|Sodium borohydride Chemical Properties|
|Melting point ||>300 °C (dec.)(lit.)|
|Boiling point ||500°C|
|density ||1.035 g/mL at 25 °C|
|Fp ||158 °F|
|storage temp. ||Store at RT.|
|Water Solubility ||550 g/L (25 ºC)|
|Stability:||Stability Stable, but reacts readily with water (reaction may be violent). Incompatible with water, oxidizing agents, carbon dioxide, hydrogen halides, acids, palladium, ruthenium and other metal salts, glass. Flammable solid. Air-sensitive.|
|CAS DataBase Reference||16940-66-2(CAS DataBase Reference)|
|NIST Chemistry Reference||Sodium tetrahydroborate(16940-66-2)|
|EPA Substance Registry System||Borate(1-), tetrahydro-, sodium(16940-66-2)|
|Sodium borohydride Usage And Synthesis|
|General description||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.
|Discovery History||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.
|Uses||The hydrogen of odium borohydride hydrogen here was -1 thus having a strong reducing property which can reduce some oxidative inorganic. It is mainly used for reducing -COOH to -CH2OH in organic synthesis. It plays such a significant role in organic synthesis that it is called as "universal reductant." 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.
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.
Common used reducing agents. It can be used as the reducing agent of aldehydes, ketones and acid chlorides, foaming agent of plastic materials, hydrogenating agent for making dihydrostreptomycin, the intermediate of making potassium borohydride, raw materials of borane synthesis, treatment agent of paper industry and mercury-containing waste water, and also paper bleaching agent.
For the manufacture of other borohydride salts, reducing agents, bleaching wood pulp, and plastics blowing agent.
|Compared with sodium cyanoborohydride||Both of them are reducing agents, sodium cyanoborohydride is milder and have a better selective ability than sodium borohydride.|
Sodium borohydride can be used for reducing carbonyl groups of aldehydes and ketones to generate an alcohol, secondary alcohols under very mild conditions. Reduction procedure: 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. 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. It generally does not react with carbon-carbon double bond and triple bonds. A small amount of sodium borohydride can reduce the nitrile to aldehydes with the excess amount being reduced to the amine.
Sodium cyanoborohydride is a mild reducing agent, often used for selectively reduce the imine obtained by aldehyde/ketone reaction to an amine. It is especially suitable for reductive amination reaction (Borch reaction). It reacts slowly with water so that water can be used as the solvent for sodium cyanoborohydride reaction. However, using nucleophilic reductant like lithium aluminum hydride and sodium borohydride cannot reduce the indole ring system. Only through acidic conditions can the heterocyclic ring be reduced. Combination of transition metal-acid has been previously applied, but now people mainly apply acid-stable metal hydrides such as sodium cyanoborohydride which can make reaction conditions be milder. This reduction is achieved by attacking the hydride of β- indole -3H-indole cation.
|Reducing ability||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.
|Toxicity||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.
|Chemical property||White crystallized powder. Relative density: 1.074. Vacuum decomposed at 400 °C. Hygroscopic, stable in dry air but decompose in wet air. Soluble in water, ammonia, amines; Slightly soluble in THF but insoluble in ether, benzene, hydrocarbons. Reaction with water produces hydrogen gas. Alkaline solution of sodium borohydride was brown.
|Production methods||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:|
|Toxicity grading||highly toxic.
|Category||water combustible goods.
|Acute toxicity||Oral- rat LD50: 162 mg / kg; Oral - Mouse LD50: 50 mg / kg.
|Explosive and hazardous characteristics||explosive with acids, water and oxidants.
|Chemical Properties||White solid|
|Flammability and hazard characteristics||Contact with water, moist air and oxidant causes release of flammable hydrogen gas.
|Usage||Nanocrystalline superlattices in gold colloid solution have been prepared by ligand-induction using AuCl3 reduced with sodium borohydride.1 Nucleophilic addition of hydride ion from sodium borohydride is an inexpensive alternative method for the Baylis-Hillman reaction to form [E]-α-methylcinnamic acids.2|
|Usage||Sodium Borohydride is used as a reagent in the reduction of amino acids and their derivatives. Also used in the catalysis of ammonia borane dehydrogenation.|
|Storage characteristics||Ventilation, low-temperature, and dry; Store separately from oxidants, halogens, and strong acids; Avoid moisture.
|Extinguishing agent||Dry powder, dry sand.
|General Description||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.|
|Air & Water Reactions||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].|
|Reactivity Profile||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.|
|Health Hazard||Solid irritates skin. If ingested can form large volume of gas and lead to a gas embolism.|
|Fire Hazard||Behavior in Fire: Decomposes and produces highly flammable hydrogen gas.|
|Sodium borohydride Preparation Products And Raw materials|