DuPont’s adiponitrile process

Addition of HCN to unsaturated compounds is often the easiest and most economical method of making organonitnles. An early synthesis of acrylonitrile involved the addition of HCN to acetylene. The addition of HCN to aldehydes and ketones is readily accompHshed with simple base catalysis, as is the addition of HCN to activated olefins (Michael addition). However, the addition of HCN to unactivated olefins and the regioselective addition to dienes is best accompHshed with a transition-metal catalyst, as illustrated by DuPont s adiponitrile process (6—9). 

Pentenenitnles are produced as intermediates and by-products in DuPont s adiponitrile process. 3-Pentenenitrile [4635-87-4] is the principal product isolated from the isomerisation of 2-methyl-3-butenenitrile (see eq. 4). It is entirely used to make adiponitrile. i7j -2-Pentenenitrile [25899-50-7] is a by-product isolated from the second hydrocyanation step. Some physical properties are Hsted in Table 13. 

Pentenenitriles are produced as intermediates and by-products in DuPont s adiponitrile process. 3-Pentenenilrile is the principal product isolated from the isomerization of 2-mcthyl-3-butcnenitrilc. 

Methylglutaronitrile (2,3-dicyanobutane) [4553-62-2], MGN, is a by-product of DuPont s adiponitrile process. The oral LD5Q (rats) is 400 mg/kg (29). Some physical properties are listed in Table 12. 

Liquid/liquid extraction of the catalyst, as in the DuPont adiponitrile process, where the nickel complex is extracted out of the product mixture after the reaction, with a solvent (see Section 7.7). In Shell s SHOP process the soluble nickel catalyst is also extracted from the reaction medium with a highly polar solvent, and reused (see Section 7.4.1). 

The most outstanding example for the applieation of homogeneously catalyzed hydrocyanation is the DuPont adiponitrile process. About 75 % of the world s demand for adiponitrile is covered by hydrocyanation of butadiene in the presence of nickel(O) phosphite species. This process is discussed for the addition of HCN to dienes as an example, because in this case a well-founded set of data is available. Though it was Taylor and Swift who referred to hydrocyanation of butadiene for the first time [45], it was to Drinkard s credit that this principle was fully exploited for the development of the DuPont adiponitrile process [18]. The overall process is described as the addition of two equivalents of HCN to butadiene in the presence of a tetrakisphosphite-nickel(O) catalyst and a Lewis acid promoter. A phosphine-containing ligand system for the catalyst is not suitable, since addition of HCN to the tetrakisphosphine-nickel complex results in the formation of hydrogen and the non-aetive dicyano complex [67], In general the reaction can... 

DuPont s process for adiponitrile, used in the manufacture of Nylon from butadiene and HCN, contains a step in which a branched chain (2-methyl-3-butenenitrile) is converted to a straight chain olefin... 

The hydrocyanation of butadienes is the basis of DuPont s process for the production of adiponitrile [hexanedinitrile (19), Scheme llj.l l The first step of the process involves hydrocyanation of huta-1,3-diene to produce an isomeric mixture of pentenenitriles. In a second step, nickel-catalyzed double-bond isomerization occurs to produce pent-4-eneni-trile followed by alkene hydrocyanation to produce adiponitrile (19). The details of the al-kene hydrocyanation reaction are discussed in further detail in Section 1.1.4.5. 

An early example of the application of this oxidative addition reaction to a catalytic process is the DuPont s production of adiponitrile, which includes a nickel-catalyzed isomerization reaction of allylic cyanides (62 -> 63 in Scheme 6.11) [33]. Thorough mechanistic studies identified a jt-allyl nickel cyanide complex formed via oxidative addition of a C-CN bond as the intermediate for this isomerization reaction [34]. 

The DuPont direct hydrocyanation of butadiene process for the production of hexamethylene diamine can also be adapted for the production of caprolactam. Partial hydrogenation of the adiponitrile intermediate in which only one cyanide group is converted to the amine, followed by hydrolysis of the remaining cyanide group and ring closure can produce s-caprolactam. The process has not been developed commercially. It is also possible that a two-stage butadiene car-bony lation process to produce caprolactam, developed by DSM and Shell, may be further developed. 

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