Cathode buffer materials

Adiponitrile is readily hydrogenated catalytically to hexamethylenediamine, which is an important starting material for the prodnction of nylons and other plastics. The electrochemical production of adiponitrile was started in the United States in 1965 at present its volume is about 200 kilotons per year. The reaction occurs at lead or cadmium cathodes with current densities of np to 200 mA/cm in phosphate buffer solutions of pH 8.5 to 9. Salts of tetrabntylammonium [N(C4H9)4] are added to the solution this cation is specihcally adsorbed on the cathode and displaces water molecules from the first solution layer at the snrface. Therefore, the concentration of proton donors is drastically rednced in the reaction zone, and the reaction follows the scheme of (15.36) rather than that of (15.35), which wonld yield propi-onitrile. 

Preparative scale reduction of nitramines and nitrosamines in acid solution is a convenient route to substituted hydrazines. Early workers used a cathode of tinned copper [120], More recently mercury has been employed as cathode material, although tin would probably be equally suitable. Nitrosamines are conveniently reduced in dilute hydrochloric acid and evaporation of the electrolyte at the end of the reaction affords the hydrazine hydrochloride [121]. Some nitroso compounds are unstable to these acidic conditions. In the case of N-nitrosoindoles, this problem has been overcome in an ingenious manner [122]. The nitroso compound and aqueous sulphuric acid are mixed just prior to reaction and then forced through a porous cathode of bronze coated with mercury at such a rate that the reduction is completed in one pass through the cathode. Other workers have overcome the instability of N-benzyl-N-nitrosoanthraniiic acid towards acid by working in an acetate buffer at below room temperature [123],... 

Fig. 1.27. Schematics of the PACIS with flow tube reactor attached to the source nozzle, (a) magnetic valve for buffer gas (He), (b) Macor insulator, (c) electrodes (the cluster material is contained in the cathode), (d) cooling coil, (e) nozzle, (f) source holder, (g) flow tube reactor, (h) reaction gas inlet, (i) pumping chaimels...

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