Alkyl benzenes and their reactions Flashcards
Why are Alkyl benzenes more reactive than Benzene?
The positive inductive effect from the alkyl group donates the electron cloud which partially overlaps and makes the π system more negative.
State the 6 reactions of Alkyl benzenes
- Complete oxidation.
- Halogenation.
- Nitration.
- Hydrogenation.
- Complete/Incomplete combustion.
- F-C.Alkylation.
Complete oxidation of Alkyl benzenes (REAGENTS, CONDITIONS, OBSERVATION)
Reactants= Alkyl benzene + ALKALI KMnO₄(aq).
Conditions= Heat and reflux.
Observation= Purple to brown colour change (MnO₂(s) forms).
Complete oxidation of Alkyl benzenes (EXAMPLE)
Methylbenzene + [O] —> Benzoic acid + H₂O
Additional step in complete oxidation of alkyl benzenes
The Benzoic acid that forms reacts with NaOH (aq) in alkali KMnO₄(aq) and forms Sodium benzoate. Acidification must be done to reform Benzoic acid.
Halogenation of Alkyl benzenes can happen at two locations, what are they?
Halogenation to the main benzene ring or Halogenation to the alkyl side chain.
Halogenation to the main benzene ring in Alkyl benzenes (REAGENTS, CATALYSTS, CONDITIONS)
Reactants= Alkyl benzene + Halogen.
Catalyst= Anhydrous Halogen carrier.
Conditions= No other conditions.
Halogenation to the main benzene ring in Alkyl benzenes (EXAMPLE)
Methylbenzene + Cl₂ —> 2-Chloromethylbenzene + HCl(g)
Halogenation to the alkyl side chain in Alkyl benzenes (REAGENTS AND CONDITIONS)
Reactants= Alkyl benzene + Halogen.
Conditions= UV light and boiling the mixture.
(Similar to free radical substitution)
Halogenation to the alkyl side chain in Alkyl benzenes (EXAMPLE)
Methylbenzene + Cl₂ —> Chlorophenylmethane + HCl
Nitration of Alkyl benzenes (REAGENTS)
Reactants= Alkyl benzene + diluted/concentrated HNO₃.
Nitration of Alkyl benzenes (EXAMPLE)
Methylbenzene + conc.HNO₃ —> 2,4,6-trinitromethylbenzene
Hydrogenation of Alkyl benzenes (REAGENTS, CATALYSTS, CONDITIONS)
Reactants= Alkyl benzene + H₂(g).
Catalyst= Pt/Ni.
Conditions= Heat (170
°C).
Hydrogenation of Alkyl benzenes (EXAMPLE)
Ethylbenzene + 3H₂ —> Ethylcyclohexane
(π system lost)
Friedel-Crafts alkylation of Alkyl benzenes (REAGENTS, CATALYSTS, CONDITIONS)
Reactants= Alkyl benzene + Halogenoalkane.
Catalyst= Anhydrous Halogen carrier.
Conditions= Heat.
Friedel-Crafts alkylation of Alkyl benzenes (EXAMPLE)
Ethylbenzene + CH₃CH₂Cl —> 1,2-diethylbenzene + HCl(g)
Electrophilic substitution mechanism steps
- Formation of electrophile.
- Attack of electrophile (π system broken).
- Reformation of π system.
