What is Borazine?

In the field of organic chemistry, the benzene ring is the most crucial ring system. Whether it exists as polynuclear hydrocarbons or as a separate entity, it is important in the study of organic chemistry nonetheless. Some of the polynuclear hydrocarbons are phenanthrene, naphthalene, anthracene, etc. There are at least two types of benzene in organic chemistry and they are trimeric cyclophosphazene compounds and borazine.

The chemical formula of borazine is B3H6N3 and it is a compound that is inorganic. The three NH units and the three BH units alternate and cycle.

Properties of Borazine

  • Borazine is isostructural and isoelectronic with benzene.
  • Borazine is colorless in appearance.
  • The physical state of borazine is liquid.
  • It has an aromatic odor.
  • When subjected to water, it hydrolyzes to ammonia, hydrogen, and boric acid.
  • Borazine is quite stable in its thermal state containing an average enthalpy formation change ∆Hf -531 kilojoule per mole.

Structure of Borazine

  • As mentioned earlier, the borazine compound is isoelectronic with benzene and because of this, it is sometimes known as “inorganic benzene”.
  • The length of the bonds found in the borazine ring is all at the equal length of 1.429Å implying that the compound possesses the properties of benzene.
  • The form of the borazine ring is not an equivalent hexagon.
  • The angle of the bond is 122.9° at the nitrogen and 117.1° at the atoms of boron which gave rise to a molecule with a unique symmetry.
  • The electronegativity of boron (2.04 on the Pauling scale) compared to nitrogen (3.04), as well as the boron atom’s electron deficit.
  • For borazine, the lone pair on nitrogen prefers alternate mesomer structures.

Borazine has been famous since the peak of Alfred Stock’s work. There were two major contributions by Alfred Stock. The first contribution was his discovery of compounds such as silanes, boranes, and non-metals that are similar. The second contribution was him perfecting the technique of vacuum lining to handle moisture and air-sensitive compounds which are now proven to be invaluable to inorganic chemists these days.

Borazine and benzene have quite distinct chemical characteristics even though both compounds exhibit aromatic electron density clouds with the potential for delocalization across all ring atoms. The cloud in borazine is “lumpy” because the higher electron density is focused on the nitrogen atoms due to the difference in electronegativity between boron and nitrogen. The π-bonding in the ring is weakened by this partial localization. Each and every nitrogen atom obtains more π-electron density from nearby boron than it gives away as a π-donor. The charge density on nitrogen increases as a result of this. Furthermore, nitrogen retains its basicity, whereas boron retains its acidity.

To produce saturated compound cyclohexane, the process of hydrogenation may be subjected to benzene and this will result in the production of polymeric materials various types of compositions.  Benzene may be hydrogenated to produce the saturated compound cyclohexane. Hydrogenation of borazine results in polymeric materials of indefinite compositions. By adding borazine to saturated cycloborazaneB3N3H12, substituted derivatives arise easily, but the parent chemical requires special procedures to manufacture.

Preparation of Borazine

There are various preparation methods that can be used for obtaining Borazine. Some of them are discussed below:

  1. In a chloro-benzene solvent, boron chloride reacts with Ammonium chloride leading to the formation of B-trichloroborazine. Next, the hydride ions replace the chlorine atoms that are present in B-trichloroborazine which results in the Borazine formation. The chemical equation involved in this preparation is given below:
  2. Another main method is by reacting diborane and ammonia where the ratio is given as 1:2 and is treated at a temperature range of 250–300°C which leads to the conversion of around 50% of Borazine.

3B₂H₆ + 6 NH₃ 2BHN + 12H

Applications of Borazine

Borazine has many applications. Some of which are listed below:

  1. Many potential ceramics can be prepared by using borazines as the starting materials in the preparation process. An example of such potential ceramic is the boron carbonitrides.
  2. This particular substance also finds application as a precursor which is responsible for the growth of h-BN (hexagonal boron nitride) thin films on many surfaces as well as for forming h-BN single layers on catalytic surfaces with the help of the Chemical Vapour deposition process. This can be on copper, nickel, platinum, iron, or nanomesh structures, and many more.
  3. This compound is widely used in the preparation of electroluminescent devices – i.e., devices that can emit light due to the flow of electrons.

Differences between Borazine and Benzene

The main difference that distinguishes benzene and borazine is that in borazine there are three boron atoms along with three nitrogen atoms in a ring structure, benzene on the other hand in the ring structure consists of six carbon atoms. Both borazine and benzene bear the same electronic structure i.e., they have the same number of electrons.

To learn more about compounds like these, refer: p block elements from class 11 chemistry – find all the questions & answers

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