Sodium Borohydride

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Introduction to Sodium Borohydride

Sodium Borohydride is a very commonly known reducing agent used in Chemistry. It has the formula NaBH4, which is made up of Sodium(Na), Boron(B), and Hydrogen(H). It is widely used in Chemistry labs as it is safer than other reagents for reduction. We know that reduction is the process of adding electrons or removal of hydrogen ions. For this purpose, different kinds of chemical reagents are available, which differ in properties, reactivity, and yield of the product given. We will discuss the structures, properties, and reactivity of NaBH4.

Methods of Preparation

There are several methods available for the synthesis of Sodium Borohydride, out of which Bayer Process and the Brown-Schlesinger process are famous ones. In the Brown-Schlesinger process, Sodium hydride (NaH) and trimethyl borate are made to react together at temperatures of 523-533 K.

This is the best method for synthesis of Sodium Borohydride at industrial scale, tons of compound is synthesized annually via this method. Instead of Na, Mg hydride can be used for synthesis.

Structure of Sodium Borohydride

Sodium and Boron hydride are attached through positive and negative interactions known as Ionic Bond. Boron hydride has 4 H atoms attached to B atoms. These impart negative charges overall. So, the structure is tetrahedral. Sodium is present as Na+. They belong to the cubic lattice structure the same as NaCl.

Physical Properties of Sodium Borohydride

The compound has the formula NaBH4 and a molar mass of 37.83 gm per mole.

It has a clear white color powder type texture and it is relatively more stable than hydrides of Lithium. The melting point of Sodium Borohydride is 673K; heating above this temperature leads to the decomposition of the compound.

Chemical Properties of Sodium Borohydride

  • The most important property of this compound is its reducing nature. Now the most important question is why is it preferable to other reducing agents? The answer is because of its mild nature and safety issues. Lithium hydride reacts violently in air and leads to disasters and also reduces from carbonyl compounds i.e. From carboxylic acid to alcohol in a single run. It is generally very difficult to stop the reaction at intermediate stages i.e. at aldehyde and ketone stages. For this purpose Sodium Borohydride is a mild reagent and it reacts slowly with polar protic solvents, hence can be stopped at aldehyde and ketone stages. Even if we want to slow it down further, we can replace H atoms of the boron hydride portion with methyl groups.

  • NaBH4 can liberate Hydrogen when treated with organometallic catalysts.

  • For the production of various medicinal compounds in industries, it is used as a reducing agent because it's cheaper.

  • It is highly selective, which means when we treat other compounds with this, it removes certain atoms from particular positions without affecting the others in the molecular structure and hence giving us the desired compound. It should be noted that reagents that react at a slower rate have selective properties while the others which react faster, have higher reactivity but less selectivity.

  • Reactivity of this compound depends upon solvents too. It works effectively in polar protic solvents but with water and ethanol, its reactivity decreases significantly.

  • Another feature is that we can use this to reduce aldehyde and ketones in presence of other functional groups like lactones, conjugated systems also.

FAQ (Frequently Asked Questions)

1. What is Sodium Borohydride used for?

Sodium Borohydride is a mild reducing agent, that is used to reduce aldehydes and ketones to respective alcohols. This is safer than other reducing agents and it reacts slowly, providing extra stability. So, it is preferable on the industrial scale.

2. What happens when sodium borohydride reacts with water?

Sodium Borohydride is a strongly basic solution. Though it is made stabilized against reaction with water. When sodium borohydride is made to react with water, it releases a lot of energy i.e. it is highly exothermic. It liberates flammable hydrogen gas which may ignite the solvent and surrounding materials.