The synthesis method of sodium cyanoborohydride

Regarding the different raw materials used, NaBH4 synthesis methods can be divided into four categories: Borane or organic boron as raw materials; Boron trihalide and sodium tetrafluoroborate as raw materials; Boric acid esters as raw materials; Boron oxide and boron phosphate And borate as raw materials.
Sodium hydride methyl borate method add boric acid and an appropriate amount of methanol into the rectification kettle, slowly heat, reflux at 54 ℃ for 2h, and then collect the azeotrope of methyl borate and methanol. The azeotropic liquid is treated with sulfuric acid and a purer product can be obtained after rectification. The sodium hydride obtained by the action of hydrogen and sodium is fed into the condensation reaction tank, heated to about 220°C under stirring, and methyl borate is added, and the heating is stopped when the temperature reaches 260°C. The feeding temperature is controlled below 280°C, and stirring is continued after feeding to make it fully react. After the reaction is completed, it is cooled to below 100°C and centrifuged to obtain a condensation product filter cake. Add an appropriate amount of water to the hydrolyzer, slowly add the filter cake to the hydrolyzer, control the temperature below 50℃, after the addition, heat up to 80℃, centrifuge, and send the hydrolysate to the layered, and then automatically after 1 hour of rest. Layers, the lower hydrolyzate is sodium borohydride solution.
Note! Hydrocyanic acid is used in this preparation, and the preparation and reaction of the co-solution should be carried out in a fume hood. A constant pressure dropping funnel, an air-driven mechanical stirrer, and a reflux condenser are installed on a clean, dry 2-liter three-neck round bottom burner. The outlet of the condenser is connected to a gas scrubber containing I moles of sodium hydroxide solution to remove the hydrogen cyanide vapor carried out, and then to the gas meter to measure the amount of hydrogen produced. The hydrogen gas is passed into the fume hood.
Put 1000 ml of tetrahydrofuran (preliminarily dried with CaH2 and filtered before use) and 80.2 g (2.09 mol) of 98.5% sodium boron chloride in the flask. Purge the flask with dry nitrogen. A solution of 16.7% (weight ratio) of hydrocyanic acid in tetrahydrofuran (294 grams, containing 58.8 grams or 2.33 moles of 98% hydrocyanic acid) was placed in the dropping funnel. The system is simply cleaned again. The hydrocyanic acid solution was slowly added to the stirring sodium hydride slurry at room temperature, and hydrogen was released slowly and immediately. Since the reaction was slightly exothermic, the flask was kept at 25°C with a water bath. After 1 hour under stirring, the mixture was gradually heated to reflux until hydrogen ceased to occur. After the reaction mixture was cooled to suffocation temperature, it was purged with nitrogen and then evacuated. A small amount of insoluble solids is filtered with a filter paper pad of activated carbon. The transparent light yellow filtrate was dried in a rotary vacuum evaporator. Remove about half of the solution before heating, and finally dry it under vacuum at 60°C. Sodium cyanoborohydride (120 g) was a white solid with a yield of 91%. This product may contain B(OH)3 impurity through elemental analysis. Dissolve this crude product in tetrahydro enanthran (20%V/V), filter, add 4 times excess dichloromethane, and recrystallize twice to obtain pure product.