Preparation of Diborane – All You Need to Know

As the name diborane suggests, in this chemical compound, two atoms of boron and six atoms of hydrogens are present. Chemically, it is written as B₂H₆. The IUPAC name of diborane is di – boron hexa – hydride. Some more synonyms used for diborane are boron ethane and boron hydride. Diborane is the specific compound of the boron composition.

Preparation of diborane 

Boron is naturally present in the mineral form with different amounts of boron compositions with oxygen in the form of borates. In the borates form, it tends to be stable. So it is difficult to prepare diborane naturally as they are not ready to break their bond to form new bonds. As we already know, in diborane molecules, a banana bond is also present in addition to a covalent bond, which cannot be easily seen in any compound. Hence, we use other preparatory methods for the formation of the diborane.

Diborane is prepared in many different ways or compositions of chemical reactions like industrial preparation, laboratory preparation, etc. We will discuss some of the critical preparation methods in the following sections.

Preparation by using iodine and sodium borohydride

It is one of the laboratory preparation methods of diborane in a small quantity from the mixture of iodine (I₂) and sodium borohydride (NaBH₄). In this reaction, iodine reacts with sodium borohydride in the presence of diglyme, which is an example of ether [(CH₂OCH₂CH₂)₂O], having a very high boiling temperature. By this preparation method, we get a 98% yield of the diborane (B₂H₆) as the product.

                 2NaBH₄ + I₂ →  B₂H₆ + 2NaI + H₂

Preparation by using phosphoric acid and magnesium boride

In this method, phosphoric acid (H₃PO₄) reacts with magnesium boride(Mg₃B₂) to obtain the mixture of boranes, which in turn produce the diborane (B₂H₆) after heating as a product.

                 Mg₃B₂   +    H₃PO₄    → (Mixture of boranes) → B₂H₆

Preparation by reduction of boron halides

Diborane can be prepared by the reduction of different boron halides under different conditions as follows:

By the reduction of boron trifluoride

When the boron trifluoride (BF₃) reacts with lithium hydride (LiH) in the presence of ether, the formation of diborane (B₂H₆) takes place:

                   8BF₃ + 6LiH  → 6LiBF₄ + B₂H₆     

By the reduction of boron trichloride

When a mixture of boron trichloride (BCl₃) and lithium aluminium hydride (LiAlH₄) reacts, the formation of diborane (B₂H₆) takes place as the result of the reduction in addition to lithium chloride (LiCl) and aluminium trichloride (AlCl₃).

                 4BCl₃ + 3LiAlH₄→ 2B₂H₆ + 3LiCl + 3AlCl₃

By the reduction of boron trichloride vapour

When we pass a silent electric discharge to the mixture of the vapour of boron trichloride (BCl₃) with the hydrogen gas (H₂) at low pressure, the formation of diborane (B₂H₆) takes place as the result of the reduction because hydrogen is added to the production of hydrochloric acid (HCI).

                   2BCl₃ + 6H₂ →  B₂H₆ + 6HCI

By the reduction of boron trifluoride

A good quantity of diborane (B₂H₆) is obtained as the product of the reduction of boron trifluoride (BF₃) molecule due to the addition of hydrogen atom, where we use the sodium borohydride (NaBH₄) as the reducing agent which itself gets oxidised.

                  4BF₃ + 3NaBH₄ →  3NaBF₄ + 2B₂H₆     

Conclusion

The preparation of diborane (B₂H₆) is not done by natural processes. It is done by laboratory or industrial methods. In the laboratory, various means are used for the preparation of diborane(B₂H₆), like reduction and different kinds of reducing agents. Other than this, diborane (B₂H₆) is also produced by heating boranes at different temperatures.