Question

Converting \(\mathrm{n}\) -hexane into benzene in the presence of chromium oxide on alumina support is an example of (1) hydrogenation reaction (2) isomerisation reaction (3) aromatisation reaction (4) substitution reaction

Short answer

(3) aromatisation reaction

Step-by-step solution

Identify the Reaction Type

Converting n-hexane (a straight-chain alkane) into benzene (an aromatic compound) involves changing the structure and properties of the molecule.

Define Reaction Options

Hydrogenation reaction adds hydrogen to a compound. Isomerisation changes the structure of a molecule without changing its molecular formula. Aromatisation converts alkanes to aromatic compounds. Substitution replaces one atom or group in a molecule with another.

Determine the Correct Option

Since the process involves converting an alkane (n-hexane) to an aromatic compound (benzene), the correct type of reaction must involve creating an aromatic structure.

Select the Correct Answer

The correct type of reaction is the one that converts alkanes to aromatic compounds, which is an aromatisation reaction.

Key concepts

organic chemistry

Organic chemistry is the branch of chemistry that deals with the study of carbon-containing compounds.
It covers a wide range of substances, including hydrocarbons, alcohols, acids, and more complex molecules found in living organisms.

Studying organic chemistry helps us understand the structure, properties, and reactions of these molecules, which is crucial for fields like medicine, agriculture, and materials science.
A key aspect is learning about different types of organic reactions.
For example, in our given exercise, we look at the aromatisation reaction, where a simple alkane is transformed into a more complex aromatic compound.

reaction mechanisms

Understanding reaction mechanisms is essential to mastering organic chemistry.
A reaction mechanism explains the step-by-step process through which reactants turn into products.
It involves details like intermediate steps, transition states, and the energy changes that occur.

In the context of our exercise, the conversion of n-hexane to benzene involves several intermediate steps:

• First, the n-hexane may undergo dehydrogenation, removing hydrogen atoms.
• Then, it undergoes cyclization, forming a ring structure.
• Finally, it may undergo further dehydrogenation to form the aromatic benzene.

These steps are facilitated by a catalyst, such as chromium oxide on alumina, which helps in speeding up the reaction without being consumed.

hydrocarbons conversion

Hydrocarbons conversion refers to the process of transforming one type of hydrocarbon into another.
This includes reactions like cracking, reforming, and in our exercise, aromatisation.

Aromatisation is a specific type of hydrocarbon conversion where alkanes are converted into aromatic compounds.
This process is particularly important in the petrochemical industry for producing valuable chemicals.

Let's break down the aromatisation of n-hexane to benzene:

• Chromium oxide on alumina acts as a catalyst.
• n-Hexane, a straight-chain alkane with 6 carbon atoms, loses hydrogen atoms in a dehydrogenation step.
• It then undergoes cyclization, forming a six-membered carbon ring.
• Finally, it loses additional hydrogen atoms to form benzene, a stable aromatic compound.

The entire process significantly enhances the value of the original hydrocarbon by converting it into a more useful and versatile chemical.