Aromatisation is the conversion of higher alkanes (C₆ or more) into aromatic hydrocarbons (benzene and its derivatives) by dehydrogenation and cyclisation at high temperature in presence of catalysts.

n-Octane (C₈) → Xylene (or ethylbenzene)

Also possible under catalytic reforming conditions.

Theoretical Point of View

There is no fixed maximum carbon limit.
Any C₆ or higher straight-chain alkane (C₆⁺) can undergo aromatisation because at least six carbons are required to form a benzene ring.

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🔹 Practical / Industrial Point of View

In petroleum refining (catalytic reforming):

✔ Most effective for C₆ to C₁₀ alkanes
✔ Above C₁₀–C₁₂, cracking and side reactions increase
✔ Very long chains prefer cracking rather than clean aromatisation

So practically:$$\boxed{\textbf{Industrially important range: C₆–C₁₀ (approx.)}}$$

Cyclohexane undergoes multiple dehydrogenations:

$$\text{Cyclohexane} \rightarrow \text{Cyclohexene} \rightarrow \text{Cyclohexadiene} \rightarrow \text{Benzene}$$

👉 Total 4 molecules of H₂ released.

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🔹 Key Concept

✔ First dehydrogenation, then cyclisation, then aromatic stabilization
✔ Metal catalyst helps in removal of hydrogen
✔ Final product gains extra stability due to aromatic resonance