关键词: 4-联苯甲酸, Suzuki-Miyaura反应, Pd/C, 空气氛围, 回收循环使用

Abstract:

The Suzuki-Miyaura coupling reaction for the synthesis of biphenyl compounds through aryl halides and aryl boronic acids has been widely used in the synthesis of natural products, drugs, and functional materials. However, there are very few relevant experiments currently in undergraduate teaching, mainly because the traditional Suzuki reaction conditions involve expensive ligand-containing Pd catalysts. Furthermore, most reaction solvents contain toxic solvents such as toluene or 1, 4-dioxane, and the reaction requires an inert gas atmosphere and heating for over 8 h. These restrictions largely prevent undergraduates from carrying out this important organic chemistry experiment. In this study, the Suzuki coupling conditions were modified as follows: ligand-free Pd/C was used as the catalyst, ethanol mixed with water was used as the reaction solvent, and then the reaction was stirred at room temperature for 30 min in the open air (oxygen) instead of in an inert atmosphere. Under these conditions, the starting materials, phenylboronic acid and 4-bromobenzoic acid, were reacted using potassium carbonate as the base, which efficiently synthesized 4-bibenzoic acid. Compared to the traditional Suzuki reaction conditions in which the catalyst cannot be recovered, the Pd/C catalyst recovered in this experiment can be recycled more than 5 times without substantial activity loss. This experiment provides the possibility for undergraduates to become familiar with the Suzuki reaction due to improvements in cost, operability, and environmental protection.

Key words: 4-Bibenzoic acid, Suzuki-Miyaura reaction, Pd/C, Air atmosphere, Recycle and reuse