New catalysts enable greener ester synthesis – Lab Manager

A new catalyst could be the catalyst for a move to a greener chemistry.

Scientists at Yokohama National University developed two innovative catalysts containing noble metals. These catalysts are highly efficient in producing ester and use oxygen as their sole oxidant. This makes the process more sustainable and environmentally friendly.

The results of the study were published recently in the Journal of the American Chemical Society .

Cross-Dehydrogenative Coupling (CDC) reactions belong to the category of C-H bond activation reactions, which play a crucial role in organic synthesis and industrial chemistry. CDC reactions are widely used as strategies for sustainable chemical synthesis due to their atom-economy, which means they minimize waste and use reactants efficiently.

CDC reactions occur between arenes and carboxylic acid to activate the CH bond in arenes (aromatic hydrocarbons like benzene), forming CO bonds with carboxylic acid to produce aryl ester. Esters are widely used chemical compounds in many industries including pharmaceuticals and polymer manufacturing.

To produce these CDC reactions however, oxidants or oxidizing substances are required.

“Cross-dehydrogenative coupling reactions of arenes and carboxylic acids have typically been conducted by homogeneous catalysts with hazardous oxidants such as hypervalent iodine reagents,” said Ken Motokura, a professor at the Faculty of Engineering of Yokohama National University and corresponding author of the study.

These oxidants are highly toxic for humans and animals. They can also cause explosions or create pollution or harmful byproducts. These methods are therefore a significant threat to the environment and safety.

In an effort to develop a more environmentally friendly approach, the team of researchers developed catalysts known as RhRu bimetallic oxygen clusters (RhRuO x/C), composed of two noble metals, Rhodium and Ruthenium, combined with oxygen. These catalysts, which have a diameter of only 1.2 nm on average, showed exceptional catalytic activity when used as sole oxidants in CDC reactions. The molecule oxygen is abundant, non-toxic and environmentally friendly. It also converts reactants into products with only water as a byproduct.

Researchers confirmed the formation and structure of bimetallic clusters RhRu using advanced imaging and spectrum techniques. The mechanism of the reaction was revealed by detailed kinetic and computer studies. It was shown that the catalysts are highly reactive with different types of carboxylic acid and arenes, which makes them very versatile in producing aryl ester.

Shingo Hasegawa is an assistant professor in the Faculty of Engineering at Yokohama National University. He was the first author of the research.

These new catalysts have the potential to make chemical reactions more efficient and sustainable, opening up opportunities for greener chemical syntheses. Researchers plan to investigate the use of these catalysers in other important chemical reaction.

Motokura stated that “our ultimate goal is to establish efficient, regioselective C–H functionalization reactions using metal oxide clusters under mild conditions. This will promote more environmentally friendly chemical practices.”

– This press release has been provided by Yokohama National University . It has been edited to improve style and clarity