Naphthalene

Structure of Naphthalene:

• It is a polycyclic aromatic hydrocarbon consisting of two fused benzene rings.
• The molecular formula is C₁₀H₈.
• The structure is planar, and it has alternating double and single bonds, which are characteristic of aromatic compounds.

Synthesis of Naphthalene:

• From Coal Tar:

  • Naphthalenes are primarily obtained from coal tar, which is distilled to separate it from other components.

• Laboratory Synthesis (Haworth Reaction):

  • Formation of 1-Tetralone: Benzene is first reacted with succinic anhydride to form 1-tetralone via the Friedel-Crafts acylation.
  • Cyclization: The intermediate is cyclized to form naphthol.
  • Dehydration and Aromatization: Finally, dehydration and aromatization produce naphthalenes.

• Benzene + Succinic anhydride → AlCl3 (reagents) → 1-Tetralone → Cyclization Naphthalenes

Reactions of Naphthalene:

• Electrophilic Substitution:

  • Nitration: Naphthalenes react with nitric acid (HNO3 HNO_3HNO3​) to form nitronaphthalene.

    • C10H8 + HNO3 → H2SO4 (reagents) C10H7NO2 + H2O

  • Sulfonation: Naphthalenes react with sulfuric acid (H2SO4H_2SO_4H2​SO4​) to form naphthalenes sulfonic acid.

    • C10H8 + H2SO4 → C10H7SO3H + H2O

• Oxidation:

  • It can be oxidized to phthalic anhydride using oxidizing agents like vanadium pentoxide (V2O5​).

    • C10H8+4O2→V2O5C6H4(CO)2O+2H2O

Derivatives:

1. Naphthols (1-Naphthol, 2-Naphthol): These are important derivatives used in dye manufacture.
2. Naphthylamines (1-Naphthylamine, 2-Naphthylamine): These are precursors to various azo dyes.

Medicinal Uses:

• Mothballs: It is used in mothballs due to its insect-repellent properties.
• Derivatives: Some derivatives of naphthalene, such as naphthoquinones, have antibacterial and antifungal properties. However, the direct medicinal use of naphthalene is limited due to its toxic nature.

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