2024-03-21 05:00:05
Palladium is widely used by the chemical industry to promote major organic chemistry reactions. Finding alternatives to this very expensive and toxic metal is a real challenge. As part of a collaboration between France and the Netherlands, chemists have developed catalysts based on cobalt, a less toxic metal and 5000 times more abundant than palladium, which outperform its performance under extremely mild reaction conditions. .
The chemical industry commonly uses palladium-based catalysts for the production of high value-added organic compounds. The most notable case is the oxidation of olefins* to obtain ketones**. These ketones are key molecules that serve as building blocks for the synthesis of many drugs or materials. One of the most powerful methods for preparing these bricks is the Wacker process which allows ketones to be obtained from olefins from oil (Petroleum is a carbonaceous liquid rock, or mineral oil. The exploitation of…). This process has been used since the 1950s to produce millions of tons of acetaldehyde per year from ethylene. It requires the addition of palladium and copper catalysts, temperature conditions and pression (Pressure is a fundamental physical concept. It can be seen as a reported force…) very high and an acidic environment. Unfortunately, palladium, a key constituent of these reactions, is present in low quantities. quantity (Quantity is a generic metrology term (account, amount); a scalar,…) in the earth’s crust and could well disappear over the next century if its use continues at the current rate. It is also toxic and must therefore be purified from the final products.
Chemists from the Institute of Chemical Sciences of Rennes (CNRS/Université Rennes/ENSCR/INSA Rennes) and the University of Amsterdam have recently shown the possibility of using cobalt instead of palladium to catalyze the oxidation of olefins to ketones. The synthesis process, published in the journal Applied Chemistry International Edition, takes place under much milder reaction conditions than the Wacker process (ambient pressure and temperature) while avoiding the copper co-catalyst. In addition, these cobalt oxidation reactions take place in ethanol which avoids the acidic conditions conventionally used with palladium catalysts. Surprisingly, the addition of a silane hydride (And3SiH) as an additive makes it possible to greatly accelerate the reaction rates which take place in 10 minutes using a very low ratio of cobalt per olefin of 1 to 100.
These values ​​make cobalt catalysts the most promising current candidates to replace palladium in the production of ketones. They largely surpass a first generation of catalysts based on iron, a very abundant and non-toxic metal, patented and published last year by the same team of scientists in the journal ACS Catalysis.
© Rafael GRAMAGE-DORIA
Computational calculations carried out in parallel with the experimental study show that the optimal functioning of cobalt requires that it be dispersed in the reaction medium by the porphyrin ligands and that the formation of bonds hydrogen (Hydrogen is a chemical element with symbol H and atomic number 1.) thanks to ethanol is a determining factor for the selective formation of ketones. This work, carried out as part of a thesis PHD (Le doctorat (from the Latin doctorem, de doctum, supin de docere, enseigner) is generally…) partly financed by the PAUSE program of the Collège de Francewill continue in the future while being supported by the CNRS prematurity program.
Notes:
* Olefins = molecules containing a carbon-carbon double bond (C=C).
**Ketones = molecules containing a carbon-oxygen double bond (C=O)
Editor: AVR
References:
Catalyst Complexity in a Highly Active and Selective Wacker-Type Markovnikov Oxidation of Olefins with a Bioinspired Iron Complex
Jonathan Trouvé, Sitthichok Kasemthaveechok, Khalil Youssef, Rafael Gramage-Doria.
ACS Catalysis 2023
https://doi.org/10.1021/acscatal.3c00593
Markovnikov-Selective Cobalt-Catalyzed Wacker-Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding
Naba Abuhafez, Andreas W. Ehlers, Bas de Bruin, Rafael Gramage-Doria.
Applied Chemistry Int. Ed. 2024
1711204478
#Replace #palladium #toxic