Background and Overview:
Tetrahydroxydiboron is mainly used in Suzuki coupling for the synthesis of pharmaceutical intermediates. The earliest synthesis of tetrahydroxydiboron can be traced back to 1955, when Wartik generated diboron tetrachloride by inserting a zinc electrode into liquid boron trichloride, and then reacted diboron tetrachloride with water to first form tetrahydroxydiboron, which was then dehydrated at 220°C to form (BO)X. In 1961, McCloskey synthesized tetrahydroxydiboron by slowly adding a quantitative amount of hydrochloric acid to a mixture of tetra(dimethylamino)borane and water at 0°C, with a yield of 56%. For nearly five decades after that, no new methods were reported in the literature until 2012 when Molander again mentioned the latter method for the synthesis of tetrahydroxydiboron.
Preparation:
In a reaction flask, 10% hydrochloric acid (4.5 eq) was added and cooled to 0°C. Tetra(dimethylamino)borane (39.6 g, 0.2 mol, 1.0 eq) was slowly dripped into the hydrochloric acid solution. During the dripping process, solid gradually precipitated. After the dripping was completed, the temperature was gradually raised to room temperature and stirred for 3 hours. The mixture was filtered, and the white solid product was vacuum dried at 40-60°C to obtain 16.9 g with a yield of 94.2%. GC derivatization (dissolving the product in methanol and adding pentaerythritol derivatization) detected a content of 97.9%, and HPLC: 99.5%. HNMR (DMSO-d6 + H2O): 8.84 (0.02), 8.61 (1.00), 7.59 (5.28), 6.50 (0.02) {Note: The values in parentheses are peak area values}. The above product was added to 60 mL of 0.05% dilute hydrochloric acid, stirred at 5-10°C for 30 minutes, filtered, and the solid was dried at 40-60°C to obtain a white product of 16.5 g. GC derivatization detected a content of 99.6%, and HPLC: 99.9%. HNMR (DMSO-d6 + H2O): 8.84 (0.03), 8.61 (1.00), 7.59 (5.35).
Application
Application One:
Tetrahydroxydiboron can be used to prepare diboronic esters. The raw material tetrahydroxydiboron reacts with alcohols/phenols in a solvent under reflux with water removal. After a certain amount of water is removed, the esterification is complete. The diboronic ester precipitates upon cooling or the solvent can be evaporated to obtain the corresponding diboronic ester. In this invention, the reaction mixture of tetrahydroxydiboron with alcohols/phenols is dispersed in an organic solvent that co-boils with water, and the reaction proceeds at reflux temperature. The yield is 85-98%. The organic solvent used for dispersion in the reaction can be directly reused in the next batch. This method is simple and easy to operate, safe and environmentally friendly, and low-cost. The diboronic esters prepared by this method have a high yield. The innovation of this method lies in its good adaptability to diboronic ester compounds that are sensitive to acids and bases. By using the method of co-boiling tetrahydroxydiboron with alcohols/phenols to remove water, diboronic esters are produced in high yield without generating any waste, and the solvent used can be recycled.
Application Two:
Tetraborane tetraol can be used for hydrogen production without the participation of metals. The method is as follows: using tetraborane tetraol as the raw material and an alkaline solution as the catalyst, the mixture is then used to achieve the effect of catalytic hydrogen production. Although this method does not involve any metals in the reaction, it has superior catalytic activity. Twelve different alkaline solutions were tested for their catalytic effect on the hydrolysis of tetraborane tetraol to produce hydrogen. Among them, triethylamine and sodium hydroxide showed the best catalytic hydrogen production effects. Since this method does not involve metals in the reaction, it not only solves the energy crisis but also protects the environment, which is in line with the national call to reduce pollution and protect the environment.
