Adiponitrile

Adiponitrile. Adiponitrile is an important intermediate in polyamide manufacture. 1,6-Hexamethylenediamine formed by the hydrogenation of adiponitrile is used in the production of nylon-6,6, one of the most important polyamides in commercial production. 

Adiponitrile, a colorless liquid, is slightly soluble in water but soluble in alcohol. The main use of adiponitrile is to make nylon 6/6. 

The production of adiponitrile from butadiene starts by a free radical chlorination, which produces a mixture of 1,4-dichloro-2-butene and 3,4-dichloro -1-butene  

The vapor-phase chlorination reaction occurs at approximately 200-300°C. The dichlorobutene mixture is then treated with NaCN or HCN in presence of copper cyanide. The product 1,4-dicyano-2-butene is obtained in high yield because allylic rearrangement to the more thermodynamically stable isomer occurs during the cyanation reaction  

The dicyano compound is then hydrogenated over a platinum catalyst to adiponitrile. 

Adiponitrile may also be produced by the electrodimerization of acrylonitrile (Chapter 8) or by the reaction of ammonia with adipic acid followed by two-step dehydration reactions  

Adiponitrile is made by two different methods. One method is by the electrohydrodimerization of acrylonitrile. It is converted into hexamethyl-enediamine (HMDA) that is used to make nylon. 

In the electrodimerization of acrylonitrile, a two-phase system containing a phase transfer catalyst tetrabutylammonium tosylate is used. 

Malononitrile is a highly toxic compound by all toxic routes. Its acute toxicity is somewhat greater than that of the aliphatic mononitriles, propionitrile, and butyronitrile. The increased toxicity may be attributed to the greater degree of reactivity in the molecule arising from two —CN functional groups. The acute toxic symptoms in test animals have not been well documented. An intraperitoneal dose of 10 mg/kg was lethal to rats. 

LD50 value, intravenous (rabbits) 28 mg/kg LD50 value, oral (mice) 19 mg/kg 

Malononitrile is an eye irritant. The irritation from 5 mg in 24 hours was severe in rabbits eyes. There is no report of teratogenic and carcinogenic action in animals or humans. 

Noncombustible solid flash point 94°C (200°F). Highly reactive reactions with strong acids and oxidizers are exothermic. HCN liberation can occur when reacted with acids. 

Malononitrile is dissolved in a combustible solvent and burned in a chemical incinerator equipped with an afterburner and scrubber. 

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H2N (CH2)a NH2- Colourless solid when pure m.p. 4LC, b.p. 204 C. Manufactured by the electrochemical combination of two molecules of acrylonitrile to adiponitrile followed by catalytic reduction, or by a series of steps from cyclohexanone via adipic acid. Used in the production of Nylon [6, 6]. 

Enone formation-aromatization has been used for the synthesis of 7-hydro-xyalkavinone (716)[456]. The isotlavone 717 was prepared by the elimina-tion[457]. The unsaturated 5-keto allyl esters 718 and 719, obtained in two steps from myreene. were subjected to enone formation. The reaction can be carried out even at room temperature using dinitriles such as adiponitrile (720) or 1,6-dicyanohexane as a solvent and a weak ligand to give the pseudo-ionone isomers 721 and 722 without giving an allylated product(458]. 

The reduction of acrylonitrile, CH2=CHCN, to adiponitrile, NC(CH2)4CN, is an important industrial process. A 0.594-g sample of acrylonitrile is placed in a 1 -L volumetric flask and diluted to volume. An exhaustive controlled-potential electrolysis of a 1.00-mL portion of the diluted acrylonitrile requires 1.080 C of charge. What is the value of n for this reduction ... 

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). 

Adiponitnle (hexanedinitnle, dicyanobutane, ADN), NC(CH2)4CN, is manufactured principally for use as an intermediate for hexamethylenediarnine (1,6-diaminohexane), which is a principal ingredient for nylon-6,6. However, in 1996, BASF aimounced the development of a process to make caprolactam from adiponitrile (44,45). Caprolactam is used to produce nylon-6. The implementation of this technology could increase the demand for adiponitrile dramatically. 

Pure adiponitrile is a colorless Hquid and has no distinctive odor some properties are shown in Table 5. It is soluble in methanol, ethanol, chloroalkanes, and aromatics but has low solubiUty in carbon disulfide, ethyl ether, and aUphatic hydrocarbons. At 20°C, the solubiUty of adiponitrile in water is ca 8 wt % the solubiUty increases to 35 wt % at 100°C. At 20°C, adiponitrile dissolves ca 5 wt % water. 

Adiponitrile undergoes the typical nitrile reactions, eg, hydrolysis to adipamide and adipic acid and alcoholysis to substituted amides and esters. The most important industrial reaction is the catalytic hydrogenation to hexamethylenediarnine. A variety of catalysts are used for this reduction including cobalt—nickel (46), cobalt manganese (47), cobalt boride (48), copper cobalt (49), and iron oxide (50), and Raney nickel (51). An extensive review on the hydrogenation of nitriles has been recendy pubUshed (10). 

Adiponitrile is made commercially by several different processes utilizing different feedstocks. The original process, utilizing adipic acid (qv) as a feedstock, was first commercialized by DuPont in the late 1930s and was the basis for a number of adiponitrile plants. However, the adipic acid process was abandoned by DuPont in favor of two processes based on butadiene (qv). During the 1960s, Monsanto and Asahi developed routes to adiponitrile by the electrodimerization of acrylonitrile (qv). 

The reaction of adipic acid with ammonia in either Hquid or vapor phase produces adipamide as an intermediate which is subsequentiy dehydrated to adiponitrile. The most widely used catalysts are based on phosphoms-containing compounds, but boron compounds and siHca gel also have been patented for this use (52—56). Vapor-phase processes involve the use of fixed catalyst beds whereas, in Hquid—gas processes, the catalyst is added to the feed. The reaction temperature of the Hquid-phase processes is ca 300°C and most vapor-phase processes mn at 350—400°C. Both operate at atmospheric pressure. Yields of adipic acid to adiponitrile are as high as 95% (57). 

In the now-obsolete furfural process, furfural was decarboxylated to furan which was then hydrogenated to tetrahydrofuran (THF). Reaction of THF with hydrogen chloride produced dichlorobutene. Adiponitrile was produced by the reaction of sodium cyanide with the dichlorobutene. The overall yield from furfural to adiponitrile was around 75%. 

In a related process, 1,4-dichlorobutene was produced by direct vapor-phase chlorination of butadiene at 160—250°C. The 1,4-dichlorobutenes reacted with aqueous sodium cyanide in the presence of copper catalysts to produce the isomeric 1,4-dicyanobutenes yields were as high as 95% (58). The by-product NaCl could be recovered for reconversion to Na and CI2 via electrolysis. Adiponitrile was produced by the hydrogenation of the dicyanobutenes over a palladium catalyst in either the vapor phase or the Hquid phase (59,60). The yield in either case was 95% or better. This process is no longer practiced by DuPont in favor of the more economically attractive process described below. 

The selective addition of the second HCN to provide ADN requires the concurrent isomerisation of 3PN to 4-pentenenitrile [592-51 -8] 4PN (eq. 5), and HCN addition to 4PN (eq. 6). A Lewis acid promoter is added to control selectivity and increase rate in these latter steps. Temperatures in the second addition are significandy lower and practical rates may be achieved above 20°C at atmospheric pressure. A key to the success of this homogeneous catalytic process is the abiUty to recover the nickel catalyst from product mixture by extraction with a hydrocarbon solvent. 2-Methylglutaronitrile [4553-62-2] MGN, ethylsuccinonitfile [17611-82-4] ESN, and 2-pentenenitrile [25899-50-7] 2PN, are by-products of this process and are separated from adiponitrile by distillation. 

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

Small amounts of propionitrile and bis(cyanoethyl) ether are formed as by-products. The hydrogen ions are formed from water at the anode and pass to the cathode through a membrane. The catholyte that is continuously recirculated in the cell consists of a mixture of acrylonitrile, water, and a tetraalkylammonium salt the anolyte is recirculated aqueous sulfuric acid. A quantity of catholyte is continuously removed for recovery of adiponitrile and unreacted acrylonitrile the latter is fed back to the catholyte with fresh acrylonitrile. Oxygen that is produced at the anodes is vented and water is added to the circulating anolyte to replace the water that is lost through electrolysis. The operating temperature of the cell is ca 50—60°C. Current densities are 0.25-1.5 A/cm (see Electrochemical processing). 

A typical composition of the catholyte is adiponitrile, 15 wt % acrylonitrile, 15 wt % quaternary ammonium salt, 39 wt % water, 29 wt % and by-products, 2 wt %. Such a solution is extracted with acrylonitrile and water, which separates the organics from the salt that can be returned to the cell. 

The acrylonitrile is distilled from the extract and the resultant residue consists of ca 91 wt % adiponitrile, which is purified further by distillation. The overall yield of acrylonitrile to adiponitrile is 92—95%. 

Production and Shipment. Estimated adiponitrile production capacities in the U.S. in 1992 were about 625 thousand metric tons and worldwide capacity was in excess of lO metric tons. The DOT/IMO classification for adiponitrile is class 6.1 hazard, UN No. 2205. It requires a POISON label on all containers and is in packing group III. Approved materials of constmction for shipping, storage, and associated transportation equipment are carbon steel and type 316 stainless steel. Either centrifugal or positive displacement pumps may be used. Carbon dioxide or chemical-foam fire extinguishers should be used. There are no specifications for commercial adiponitrile. The typical composition is 99.5 wt % adiponitrile. Impurities that may be present depend on the method of manufacture, and thus, vary depending on the source. 

Health and Safety Factors. See "General Health and Safety Eactors." The following toxicides for adiponitrile have been reported oral LD q (rats), 300 mg/kg dermal LD q (rabbits), 2,134 mg/kg and inhalation 4-h LC q (i ts), 1.7 mg. NIOSH has proposed an exposure limit of 4 ppm as a TWA (68). 

Uses. The principal use of adiponitrile is for hydrogenation to hexamethylene diamine leading to nylon-6,6. However, as a result of BASE s new adiponitrile-to-caprolactam process, a significant fraction of ADN produced may find its way into nylon-6 production. Adipoquanamine, which is prepared by the reaction of adiponitrile with dicyandiamide [461-58-5] (cyanoguanidine), may have uses in melamine—urea amino resins (qv) (see "Benzonitrile, Uses"). Its typical Hquid nitrile properties suggest its use as an extractant for aromatic hydrocarbons. 

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. 

Uses. 3-Pentenenitrile, 3PN, is used entirely by the manufacturers to make adiponitrile. i7j -2-Pentenenitrile, 2PN, can be cycli2ed catalyticaHy at high temperature to produce pyndine, a solvent and agncultural chemical intermediate. 2PN is also chlorinated to manufacture pentachloropyndine, an intermediate in the insecticide Dursban produced by Dow. Addition of ammonia to 2PN foUowed by reduction leads to 1,3-pentadiamine (Dytek ep), which is used as a curing agent for epoxy coatings and as a chain modifier in polyurethanes. 

Another example is the du Pont process for the production of adiponitrile. Tetrakisarylphosphitenickel(0) compounds are used to affect the hydrocyanation of butadiene. A multistage reaction results in the synthesis of dinitrile, which is ultimately used in the commercial manufacture of nylon-6,6 (144-149). 

Catalytic hydtogenation is the most efficient method for the large scale manufacture of many aromatic and ahphatic amines. Some of the commercially important amines produced by catalytic hydrogenation include aniline (from nitrobenzene), 1,6-hexanediamine (from adiponitrile), isophoronediamine (from 3-nitro-l,5,5-trimethylcyclohexanecarbonitrile), phenylenediamine (from dinitrobenzene), toluenediamine (from dinitrotoluene), toluidine (from nitrotoluene), and xyhdine (from nitroxylene). As these examples suggest, aromatic amines ate usually made by hydrogenating the... 

In an alternative approach, 2-methylglutaronitrile (8) is hydrogenated and cyclized to give high yields of 3-methylpyridine. The feedstock for this process is produced as a by-product of the production of adiponitrile. Oxidative cyclization of 2-methylglutaronitrile to nicotinonitrile (9) has been described (4). 

Estimates of various uses for hydrogen cyanide in the United States ate adiponitrile for nylon, 41% acetone cyanohydrin for acryhc plastics, 28% sodium... 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

Asahi also reports an undivided cell process employing a lead alloy cathode, a nickel—steel anode, and an electrolyte composed of an emulsion of 20 wt % of an oil phase and 80 wt % of an aqueous phase (125). The aqueous phase is 10 wt % K HPO, 3 wt % K B O, and 2 wt % (C2H (C4H )2N)2HP04. The oil phase is about 28 wt % acrylonitrile and 50 wt % adiponitrile. The balance of the oil phase consists of by-products and water. The cell operates at a current density of 20 A/dm at 50°C. Circulated across the cathode surface at a superficial velocity of 1.5 m/s is the electrolyte. A 91% selectivity to adiponitrile is claimed at a current efficiency of 90%. The respective anode and cathode corrosion rates are about mg/(Ah). Asahi s improved EHD process is reported to have been commercialized in 1987. 

Hexamethylenediamine may be conveniently prepared from adipic acid via adiponitrile... 

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