Hydrocyanation of alkenes and dienes

While hydrocyanation, the addition of HCN to an unsaturated substrate, is not the only method of producing an organonitrile, it is often the easiest and most economical. The addition of HCN to aldehydes and ketones is readily accomplished with simple base catalysis, as is its addition to activated aUcenes (Michael addition). However, the addition of HCN to unactivated alkenes and dienes is best accomplished with a transition metal catalyst. The hydrocyanation of alkenes and dienes is the most important way to prepare nitriles and is the focus of this article. 

The hydrocyanation of alkenes and dienes has similarly provided an exceptionally useful process for the conversion of simple feedstocks into more complex structures. [Caution Hydrogen cyanide is a highly toxic gas.] The process is best known as a key step in the DuPont adiponitrile process, which involves the dihydrocyanation of 1,3-butadiene (Scheme 3-95). The overall sequence first involves butadiene hydrocyanation to afford a mixture of 3-pentenenitrile and 2-methyl-3-butenenitrile. The unwanted branched isomer 2-methyl-3-butenenitrile is isomerized to 3-pentenenitrile under different conditions, and then 3-pentenenitrile is isomerized to 4-pentenenitrile in a subsequent nickel-catalyzed process in the presence of Lewis acidic additives. Finally, hydrocyanation of the remaining alkene generates the desired product adiponitrile, which serves as a precursor for nylon. A vast number of studies describing the optimization and mechanistic study of this process has appeared, and the interested reader is referred to the many excellent studies describing the details of this process. " ... 

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