Direct Electrochemical Reduction of Acetochlor at Carbon and Silver Cathodes in Dimethylformamide

Abstract

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been employed to investigate the direct electrochemical reduction of acetochlor (1) at carbon and silver cathodes in dimethylformamide. Voltammograms of 1 exhibit a single irreversible cathodic peak at both cathode materials. Catalytic properties of silver towards carbon–halogen bond cleavage are evidenced by a positive shift in the reduction of acetochlor as compared to the more inert glassy carbon electrode. Voltammograms in the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and comparisons of calculated relative interaction energies between acetochlor, possible intermediates, and deschloroacetochlor in the presence of different proton donors, suggest strong hydrogen-bonding interactions between HFIP and a carbanion intermediate. Addition of HFIP to electrolysis conditions promotes complete reduction at both cathode materials, with formation of deschloroacetochlor in high yields. In deuterium labelling studies, the use of DMF-d 7 led to no evidence for deuterium atom incorporation. However, when HFIP-OD or D2O were employed as a proton source, substantial amounts of deuterated deschloroacetochlor were observed. A mechanism for the reduction of acetochlor is proposed, in which radical intermediates do not play a significant role in reduction, rather a carbanion intermediate pathway is followed.

Versatile Tools for Understanding Electrosynthetic Mechanisms

“…In the case of an overall two-electron process, a second electron is transferred to the radical intermediate, forming a subsequent carbanion intermediate, which can then react with a suitable electrophile. Both radical and carbanion intermediates can be detected through incorporation of a deuterium (D • ) or deuteron (D + ). − A pertinent example from the Peters’ group involves electroreduction of acetochlor ( 48 ) in DMF, as illustrated in Scheme . Reduction in the presence of a D • (DMF- d 7 ) and D + (D 2 O and HFIP–OD) source was conducted to validate possible pathways.…”

Mechanistic Insights into Electrocatalytic Carbon−Bromine Bond Cleavage in Polybrominated Phenols

“…Alternatively, the carbanion can receive a proton from an adventitious water molecule or any suitable proton donor in solution . Recently, our laboratory has moved toward the investigation of more complex substrates with varying functional groups, such as acetamides, − esters, , and aldehydes . However, the electrochemical behavior of halogenated phenolic compounds has not been widely studied. − The moderate acidity of these species leads to enhanced hydrogen evolution with an increased concentration of protons in solution; as a result, the faradaic efficiency of dehalogenation is significantly lowered.…”

A Theoretical Study of the C–X Bond Cleavage Mediated by Cob(II)Aloxime

“…On such panorama, intense research has been conducted to develop viable organohalide degradation methods. It is well known that organohalides are resistant to traditional physical and chemical treatments; therefore, the proposed methods for the degradation of these very recalcitrant compounds consider either high-energy electrochemical processes [ 11 , 12 ] or photocatalytic oxidation [ 13 ]. Although the latter have proved to be highly effective in the elimination of organohalides, several drawbacks avoid their application at an industrial level [ 7 , 10 ].…”