Sodium Cyanoborohydride is an organic compound that can be used to reduce acyl compounds and other organic compounds, so it is one of the commonly used reducing agents in organic synthesis. The following are two common synthetic routes of Sodium Cyanoborohydride:
1. Reaction of sodium cyanide and sodium borohydride
Sodium cyanide and sodium borohydride are first mixed and reacted at room temperature. Sodium Cyanoborohydride and hydrogen are generated during the reaction:
NaCN + NaBH4 → NaBH3CN + H2
After the reaction, the resulting Sodium Cyanoborohydride can be obtained by filtering and drying under vacuum to obtain the pure product.
The detailed steps of the reaction are as follows:
(1) In a dry environment, mix sodium cyanide and sodium borohydride at a molar ratio of 1:1, and add the mixture to dry anhydrous methanol.
(2) Add the methanol mixture into the reactor and heat to the reaction temperature with stirring. Usually the reaction temperature is 0-5°C, which can be controlled with an ice-salt bath.
(3) Slowly add an appropriate amount of water dropwise to the reaction mixture to promote the reaction. During the reaction, methanol decomposes to formaldehyde and hydrogen gas, while sodium cyanide and sodium borohydride react to form NaBH3CN.
(4) After the reaction is completed, the reaction mixture is filtered to remove the residual solid, and then the product is washed with water or methanol.
2. Reaction of sodium cyanide and boron trichloride
Sodium cyanide and boron trichloride are first mixed and reacted at room temperature. The reaction produces cyanide and hydrogen, and forms the intermediate sodium trichloride borocyanide (NaCN·BCl3). Then, sulfuric acid was added, the intermediate was hydrolyzed and dried under vacuum to give Sodium Cyanoborohydride:
NaCN + BCl3 → NaCN BCl3
NaCN BCl3 + H2O + H2SO4 → NaBH3CN + H3BO3 + NaHSO4
The reaction process is relatively simple, the steps are as follows:
(1) Mix sodium cyanide and boron trichloride at a molar ratio of 1:1, and add a sufficient amount of acetonitrile, DMF or DMSO and other organic solvents.
(2) Slowly add dilute acid (such as HCl or H2SO4) to the reaction mixture under stirring, and it can be observed that the mixture turns into a white suspension during the reaction.
(3) The reaction is generally carried out at room temperature, and cooling water or ice water can be used to maintain the reaction temperature, and the reaction usually takes 2-4 hours.
(4) After the reaction is completed, dilute the reaction mixture with water, then wash the product with an inorganic salt solution (such as sodium acetate solution), and finally wash with ethanol.
(5) Dry the washed product to obtain high-purity NaBH3CN.
Both of the above methods can prepare Sodium Cyanoborohydride, but the first method is more convenient, so it is more common in the laboratory
Here are some other synthetic methods for the synthesis of Sodium cyanoborohydride:
1. Boron trichloride method:
After mixing sodium borate and hydrocyanic acid, boron trichloride is added and heated to obtain NaBH3CN.
Proceed as follows:
(1) In a dry environment, mix boron trichloride and methanol at a molar ratio of 1:1.
(2) Slowly add hydrocyanic acid under stirring conditions, and the reaction mixture will produce boron cyanide. During the course of the reaction, the mixture was observed to change from dark red to orange and then to light yellow.
(3) Add sodium cyanide and a sufficient amount of methanol, and continue to stir the reaction mixture. In this step, boron cyanide reacts with sodium cyanide to form NaBH3CN and NaCl.
(4) After the reaction is completed, the reaction mixture is filtered to remove residual solid matter. The product is then washed with water or methanol.
(5) Finally, the washed product is dried to obtain high-purity NaBH3CN.
2. Formaldehyde method:
After mixing formaldehyde and hydrocyanic acid, sodium hydroxide is added under the action of alkali to obtain NaBH3CN.
Specific steps are as follows:
(1) Mix formaldehyde and sodium cyanide at a molar ratio of 2:1, and add a sufficient amount of acetonitrile, DMF or DMSO and other organic solvents.
(2) Slowly add boron cyanide under stirring, usually the amount of boron cyanide is 1.2-1.5 times that of formaldehyde, and it can be diluted with organic solvents such as acetonitrile, DMF or DMSO.
(3) After adding boron cyanide, continue to stir the reaction mixture. The reaction is generally carried out at room temperature, and the pH needs to be controlled at around neutral. The reaction time is usually several hours.
(4) After the reaction, the reaction mixture can be diluted with water, and the product is washed with an inorganic salt solution (such as sodium acetate solution), and finally washed with ethanol.
(5) Dry the washed product to obtain high-purity NaBH3CN.
3. Acrylonitrile method:
After mixing acrylonitrile and hydrocyanic acid, sodium hydroxide and boric acid are added to obtain NaBH3CN.
Specific steps are as follows:
(1) Mix acrylonitrile and sodium cyanide at a molar ratio of 1:1.5, and add a sufficient amount of organic solvent such as methanol or acetonitrile.
(2) Slowly add boron cyanide under stirring, usually the amount of boron cyanide is 1.2-1.5 times that of acrylonitrile, and it can be diluted with organic solvent.
(3) After adding boron cyanide, continue to stir the reaction mixture. The reaction temperature is generally at room temperature, and the reaction time is usually several hours.
(4) After the reaction, the reaction mixture can be diluted with water, and the product is washed with an inorganic salt solution (such as sodium acetate solution), and finally washed with ethanol.
(5) Dry the washed product to obtain high-purity NaBH3CN.
4. Sodium hydrocyanate method:
After mixing sodium hydrocyanate and sodium hydroxide, add sodium borohydride and heat to 60°C to obtain NaBH3CN.
Specific steps are as follows:
(1) Mix sodium cyanide and sodium hydrocyanate in a molar ratio of 2:1, and add enough water.
(2) Slowly add sodium hydroxide under stirring until the pH value of the solution reaches 10-11.
(3) Next, slowly add hydrocyanic acid to control the pH value at around 7-8, usually requiring continuous stirring and heating (around 60°C).
(4) Under the condition of stirring and heating, add boron cyanide slowly, usually the amount of boron cyanide is 1.2-1.5 times that of hydrocyanic acid, and it can be diluted with water.
(5) After the reaction, the product can be washed with an inorganic salt solution (such as sodium acetate solution), and finally washed with ethanol.
(6) Dry the washed product to obtain high-purity NaBH3CN.
Among these other synthetic methods, the boron trichloride method is one of the most commonly used methods. Other methods can also be carried out in the laboratory, but it is necessary to choose the most suitable method for production according to the experimental environment and its own needs.