Acrylonitrile, hydrodimerization

Dir, whereas for small distances d < r), /r Did. The large effective obtainable enables fast heterogeneous reaction rates to be measured under steady-state conditions. Zhou and Bard measured a rate constant of 6 x 10 Ms for the electro-hydrodimerization of acrylonitrile (AN) and observed the short-lived intennediate AN for this process [65]. 

Until the 1960s, adipic acid [124-04-9] was virtually the sole intermediate for nylon-6,6. However, much hexamethylenediamine is now made by hydrodimerization of acrylonitrile (qv) or via hydrocyanation of butadiene (qv). Cyclohexane remains the basis for practically the entire world output of adipic acid. The U.S. capacity for adipic acid for 1993 was 0.97 X 10 t/yr (233). 

Perhaps the best known example of adsorption effects in electrosynthetic reactions is the beneficial role of tetraalkylammonium ions in the hydrodimerization of acrylonitrile... 

Reactions of this type are called electrochemical hydrodimerization. They are of great value for the synthesis of various bifunctional compounds. A reaction that has found wide commercial nse is the hydrodimerization of acrylonitrile to adiponitrile (the dinitrile of adipic acid) ... 

Rate data have appeared (161) for the hydrodimerization of acrylonitrile to adiponitrile, which is catalyzed by various ruthenium-phosphine complexes (/, p. 101). 

Monsanto (1) A process for making adiponitrile, an intermediate in the manufacture of Nylon 66, by the electrolytic hydrodimerization (EHD) of acrylonitrile ... 

Scheme 4. Possible reaction pathways for the hydrodimerization of acrylonitrile to adiponitrile. The asterisk indicates that electron transfer can be from the cathode or from [CH2CHCN] in homogeneous solution...

At the cathode, olefins with electron deficient double bonds can be hydrodimer-ized (Eq. 1). This reaction has been developed for acrylonitrile [22] in a technical adipodinitrile synthesis [23] with a scale of more than 300.000 tons per year. The scope of this hydrodimerization has been substantiated with many examples [24-33]. 

It is commercially advantageous to operate cells with no diaphragm since the cell diaphiagm is the weakest point in the system. Achievement of this aim rests upon finding an anode reaction that destroys neither the substrate nor the product. Russian workers [63] showed that up to 90 % yields of adiponitrile can be obtained at a graphite cathode in an undivided cell with an iron oxide anode, provided that phosphate and tetraalkylammomum ions are present. Further research contributions from Monsanto, BASF and Japanese companies led to the present system for hydrodimerization of acrylonitrile using an undivided cell [64,65]. 

Adiponitrile may be produced from the hydrodimerization of acrylonitrile or from 1,3-butadiene via l,4-dicyanobutene-2. Adiponitrile is then hydrogenated forming 1,6-hexane-diamine. 

Electroorganic synthesis deals with conversion of organic compounds into useful products by anodic oxidation or cathodic reduction. Today there exist literally thousands of published examples of electrosynthesis reactions but only a very small number—certainly not more than several tens—are really exploited commercially, the best known example being the cathodic hydrodimerization of acrylonitrile to adipodinitrile, a precursor to hexam-ethylene diamine, which is the aminoconstituent of nylon 6,6 (779) ... 

Cathodic hydrodimerization has been applied to a large number of electron-poor olefins. The most prominent example is the hydrodimerization of acrylonitrile to give adipodinitrile. This so-called Monsanto process has a production capacity of about 300,000 tons per year worldwide [20] ... 

Ruthenium-catalyzed hydrodimerization of acrylonitrile under hydrogen atmosphere to give adiponitrile (393) is a useful coupling reaction [154], Dimethyl hexenedioates (394a and 394b) are formed by dimerization of methyl acrylate by Pd, Ru and Rh catalysts. In particular the catalyst prepared by the treatment of RuC12 with Zn and... 

From the industry s point of view the most important electroorganic reaction is the cathodic hydrodimerization of acrylonitrile to adipodinitrile. The basic work and scaling up of the process were carried out by Monsanto. 

However, the synthesis cannot compete with the cathodic hydrodimerization of acrylonitrile. 

A drastic example of this phenomenon is encountered in the cathodic hydrodimerization 76>8°1 of acrylonitrile to adiponitrile. This can be accomplished in very high yield in a concentrated solution of a tetraalkylammonium tosylate in water. Practically no propionitrile, the product of hydrogen addition, is formed. The reaction is believed to occur via formation of the acrylonitrile anion radical (6), which then attacks a second molecule of acrylonitrile. Further reduction of the resulting anion radical (7) followed by protonation of the dianion gives adiponitrile (Eqs. (21), (22) and (23) ). 

In 2000, about 110 chemicals were being produced by electro-organic syntheses at a rate of more than 10,000 tons/year. The best-known method has already been presented in this chapter (Section 11.2.3) it is the electro-hydrodimerization of acrylonitrile to adiponitrile as part of the synthesis of nylon. 

To orient the reader in this maze of reactions, all electron transfer steps have been arranged vertically and C steps horizontally. Furthermore we have not indicated whether the electron transfer steps are of the E or C type, another factor to take into account. The somewhat complex appearance of the scheme should not, however, obscure the fact that suitable manipulation of the experimental variables can give either of the two products, E—M—E or E—M—M—E in nearly quantitative yield, as for example in the cathodic hydrodimerization (34) of acrylonitrile. A dependence of the product distribution on potential is observed in cases where the radical ion and doubly charged ion follow differing reaction paths. Thus, 4,4 -dimethoxystilbene shows two anodic waves in acetonitrile/LiC104 at 090 and 1 15 V versus... 

The industrial organic electrosynthesis reaction of greatest impact must be the Monsanto process for the hydrodimerization of acrylonitrile to... 

For cells with continuous addition of reducible material and removal of product, the design depends on the techniques for the addition and removal. A cell designed for the hydrodimerization of acrylonitrile to adiponitrile is shown in Fig. 7.58... 

C3H9N [107-10-8]), and the industrially important hydrodimerization to produce adiponitrile (C6HgN2 [111-69-3 f) (25—27). Other reactions include addition of halogens across the double bond to produce dihalopropionitriles, and cyanoetliylation by acrylonitrile of alcohols, aldehydes, esters, amides, nitriles, amines, sulfides, sulfones, and halides. 

The fact that the iR drop is a smaller problem for UMEs compared to microelectrodes has another straightforward advantage, the substrate concentration can be increased substantially this makes the performance of electroanalytical studies under conditions similar to industrial conditions possible. For instance, the industrially important hydrodimerization of acrylonitrile to adiponitrile takes place at high concentrations in aqueous medium in the presence of tetraalkylammonium salts that form an aprotic medium in the vicinity of the electrode surface. The mechanism consists of a dimerization reaction of the radical anions of acrylonitrile formed upon reduction of acrylonitrile in the aprotic tetraalkylammonium layer, followed by protonation of the dimer in the aqueous phase (Eq. 87). However, at low to moderate concentrations of acrylonitrile, a change in mechanism occurs in favor of a two-electron reduction of acrylonitrile to propionitrile (Eq. 88). 

Irreversible electrode reactions predominate in preparatively oriented organic electrochemistry [4,67]. Examples are the cathodic hydrodimerization of acrylonitrile to yield adiponitrile ... 

The hydrogen overvoltage of cadmium is rather large and cadmium may be used, plated on steel, as an alternative to lead. Cadmium has been used as cathode material in the hydrodimerization of acrylonitrile (Chapter 31). Magnesium may be used in reductive dimerization of aliphatic esters [459]. 

Many salts are soluble in DMSO, so the choice of supporting electrolyte is less restricted than in most other nonaqueous solvents. In general, perchlorates, even KCIO4, nitrates, and halides, are soluble, whereas fluorides, cyanides, sulfates, and carbonates are not thus not only NaC104, LiCl, NaNO, and tetraalkylammonium salts can be used but also such salts as NH4PF6 and NH4SCN. The ability of DMSO to solvate ions is also of importance in the indirect electrolytic hydrodimerization of, for example, acrylonitrile using Na(Hg) [388]. 

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