Hydrocyanation DuPont process

Hydrocyanation represents a reaction of considerable economic importance largely due to the value of the DuPont process involving HCN addition to butadiene to afford adiponitrile.61,62 The mechanism is well known, and involves (i) oxidative addition of H-CN to a coordinatively unsaturated metal complex, (ii) coordination of an alkene to the H-M-CN species, (iii) migratory... 

Isomerisation is also an important step in the DuPont process for making adiponitrile (Chapter 11) in which internal pentenenitriles must be converted to the terminal alkene. The catalyst is the same as that used for the hydrocyanation reaction, namely nickel(II) hydrides containing phosphite ligands. 

Among other nonaddition processes, adiponitrile may be manufactured by the direct hydrocyanation of 1,3-butadiene (DuPont process).169 172,187 196 A homogeneous Ni(0) complex catalyzes both steps of addition of HCN to the olefinic bonds (Scheme 6.4). The isomeric monocyano butenes (20 and 21) are first formed in a ratio of approximately 1 2. All subsequent steps, the isomerization of 20 to the desired 1,4-addition product (21), a further isomerization step (double-bond migration), and the addition of the second molecule of HCN, are promoted by Lewis acids (ZnCl2 or SnCl2). Without Lewis acids the last step is much slower then the addition of the first molecule of HCN. Reaction temperatures below 150°C are employed. 

Several large-scale industrial processes use homogeneous catalysts [e.g., hydrofor-mylation, hydrocyanation (DuPont), ethene-oligomerization (SHOP), acetic add (Eastman Kodak), acetic acid anhydride (Tennessee-Eastman), acetaldehyde (Wacker) and terephthalic acid (Amoco)] as well as smaller scale applications [e.g., metolachlor (Novartis), citronellal (Takasago), indenoxide (Merck) and glycidol (ARCO, SIPSY)]. 

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. 

The transition metal catalysed addition of HCN to alkenes is potentially a very useful reaction in organic synthesis and it certainly would have been more widely applied in the laboratory if its attraction were not largely offset by the toxicity of HCN. Industrially the difficulties can be minimised to an acceptable level and we are not aware of major accidents. DuPont has commercialised the addition of HCN to butadiene for the production of adiponitrile [ADN, NC(CH2)4CN], a precursor to 1,6-hexanediamine, one of the components of 6,6-nylon and polyurethanes (after reaction with diisocyanates). The details of the hydrocyanation process have not been released, but a substantial amount of related basic chemistry has been published. The development of the ligand parameters % and 0 by Tolman formed part of the basic studies carried out in the Du Pont labs related to the ADN process [1],... 

The hydrocyanation of alkenes [1] has great potential in catalytic carbon-carbon bond-formation because the nitriles obtained can be converted into a variety of products [2]. Although the cyanation of aryl halides [3] and carbon-hetero double bonds (aldehydes, ketones, and imines) [4] is well studied, the hydrocyanation of alkenes has mainly focused on the DuPont adiponitrile process [5]. Adiponitrile is produced from butadiene in a three-step process via hydrocyanation, isomerization, and a second hydrocyanation step, as displayed in Figure 1. This process was developed in the 1970s with a monodentate phosphite-based zerovalent nickel catalyst [6],... 

Large-scale manufacturing processes involving isomerization reactions by homogeneous catalysts are few. Two important ones are the isomerization step in the SHOP process and the enantioselective isomerization of diethylgeranyl or diethylnerylamine as practiced by the Takasago Perfumery. The isomerization step in the SHOP process is discussed later on in this chapter. The Takasago process is discussed in Chapter 9. Isomerization of alkenes with nitrile functionalities is very important in DuPont s hydrocyanation process. The mechanism for this reaction is discussed in Section 7.7. 

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... 

Hydrocyanation is the addition of HCN across a C=C bond. In 1971, Dupont reported a new process that added two equivalents of HCN, in an anti-Markovnikov manner, to 1,3-butadiene to yield adiponitrile (equation 9.38).96 The process is catalyzed overall by a Ni(0) triarylphosphite complex. 

The addition of HCN to C=C double bonds can be effected in low yields to produce Markovnikov addition products. However, through the use of transition metal catalysts, the selective anti-Markovnikov addition of HCN to alkenes can take place. The most prominent example of the use of aqueous media for transition metal-catalyzed alkene hydrocyanation chemistry is the three-step synthesis of adi-ponitrile from butadiene and HCN (Eqs. 5-7). First discovered by Drinkard at DuPont [14], this nickel-catalyzed chemistry can use a wide variety of phosphorus ligands [15] and is practiced commercially in nonaqueous media by both DuPont and Butachimie, A DuPont/Rhone-Poulenc joint venture. Since the initial reports of Drinkard, first Kuntz [16] and, more recently, Huser and Perron [17, 18] from Rhone-Poulenc have explored the use of water-soluble ligands for this process to facilitate catalyst recovery and recycle from these high-boiling organic products. 

The mechanism and regioselectivity of hydrocyanation is discussed in several reviews13 and a short recent survey on the current status of knowledge about stereochemistry and asymmetric induction is available9. In particular, synthetic and mechanistic aspects of the nickel-catalyzed hydrocyanatioii of butadiene is examined10 in view of the importance of the DuPont adiponi-trile process. 

One of the few available examples is represented by the synthesis of cilastatine by a chiral Cu complex promoted cyclopropanation reaction developed by Sumitomo Chemical Co. [78]. Another is the catalytic asymmetric hydrocyanation of vinylarenes developed at DuPont [79]. In this process (Fig. 27) sugar-derived phosphinites are used in combination with a Ni catalyst to prepare enantiomerically enriched precursors of the NSAID naproxen. 

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. " ... 

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. 

The addition of HCN to olefins catalyzed by complexes of transition metals has been studied since about 1950. The first hydrocyanation by a homogeneous catalyst was reported by Arthur with cobalt carbonyl as catalyst. These reactions gave the branched nitrile as the predominant product. Nickel complexes of phosphites are more active catalysts for hydrocyanation, and these catalysts give the anti-Markovnikov product with terminal alkenes. The first nickel-catalyzed hydrocyanations were disclosed by Drinkard and by Brown and Rick. The development of this nickel-catalyzed chemistry into the commercially important addition to butadiene (Equation 16.3) was conducted at DuPont. Taylor and Swift referred to hydrocyanation of butadiene, and Drinkard exploited this chemistry for the synthesis of adiponitrile. The mechanism of ftiis process was pursued in depth by Tolman. As a result of this work, butadiene hydrocyanation was commercialized in 1971. The development of hydrocyanation is one of tfie early success stories in homogeneous catalysis. Significant improvements in catalysts have been made since that time, and many reviews have now been written on this subject. ... 

Though how optimized and elaborate the process has become, it competes with other routes. For adiponitrile, the nickel-catalyzed hydrocyanation of butadiene is today regarded as the most cost-effective route [28]. This route has originally been developed at DuPont [27] and it is sensitive to the natural gas price, while for the electrohydrodimerization, the propylene price is of interest. Today adiponitrile is produced for the most part by hydrocyanation [28]. This makes an industrial aspect of organic electrochemistry very clear the electrolysis has to generate a profitable product. The efficiency of a process with high yields is one step to this profitable product. In the end factors like the raw material basis may make the difference between being competitive and not especially for a commodity like adiponitrile. 

The famous Ni-catalyzed hydrocyanation of 1,3-butadiene to adiponitrile (the DuPont or ADN process) opens the pathway to the homogeneously catalyzed, large-scale production of Nylon-6,6 via adipic acid and 1,6-diaminohexane, both downstream products of adiponitrile. This reaction today, of course. 

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. 

DuPont developed a manufacturing process for adiponitrile (ADN), a raw material for nylon 6,6, by the hydrocyanation of butadiene using homogeneous nickel catalysts. As shown by reaction 5.6.1, this involves the addition of two molecules of HCN to butadiene. 

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