Approaching Bulk Chemical Nitriles from Alkenes: A Hydrogen Cyanide-Free Approach through a Combination of Hydroformylation and Biocatalysis

A current challenge in catalysis is the development of methodologies for the production of bulk chemicals needed at levels of tens and hundreds of thousands of tons per year with the requirement to be produced at very low costs often being in the single-digit US dollar range. At the same time, such methodologies should address challenges raised by current manufacturing processes. Within this research area, a cyanide-free approach toward aliphatic nitriles used as industrial chemicals was developed starting from readily accessible n-alkenes as starting materials available in bulk quantities. This chemoenzymatic process concept is exemplified for the synthesis of nonanenitrile (as an n-/iso-mixture) and runs in water at low to moderate temperatures without the need for any types of cyanide sources. The process is based on a combination of a metal-catalyzed hydroformylation as the world-leading production technology for alkyl aldehydes with an emerging enzyme technology, namely, the recently developed transformation of aldoximes into nitriles through dehydration by means of aldoxime dehydratases. As a missing link, an efficient aldoxime formation with subsequent removal of remaining traces of hydroxylamine as an enzyme-deactivating component was found, which enabled the merging of these three steps, hydroformylation, aldoxime formation, and enzymatic dehydration, toward a nitrile synthesis without the need for purification of intermediates.