Electrohyd rodimerization Reactions V. Liquid Ammonia as a Solvent for Reductive Coupling of Diethyl Fumarate, Cinnamonitrile, and Acrylonitrile

Cyclic voltammetric (CV) and controlled potential coulometric investigations of the reduction of several activated olefins in anhydrous liquid ammonia containing either 0.1M methyl-tri-n-but ylammonium iodide or 0.1M potassium iodide as supporting electrolytes are reported. For diethyl fumarate and cinnamonitrile the studies provide evidence for formation of a radical anion, which undergoes dimerization and polymerization reactions, and of dianion formation at more negative potentials. The effect of adding isopropanol and glacial acetic acid was also investigated. The reduction of activated olefins in aprotic media has been the subject of numerous investigations [see (1, 2) and references therein]. Diactivated olefins (R) react via formation of the radical anion and produce, depending upon the acidity of the medium, hydrodimer (R2H2), reduced monomer (RH2), and polymer. At more negative potentials, where dianion is produced, extensive polymerization apparently occurs, so that the second reduction waves observed in voltammetry are frequently much smaller than the first waves. We have previously shown that anhydrous liquid ammonia is a useful medium for studies of the electroreduction of organic compounds (3, 4) and that stable dianions of benzophenone and nitrobenzene could be prepared in this solvent. This stability of radical anions and dianions in ammonia can be attributed to the low acidity of the solvent, the possibility of preparing highly pure solutions through the use of vacuum line techniques and solvent treatment with sodium, and the fact that these studies are carried out at low temperatures, decreasing the rate of homogeneous chemical reactions following the electron transfer steps. Previous studies of amalgam reductions leading to hydrodimerizatio n in liquid ammonia have also been described (5). In this paper we describe preliminary cyclic voltammetric and coulometric experiments on the reduction of several activated olefins in liquid ammonia; the structures of the substances studied are shown below