Electrolytic Reductive Coupling

Abstract

It is shown that in mixed reductive coupling of activated olefins A and B, in which A is reduced at the more anodic voltage, the ratio of cross‐coupled product HABH to self‐coupled product HAAH rises substantially as the controlled potential is made more negative. Diethyl maleate (DEM) was chosen as an example of A and ethyl acrylate (EA) and acrylonitrile (AN) as examples of B. Previously reported fluctuations of voltage along the cathode surface are confirmed and may lead to unexpected formation of HBBH. The results of cyclic voltammetry of DEM in the presence of EA or AN and of a kinetic study of the addition of a carbanion to these same acceptors in bulk are interpreted to indicate that the reductive coupling of DEM with the acceptors occurs largely but not exclusively at the electrode surface.

Electrohydrodimerization Reactions

“…Coulometry at --1.625V vs. SCE in the absence of cinnamonitrile yielded an n~pp-value of 0.62. If the ECE mechanism involving reactions [5] and [6] occurred, the napp in the presence of CN should have been greater than 0.62, and possibly even greater than one.…”

“…They also found that the yield of cross-coupled product was substantially increased when electrolysis was conducted at potentials where both R and R' were reduced; this is an indication that cross-coupling via a radical ion-radical ion-coupling mechanism was occurring at a faster rate than the ECE R 7 + R'--~ (RR') '2- [7] mechanism postulated in Eq. [5] and [6]. Dimethyl fumarate was chosen to serve as the species R. Its radical decay rate constant (i.e., dimerization rate constant) is at the lower limit of rate constants measurable with the particular RRDE used and thus any increase in the velocity of that reaction, as explained above, would still result in reasonable current levels at the ring.…”

“…CN was chosen because its hydrodimerization has been studied (1), because its secondorder rate constant is only eight times that of dimethyl fumarate, and because it is more difficult to reduce than dimethyl fumarate. Acrylonitrile was chosen because of its use in previous studies (4)(5)(6)(7). The mechanism and rate of dimerization of AN, however, have not been determined because the electrogenerated product reacts very quickly (9).…”

Dimerization of electrochemically generated ion radicals: mechanisms and reactivity factors

“…Early applications of cyclic voltammetry to the reduction of aromatic carbonyl compounds [7] were indicative of a mechanism of pinacol formation involving the coupling of two anion radicals to give the pinacolate that protonates further to pinacol [7][8][9]. Intense mechanistic activity on reductive electrodimerization via ion radicals followed the publication of the Baizer-Monsanto electrochemical synthesis of adiponitrile from acrylonitrile and of many similar examples in the activated olefin family [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. It is a pleasure to emphasize here the importance of the contribution of Prof. Rolando Guidelli and his coworkers to the understanding of the mechanism of activated olefin electrodimerization under the very conditions where the Baizer-Monsanto reaction is carried out.…”

Electrolytic Reductive Coupling

“…voltage can be controlled at a value required for the reduction of A but not of B, only products 3 and 4 are formed (2) ; the more negative the cathode voltage can be made without reducing B2 the higher the ratio of 4 to 3 (3). Even under the latter circumstances, however, if the reduction potentials of A and B are more than ca.…”