Electrochemistry Carboxylation of Bromothiazoles with CO2: An Environmentally Friendly Synthesis of Thiazole Carboxylic Acids

Electrocarboxylation of aromatic halides with carbon dioxide (CO2) to high-value aromatic carboxylic acids under mild conditions offers a promising approach for CO2 resource utilization and the preparation of valuable aromatic carboxylic acids. However, studies on the electrocarboxylation of heterocyclic halides with CO2 remain relatively limited, and, in particular, the electrocarboxylation of thiazole halides with CO2 has not yet been reported in the literature. Herein, the electrocarboxylation of bromothiazoles (BTs) with CO2 was successfully achieved on a silver (Ag) cathode and a Magnesium (Mg) anode under mild conditions, yielding the corresponding thiazole carboxylic acids (TCAs). Using 4-bromothiazole (4-BT) as a model substrate, the effects of solvent, supporting electrolyte, electrode material, current density, charge passed (Q), and temperature on the yield of the target product 4-thiazolecarboxylic acid (4-TCA) were systematically investigated. Under optimized reaction conditions, this electrocarboxylation strategy proceeded smoothly to other BTs, providing synthetically useful TCAs with moderate to good yields and FEs. Additionally, the electrochemical behavior of bromothiazole on the Ag electrode was investigated using cyclic voltammetry, and a possible reaction mechanism for the formation of the carboxylated product was proposed based on the results.