Acrylonitrile to adiponitrile

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]. 

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%. 

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). 

EHD [Electrohydrodimerization] Also known as Electrodimerization. An electrolytic process for converting acrylonitrile to adiponitrile. See Monsanto. 

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...

Development of the industrial process for electrochemical conversion of acrylonitrile to adiponitrile led to extensive investigation into the mechanism of the dimerization process. Reactions of acrylonitrile radical-anion are too fast for investigation but the dimerization step, for a number of more amenable substrates, has been investigated in aprotic solvents by electrochemical techniques. Pulse-radiolysis methods have also been used to study reactions in aqueous media. 

Electrochemical reactions may be carried out at any scale from the smallest to the largest and progress in nanotechnology has made it possible to address electron transfer at the single molecule level [26, 27]. Conversions at the laboratory scale are well established and have been addressed by numerous authors [1, 2] and, at the industrial scale, more than 50 electrochemical processes have reached a respectable level with the reductive hydrodimeri-sation of acrylonitrile to adiponitrile topping the list with an annual production of about 300 000 tons [28],... 

Using ultramicroelectrodes, it is possible to study reactions under the conditions of synthesis, including electrosynthesis. An example is the electrohydrodimerisation of acrylonitrile to adiponitrile (Scheme 6.11, top) mentioned in the introduction in industry this is typically carried out with an emulsion of acrylonitrile in an aqueous phosphate buffer as electrolyte. At substrate concentrations in the mM level, the reduction of acrylonitrile takes another route leading to saturation of the C—C double bond (Scheme 6.11, bottom). This precludes studies of the dimerisation using substrate concentrations at the mM level and thereby working electrodes of conventional sizes. The transition between the two mechanisms could be studied conveniently using an ultramicro electrode as the working electrode... 

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) ). 

The first step in the synthesis is the polymerization of acrylonitrile to adiponitriles... 

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. 

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). 

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. 

The first sodium amalgam-induced dimerization of acrylonitrile to adiponitrile [29] was performed in aqueous solution, and the yield was discouragingly low (5%). Mainly, a base-induced addition of water resulting in p, -bis(cyanoethyl) ether occurred together with a reduction to propionitrile (PN). 

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... 

Propionitrile is used as a chemical intermediate. It is formed as a by-product of the electrodimerization of acrylonitrile to adiponitrile. 

Acrylonitrile to adiponitrile C Monsanto, BASF, Asahi, UCB Danly (1981) Danly and Campbell (1982)... 

Processes 4, 5, and 6 in Figure 2.13 are based on acrylonitrile. Among them, process 6 is the oldest. Introduced in 1965 as a technical process by Monsanto [175], it involves the electrolytic dimerization of acrylonitrile to adiponitrile. The process is carried out in a system of electrolytic cells containing sulfonated polystyrene membranes. An aqueous solution of tetraethylammonium- -toluyl sulfonate is used as the catholyte and aqueous sulfuric add as the anolyte. Using a 40% aqueous solution of acrylonitrile at temperatures of 25 35°C, the following reaction sequences occur ... 

Many examples of electroorganic synthesis have been reported and a few are commercial. The first significant commercialization of electroorganic synthesis was the electrohydrodimerization (EHD) of acrylonitrile to adiponitrile, an intermediate for hexamethylenediamine, which is a monomer for nylon. 

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. 

Owing to the high catholyte flow rate necessary to avoid side reactions the conversion of acrylonitrile to adiponitrile per pass of the catholyte through the cell is only 0.2%. Hence the catholyte streams in each stack were coupled to a reservoir tank and the catholyte was continuously recirculated through the cell stack. A fraction of the solution in the reservoir passed into an extraction plant and hence the reservoir combined with the cell stack operated in the same way as a continuous stirred tank reactor. 

Figure 6.5 Flow sheet for Monsanto hydro dimerization of acrylonitrile to adiponitrile, AN, acrylonitrile ADN, adiponitrile QS, tetraethylammonium ethylsulphate.

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