What is Sodium Borohydride?
Sodium borohydride is an inorganic compound whose chemical formula is NaBH4. Under normal conditions, this compound exists as a white, powdery solid. NaBH4is a reducing agent which is widely used both industrially and on the laboratory scale. It can be noted that sodium borohydride is also known as sodium tetrahydroborate and sodium tetrahydridoborate.
Sodium borohydride can be prepared on an industrial scale by treating trimethyl borate with sodium hydride at a temperature range of 250-27oC. The balanced chemical equation for this reaction is given by:
4NaH + B(OCH3)3 → 3NaOCH3 + NaBH4
Alternately, this compound can also be prepared by reacting borax, metallic sodium, dihydrogen, and silicon dioxide at a temperature of 700oC. This reaction can be represented as follows:
Na2B4O7 + 8H2 + 16Na + 7SiO2 → 7Na2SiO3 + 4NaBH4
Structure of NaBH4
The structure of NaBH4 molecules is illustrated below.
This salt consists of the Na+ cation and the BH4– anion. It can be noted that the BH4– ion has a tetrahedral structure. NaBH4 has three stable polymorphs, namely the α, β, and γ polymorphs.
Properties of Sodium Borohydride
Physical Properties of NaBH4
- The molar mass of NaBH4 is 37.83 grams per mole.
- This compound does not have any characteristic odour.
- The density of sodium borohydride at STP corresponds to 1.07 grams per cubic centimetre.
- It has a melting point of 673K. However, it tends to undergo decomposition at this temperature.
Chemical Properties of NaBH4
- Despite being soluble in most protic solvents (like water), this compound slowly reacts with the protic solvent, resulting in the formation of dihydrogen.
- Sodium borohydride generally undergoes decomposition in acidic and aqueous media but not in basic media.
- This compound is a reducing agent and can reduce a wide spectrum of organic carbonyls.
- NaBH4 also releases hydrogen when exposed to many metal catalysts.
Uses of Sodium Borohydride
- The primary use of NaBH4 is in the preparation of Na2S2O4 (sodium dithionite, which is a bleaching agent for wood pulp) from SO2.
- Aldehydes & ketones can be converted into the corresponding alcohols with the help of this compound.
- Several antibiotics such as thiophenicol, dihydrostreptomycin, and chloramphenicol are produced by employing NaBH4 as a reducing agent.
- It can also be used to reduce foxing in aged documents and books.
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