Selective catalytic hydrodebromination of 2,3,4,5-tetrabromothiophene with hydrogen on a palladium catalyst

A study on the Pd-catalyzed hydrodebromination of 2,3,4,5-tetrabromothiophene (1) to 3,4-dibromothiophene (2) is reported. The effect of the solvent nature, main agent, temperature and concentration of 1 on the yield of 2 was studied. Optimal conditions of the process were found: a 5 % Pd/Sibunit catalyst constituting 10 % of the substrate weight, a temperature of 80 °С, a pressure of 0.7 MPa, dimethyl formamide with the addition of triethylamine as the main agent in the amount of 2.2 equiv per 1 equiv of the initial substance 1, and the yield of 2 constituting up to 97.5 %. It was shown that the catalyst could be reused with the preservation of the high yield of 2. In comparison with the conventional method of chemical reduction of 1 under the action of zinc in acetic acid, the novel method ensures high output and low wastes.