Cycloalkanes, Arenes, and PAHs: Reactions, Synthesis, and Uses

Posted on Nov 4, 2024 in Chemistry

Cycloalkanes

What are Cycloalkanes?

Cycloalkanes are saturated hydrocarbons containing a ring of carbon atoms with the general formula C_nH_2n.

Methods of Preparation (Synthesis Reactions)

1. Cyclization of Alkenes: Alkenes can undergo cyclization reactions to form cycloalkanes.
   Example: Cyclohexane synthesis from hexene
   n-Hexene → Cyclohexane
2. Cyclization of Alkynes: Alkynes can undergo cyclization reactions to form cycloalkanes.
   Example: Cyclohexane synthesis from hexyne
   Hexyne → Cyclohexane
3. Friedel-Crafts Alkylation: Aromatic compounds can undergo alkylation reactions to form cycloalkanes.
   Example: Cyclohexane synthesis from benzene and hexyl chloride
   Benzene + Hexyl chloride → Cyclohexane
4. Diels-Alder Reaction: A [4+2] cycloaddition reaction between a diene and a dienophile forms cycloalkenes, which can be reduced to cycloalkanes.
   Example: Cyclohexene synthesis from butadiene and ethene
   Butadiene + Ethene → Cyclohexene

Theories of Cycloalkanes

1. Baeyer’s Strain Theory: Cycloalkanes exhibit strain due to bent bonds, leading to increased reactivity.
2. VSEPR Theory: Valence Shell Electron Pair Repulsion Theory explains the shape and stability of cycloalkanes.
3. Molecular Orbital Theory: Describes the electronic structure and stability of cycloalkanes.

Models of Cycloalkanes

1. Ball-and-Stick Model: Represents cycloalkanes as balls (atoms) connected by sticks (bonds).
2. Space-Filling Model: Displays the actual shape and size of cycloalkane molecules.
3. Line-Angle Formula: A 2D representation of cycloalkane structures.

Chemical Reactions of Cycloalkanes

1. Combustion: Cycloalkanes undergo combustion reactions to form CO₂ and H₂O.
2. Halogenation: Cycloalkanes undergo substitution reactions with halogens.
3. Oxidation: Cycloalkanes undergo oxidation reactions to form alcohols, aldehydes, or ketones.

Arenes: Phenol and Aromatic Acids

Phenol

Chemical Structure: C₆H₅OH

Methods of Preparation

1. Cumene Process: Cumene (isopropylbenzene) is oxidized to form phenol.
   Cumene + O₂ → Phenol + Acetone
2. Dow Process: Benzene is reacted with propylene to form cumene, which is then oxidized.
   Benzene + Propylene → Cumene → Phenol + Acetone
3. Raschig Process: Benzene is reacted with chlorine to form chlorobenzene, which is then hydrolyzed.
   Benzene + Cl₂ → Chlorobenzene → Phenol

Synthesis Reactions

1. Hydrolysis of Chlorobenzene: Chlorobenzene is reacted with water to form phenol.
   C₆H₅Cl + H₂O → C₆H₅OH + HCl
2. Oxidation of Cyclohexanol: Cyclohexanol is oxidized to form phenol.
   C₆H₁₁OH → C₆H₅OH + H₂

Aromatic Acids

Chemical Structure: C₆H₅COOH (Benzoic Acid)

Methods of Preparation

1. Oxidation of Toluene: Toluene is oxidized to form benzoic acid.
   Toluene + O₂ → Benzoic Acid
2. Carbonylation of Benzene: Benzene is reacted with CO and H₂O to form benzoic acid.
   Benzene + CO + H₂O → Benzoic Acid
3. Hydrolysis of Benzoyl Chloride: Benzoyl Chloride is reacted with water to form benzoic acid.
   C₆H₅COCl + H₂O → C₆H₅COOH + HCl

Synthesis Reactions

1. Oxidation of Aldehydes: Aromatic aldehydes are oxidized to form aromatic acids.
   C₆H₅CHO → C₆H₅COOH
2. Hydrolysis of Nitriles: Aromatic nitriles are hydrolyzed to form aromatic acids.
   C₆H₅CN → C₆H₅COOH

Important Reactions

1. Kolbe’s Reaction: Aromatic acids undergo electrolytic oxidation to form diacids.
   C₆H₅COOH → C₆H₄(COOH)₂
2. Perkin’s Reaction: Aromatic acids undergo condensation with aldehydes to form cinnamic acids.
   C₆H₅COOH + C₆H₅CHO → C₆H₅CH=CHCOOH

Polycyclic Aromatic Hydrocarbons (PAHs)

Naphthalene

Chemical Structure: C₁₀H₈

Methods of Preparation

1. Coal Tar Distillation: Naphthalene is obtained from coal tar.
2. Synthesis from Benzene and Ethylene: Benzene and ethylene undergo Friedel-Crafts alkylation.
   Benzene + Ethylene → Ethylbenzene → Naphthalene

Synthesis Reactions

1. Haworth Synthesis: Benzene and succinic anhydride react to form naphthalene.
   Benzene + Succinic Anhydride → Naphthalene

Structure: Naphthalene has a planar, fused-ring structure.

Uses

1. Synthesis of Phthalic Anhydride
2. Insecticides
3. Dyes
4. Plastics
5. Pharmaceuticals

Phenanthrene

Chemical Structure: C₁₄H₁₀

Methods of Preparation

1. Coal Tar Distillation: Phenanthrene is obtained from coal tar.
2. Synthesis from Naphthalene and Acetylene: Naphthalene and acetylene undergo Diels-Alder reaction.
   Naphthalene + Acetylene → Phenanthrene

Synthesis Reactions

1. Bucherer Synthesis: Naphthalene and succinic anhydride react to form Phenanthrene.
   Naphthalene + Succinic Anhydride → Phenanthrene

Structure: Phenanthrene has a planar, fused-ring structure.

Uses

1. Dyes
2. Pharmaceuticals
3. Insecticides
4. Lubricants

Anthracene

Chemical Structure: C₁₄H₁₀

Methods of Preparation

1. Coal Tar Distillation: Anthracene is obtained from coal tar.
2. Synthesis from Benzene and Butadiene: Benzene and butadiene undergo Diels-Alder reaction.
   Benzene + Butadiene → Anthracene

Synthesis Reactions

1. Elbs Synthesis: Benzene and phthalic anhydride react to form anthracene.
   Benzene + Phthalic Anhydride → Anthracene

Structure: Anthracene has a planar, fused-ring structure.

Uses

1. Dyes
2. Pharmaceuticals
3. Insecticides
4. Electronics

Derivatives

Naphthalene Derivatives

1. Naphthol
2. Naphthylamine
3. Phthalic Anhydride

Phenanthrene Derivatives

1. Phenanthroline
2. Phenanthrenequinone

Anthracene Derivatives

1. Anthraquinone
2. Anthranilic Acid