Hydrodimerization of acrylonitril

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). 

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...

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. 

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. 

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... 

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]. 

Baizer and coworkers established the most brilliant industrial electroorganic synthesis of the hydrodimerization of acrylonitrile to adiponitrile. They extended this hydrodimerization to a variety of activated olefins and in some cases [41 3] paid attention to the stereochemistry of products. However, their stereochemical data were not enough to discuss the stereochemical course of the reaction. Afterward, an attempt was made to provide a working hypothesis in the hydrodimerization of cinnamates by considering an orientated adsorption of radical anion intermediates on a cathode surface, but this was not persuasive because of a lack of experimental data on the stereochemistry of both the starting olefins and products. Recently Utley and coworkers [44-46] have reported stereochemical data of hydrodimers derived from a variety of cinnamic acid esters with chiral alcohol components. 

After the development of the electrolytic reductive coupling of acrylonitrile to adiponitrile (Chapter 21), many investigations have been directed toward developing an alternative, indirect electrolytic process. The electrolytic hydrodimerization reaction in neutral solution [32,33] is critically dependent on the proton activity at the electrode. If the proton activity is too high, the product is predominantly propionitrile, whereas oligo-or polymerization occurs at too low a proton activity. The establishment of a reaction layer with a suitable proton activity in which conditions are favorable for a hydrodimerization of acrylonitrile to adiponitrile is, thus, of paramount importance. This can be accomplished in different ways. 

A very impressive illustration of the relative costs of the electrolysis step compared to workup and purification procedures is given in Ref. 14. The electrochemical hydrodimerization of acrylonitrile to adiponitrile is reported here. The electrolytic part makes up less than 20% of the whole process sheet, and the costs for the electrolytic part are less than 30%. The process is later discussed in more detail. 

An oxidation using a nickel hydroxide electrode is shown in 15.8.433 Electrochemistry is also a way to produce radicals and anions. The hydrodimerization of acrylonitrile to adiponitrile just mentioned may involve the coupling of free radicals. The coupling of carbonyl compounds, such as p lolualdehyde, to form pinacols with up to 100% selectivity, by way of free radicals, can be done electrically.434 Anions can also be formed electrochemically and used in situ, as in example (15.9).435... 

Conjugated Alkenes. - By far the largest and best known industrial electro-organic reduction is the hydrodimerization of acrylonitrile to adiponitrile, an important precursor in nylon manufacture. Plants where this process... 

In this chapter we shall consider first the largest-scale industrial process, the Monsanto hydrodimerization of acrylonitrile to adiponitrile, and then go on to discuss the other processes presently used or likely to be introduced in the near future. 

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