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). 

The Monsanto adiponitrile process, first commercialized in 1965 (65—67), involves the dimerization of acrylonitrile at the cathode in an electrolytic cell (eq. 7) ... 

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. 

Danly DE (1979) Discovery, development and commercialization of the electrochemical adiponitrile process, Amstrong Lecture, Part 2 Chem and Ind (London) (13)439 Client Abstr 92 (1980) 42379k... 

Monoterpenoid ketones, 24 536-541 Monoterpenoids, 24 468, 470, 472, 484-541 Monothiocarboxylic acids, 23 739 Monotropic phase transitions, 15 101 Monounsaturated fatty acids, 10 830 Monounsaturated olefins, hydrogenation of, 26 879-880 Monovinylacetylene, 1 230 Monsanto acetic acid process, 19 646 Monsanto adiponitrile process, 17 236 Monsanto aluminum chloride-based Alkylation process, 23 333 Monsanto Prism separator, 16 21 Monsanto process (Lummus-UOP Classic process), 16 74 23 339, 341 Monsanto-Washington University collaboration, 24 390, 400-401 Montanic acid... 

Figure 19.16. Basic designs of electrolytic cells, (a) Basic type of two-compartment cell used when mixing of anolyte and catholyte is to be minimized the partition may be a porous diaphragm or an ion exchange membrane that allows only selected ions to pass, (b) Mercury cell for brine electrolysis. The released Na dissolves in the Hg and is withdrawn to another zone where it forms salt-free NaOH with water, (c) Monopolar electrical connections each cell is connected separately to the power supply so they are in parallel at low voltage, (d) Bipolar electrical connections 50 or more cells may be series and may require supply at several hundred volts, (e) Bipolar-connected cells for the Monsanto adiponitrile process. Spacings between electrodes and membrane are 0.8-3.2 mm. (f) New type of cell for the Monsanto adiponitrile process, without partitions the stack consists of 50-200 steel plates with 0.0-0.2 ram coating of Cd. Electrolyte velocity of l-2 m/sec sweeps out generated Oz.

In this article, we will discuss the chemistry behind the du Pont adiponitrile process from a mechanistic viewpoint (10). It is not intended to be a comprehensive review of the hydrocyanation literature. We will restrict ourselves rather to homogeneous nickel-catalyzed hydrocyanation of olefins and will depend primarily on du Pont studies. Reviews which explore hydrocyanation in a more general way include those of Brown (77), Hubert and Puentes (72), and James (73). A general review of low-valent organo-nickel chemistry has been published by Jolly and Wilke (14). 

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. 

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],... 

Tolman, Druliner, and McKinney [5] were pioneers in nickel-catalyzed hydrocyanation they used monodentate phosphites mainly to understand and improve the adiponitrile process. Although bidentate ligands give better results in the adiponi-trile process [21], mechanistic studies with these systems are rare bidentate phos-phinites have been studied in the asymmetric hydrocyanation of MVN [19]. 

In asymmetric hydrocyanation reactions the desired isomers are the chiral branched products only. Good regioselectivity toward the branched product (>98%) is limited to vinylarenes. Hydrocyanation of 1,3-dienes gives a variety of mixtures depending on the catalyst and conditions 1-alkenes give the linear nitrile as major product [34]. Both are seen in the adiponitrile process in which the unwanted branched 2M3BN (hydrocyanation product from 1,3-butadiene) is isomerized to the linear product 3-pentenenitrile, which is then hydrocyanated by in-situ isomerization to 4-pentenenitrile, resulting in the linear adiponitrile. Thus vinylarenes and cyclic alkenes (mainly norbomene) are usually the substrates of choice for the asymmetric hydrocyanation. Hopefully 1,3-dienes will become feasible substrates in the near future. 

The application of electrochemistry in organic synthesis had already served to bring on stream in the United States in 1965 Monsanto s first industrial adiponitrile process from acrylonitrile. This was followed in 1977 by a similar installation in Seal Sands, England, which was later bought up by BASF. 

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). 

A new route to prepare nicotinic acid starts from 2-methylglutaronitrile, a major side-product in the adiponitrile process and, as such, a readily available starting-material. It is easily hydrogenated to 2-methylpentanediamine, which is then condensed to methyl piperidine and dehydrogenated to 3-picoline. The gas-phase ammoxidation of the latter to cyanopyridine is followed by hydrolysis to either nicotinamide or nicotinic acid (Scheme 20.4). The cyanopyridine route for the production of nicotinic acid has the advantage of a significantly better selectivity with respect to the direct oxidation route from 3-picoline owing to the easy decar-... 

Palladium-catalyzed hydrocyanation of olefins has been reported [31]. However, the corresponding reactions with conjugated dienes have not been reported explicitly. The analogous nickel-catalyzed hydrocyanation of conjugated dienes has been described [32] and is the basis for the commercial adiponitrile process. In this case, it has been shown [33] that the overall addition of HCN to the 1,3-diene occurs with cis stereochemistry consistent with path B in Scheme 8-1. 

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... 

FIGURE 26.19 Schematic diagram of the adiponitrile process flowsheet. AN = acrylonitrile, ADN = adiponi-hile, QS = quaternary ammonium salt [30] (with kind permission from Springer Science and Business Media). 

During fhel970s, bofh a larger plant and a second plant were built. These expansions employed a second-generation, undivided cell design, with an emulsified reaction medium composed of 7% acrylonitrile in an aqueous solution of 15% disodium hydrogen phosphate with a low concentration (0.4%) of a quaternary ammonium salt. More information on the Monsanto adiponitrile process are found in [28-30, 42 (Part III), 65, 66]. 

Ever since Monsanto commercialized their adiponitrile process in 1965 by electrolytic reductive coupling of acrylonitrile, a number of attempts at the commercialization of electrochemical reductions have been made. None of these attempts has succeeded in producing the tonnages involved in the adiponitrile process of approximately 100 000 tonne p.a. on plants both in the U.K and the U.S.A. However a number of significant tonnage production operations have been built and are outlined below. 

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