Nitrile compounds (R–N≡N) are important for the manufacturing of fragrances, pharmaceuticals, superglue and chemical-resistant gloves. Currently, such nitrile compounds require the use of highly toxic cyanide in their synthesis. Now, an alternative cyanide-free chemo-enzymatic cascade process is being developed by a research team from Graz University of Technology (TU Graz; Austria; www.tugraz.at) and the Czech Academy of Sciences (Prague; www.avcr.cz) in a project funded by the Austrian Science Fund FWF and the Czech Science Foundation (GACR).
The project, led by Margit Winkler from the Institute of Molecular Biotechnology at TU Graz and Ludmila Martínková from the Institute of Microbiology at the Czech Academy of Sciences, revolves around a biocatalytic process that does not require cyanide, works at room temperature and therefore requires less energy and produces less harmful waste. To replace the cyanide, the research group uses enzymes and combines three individual reactions into a cascade (diagram). In the first step, a carboxylic acid (such as fatty acids from plant oils or lignin, a byproduct of wood processing) is converted to an aldehyde by adding sugar, oxygen and the enzyme carboxylate reductase contained in living bacterial cells. This highly reactive, unstable aldehyde is reacted with hydroxylamine to make a stable oxime. In the final step, the enzyme aldoxime dehydratase is used to remove water from the oxime to give the desired nitrile.
So far, the method has only produced small quantities of nitriles — which may be sufficient for potent fragrances, but has not been optimized for scaling up to larger amounts. Winkler is currently conducting research on how to make the first step more efficient. Dehydration of the oxime alone, on the other hand, is extremely efficient and already reached technical maturity for production today.
Source: IMBT — TU Graz