Sodium borohydride

From Sciencemadness Wiki
Revision as of 18:34, 9 July 2023 by Mabus (Talk | contribs)

Jump to: navigation, search
Sodium borohydride
Sodium borohydride bottle sample.jpg
NaBH4 sample
Names
IUPAC name
Sodium tetrahydridoborate
Other names
Sodium boranuide
Sodium tetrahydroborate
Properties
NaBH4
Molar mass 37.83 g/mol
Appearance White or grayish solid
Odor Odorless
Density 1.0740 g/cm3
Melting point 400 °C (752 °F; 673 K)
Boiling point 500 °C (932 °F; 773 K) (decomposes)
25 g/100 ml
Reacts slowly
Solubility Reacts with acids, alcohols, aldehydes, carboxylic acids, halocarbons, ketones
Soluble in liquid ammonia, amines, isopropylamine, methylamine, pyridine
Slightly soluble in DMSO, ethanol, THF, toluene
Insoluble in diethyl ether, hexane, pentane
Solubility in acetonitrile 2 g/100 ml (28 °C)
Solubility in ammonia 104 g/100 ml (-33.3 °C)
Solubility in diethyl ether 0.02 g/100 ml
Solubility in diglyme 5.15 g/100 ml
24 g/100 ml (25 °C)
Solubility in dimethoxyethane 0.567488 g/100 ml (25 °C)
Vapor pressure ~0 mmHg
Thermochemistry
190 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point 70 °C (158 °F; 343 K)
Lethal dose or concentration (LD, LC):
160 mg/kg (rat, oral)
230 mg/kg (rabbit, dermal)
Related compounds
Related compounds
 Lithium borohydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the chemical formula NaBH4. It is widely used as a reducing agent.

Properties

Chemical

Sodium borohydride reacts with water to release hydrogen, though the reaction is very slow.

Addition of acids speeds up the decomposing reaction. Boron trioxide has been found to be quite effective, while cobalt(II) chloride as been found to be even more effective.[1]

Sodium borohydride is a strong reducing agent, albeit not as strong as lithium borohydride. It is capable of reducing ketones and aldehydes into their corresponding alcohols. It efficiently reduces acyl chlorides, anhydrides, α-hydroxylactones, thioesters, and imines at room temperature or below. It reduces esters slowly and inefficiently with excess reagent and/or elevated temperatures, while carboxylic acids and amides are not reduced at all. However, in the presence of elemental iodine, NaBH4 has been shown to reduce carboxylic acids to their corresponding alcohols. Tetrahydrofuran is often used as solvent in this case.[2]

Physical

Sodium borohydride is a white solid, which reacts with water and alcohols, though the reaction is fairly slow. Complete decomposition in excess methanol can take nearly 90 min at 20 °C. It will decompose in neutral or acidic aqueous solutions but is stable at pH ~ 14. It has good solubility in amines and poor solubility in ethers.

Availability

Sodium borohydride is sold by chemical suppliers. It can also sometimes be found on eBay and Amazon.

Preparation

Can be prepared by reacting sodium hydride with trimethyl borate, at 250–270 °C:

B(OCH3)3 + 4 NaH → NaBH4 + 3 NaOCH3

Reaction of boron trifluoride with sodium hydride will give sodium borohydride.[3]

BF3 + 4 NaH → NaBH4 + 3 NaF

Trimethyl borate can also be replaced with boron trioxide.[4]

Reaction of diborane with sodium amalgam is another route.[5] Using sodium hydride instead of sodium amalgam will also work, with THF or diethylene glycol being used as reaction solvent.[6][7]

Projects

  • Make hydrogen
  • Reduce organic compounds (reducing agent)
  • Fuel cells

Handling

Safety

Sodium borohydride reacts with water to release hydrogen and may be pyrophoric if finely divided. Sodium borohydride itself is very flammable and burns with a bright yellow flame, leaving behind a residue of sodium and boron oxides.[8]

Storage

Sodium borohydride should be kept air-tight containers, away from moisture and air. While it can be stored in most bottles, it will not tolerate prolonged exposure to moisture, so it's best to use an air-tight cap or seal the bottle with parafilm, if you intend on using the borohydride for a long period of time.

Disposal

Can be neutralized safely by adding it in a large volume of water, aq. acids or alcohol. Controlled incineration is also an option.

References

  1. ↑ https://www.thevespiary.org/rhodium/Rhodium/Vespiary/talk/files/2203-Schlesinger.etal.Sodium.Borohydride.Its.Hydrolysis.and.Its.Use.as.a.Reducing.Agent.and.in.the.Generation.of.Hydrogen0b86.pdf
  2. ↑ https://pubs.acs.org/doi/abs/10.1021/jo00020a052
  3. ↑ Hurd, D. T.; Journal of the American Chemical Society; vol. 71; (1949); p. 20 - 22
  4. ↑ Gaylord, N. G.; Journal of the American Chemical Society; vol. 75; (1953); p. 186 - 190
  5. ↑ Kasper, J. S.; McCarty, L. V.; Newkirk, A. E.; Journal of the American Chemical Society; vol. 71; (1949); p. 2583
  6. ↑ Noeth,H.; Beyer,H.; Chemische Berichte; vol. 93; (1960); p. 928 - 938
  7. ↑ Schlesinger, H. I.; Brown, H. C.; Hoekstra, H. R.; Rapp, L. R.; Journal of the American Chemical Society; vol. 75; (1953); p. 199 - 204
  8. ↑ https://www.youtube.com/watch?v=OLUKSd5MtR8

Relevant Sciencemadness threads

Retrieved from "https://www.sciencemadness.org/smwiki/index.php?title=Sodium_borohydride&oldid=15061"