(28f) Cyanide-Free Adiponitrile Production from Biomass-Derived Adipaldehyde

Adiponitrile is a petroleum-based intermediate in the synthesis of Nylon 6,6 that is produced on a scale of 1 million tons annually. The dominant method consists of hydrocyanation of butadiene. This method requires the use of hazardous hydrogen cyanide and leads to significant byproducts such as 2-methylglutaronitrile. Adiponitrile can also be made from the electrochemical hydrodimerization of acrylonitrile. Acrylonitrile is a petroleum-derived platform chemical, and the dimerization suffers from selectivity issues.

A new renewable intermediate suitable for adiponitrile production is adipaldehyde. Adipaldehyde, or hexanedialdehyde, can be derived from processing either lignin or cellulose. Adipaldehyde can be converted into adiponitrile via a two-step process. First, adipaldehyde can combine with hydroxylamine to form adipaldehyde dioxime. Then, the dioxime can be dehydrated to adiponitrile.

The dehydration of adipaldehyde dioxime has been performed using enzymatic systems, but the time required was over a day. Oxime dehydration has been performed at mild temperatures for a range of oximes using nickel salts in acetonitrile. The reaction time required was only 3 hours.

Here, we implement the nickel catalyst system for the dehydration of adipaldehyde dioxime to adiponitrile. High yields are obtained after three hours at acetonitrile reflux. It was found that the nitrile solvent participates in the reaction and forms significant amounts of the corresponding amide as byproduct. Using acetonitrile as solvent ensured consumption of the acetonitrile and allowed high yields of adiponitrile. This process could be a viable route to produce drop-in adiponitrile for Nylon 6,6 production with high yields and no cyanide required.