynyl anion equivalent. This approach allowed efficient single-carbon insertion into a range of polysubstituted pyrroles, affording structurally diverse pyridine derivatives. They controlled the insertion position through electronic perturbation by the N-protecting group (PG), and achieved unprecedented para-selective insertion by introducing an electron-withdrawing protecting group to the pyrrole derivatives.

The team used in-situ spectroscopy and theoretical calculations to support the reaction mechanism involving a distonic radical cation intermediate. The spectroscopy and calculations suggest distonic radical cation intermediates are involved, facilitating carbon-atom migration on the aromatic ring and enabling insertion at different positions.

Approved drugs like Netupitant, Esomeprazole, Pyridoxine, and Opicapone contain benzene and pyridine rings with more than three substituents. These drugs are important medications for wide-ranging health challenges, such as Parkinson’s disease, stomach ulcers, or the control of chemotherapy-induced nausea. To synthesize these compounds, researchers have used multiple methods, such as coupling reactions, carbon-hydrogen functionalization, and cyclization reactions.

Single-carbon insertion is yet another approach scientists have used to modify polysubstituted (hetero)aromatic compounds. The single-carbon insertion approach significantly alters the structure of the parent skeletons. But up to this point in time, controlling the insertion position had been a significant challenge for researchers. The team’s novel electrochemical method introduces a new concept for single-carbon insertion chemistry.

Looking to the Future

Looking ahead, the team’s next step is to expand the scope of this reaction to a broader range of heteroaromatic compounds and complex molecules, including pharmaceutical intermediates.

“We also aim to integrate this methodology into flow electrolysis systems to improve scalability and efficiency. Ultimately, our goal is to establish a general platform for precise molecular editing of aromatic frameworks using electricity as a clean and controllable driving force,” said Atobe.

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Scientists Use Lightning To Make Ammonia out of Thin Air

A lightning-inspired process creates ammonia from air. The approach may support future green energy solutions.

Researchers at the University of Sydney have used artificial lightning to create a more efficient technique for producing ammonia, a chemical essential to modern life. Ammonia plays a key role in fertilizers that contribute to nearly half of global food production.

The team developed a simplified process to produce ammonia (NH₃) directly in its gaseous form. In contrast, earlier methods developed by other labs yielded ammonium (NH₄⁺) in solution, which demands additional energy and conversion steps to obtain usable ammonia gas.

Traditionally, ammonia is produced using the Haber-Bosch process, a method with a substantial environmental impact due to its high carbon emissions. This approach also requires large-scale infrastructure and proximity to inexpensive natural gas sources to remain economically viable.

The chemical process that fed the world, and the Sydney team looking to revolutionize it

Ammonia was once so highly valued primarily in the form of bird droppings that it became a source of conflict.

The development of the Haber-Bosch process in the 19th century enabled the large-scale production of synthetic ammonia, transforming both agriculture and industry. Today, approximately 90 percent of the world’s ammonia is still produced using this method.

“Industry’s appetite for ammonia is only growing. For the past decade, the global scientific community, including our lab, wants to uncover a more sustainable way to produce ammonia that doesn’t rely on fossil fuels.

“Currently, generating ammonia requires centralized production and long-distance transportation of the product. We need a low-cost, decentralized and scalable ‘green ammonia’,” said lead researcher Professor PJ Cullen from the University of Sydney’s School of Chemical and Biomolecular Engineering and the Net Zero Institute. His team has been working on ‘green ammonia’ production for six years.

“In this research, we’ve successfully developed a method that allows air to be converted to ammonia in its gaseous form using electricity. A huge step towards our goals.”

Ammonia is composed of three hydrogen atoms, making it a promising carrier and source of hydrogen for energy applications. It also offers potential for storing and transporting hydrogen, as the hydrogen can be extracted by a process known as “cracking,” which separates the molecules.

Because of its chemical properties, ammonia is being explored as a carbon-free fuel alternative. This has drawn attention from the shipping sector, which contributes roughly 3 percent of global greenhouse gas emissions.

Cracking a chemical conundrum

Professor Cullen’s team’s new method to generate ammonia works by harnessing the power of plasma, by electrifying or exciting the air.

But the star is a membrane-based electrolyzer, a seemingly non-descript silver box, where the conversion to gaseous ammonia happens.

During the Haber-Bosch process, ammonia (NH3) is made by combining nitrogen (N2) and hydrogen (H2) gases under high temperatures and pressure in the presence of a catalyst (a substance that speeds up a chemical reaction).

The plasma-based method Professor Cullen’s team developed uses electricity to excite nitrogen and oxygen molecules in the air. The team then passes these excited molecules to the membrane-based electrolyser to convert the excited molecules to ammonia.

The researchers said this is a more straightforward pathway for ammonia production.

Professor Cullen said the findings signal a new phase in making green ammonia possible. The team is now working on making the method more energy efficient and competitive compared to the Haber-Bosch process.

“This new approach is a two-step process, namely combining plasma and electrolysis. We have already made the plasma component viable in terms of energy efficiency and scalability.

“To create a more complete solution to a sustainable ammonia productive, we need to push the energy efficiency of the electrolyser component,” Professor Cullen said.

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New Catalyst Breakthrough Slashes Platinum Use in Green Hydrogen Tech

Researchers engineered a graphene-encased catalyst with ultra-low platinum use that delivers high-efficiency, industrial-scale hydrogen production.

Proton exchange membrane (PEM) water electrolysis plays a key role in the production of green hydrogen on a large scale. One of the most commonly used materials in this process is Platinum on Carbon (Pt/C), which serves as an advanced cathode catalyst. Its popularity comes from its ability to effectively bind hydrogen and its strong resistance to acidic environments. However, using high amounts of platinum makes this approach expensive and limits its broader adoption.

Their innovation centers around a unique “chainmail” catalyst made from a cobalt-nickel (CoNi) nano-alloy that is enclosed within a single layer of graphene. The team found that electrons transferred from the CoNi alloy into the surrounding carbon layer. This process, combined with a 3d-2p electronic interaction, caused the surface of the graphene to accumulate an uneven distribution of π electronic states, which played a critical role in enhancing catalytic behavior.
Synergistic Confinement and Platinum Stability

After depositing Pt single atoms using atomic layer deposition, these enriched asymmetric π electrons exhibited a unique confinement effect on the Pt atoms.

This confinement operated through two synergistic mechanisms. Electron transfer from CoNi to Pt via the graphene layer resulted in an electron-rich Pt site, optimizing hydrogen adsorption energy and promoting hydrogen desorption, thereby improving catalytic activity. Besides, strong interactions between the asymmetric π electrons and the Pt 5d orbital enhanced the structural stability of Pt sites, boosting the durability of the catalyst.

The researchers assembled a PEM water electrolyzer using this catalyst, which achieved an ultra-high current density of 4.0 A cm−2 at 2.02 V and maintained excellent durability over 1,000 hours at 2 A cm−2, using only 1.2 μgPt cm−2 Pt loading. They also assembled a 2.85 kW PEM water electrolyzer using this catalyst, which operated stably for over 300 hours at an industrial current density of 1.5 A cm−2, highlighting its outstanding industrial application potential.

“This work provides a new idea for developing high-performance, long-life, and low-cost catalysts for hydrogen production via acid water electrolysis,” said Prof. Deng.

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Rewriting Chemical Rules: Researchers Accidentally Create Unprecedented New Gold Compound

SLAC scientists created gold hydride in extreme lab conditions. The work sheds light on dense hydrogen and fusion processes.

By chance and for the first time, an international team of researchers led by scientists at the U.S. Department of Energy’s SLAC National Accelerator Laboratory succeeded in creating solid binary gold hydride a compound composed solely of gold and hydrogen atoms.

The team had originally set out to investigate how hydrocarbons, molecules made of carbon and hydrogen, transform into diamonds under extreme pressure and heat. During experiments at the European XFEL (X-ray Free-Electron Laser) in Germany, they placed hydrocarbon samples with a thin layer of gold foil, intended only to absorb X-rays and transfer heat to the relatively weakly absorbing hydrocarbons. Unexpectedly, alongside diamond formation, they observed the creation of gold hydride.

“It was unexpected because gold is typically chemically very boring and unreactive – that’s why we use it as an X-ray absorber in these experiments,” explained Mungo Frost, a staff scientist at SLAC and the study’s lead author. “These results suggest there’s potentially a lot of new chemistry to be discovered at extreme conditions where the effects of temperature and pressure start competing with conventional chemistry, and you can form these exotic compounds.”

The findings, published in Angewandte Chemie International Edition, demonstrate how chemical behavior can shift dramatically under extreme environments, such as those found deep inside planets or within hydrogen-fusing stars.

Studying dense hydrogen

To achieve these results, the researchers compressed hydrocarbon samples to pressures exceeding those inside Earth’s mantle using a diamond anvil cell. They then exposed the samples to bursts of X-ray pulses from the European XFEL, heating them above 3,500 degrees Fahrenheit. By analyzing how the X-rays scattered from the samples, the team tracked the structural changes taking place.

As anticipated, the data confirmed that carbon atoms had arranged into a diamond lattice. However, they also revealed unexpected signals: hydrogen atoms had reacted with the gold foil to form gold hydride.

At the conditions generated in the experiment, hydrogen existed in a dense, “superionic” state, in which hydrogen atoms moved freely within the rigid gold lattice. This behavior enhanced the conductivity of the gold hydride, offering new insight into the behavior of materials under extreme pressures and temperatures.

Hydrogen, which is the lightest element of the periodic table, is tricky to study with X-rays because it scatters X-rays only weakly. Here, however, the superionic hydrogen interacted with the much heavier gold atoms, and the team was able to observe hydrogen’s impact on how the gold lattice scattered X-rays. “We can use the gold lattice as a witness for what the hydrogen is doing,” Mungo said.

The gold hydride offers a way to study dense atomic hydrogen under conditions that might also apply to other situations that are experimentally not directly accessible. For example, dense hydrogen makes up the interiors of certain planets, so studying it in the lab could teach us more about those foreign worlds. It could also provide new insights into nuclear fusion processes inside stars like our sun and help develop technology to harness fusion energy here on Earth.

Exploring new chemistry

In addition to paving the way for studies of dense hydrogen, the research also offers an avenue for exploring new chemistry. Gold, which is commonly regarded as an unreactive metal, was found to form a stable hydride at extremely high pressure and temperature. In fact, it appears to be only stable at those extreme conditions as when it cools down, the gold and hydrogen separate. The simulations also showed that more hydrogen could fit in the gold lattice at higher pressure.

The simulation framework could also be extended beyond gold hydride. “It’s important that we can experimentally produce and model these states under these extreme conditions,” said Siegfried Glenzer, High Energy Density Division director and professor for photon science at SLAC and the study’s principal investigator. “These simulation tools could be applied to model other exotic material properties in extreme conditions.”

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