Sacrificial Anode-Free Electrosynthesis of α-Hydroxy Acids via Electrocatalytic Coupling of Carbon Dioxide to Aromatic Alcohols

Abstract

Electrocarboxylation of organic compounds using CO2 is a promising approach towards a sustainable low-carbon society, but it is desirable to avoid the use of conventional sacrificial anodes in terms of green chemistry. Here, we report a novel electrocarboxylation methodology operating in a simple undivided cell with a non-sacrificial anode, at which tetramethylpiperidine-2 1-oxyl (TEMPO)-mediated alcohol oxidation takes place. Aromatic alcohols can be oxidized with high efficiency to ketones or aldehydes at the anode in the presence of a small amount of water, and then converted to α-hydroxy acids in yields of up to 61 % by coupling with CO2 at the cathode.The electrocarboxylation mechanism comprising electron and proton transfers at the cathode is discussed along with experiments using various cathode materials. Electron and proton transfers are influenced by the hydrogen adsorption energy of the cathode material, which plays an important role in the electrocarboxylation efficiency.

Suppressing carboxylate nucleophilicity with inorganic salts enables selective electrocarboxylation without sacrificial anodes

“…17,31 All of these strategies rely on alternative oxidation chemistries including oxidation of oxalate, 32,33 trimethylamine, 34 acetonitrile (MeCN), 35 N,N-dimethylformamide (DMF), 36 halides, [37][38][39] water, 40,41 H 2 , 42 conjugated dienes, 43 and alcohols. 44 Several of these alternative oxidation chemistries have also been accompanied by improved cell designs to achieve better carboxylation selectivities. 40,45 While simply changing the anodic chemistry has worked well for carboxylating substrates without good leaving groups such as olens and ketones, many organic halides have proved to be more challenging to carboxylate without a sacricial anode.…”

Organic Electrosynthesis Towards Sustainability: Fundamentals and Greener Methodologies

“…Other well‐known methodology to obtain carboxylic acids takes advantage of the electrophilic character of carbon dioxide versus electrogenerated anions. An example of this strategy is the variant of sequential paired electrosynthesis, mediated by TEMPO, that has been reported in 2019 by De Vos and Kim for the preparation of α‐hydroxy acids from easy accessible alcohols (Scheme 12b) [71] . Regarding different mediated electrochemical processes it should be also noted, as a curious example the convergent paired electrosynthesis of aromatic sulfones from nitro‐catechols and benzene‐sulfinic acids, whose efficiency and performance was highly improved in the presence of ferrocyanide as a redox mediator [72] …”

Electrochemical Approaches to Carbonylative Coupling Reactions

“…In recent years, the rise of electrochemical carboxylation of benzene substrates with CO 2 as the C1 source is a breakthrough in the development of green chemistry. [59,60] The development of sacrificial anode-free has always been a challenge. Kim et al designed a system: useing tetramethylpiperidine-1-oxyl(TEMPO)-mediated anode replaced Mg and Al materials.…”

“…Electrochemical coupling of aromatic compounds with CO 2 as carbonyl source. [59] Scheme 13. Electrochemical carbonyl coupling of olefins based on sacrificial anode.…”