Groundbreaking research at the Max Planck Institute has transformed chemical safety by developing a new synthesis protocol that combines steps to prevent accumulations of hazardous chemicals, reducing explosion risks and production costs. Credit: Issues.fr.com
The chemical industry has used a reaction with explosive chemicals for over 100 years. Now scientists from Mülheim have discovered a safer alternative.
Explosions and poisonings. Serious injuries or even deaths. In the history of the chemical industry, there have been repeated accidents, sometimes fatal, often caused by dangerous and explosive chemicals required for certain reactions.
Aryldiazonium salts, used for 140 years, are such chemicals. They are very reactive and therefore extremely useful for producing other compounds – dyes for example. However, due to their high reactivity, isolated aryldiazonium salts are not very stable and can therefore react unintentionally and sometimes explosively. On December 23, 1969, a particularly serious explosion involving these chemicals occurred at Ciba AG in Basel. A building was destroyed and heavy pieces of the reactor flew into the air. Three workers lost their lives and 31 were seriously injured. Despite these horrific reports, work continues with aryldiazonium salts.
Innovations in chemical safety
A team led by Professor Tobias Ritter, director of the Max Planck Institute for Kohlenforschung, has succeeded in making risky chemistry with aryldiazonium salts much safer. The Mülheim protocol not only makes the use of these compounds less dangerous, but also potentially opens up opportunities for the development of new reactions.
“Normally, the use of diazonium salts takes place in two stages: first the diazonium salt, which is dangerous, is isolated or accumulated, and then it is subsequently transformed into the desired product. In our project, we combine the two synthesis steps and obtain the desired product without accumulating the diazonium salt, which significantly reduces the risk of explosion,” explains Tim Schulte, doctoral student in Tobias Ritter’s group.
Javier Mateos (left), Tim Schulte and Tobias Ritter discuss their project in the laboratory. Credit: Gombert/MPI KOFO
New synthesis methods and their implications
Traditionally, aryldiazonium salts are synthesized from anilines with nitrous compounds. acid, or with nitrite compounds, a reaction that has seen little innovation over the years. The reaction must be carried out at low temperature (below 5°C) because aryldiazonium salts are unstable at higher temperatures. However, Javier Mateos, a postdoctoral researcher in the group, and Tim Schulte discovered a new method that allows for the presence of different nucleophiles in the reaction mixture.
The new strategy is based on the use of a natural process, the reduction of nitrates, carried out in plants. Researchers were able to mimic the natural process in a test tube and combine it with aryl diazonium chemistry to develop a safer synthesis method. In this way, the aforementioned limitations associated with traditional methods such as temperature sensitivity and the need for strong acids can be avoided.
Because the researchers combine several steps in their new protocol, large concentrations of dangerous substances do not occur in the first place. And that’s not all that the Mülheim scientists discovered: “For our synthesis method, we use chemicals that are used in large quantities in the fertilizer and fuel industry and are therefore inexpensive” , explains Tim Schulte. This could make the synthesis route extremely attractive for companies in the chemical industry, as it would result in reduced production costs.
“The solution to the problem could have been found 100 years ago, but the reaction as discovered today would probably not have been planned in the same way,” explains Tobias Ritter. “The combination of chemicals that ultimately gave good results was discovered by chance while we were working on another project,” reveals Javier Mateos. Although the reagents used have been known for a long time, their potential for diazonium chemistry was until now simply overlooked.
The new method is also scientifically exciting, because new chemical approaches can now be pursued, which would not be possible with the classical method due to the high explosion risk and the instability of the connections.
