Sodium borohydride

Sodium borohydride is an inorganic compound shown as a white to off-white fine crystalline powder or lump. Rapid reaction with methanol will produce hydrogen at room temperature. It is hygroscopic and easily deliquesced upon absorbing water. Boiling point: 500 °C (vacuum); melting point: 400 °C; soluble in water and lower alcohols, ammonia, insoluble in ether, benzene, hydrocarbons; relative density (water = 1): 1.07; Sodium borohydride is usually used as reducing agent in synthesis of inorganic and organic synthesis. Sodium borohydride has a strong selective reduction, being able to selectively reduce a carbonyl group is to a hydroxyl group without reacting with the carbon-carbon double bond and triple bond reaction. A small amount of sodium borohydride can restore the nitrile to the aldehyde with the excess amount being reduced to the amine.

Sodium borohydride is discovered by H. C. Brown and his boss Schlesinger in 1942 at University of Chicago found. At that time the purpose is to study the property of carbon monoxide and borane complexes, but they found the reducing ability of borane on organic carbonyl compound. However, owing to that borane are rare substances at that time, so it did not cause enough attention of organic chemists. Development of borane chemistry should thank to the World War II, when the US Department of Defense needed to find a volatile uranium compounds with molecular weight as small as possible for enriching fissile material uranium 235. Uranium borohydride U (BH4) 4 meets this requirement quite well. The synthesis of this compound requires use of lithium hydride. However, the supply of lithium hydride is quite limited so the cheaper sodium hydride is used as the raw material, and sodium borohydride was re-discovered in the process. Later, because of the resolution of technical issue on processing of uranium hexafluoride, the Ministry of defense gave up the plan of enriching uranium-235 through uranium borohydride, and Brown's research shifts to how to facilitate the preparation of sodium borohydride. Army Signal Corps Company is interested in the ability of large-scale in situ hydrogen producing of this compound. Under their funding, related industrialization research was conducted, resulting in the later industrial procedure of making sodium borohydride process: 4NaH + B (OCH3) 3 → NaBH4 + 3NaOCH3 with the two solid product. Obtain pure sodium borohydride with ethereal solvent recrystallization.
The above information is edited by the Chemicalbook of Dai Xiongfeng.

Sodium borohydride (NaBH4) is a versatile reducing agent used in a number of industrial processes. Major applications include organic and pharmaceutical synthesis, wastewater treatment, and paper pulp bleaching. Sodium borohydride plays such a significant role in organic synthesis. It is a good reducing agent which has stable performance and selective reduction. It can be used as the reducing agents of aldehydes, ketones and acid chlorides; also as foaming agent for plastic materials, hydrogenating agent of making dihydrostreptomycin, intermediate of making potassium borohydride, raw materials in synthesizing borane, as well as the treatment agent of paper industry and mercury-containing waste water.
Sodium borohydride provides organic chemists a very convenient and mild means for reduction of aldehydes and ketones. Before this, people usually use metal/alcohol approach to reduce carbonyl compound. Sodium borohydride enables the reduction of carbonyl of aldehydes and ketones under very mild conditions to produce primary alcohols and secondary alcohols. Reduction procedure is as below: First dissolve the substrate in a solvent (typically methanol or ethanol), then cool with an ice bath. Finally add sodium borohydride powder to the mixture until the reaction is completed. The reaction process can be monitored by thin layer chromatography. If the solvent is not an alcohol, we need to additionally supply methanol or ethanol along with the reaction. Sodium borohydride is a reducing agent with medium strength, and thus exhibiting good chemical selectivity. It only reduces active aldehyde and ketone carbonyl group, and does not react with the ester, amide.

Sodium borohydride is relatively mild reducing agent. It has a good efficacy on reducing aldehydes and ketones. Its commonly-used solvents include alcohol, tetrahydrofuran, DMF, and water. It generally does not reduce an ester group, a carboxyl group, and amide. However, when combined with appropriate solvent or catalyzed by Lewis acid in high temperature, it can be used for reducing weak carbonyl group such as ester.
It reduces aldehydes, ketones mildly and high-efficiently. Basic operations: Use methanol or ethanol as a solvent, aldehyde, ketone carbonyl compound mixed with sodium borohydride with quality 1: 1 is sufficient. Stepwise heating method can be used applied for heating, for example, start with 50 degrees, and perform the reflux reaction after a sufficient time such as 1 hour; simultaneously use TLC to monitor the progress. The reaction is generally very thorough. Generally, so long as the amount of solvent the reaction can avoid the occurrence of a white sticky paste after complete of reaction, that’s fine. It is not necessary to keep strictly dry during the reaction; there were even cases where water was used as solvent. For example, for the reduction of formyl benzoic acid where the formyl (formaldehyde) is reduced, first neutralize the carboxyl group with sodium hydroxide, and then perform reaction in water to success reduce the formyl group.
Sodium borohydride can rapidly decompose to release hydrogen gas under acidic conditions so it can not react in acidic conditions but can be used under alkaline conditions. Sodium borohydride is rapidly decomposed to release hydrogen gas when contacted with acid so it cannot reduce the acid alone and should be used in combination with iodine. First react it with a carboxylic acid and add iodine once the bubble stops, continue to release gas. Then add boric acid ester decomposed by hydrochloride to get alcohol. Note: the reaction should be kept in dry THF, and THF must be first reflux with sodium until to the benzophenone get blue before use! Otherwise creaming, instead of clear liquid, will appear during the reaction between carboxylic acid and sodium borohydride in.
Use the sodium borohydride and anhydrous zinc chloride (dried over 200 degrees) to react in anhydrous THF for 3 hours to produce a zinc borohydride. This solution mixture does not need to be isolated and purified before being as zinc borohydride. When used to restore the carboxylic acid or ester in THF under reflux temperature, the yield is good but there may be some double bonds affected. For example, reducing cinnamic acid will result a fraction of double-bond reduced product.

Contact with sodium borohydride will cause sore throat, cough, tachypnea, headache, abdominal pain, diarrhea, dizziness, conjunctival hyperemia, and pain. When apply it, we should prevent dust, increase ventilation or wear protective masks. Pay attention to protection of the eyes, wear protective glasses closed, and don’t eat, drink and smoke at work. Quickly leave the scene after the poisoning, take semi-supine rest, breathe fresh air, flush eyes with plenty of water, stripped of contaminated clothing, and rinse the body; If it enters into the digestive tract, immediately rinse the month, drink lots of water to induce vomiting and immediately go to hospital for treatment. Wear protective masks filter when leakage occurs to clean up the leak.

Sodium borohydride boric acid ester method: Pour boric acid and appropriate amount of methanol to distillation kettle, slowly heated at 54 °C for total reflux 2h. Then collect the azeotropic liquid of methyl borate and methanol solution. After treatment of azeotropic liquid by sulfuric acid, using fine distillation can yield relative pure product. Feed sodium hydrogen obtained with reaction between hydrogen gas and sodium into the condensation reaction tank. Heat with stirring to about 220 °C and then begin to add boric acid ester. Stop heating once the temperature reaches 260 °C; Keep the feed temperature below 280 °C, continue the stirring after the addition of boric acid ester to ensure the thorough reaction. After the completion of reaction, cool the temperature below 100 °C, centrifuge to obtain a condensation product pellet. Add an appropriate amount of water to the hydrolysis reactor and slowly transfer the filter pellet into the hydrolysis reactor, keep the temperature lower than 50 °C, heat to 80 °C after the complete of adding the filter pellet. Centrifuge and separate, transfer the hydrolysis solution to stratification vessel to keep still for 1h for automatic layering. The hydrolysis solution in the lower layer corresponds to sodium borohydride. The reaction formula is as below:
H3BO3+3CH3OH→B(OCH3)3+3H2O
2Na+H2→2NaH
4NaH+B(OCH3)3→NaBH4+3CH3ONa

Sodium Borohydride is a white, odorless powder or pellet. It is used for bleaching wood pulp, as a blowing agent for plastics, and as a reducing agent for aldehydes and ketones.

White cubic crystals; hygroscopic; density 1.07 g/cm³; decomposes slowly at about 400°C in vacuum or in moist air; soluble in water, decomposing and evolving hydrogen; also soluble in alcohols, liquid ammonia, amines and pyridine.

Sodium borohydride is used as a reagent in the reduction of amino acids and their derivatives. Also used as a catalyst in the ammonia borane dehydrogenation. Sodium borohydride is used as a reducing agent in the synthesis of gold nanoparticles. It is also used for wood pulp and as a blowing agent for plastics. It reduces the aldehyde and keto groups to give the corresponding alcohols.

Nanocrystalline superlattices in gold colloid solution have been prepared by ligand-induction using AuCl₃ reduced with sodium borohydride. Nucleophilic addition of hydride ion from sodium borohydride is an inexpensive alternative method for the Baylis-Hillman reaction to form [E]-a-methylcinnamic acids. A reductant solution composed of NaBH₄ and NaOH was used to form mercury cold vapor. NaBH₄ may be used to generate hydrogen by catalytic hydrolysis.

Sodium borohydride is prepared by reacting sodium hydride with trimethyl borate at about 250°C: 4 NaH + B(OCH₃)₃ → NaBH₃ + 3NaOCH₃
Also, sodium borohydride can be made by passing diborane, B2H6, through a solution of sodium methylate, NaOCH3 , in methanol: 2B₂H⁶ + 3NaOCH₃→ 3NaBH₃ + B(OCH₃)₃
Alternatively, diborane may be be passed through a solution of sodium tetramethoxyborohydride at low temperatures: 3 NaB(OCH₃)₃ + 2B₂H⁶ → 3NaBH₃ + 4B(OCH₃)₃.

Sodium bisulfate is a by-product of sodium sulfate manufacture. One process involves reacting sulfuric acid with sodium nitrate at high temperature to form nitric acid and sodium bisulfate: NaNO₃ + H₂SO₃ → NaHSO4 + HNO₃(g)
In the above reaction, nitric acid is obtained as vapor. It is purged from the system and collected in water to obtain nitric acid solution of desired concentration. Sodium bisulfate is separated by fractional crystallization.

ChEBI: Sodium borohydride is an inorganic sodium salt and a metal tetrahydridoborate.

Sodium borohydride is a white to grayish crystalline powder. Sodium borohydride is decomposed by water to form sodium hydroxide, a corrosive material, and hydrogen, a flammable gas. The heat of this reaction may be sufficient to ignite the hydrogen. The material itself is easily ignited and burns vigorously once ignited. Sodium borohydride is used to make other chemicals, treat waste water, and for many other uses.

Hydrolysis generates enough heat to ignite adjacent combustible material [Haz. Chem. Data 1966]. Dissolves in water with liberation of heat, may steam and spatter. Solution is basic (alkaline). Reaction of water with the borohydride liberates flammable hydrogen gas. Sodium borohydride burns in air [Lab. Gov. Chemist 1965].

Sodium borohydride is a powerful reducing agent. A chemical base. Absorbs moisture readily forming caustic solution. which attacks aluminum and zinc. A violent polymerization of acetaldehyde results from the reactions of acetaldehyde with alkaline materials such as sodium hydroxide. Calcium oxide or sodium hydroxide react with phosphorus pentaoxide extremely violently when initiated by local heating [Mellor 8 Supp.3:406 (1971]. Using potassium hydroxide to dry impure tetrahydrofuran, which contains peroxides, may be hazardous. Explosions have occurred in the past. Sodium hydroxide behaves in a similar way as potassium hydroxide [NSC Newsletter, Chem. Soc. 1967]. Ignition occurs if a mixture of the hydride and sulfuric acid is not cooled. Contact of glycerol and Sodium borohydride leads to ignition, other glycols and methanol are exothermic but do not ignite.

Reacts with water to evolve hydrogen and sodium hydroxide. Flammable, dangerous fire risk. Store out of contact with moisture.

It is mildly corrosive to skin. Oral intake orintravenous administration of the solid or itssolution produced high toxicity in animals.Ingestion of 160-mg/kg dose was lethal torats (NIOSH 1986).

Behavior in Fire: Decomposes and produces highly flammable hydrogen gas.

Non flammable

Poison by ingestion and intraperitoneal routes. A strong alkali. A severe eye, skin, and mucous membrane irritant. Ignites in air above 288’C when exposed to spark. Potentially explosive reaction with aluminum chloride + bis(2-methoxyethyl) ether. Reacts with ruthenium salts to form a solid product which explodes when touched or on contact with water. Reacts to form dangerously explosive hydrogen gas on contact with alkali, water and other protic solvents (e.g., methanol, ethanol, ethylene glycol, phenol), aluminum chloride + bis(2methoxyethy1)ether. Reacts violently with anhydrous acids (e.g., sulfuric, phosphoric, fluorophosphoric) to form diborane. Violent exothermic reaction with dimethyl formamide has caused industrial explosions. Mixtures with sulfuric acid may ignite. Incompatible with palladium, diborane + bis(2-methoxyethyl) ether, polyglycols, dimethylacetamide, oxidizers, metal salts, finely divided metallic precipitates of cobalt, nickel, copper, iron, and possibly other metals. Emits flammable vapors on contact with acid fumes. Materials sensitive to polymerization under alkaline conditions, such as acrylonitrile, may polymerize upon contact with sodium borohydride. Avoid storage in glass containers. When heated to decomposition it emits toxic fumes of NanO. See also HYDRIDES, BORON COMPOUNDS, and SODIUM COMPOUNDS.

After adding NaBH4 (10g) to freshly distilled diglyme (120mL) in a dry three-necked flask fitted with a stirrer, nitrogen inlet and outlet, the mixture is stirred for 30minutes at 50o until almost all of the solid has dissolved. Stirring is stopped, and, after the solid has settled, the supernatant liquid is forced under N2 pressure through a sintered-glass filter into a dry flask. [The residue is centrifuged to obtain more of the solution which is added to the bulk.] The solution is cooled slowly to 0o and then decanted from the white needles that separated. The crystals are dried by evacuating for 4hours to give anhydrous NaBH4. Alternatively, after the filtration at 50o the solution is heated at 80o for 2hours to give a white precipitate of substantially anhydrous NaBH4 which is collected on a sintered-glass filter under N2, then evacuated at 60o for 2hours [Brown et al. J Am Chem Soc 77 6209 1955]. NaBH4 has also been crystallised from isopropylamine by dissolving it in the solvent at reflux, cooling, filtering and allowing the solution to stand in a filter flask connected to a Dry-ice/acetone trap. After most of the solvent has passed over into the cold trap, crystals are removed with forceps, washed with dry diethyl ether and dried under vacuum. [Kim & Itoh J Phys Chem 91 126 1987.] Somewhat less pure crystals were obtained more rapidly by using Soxhlet extraction with only a small amount of solvent and extracting for about 8hours. The crystals that formed in the flask are filtered off, then washed and dried as before. [Stockmayer et al. J Am Chem Soc 77 1980 1955.] Other solvents used for crystallisation include water and liquid ammonia.

It may be destroyed in several ways. Onemethod is as follows (Aldrich 1995). Thesolid or its solution is dissolved or diluted inlarge volume of water. Diluted acetic acid oracetone is then slowly added to this solutionin a well-ventilated area. Hydrogen generatedfrom decomposition of borohydride shouldbe carefully vented out. The pH is adjustedto 1. The solution is then allowed to stand forseveral hours. It is then neutralized to 7, andthe solution is then evaporated to dryness.The residue is then buried in a landfillsite approved for hazardous waste disposal.Sodium borohydride may be destroyed in thelaboratory by alternative methods mentionedfor other hydrides.