General Description
SODIUM BOROHYDRIDE(16940-66-2) is a white to grayish crystalline powder. SODIUM BOROHYDRIDE(16940-66-2) 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(16940-66-2) is used to make other chemicals, treat waste water, and for many other uses.
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.
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].
Hazard
Reacts with water to evolve hydrogen and
sodium hydroxide. Flammable, dangerous fire risk.
Store out of contact with moisture.
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.
Chemical Properties
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.
Physical properties
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.
Definition
ChEBI: Sodium borohydride is an inorganic sodium salt and a metal tetrahydridoborate.
Preparation
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.
Flammability and Explosibility
Nonflammable
reaction suitability
reagent type: reductant
Purification Methods
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.
Waste Disposal
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.
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