Aromatic Hydrocarbons
Benzene: Comprehensive Reaction Chart & Properties
Benzene ($\text{C}_6\text{H}_6$) is the parent compound of aromatic hydrocarbons. Its unique resonance stability makes it less reactive toward addition but highly active toward substitution. This guide explores its preparation and chemical behavior.
1. Preparation of Benzene
Benzene can be synthesized using laboratory methods such as decarboxylation of aromatic acids or industrial pathways like the cyclic polymerization of ethyne.
Key Synthesis Methods
- Cyclic Polymerization: Ethyne passed through a red-hot iron tube ($873\text{ K}$) yields Benzene.
- Decarboxylation: Heating Sodium Benzoate with Sodalime ($\text{NaOH} + \text{CaO}$).
- Reduction of Phenol: Distilling Phenol with Zinc dust ($\text{C}_6\text{H}_5\text{OH} + \text{Zn} \rightarrow \text{C}_6\text{H}_6 + \text{ZnO}$).
2. Chemical Properties of Benzene
Benzene primarily undergoes Electrophilic Aromatic Substitution (EAS) reactions where the stability of the aromatic ring is preserved.
Must-Know Substitution Patterns
- Nitration: Reaction with Conc. $\text{HNO}_3$ and Conc. $\text{H}_2\text{SO}_4$ to form Nitrobenzene.
- Friedel-Crafts Alkylation: Treatment with Alkyl halides in the presence of anhydrous $\text{AlCl}_3$.
- Friedel-Crafts Acylation: Treatment with Acyl halides to yield Acetophenone.
- Halogenation: Reaction with $\text{Cl}_2$ or $\text{Br}_2$ using Lewis acid catalysts ($\text{FeCl}_3/\text{AlCl}_3$).
Addition & Oxidation
- BHC Formation: Addition of $\text{Cl}_2$ in presence of UV light yields Benzene Hexachloride (Gammaxene).
- Hydrogenation: Under high pressure/temp with Ni catalyst, Benzene reduces to Cyclohexane.
- Combustion: Burns with a sooty flame due to high carbon content.
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