Sodium Borohydride (NaBH₄)

Table of Contents

• What is Sodium Borohydride?
• Preparation
• Structure of NaBH4
• Properties of Sodium Borohydride
• Uses of Sodium Borohydride
• Frequently Asked Questions

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. NaBH₄ is 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.

Preparation

Sodium borohydride can be prepared on an industrial scale by treating trimethyl borate with sodium hydride at a temperature range of 250-27^oC. 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 700^oC. 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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