Polarographic Reductions of Benzyl Halides

Abstract

A polarogram for benzyl chloride in a supporting electrolyte of lithium chloride has a dip in the limiting current due to electrostatic repulsion from the interface of the monovalent anion produced by transfer of the first electron. The dip is decreased by the presence of electronegative substituents on the ring and is eliminated by a moderate concentration of surface-active tetra~ methylammonium ions in the solution.Benzyl bromide and iodide each undergo two widely separated one-electron reduction steps at concentrations less than 10-'M. At higher concentrations, adsorption phenomena are encountered in the region of potential between the two waves due to the presence of bibenzyl, a by-product of the first reduction step.The exploratory work of von Stackelberg and Stracke (1) showed that reductions of organic halogen compounds became easier on going from chloride to bromide to iodide. The over-all reaction usually involved replacement of the halogen atom with a hydrogen atom. The half-wave potentials were independent of pH, showing that addition of hydrogen did not occur in the rate-determining step, but after the transfer of electrons.The steps in the polarographic reduction of an organic halogen compound, RX, can be represented by the following reactions (1, 2) :RX + e--> RX- [1]

Catalytic and Kinetic Waves in Polarography

“…The second wave, the normal wave, corresponds to the discharge of nonadsorbed (or weakly adsorbed, less favorably oriented) depolarizer molecules [663]. The doubling of waves for certain organic halide derivatives on their polarograms observed by several investigators [664][665] can be explained by the effect of depolarizer adsorption (see also Fig. 209 in [370]).…”

Electrochemical Formation and Dimerization of α-Substituted Benzyl Radicals. Steric Effects on Dimerization

“…In this context, benzylic halides represent an interesting situation. Benzyl chlorides undergo the usual two-electron reduction to a benzylic carbanion, but benzyl bromides 1d − f exhibit two closely-spaced voltammetric waves in dimethylformamide (DMF), and the products change from radical type (RR) to carbanion type (RH) over electrolysis potentials of just a few tenths of a volt. , The α - chlorobenzyl radical ( 2a ) is easier to reduce than benzal chloride (C 6 H 5 CHCl 2 ), so it cannot be produced by direct electrochemical reduction of benzal chloride …”

Meso‐ and Dl‐ Diethyl 2,3‐Diphenylsuccinate from the Electrochemical Reduction of Ethyl α‐Bromophenylacetate

“…The presence of dimers in the products of electrochemical reduction of monosubstituted halides has been reported (16) or suggested (17). Figure 3 shows the polarographic behavior of RBr in the presence of Bu4NBr, C(RBr)/C(Bu4NBr) = 1/1, at various concentrations of RBr.…”

“…K. Tokuda and H. Matsuda, ibid., 90, 149 (1978). 16. K. Tokuda and H. Matsuda, ibid., 95, 147 (1979).…”