Electrocarboxylation of Benzyl Halides through Redox Catalysis on the Preparative Scale

Abstract

The electrocarboxylation of benzyl halides to the corresponding carboxylic acids through homogeneous charge-transfer catalysis was investigated both theoretically and experimentally to determine the influence of the operative parameters on the yield of the process and on the catalyst consumption. Theoretical considerations, based on fast kinetics of redox catalysis, were confirmed by the electrocarboxylation of 1-phenyl-1-chloroethane catalyzed by 1,3-benzenedicarboxylic acid dimethyl ester performed at a carbon cathode under different operative conditions. We obtained high yields of the target carboxylic acid and experienced a low catalyst consumption by operating with optimized [RX]bulk/[CO2]bulk and [RX]bulk/[catalyst] ratios.

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

“…In a first step, a one electron reduction causes a halide anion to dissociate, forming a reactive radical. The latter undergoes a second reduction in the presence of CO 2 , yielding a monocarboxylate anion (Scheme 17) [122,124–126 128]. …”

“…The cathode material is again of great importance, with silver and platinum giving the highest carboxylation selectivity [119–125]. Redox mediators allow working at a less negative cathodic potential, which results in a better energy efficiency and a more selective CO 2 fixation [128]. The most common redox mediators are organometallic nickel [129–131], palladium [132] and cobalt complexes [133–137].…”

Electrocarboxylation and related radical coupling processes of aryl and benzyl halides in microemulsion

“…Further improvements in the electrocarboxylation processes employing redox mediators [3][4][5] and silver cathodes [6,7] have been reported. Poly halogenated aromatic compounds [8], iodo aromatic compounds [9] and aliphatic halides [10,11] also undergo facile electrocarboxylation.…”

Electrocatalytic carboxylation of chloroacetonitrile at a silver cathode for the synthesis of cyanoacetic acid

“…To model the process we will follow a first approximation approach similar to one previously developed for the electrocarboxylation of aromatic ketones [47,48] and benzyl halides [28,44]. It is based on the following three assumptions: [11] and the value in CH 3 CN should be very similar.…”

“…For example, in catalysis with some Ni phosphine complexes, carboxylation occurs by insertion of CO 2 into a nickel-carbon bond [17,19], whereas other complexes such as Pd(PPh 3 ) 2 Cl 2 and square planar Co and Ni complexes promote the formation of free carbanions which are captured by CO 2 [18,20,23]. Use of organic radical anions acting as outer-sphere electron transfer redox mediators has also been investigated [25,27,28]. In this case, the redox mediator undergoes a one-electron reduction at its reversible reduction potential, which is much less negative than that of RX, followed by an homogeneous electron transfer between the reduced mediator and RX.…”