Electrolytic Reductive Coupling

Abstract

The electrolytic reductive coupling of a variety of diactivated olefins, XCH‒CHY , has been studied. The reduced dimeric products have been isolated and carefully identified. Both symmetrical and unsymmetrical dimers were observed. The dimeric products are formed by two paths: the first involves the attack of the electrochemically generated anion radical on unreduced olefin; the second involves the protonation of the anion radical followed by reduction to an anion and subsequent attack on the olefin. The isomer distribution in the dimeric product obtained by the first route is rationalized on the basis of the relative anion stabilizing ability of the activating groups in the acceptor molecule and the relative ability toward stabilizing a radical site in the donor molecule. The possibility of forming cross‐coupled products (between a diactivated olefin and a Michael acceptor) is limited to systems in which the electrochemically generated anion radical is relatively stable toward its parent olefin or in which the reduction potentials of the pair are similar, i.e., normalΔE½<0.4normalv .

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.…”

Electrohydrodimerization Reactions

“…They surmised that in the presence of a second olefin R', because of its greater concentration at the electrode surface when compared with R, nucleophilic attack by R-: on R' to form the electroactive species k2" R-+ R'~ (RR')- [5] (RR') occurs. This species can undergo further reduction to yield a cross-coupled product (9) n (RR') + e--> (RR') 2- [6] The ratio of cross-coupled product to simple dimer (R2H2) would be dependent on the concentration ratio of R and R', on the rate of formation of the crosscoupled product relative to the rates of formation of the simple dimers (R2H2 and R'2H2), and on the rates of formation of the simple dimers relative to each other. 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.…”

“…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). The diagnostic criteria which were used to determine the reaction path consisted of a qualitative examina-tion of the dependence of the ring current (it) on disk potenital (Ed) at constant ring potential (Er), a quantitative examination of the dependence of the kinetic collection efficiency, NK, on the rotation rate and concentration (XKTC) (10)(11)(12), where XKTC --(0.51) -2/~v-1/~D1/~C~ [8] and ~ is the kinematic viscosity, D is the diffusion coefficient, C ~ is the initial concentration, ~ is the rotation rate, and ks is the second-order homogeneous rate constant, on the behavior of NK with various disk currents (CONI) (3) CONI --ie/id,1 [9] where id is the disk current and id.1 is the disk current at the limiting current plateau, and finally, controlled potential coulometric analysis.…”

Electrocarboxylation Reactions: Rotating Ring‐Disk Electrode, Voltammetric, and Electron Spin Resonance Studies of Dialkyl Fumarates and Maleates

“…--1.60V) in id after development of a well-defined plateau (22,23). --1.60V) in id after development of a well-defined plateau (22,23).…”