Cathodic Hydrodimerization of Activated Olefins

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. 

Baizer 337) and Danly 338 - 341) wrote many detailed reports on the development of this synthesis from the early laboratory experiments to the production stage. The process was initially carried out in divided cells but was subsequently made much more cost-effective by changing over to undivided cells. Some important characteristic data of the two versions of the process 341 are summarized in the table below. 

Electrolyte (wt %) Et4NS04Et (40) EtBu2N(CH2)6— NBu2Et phosphate (0.4) Na2HP04 (10) Na2B407 2) Na4EDTA (0.5) 

The process was also investigated by Asahi 342), BASF 343 , Phillips 344), and others. It is now carried out industrially by Monsanto, Asahi, and BASF. Whereas Monsanto and BASF now use undivided cells in their industrial plants, Asahi 345) is still planning a changeover to undivided cells. 

Adipodinitrile is an intermediate for hexamethylenediamine, the amine component of nylon 66. The electrochemical process is economically superior to the synthesis of adipodinitrile from cyclohexanone. Today, it essentially competes with the addition reaction of HCN to butadiene. The total capacity of the electrochemical ADN synthesis is currently about 250,000 tonnes/year. The process is industrially fully developed. Recent work 34 347) is aimed at reducing the oxygen evolution potential at the anode in order to save further energy. 

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Cathodic hydrodimerization of active olefins and carbonyl compounds. 

In addition to the cathodic hydrodimerization of activated olefins [see 3.2.1.1], the electrosyntheses of substituted benzaldehydes are among the few electroorganic reactions which are carried out on a large scale industrially. 

In addition to the cathodic hydrodimerization of activated olefins and the Kolbe reaction, the anodic dimerization of CH-acidic compounds is another possibility for the electrochemical C—C coupling. Monsanto 281 > has used the anodic dimerization of malonates in a laboratory synthesis of intermediates for useful sequestrants and detergency builders. 

Anodic dimerization of electron-rich olefins, the mirror image process to cathodic hydrodimerization of activated olefins (Sect. 12.2), affords a one-step synthesis for substituted butanes(Eq. (175) ) 268)( dienes (Eq. (176) ) 26S precursors of polyenes (Eq. (177)) 36,385 and 1,4-dicarbonyl compounds (Eq. (178)) 35>36). 

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. 

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