Chemistry: a hammer for molecular bartering!

A safe variant of hydrocyanation gives chemists a versatile tool with a reversible function

February 24, 2016

Chemistry is like a toolbox. To synthesize pharmaceuticals, plastics or dyes, chemists reach for various reagents and methods like craftspeople reach for their tools. Scientists from the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr have now presented a new chemical tool that facilitates an important synthesis step, hydrocyanation, in a safer manner than the conventional method. This is like inventing a hammer that would make it impossible to hit your thumb. The researchers have swapped two functional groups – a cyano group and a double bond – between molecules. Functional groups are like hooks or eyelets for molecules. Attaching a cyano group to a molecule creates a range of possibilities for modifying it and is an important reaction step, for example in the production of nylon. Until now, hydrocyanation required the use of toxic hydrogen cyanide, more commonly known as prussic acid.

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Molecular bartering: Chemists at the Max-Planck-Institut für Kohlenforschung have found a safe way for transposing a cyanide group (CN), a functional group that creates many possibilities for reacting a substance, from one molecule (R’-) to another (R-). In the process, the donor molecule receives the double bond (=) of its reaction partner.
Molecular bartering: Chemists at the Max-Planck-Institut für Kohlenforschung have found a safe way for transposing a cyanide group (CN), a functional group that creates many possibilities for reacting a substance, from one molecule (R’-) to another (R-). In the process, the donor molecule receives the double bond (=) of its reaction partner.

Sometimes even chemists don’t like chemistry. “We wondered why hydrocyanation is so rarely used, especially in research labs,” says Bill Morandi, Leader of a Research Group at the Max-Planck-Institut für Kohlenforschung. In this reaction, chemists attach a cyano group to a molecule. In doing so, they add an extra atom to the carbon skeleton of an organic molecule. Moreover, the cyano group can be converted into other functional groups that can be used to carry out further reaction steps or that decisively determine the properties of the final product, such as pharmaceuticals.

“Hydrocyanation is a very important industrial process,” Bill Morandi explains. The chemical industry uses the reaction to synthesize around a million metric tons of adiponitrile, an intermediate for the production of nylon, every year. However, until now this reaction has only worked with hydrogen cyanide or similarly toxic substances containing cyanide. For this reason, many chemists, especially those working in research, evidently avoid hydrocyanation in the search for new substances that could be useful to medicinal chemistry or the chemical industry. Chemists in Bill Morandi’s Group have now found a safe way to transfer a cyano group from one organic molecule to another. Specifically, one molecule swaps a cyano group for the other molecule’s double bond. Double bonds are something that even have their place in the supermarket, as they make unsaturated fatty acids healthier than their saturated counterparts.

“Surprising that alternative hydrocyanation has only now been discovered”

The swapping of chemical groups became possible because the Max Planck researchers were able to find a suitable catalyst. Catalysts accelerate chemical reactions and facilitate many conversions, such as the chemical exchange reaction discovered in Mülheim. As Morandi’s team has demonstrated in reactions with a wide range of starting molecules, the new catalyst transfers the cyano group in a precisely predictable manner. That is not always the case when functional groups are added, but it is essential for obtaining the desired substance. In some of the cases that Morandi’s team studied, the chemical group ended up in positions where it was previously impossible to attach it.

“It’s surprising that this alternative method of hydrocyanation has only now been discovered,” says Bill Morandi. Indeed, the catalyst resembles the reaction accelerator that is already being used for hydrocyanation. It is therefore to the credit of Bill Morandi and his colleagues that a harmless replacement has been developed for an important but dangerous tool.

A chemical tool whose effect can be reversed

The new reaction is not only safer than the conventional method of hydrocyanation, “it can also be easily reversed,” Morandi says. It’s as if the new hammer in the chemical toolbox therefore not only prevents bruised thumbs but also doubles as pliers. That could be particularly useful in research where the aim is to insert double bonds precisely at sites in a molecule where they cannot be created by any other means. The researchers also demonstrated this property in a broad range of exchange reactions. They even succeeded in inserting a double bond at a precise location in an estrogen. The fact that the tool reliably performs such specific and challenging tasks should be of interest not only to researchers but also to industry.

“The new form of hydrocyanation is probably still too expensive to replace the old industrial process,” Bill Morandi says. However, the team has already tested a cost-effective variant. In addition, the researchers want to swap other functional groups. This reaction principle, known as metathesis, earned its discoverers the 2005 Nobel Prize for Chemistry. In this way, the Mülheim-based researchers may in future develop additional reliable, versatile, and above all, safe tools for chemistry.

PH

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