Adiponitrile synthesis

The largest use of acrylonitrile is the manufacture of adiponitrile, made by two different methods. One method is by the electrohydrodimerization of acrylonitrile. It is converted into hexamethylenediamine (HMDA), which is used to make nylon. The other adiponitrile synthesis is C4 chemistry, which will be discussed later in this chapter. Section 8. 

Retrosynthetic analysis of the adiponitrile synthesis leads to one synthon with reversed polarity and another with normal polarity ... 

This type of reaction is now of major industrial importance because it constitutes a straiglitforward synthesis of nitriles. Wlien it is applied to a diolefm, such as butadiene, it leads to the formation of dinitriles, which are precursors of valuable monomers for the preparation of polymers (butadiene leads to adipo-nilrile. a nylon-b, fvprecursor). Du Font developed the first commercial process using butadiene and HCN for adiponitrile synthesis from butadiene, but this process does nut proceed through a hydrocyanation reaction it is. in fact, a copper-catalyzed halogenation reaction followed by a cyanaikm reaction (tquaiion (16)) of the chlorinated intermediate (Fquation (17)). 

Example 8.7. Adiponitrile synthesis via hydrocyanation. Hydrocyanation of 4-pen-tenenitrile (4-PN) to adiponitrile (ADN) in the presence of an arylborane modifier ... 

Examples include acetal hydrolysis, base-catalyzed aldol condensation, olefin hydroformylation catalyzed by phosphine-substituted cobalt hydrocarbonyls, phosphate transfer in biological systems, enzymatic transamination, adiponitrile synthesis via hydrocyanation, olefin hydrogenation with Wilkinson s catalyst, and osmium tetroxide-catalyzed asymmetric dihydroxylation of olefins. 

In the DuPont butadiene-to-adiponitrile synthesis (see Section 2.5.5.1 and [1]), two olefin isomerization steps are employed rearrangement of 8 via C-C cleavage to the linear isomer 9 (a) is followed by a double-bond shift yielding the terminal olefin 10 (b). The latter is thermodynamically more stable because of the cyano functionality (cf eq. (13) and Section 2.5). 

Figure 6.3 Monsanto adiponitrile synthesis cell house at Decatur, Alabama, The cell stacks are placed in a filter press arrangement. Photograph supplied by Monsanto Corp.

Hydrogen cyanide is a large volume-hazardous chemical that serves diverse functions. DuPont is the single largest manufacturer of HCN in the world, producing 500 million pounds each year, both for internal use in synthesis and for external sales. The majority of HCN manufactured at DuPont is used internally, primarily for adiponitrile synthesis en route to production of nylon. In that case, HCN is reacted with butadiene to produce adiponitrile, an intermediate in the manufacture of nylon polymer. In addition, over one million lbs per year are shipped out in gas cylinders (approximately 4000 cylinders/year). 

---